Faculty
Prof. Dr. M. İ. Can Dede
Chair
Educational Background
B.Sc. İstanbul Technical University, Turkey, Mechanical Engineering, 1999
M.Sc. Middle East Technical University, Turkey, Mechanical Engineering, 2003
Ph.D. Florida International University, USA, Mechanical Engineering, 2007
Research Interests
- Haptics
- Teleoperation
- Robot Controller Design
- Unmanned Underwater Vehicles
- +90 232 750 6704 - 6778
- +90 232 750 6701
- Mechanical Engineering Building (Z18)
Publications
2024 |
Emet, Hazal; Gür, Berke; Dede, Mehmet İsmet Can The design and kinematic representation of a soft robot in a simulation environment Journal Article Robotica, 42 (1), pp. 139 – 152, 2024. @article{Emet2024139, title = {The design and kinematic representation of a soft robot in a simulation environment}, author = {Hazal Emet and Berke Gür and Mehmet İsmet Can Dede}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85177169148&doi=10.1017%2fS026357472300139X&partnerID=40&md5=9d8bb2595da002ed43f0667f2d03c7f8}, doi = {10.1017/S026357472300139X}, year = {2024}, date = {2024-01-01}, journal = {Robotica}, volume = {42}, number = {1}, pages = {139 – 152}, abstract = {The increase of human presence in the subsea and seabed environments necessitates the development of more capable and highly dexterous, innovative underwater manipulators. Biomimetic soft-robot arms represent a promising candidate for such manipulation systems. However, the well-known modeling techniques and control theories of traditional rigid robots do not apply to soft robots. The challenges of kinematic and dynamic modeling of soft robots with infinite degrees of freedom require the development of dedicated modeling methods. A novel procedure for representing soft-robotic arms and their motion in a rigid-body simulation environment is proposed in this paper. The proposed procedure relies on the piecewise constant curvature approach to simplify the very complex model of hyper-redundant soft-robotic arms, making it suitable for real-time applications. The proposed method is implemented and verified to be used in model-mediated teleoperation of the soft arms of a biomimetic robotic squid designed for underwater manipulation as a case study. © 2023 The Author(s). Published by Cambridge University Press.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The increase of human presence in the subsea and seabed environments necessitates the development of more capable and highly dexterous, innovative underwater manipulators. Biomimetic soft-robot arms represent a promising candidate for such manipulation systems. However, the well-known modeling techniques and control theories of traditional rigid robots do not apply to soft robots. The challenges of kinematic and dynamic modeling of soft robots with infinite degrees of freedom require the development of dedicated modeling methods. A novel procedure for representing soft-robotic arms and their motion in a rigid-body simulation environment is proposed in this paper. The proposed procedure relies on the piecewise constant curvature approach to simplify the very complex model of hyper-redundant soft-robotic arms, making it suitable for real-time applications. The proposed method is implemented and verified to be used in model-mediated teleoperation of the soft arms of a biomimetic robotic squid designed for underwater manipulation as a case study. © 2023 The Author(s). Published by Cambridge University Press. |
2023 |
Gorgulu, Ibrahimcan; Dede, Mehmet Ismet Can; Kiper, Gokhan Stiffness modeling of a 2-DoF over-constrained planar parallel mechanism Journal Article MECHANISM AND MACHINE THEORY, 185 , 2023. @article{WOS:000966404700001, title = {Stiffness modeling of a 2-DoF over-constrained planar parallel mechanism}, author = {Ibrahimcan Gorgulu and Mehmet Ismet Can Dede and Gokhan Kiper}, doi = {10.1016/j.mechmachtheory.2023.105343}, year = {2023}, date = {2023-07-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {185}, abstract = {Stiffness model acquisition of over-constrained parallel mechanisms is relatively difficult since they have more than necessary kinematic loops. In this study, a stiffness modeling solution for over-constrained parallel mechanisms is proposed while considering the computational cost efficiency. Three contributions of the paper are: (1) Presenting the stiffness modeling procedure for serially connected closed-loop structures by using the Virtual Joint Method (2) Considering the effect of dynamic auxiliary forces and dynamic external forces on the mobile platform's deflection and achieving a direct solution by using superposition principle (3) A model fitting procedure for modifying the stiffness coefficients to comply with the experimental data. A 2 degrees-of-freedom over-constrained parallel mechanism is investigated as a case study. However, the proposed stiffness model is 6-DoF since compliant deflections occur in any direction. A finite element analysis and an experimental study verify the model's results.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Stiffness model acquisition of over-constrained parallel mechanisms is relatively difficult since they have more than necessary kinematic loops. In this study, a stiffness modeling solution for over-constrained parallel mechanisms is proposed while considering the computational cost efficiency. Three contributions of the paper are: (1) Presenting the stiffness modeling procedure for serially connected closed-loop structures by using the Virtual Joint Method (2) Considering the effect of dynamic auxiliary forces and dynamic external forces on the mobile platform's deflection and achieving a direct solution by using superposition principle (3) A model fitting procedure for modifying the stiffness coefficients to comply with the experimental data. A 2 degrees-of-freedom over-constrained parallel mechanism is investigated as a case study. However, the proposed stiffness model is 6-DoF since compliant deflections occur in any direction. A finite element analysis and an experimental study verify the model's results. |
Aldanmaz, Ataol Behram; Ayit, Orhan; Kiper, Gökhan; Dede, Mehmet İsmet Can Gravity compensation of a 2R1T mechanism with remote center of motion for minimally invasive transnasal surgery applications Journal Article Robotica, 41 (3), pp. 807 – 820, 2023, (All Open Access, Green Open Access). @article{Aldanmaz2023807, title = {Gravity compensation of a 2R1T mechanism with remote center of motion for minimally invasive transnasal surgery applications}, author = {Ataol Behram Aldanmaz and Orhan Ayit and Gökhan Kiper and Mehmet İsmet Can Dede}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85148022623&doi=10.1017%2fS0263574722000534&partnerID=40&md5=d9e00d3ba2c7864df127963817903586}, doi = {10.1017/S0263574722000534}, year = {2023}, date = {2023-01-01}, journal = {Robotica}, volume = {41}, number = {3}, pages = {807 – 820}, abstract = {This work addresses the gravity balancing of a 2R1T (2 rotations - 1 translation) mechanism with remote center of motion. A previously developed balancing solution is modified and applied to a prototype, and test results are presented. The mechanism is an endoscope holder for minimally invasive transnasal pituitary gland surgery. In this surgery, the endoscope is inserted through a nostril of the patient through a natural path to the pituitary gland. During the surgery, it is vital for the manipulator to be statically balanced so that in case of a motor failure, the patient is protected against any harmful motion of the endoscope. Additionally, static balancing takes the gravitational load from the actuators and hence facilitates the control of the mechanism. The mechanism is a 2URRR-URR type parallel manipulator with three legs. The payload mass is distributed to the legs on the sides. By using counter-masses for two links of each leg, the center of mass of each leg is lumped on the proximal link which simplifies the problem of balancing of a two degree-of-freedom inverted pendulum. The two proximal links with the lumped mass are statically balanced via springs. Dynamic simulations indicate that when the mechanism is statically balanced, generated actuator torques are reduced by 93.5%. Finally, the balancing solution is implemented on the prototype of the manipulator. The tests indicate that the manipulator is statically balanced within its task space when the actuators are disconnected. When the actuators are connected, the torque requirements decrease by about 37.8% with balancing. © The Author(s), 2022. Published by Cambridge University Press.}, note = {All Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } This work addresses the gravity balancing of a 2R1T (2 rotations - 1 translation) mechanism with remote center of motion. A previously developed balancing solution is modified and applied to a prototype, and test results are presented. The mechanism is an endoscope holder for minimally invasive transnasal pituitary gland surgery. In this surgery, the endoscope is inserted through a nostril of the patient through a natural path to the pituitary gland. During the surgery, it is vital for the manipulator to be statically balanced so that in case of a motor failure, the patient is protected against any harmful motion of the endoscope. Additionally, static balancing takes the gravitational load from the actuators and hence facilitates the control of the mechanism. The mechanism is a 2URRR-URR type parallel manipulator with three legs. The payload mass is distributed to the legs on the sides. By using counter-masses for two links of each leg, the center of mass of each leg is lumped on the proximal link which simplifies the problem of balancing of a two degree-of-freedom inverted pendulum. The two proximal links with the lumped mass are statically balanced via springs. Dynamic simulations indicate that when the mechanism is statically balanced, generated actuator torques are reduced by 93.5%. Finally, the balancing solution is implemented on the prototype of the manipulator. The tests indicate that the manipulator is statically balanced within its task space when the actuators are disconnected. When the actuators are connected, the torque requirements decrease by about 37.8% with balancing. © The Author(s), 2022. Published by Cambridge University Press. |
Dede, Mehmet İsmet Can; Büyüköztekin, Tarlk; Hanalioǧlu, Şahin; Işlkay, İlkay; Berker, Mustafa Enabling personalization of a robotic surgery procedure via a surgery training simulator Journal Article Robotica, 41 (3), pp. 869 – 884, 2023. @article{Dede2023869, title = {Enabling personalization of a robotic surgery procedure via a surgery training simulator}, author = {Mehmet İsmet Can Dede and Tarlk Büyüköztekin and Şahin Hanalioǧlu and İlkay Işlkay and Mustafa Berker}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85148013607&doi=10.1017%2fS0263574722001023&partnerID=40&md5=2ca0aadba08af765e6eb072301e16eaa}, doi = {10.1017/S0263574722001023}, year = {2023}, date = {2023-01-01}, journal = {Robotica}, volume = {41}, number = {3}, pages = {869 – 884}, abstract = {Although robotic or robot-assisted surgery has been increasingly used by many surgical disciplines, its application in cranial or skull base surgery is still in its infancy. Master-slave teleoperation setting of these robotic systems enables these surgical procedures to be replicated in a virtual reality environment for surgeon training purposes. A variety of teleoperation modes were previously determined with respect to the motion capability of the surgeon's hand that wears the ring as the surgeon handles a surgical tool inside the surgical workspace. In this surgery training simulator developed for a robot-assisted endoscopic skull base surgery, a new strategy is developed to identify the preferred motion axes of the surgeon. This simulator is designed specifically for tuning the teleoperation system for each surgeon via the identification. This tuning capability brings flexibility to adjust the system operation with respect to the motion characteristics of the surgeon. © The Author(s), 2022. Published by Cambridge University Press.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Although robotic or robot-assisted surgery has been increasingly used by many surgical disciplines, its application in cranial or skull base surgery is still in its infancy. Master-slave teleoperation setting of these robotic systems enables these surgical procedures to be replicated in a virtual reality environment for surgeon training purposes. A variety of teleoperation modes were previously determined with respect to the motion capability of the surgeon's hand that wears the ring as the surgeon handles a surgical tool inside the surgical workspace. In this surgery training simulator developed for a robot-assisted endoscopic skull base surgery, a new strategy is developed to identify the preferred motion axes of the surgeon. This simulator is designed specifically for tuning the teleoperation system for each surgeon via the identification. This tuning capability brings flexibility to adjust the system operation with respect to the motion characteristics of the surgeon. © The Author(s), 2022. Published by Cambridge University Press. |
Ayit, Orhan; Dede, Mehmet İsmet Can A study on a computationally efficient controller design for a surgical robotic system Journal Article International Journal of Dynamics and Control, 11 (6), pp. 3176 – 3187, 2023. @article{Ayit20233176, title = {A study on a computationally efficient controller design for a surgical robotic system}, author = {Orhan Ayit and Mehmet İsmet Can Dede}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85153031240&doi=10.1007%2fs40435-023-01164-y&partnerID=40&md5=cdb5797de4d939164cc1a564579d738c}, doi = {10.1007/s40435-023-01164-y}, year = {2023}, date = {2023-01-01}, journal = {International Journal of Dynamics and Control}, volume = {11}, number = {6}, pages = {3176 – 3187}, abstract = {The control algorithms of the surgical robotic system using the robot’s dynamics produce a relatively high computational load on the processor. This paper develops a computationally efficient computed torque controller by using a simplified dynamic modeling method and implemented in a novel surgical robot experimentally. In addition, an independent joint controller is designed and implemented to compare the results of the computed torque controller. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The control algorithms of the surgical robotic system using the robot’s dynamics produce a relatively high computational load on the processor. This paper develops a computationally efficient computed torque controller by using a simplified dynamic modeling method and implemented in a novel surgical robot experimentally. In addition, an independent joint controller is designed and implemented to compare the results of the computed torque controller. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature. |
2022 |
Şahin, O N; Dede, M İ C Model-based detection and isolation of the wheel slippage and actuator faults of a holonomic mobile robot Journal Article Industrial Robot, 49 (6), pp. 1202-1217, 2022. @article{Şahin20221202, title = {Model-based detection and isolation of the wheel slippage and actuator faults of a holonomic mobile robot}, author = {O N Şahin and M İ C Dede}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85130240953&doi=10.1108%2fIR-01-2022-0001&partnerID=40&md5=bfe89d019e1f0a22ac5484fcb26a7655}, doi = {10.1108/IR-01-2022-0001}, year = {2022}, date = {2022-01-01}, journal = {Industrial Robot}, volume = {49}, number = {6}, pages = {1202-1217}, abstract = {Purpose: Mobile robots may perform very critical tasks under difficult operating conditions. Faults encountered during their tasks may cause the task to be interrupted or failed completely. In the active fault tolerant control methods, it is very important not only to detect the faults that occur in the robot, but also to isolate these faults to develop a fault recovery strategy that is suitable for that specific type of fault. This study aims to develop a model-based fault detection and isolation method for wheel slippage and motor performance degradation that may occur in wheeled mobile robots. Design/methodology/approach: In the proposed method, wheel speeds can be estimated via the dynamic model of the mobile robot, which includes a friction model between the wheel and the ground. Four residual signals are obtained from the differences between the estimated states and the measured states of the mobile robot. Mobile robot’s faults are detected by using these signals. Also, two different residual signals are generated from the calculation of the traction forces with two different procedures. These six residual signals are then used to isolate possible wheel slippage and performance degradation in a motor. Findings: The proposed method for diagnosing wheel slip and performance degradation in motors are tested by moving the robot in various directions. According to the data obtained from the test results, a logic table is created to isolate these two faults from each other. Thanks to the created logic table, slippage in any wheel and performance degradation in any motor can be detected and isolated. Originality/value: Two different recovery strategies are needed to recover temporary wheel slippage and permanent motor faults. Therefore, it is important to isolate these two faults that create similar symptoms in robot’s general movement. Thanks to the method proposed in this study, it is not only possible to isolate the slipping wheel with respect to the non-slipping wheels or to isolate the faulty motor from the non-faulty ones, but also to isolate these two different fault types from each other. © 2022, Emerald Publishing Limited.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Purpose: Mobile robots may perform very critical tasks under difficult operating conditions. Faults encountered during their tasks may cause the task to be interrupted or failed completely. In the active fault tolerant control methods, it is very important not only to detect the faults that occur in the robot, but also to isolate these faults to develop a fault recovery strategy that is suitable for that specific type of fault. This study aims to develop a model-based fault detection and isolation method for wheel slippage and motor performance degradation that may occur in wheeled mobile robots. Design/methodology/approach: In the proposed method, wheel speeds can be estimated via the dynamic model of the mobile robot, which includes a friction model between the wheel and the ground. Four residual signals are obtained from the differences between the estimated states and the measured states of the mobile robot. Mobile robot’s faults are detected by using these signals. Also, two different residual signals are generated from the calculation of the traction forces with two different procedures. These six residual signals are then used to isolate possible wheel slippage and performance degradation in a motor. Findings: The proposed method for diagnosing wheel slip and performance degradation in motors are tested by moving the robot in various directions. According to the data obtained from the test results, a logic table is created to isolate these two faults from each other. Thanks to the created logic table, slippage in any wheel and performance degradation in any motor can be detected and isolated. Originality/value: Two different recovery strategies are needed to recover temporary wheel slippage and permanent motor faults. Therefore, it is important to isolate these two faults that create similar symptoms in robot’s general movement. Thanks to the method proposed in this study, it is not only possible to isolate the slipping wheel with respect to the non-slipping wheels or to isolate the faulty motor from the non-faulty ones, but also to isolate these two different fault types from each other. © 2022, Emerald Publishing Limited. |
Kanlk, M; Ayit, O; Dede, M I C; Tatlicioglu, E Robotica, 40 (7), pp. 2112-2127, 2022. @article{Kanlk20222112, title = {Toward safe and high-performance human-robot collaboration via implementation of redundancy and understanding the effects of admittance term parameters}, author = {M Kanlk and O Ayit and M I C Dede and E Tatlicioglu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85119673140&doi=10.1017%2fS0263574721001569&partnerID=40&md5=97f95f7fba03b5aece75e8580f8a1977}, doi = {10.1017/S0263574721001569}, year = {2022}, date = {2022-01-01}, journal = {Robotica}, volume = {40}, number = {7}, pages = {2112-2127}, abstract = {Today, demandsin industrial manufacturing mandate humans to work with large-scale industrial robots, and this collaboration may result in dangerous conditions for humans. To deal with this situation, this work proposes a novel approach for redundant large-scale industrial robots. In the proposed approach, an admittance controller is designed to regulate the interaction between the end effector of the robot and the human. Additionally, an obstacle avoidance algorithm is implemented in the null space of the robot to prevent any possible unexpected collision between the human and the links of the robot. After safety performance of this approach is verified via simulations and experimental studies, the effect of the parameters of the admittance controller on the performance of collaboration in terms of both accuracy and total human effort is investigated. This investigation is carried out via 8 experiments by the participation of 10 test subjects in which the effect of different admittance controller parameters such as mass and damper are compared. As a result of this investigation, tuning insights for such parameters are revealed. © 2021 The Author(s). Published by Cambridge University Press.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Today, demandsin industrial manufacturing mandate humans to work with large-scale industrial robots, and this collaboration may result in dangerous conditions for humans. To deal with this situation, this work proposes a novel approach for redundant large-scale industrial robots. In the proposed approach, an admittance controller is designed to regulate the interaction between the end effector of the robot and the human. Additionally, an obstacle avoidance algorithm is implemented in the null space of the robot to prevent any possible unexpected collision between the human and the links of the robot. After safety performance of this approach is verified via simulations and experimental studies, the effect of the parameters of the admittance controller on the performance of collaboration in terms of both accuracy and total human effort is investigated. This investigation is carried out via 8 experiments by the participation of 10 test subjects in which the effect of different admittance controller parameters such as mass and damper are compared. As a result of this investigation, tuning insights for such parameters are revealed. © 2021 The Author(s). Published by Cambridge University Press. |
Maaroof, O W; Dede, M İ C; Aydin, L A Robot Arm Design Optimization Method by Using a Kinematic Redundancy Resolution Technique Journal Article Robotics, 11 (1), 2022. @article{Maaroof2022, title = {A Robot Arm Design Optimization Method by Using a Kinematic Redundancy Resolution Technique}, author = {O W Maaroof and M İ C Dede and L Aydin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85122955998&doi=10.3390%2frobotics11010001&partnerID=40&md5=88885649cc03fbdcd72af784eae80615}, doi = {10.3390/robotics11010001}, year = {2022}, date = {2022-01-01}, journal = {Robotics}, volume = {11}, number = {1}, abstract = {Redundancy resolution techniques have been widely used for the control of kinematically redundant robots. In this work, one of the redundancy resolution techniques is employed in the mechanical design optimization of a robot arm. Although the robot arm is non-redundant, the proposed method modifies robot arm kinematics by adding virtual joints to make the robot arm kinematically redundant. In the proposed method, a suitable objective function is selected to optimize the robot arm’s kinematic parameters by enhancing one or more performance indices. Then the robot arm’s end-effector is fixed at critical positions while the redundancy resolution algorithm moves its joints including the virtual joints because of the self-motion of a redundant robot. Hence, the optimum values of the virtual joints are determined, and the design of the robot arm is modified accordingly. An advantage of this method is the visualization of the changes in the manipulator’s structure during the optimization process. In this work, as a case study, a passive robotic arm that is used in a surgical robot system is considered and the task is defined as the determination of the optimum base location and the first link’s length. The results indicate the effectiveness of the proposed method. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Redundancy resolution techniques have been widely used for the control of kinematically redundant robots. In this work, one of the redundancy resolution techniques is employed in the mechanical design optimization of a robot arm. Although the robot arm is non-redundant, the proposed method modifies robot arm kinematics by adding virtual joints to make the robot arm kinematically redundant. In the proposed method, a suitable objective function is selected to optimize the robot arm’s kinematic parameters by enhancing one or more performance indices. Then the robot arm’s end-effector is fixed at critical positions while the redundancy resolution algorithm moves its joints including the virtual joints because of the self-motion of a redundant robot. Hence, the optimum values of the virtual joints are determined, and the design of the robot arm is modified accordingly. An advantage of this method is the visualization of the changes in the manipulator’s structure during the optimization process. In this work, as a case study, a passive robotic arm that is used in a surgical robot system is considered and the task is defined as the determination of the optimum base location and the first link’s length. The results indicate the effectiveness of the proposed method. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. |
2021 |
Şahin, O N; Dede, M İ C Investigation of longitudinal friction characteristics of an omnidirectional wheel via LuGre model Journal Article Robotica, 39 (9), pp. 1654-1673, 2021. @article{Şahin20211654, title = {Investigation of longitudinal friction characteristics of an omnidirectional wheel via LuGre model}, author = {O N Şahin and M İ C Dede}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85100396480&doi=10.1017%2fS0263574720001423&partnerID=40&md5=87b564f58915fb537015ba9bc579f540}, doi = {10.1017/S0263574720001423}, year = {2021}, date = {2021-01-01}, journal = {Robotica}, volume = {39}, number = {9}, pages = {1654-1673}, abstract = {In recent years, omnidirectional wheels have found more applications in the design of automated guided vehicles (AGV). In this work, LuGre friction model is used for an omnidirectional wheel. A test setup that includes a single omnidirectional wheel is designed and constructed to identify the model parameters. With the help of the constructed test setup, the longitudinal friction characteristic of the omnidirectional wheel is obtained, and the model is verified via validation tests. In addition, for the first time, the effect of lateral frictional force on longitudinal motion is examined for an omnidirectional wheel through experiments. © 2021 Cambridge University Press. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In recent years, omnidirectional wheels have found more applications in the design of automated guided vehicles (AGV). In this work, LuGre friction model is used for an omnidirectional wheel. A test setup that includes a single omnidirectional wheel is designed and constructed to identify the model parameters. With the help of the constructed test setup, the longitudinal friction characteristic of the omnidirectional wheel is obtained, and the model is verified via validation tests. In addition, for the first time, the effect of lateral frictional force on longitudinal motion is examined for an omnidirectional wheel through experiments. © 2021 Cambridge University Press. All rights reserved. |
Dede, M I C; Kiper, G; Ayav, T; Ozdemirel, B; Tatlıcıoglu, E; Hanalioglu, S; Işıkay, I; Berker, M Human–robot interfaces of the neuroboscope: A minimally invasive endoscopic pituitary tumor surgery robotic assistance system Journal Article Journal of Medical Devices, Transactions of the ASME, 15 (1), 2021. @article{Dede2021, title = {Human–robot interfaces of the neuroboscope: A minimally invasive endoscopic pituitary tumor surgery robotic assistance system}, author = {M I C Dede and G Kiper and T Ayav and B Ozdemirel and E Tatlıcıoglu and S Hanalioglu and I Işıkay and M Berker}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85107958529&doi=10.1115%2f1.4049394&partnerID=40&md5=975e1687eb1d91a0fe45def8948da24f}, doi = {10.1115/1.4049394}, year = {2021}, date = {2021-01-01}, journal = {Journal of Medical Devices, Transactions of the ASME}, volume = {15}, number = {1}, abstract = {Endoscopic endonasal surgery is a commonly practiced minimally invasive neurosurgical operation for the treatment of a wide range of skull base pathologies including pituitary tumors. A common shortcoming of this surgery is the necessity of a third hand when the endoscope has to be handled to allow active use of both hands of the main surgeon. The robot surgery assistant NeuRoboScope system has been developed to take over the endoscope from the main surgeon’s hand while providing the surgeon with the necessary means of controlling the location and direction of the endoscope. One of the main novelties of the NeuRoboScope system is its human–robot interface designs which regulate and facilitate the interaction between the surgeon and the robot assistant. The human–robot interaction design of the NeuRoboScope system is investigated in two domains: direct physical interaction (DPI) and master–slave teleoperation (MST). The user study indicating the learning curve and ease of use of the MST is given and this paper is concluded via providing the reader with an outlook of possible new human–robot interfaces for the robot assisted surgery systems. Copyright VC 2021 by ASME}, keywords = {}, pubstate = {published}, tppubtype = {article} } Endoscopic endonasal surgery is a commonly practiced minimally invasive neurosurgical operation for the treatment of a wide range of skull base pathologies including pituitary tumors. A common shortcoming of this surgery is the necessity of a third hand when the endoscope has to be handled to allow active use of both hands of the main surgeon. The robot surgery assistant NeuRoboScope system has been developed to take over the endoscope from the main surgeon’s hand while providing the surgeon with the necessary means of controlling the location and direction of the endoscope. One of the main novelties of the NeuRoboScope system is its human–robot interface designs which regulate and facilitate the interaction between the surgeon and the robot assistant. The human–robot interaction design of the NeuRoboScope system is investigated in two domains: direct physical interaction (DPI) and master–slave teleoperation (MST). The user study indicating the learning curve and ease of use of the MST is given and this paper is concluded via providing the reader with an outlook of possible new human–robot interfaces for the robot assisted surgery systems. Copyright VC 2021 by ASME |
Görgülü, I; Dede, M I C; Carbone, G Experimental structural stiffness analysis of a surgical haptic master device manipulator Journal Article Journal of Medical Devices, Transactions of the ASME, 15 (1), 2021. @article{Görgülü2021, title = {Experimental structural stiffness analysis of a surgical haptic master device manipulator}, author = {I Görgülü and M I C Dede and G Carbone}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85104310305&doi=10.1115%2f1.4049515&partnerID=40&md5=048e166dbd6c463f1f09a4381bcbab93}, doi = {10.1115/1.4049515}, year = {2021}, date = {2021-01-01}, journal = {Journal of Medical Devices, Transactions of the ASME}, volume = {15}, number = {1}, abstract = {This paper deals with haptic devices for master-slave telesurgical applications. Namely, a stiffness model fitting methodology and its fine-tuning are proposed based on experimental results. In particular, the proposed procedure is based on virtual joint structural stiffness modeling to be applied in time-efficient compliance compensation strategies. A specific case study is discussed by referring to the HISS haptic device that has been developed and built at Izmir Institute of Technology. Two different experimental setups are designed for stiffness evaluation tests. Experimental results are discussed to demonstrate their implementation in the proposed methodology for the fine-tuning of stiffness model. © 2021 by ASME}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper deals with haptic devices for master-slave telesurgical applications. Namely, a stiffness model fitting methodology and its fine-tuning are proposed based on experimental results. In particular, the proposed procedure is based on virtual joint structural stiffness modeling to be applied in time-efficient compliance compensation strategies. A specific case study is discussed by referring to the HISS haptic device that has been developed and built at Izmir Institute of Technology. Two different experimental setups are designed for stiffness evaluation tests. Experimental results are discussed to demonstrate their implementation in the proposed methodology for the fine-tuning of stiffness model. © 2021 by ASME |
Uzunoǧlu, E; Tatlicioǧlu, E; Dede, M İ C A Multi-Priority Controller for Industrial Macro-Micro Manipulation Journal Article Robotica, 39 (2), pp. 217-232, 2021. @article{Uzunoǧlu2021217, title = {A Multi-Priority Controller for Industrial Macro-Micro Manipulation}, author = {E Uzunoǧlu and E Tatlicioǧlu and M İ C Dede}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85085752198&doi=10.1017%2fS0263574720000338&partnerID=40&md5=95fe3fbdfd64d096223263ac48141bbb}, doi = {10.1017/S0263574720000338}, year = {2021}, date = {2021-01-01}, journal = {Robotica}, volume = {39}, number = {2}, pages = {217-232}, abstract = {In this study, a control algorithm is proposed and evaluated for a special type of kinematically redundant manipulator. This manipulator is comprised of two mechanisms, macro and micro mechanisms, with distinct acceleration and work space characteristics. A control algorithm is devised to minimize the task completion duration and the overall actuator effort with respect to the conventional manipulator. A general framework multi-priority controller for macro-micro manipulators is introduced by utilizing virtual dynamics, which is introduced in null-space projection to achieve secondary tasks. The proposed controller is evaluated on a simulation model based on a previously constructed macro-micro manipulator for planar laser cutting. Task completion duration and the total actuator effort are investigated and the results are compared. Copyright © The Author(s), 2020. Published by Cambridge University Press.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, a control algorithm is proposed and evaluated for a special type of kinematically redundant manipulator. This manipulator is comprised of two mechanisms, macro and micro mechanisms, with distinct acceleration and work space characteristics. A control algorithm is devised to minimize the task completion duration and the overall actuator effort with respect to the conventional manipulator. A general framework multi-priority controller for macro-micro manipulators is introduced by utilizing virtual dynamics, which is introduced in null-space projection to achieve secondary tasks. The proposed controller is evaluated on a simulation model based on a previously constructed macro-micro manipulator for planar laser cutting. Task completion duration and the total actuator effort are investigated and the results are compared. Copyright © The Author(s), 2020. Published by Cambridge University Press. |
2020 |
Yasir, Abdullah; Kiper, Gokhan; Dede, Can M I Kinematic design of a non-parasitic 2R1T parallel mechanism with remote center of motion to be used in minimally invasive surgery applications Journal Article MECHANISM AND MACHINE THEORY, 153 , 2020, ISSN: 0094-114X. @article{ISI:000566908100008, title = {Kinematic design of a non-parasitic 2R1T parallel mechanism with remote center of motion to be used in minimally invasive surgery applications}, author = {Abdullah Yasir and Gokhan Kiper and Can M I Dede}, doi = {10.1016/j.mechmachtheory.2020.104013}, issn = {0094-114X}, year = {2020}, date = {2020-11-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {153}, abstract = {In minimally invasive surgery applications, the use of robotic manipulators is becoming more and more common to enhance the precision of the operations and post-operative processes. Such operations are often performed through an incision port (a pivot point) on the patient's body. Since the end-effector (the handled surgical tool) move about the pivot point, the manipulator has to move about a remote center of motion. In this study, a 3-degrees-of-freedom parallel mechanism with 2R1T (R: rotation, T: translation) remote center of motion capability is presented for minimally invasive surgery applications. First, its kinematic structure is introduced. Then, its kinematic analysis is carried out by using a simplified kinematic model which consists of three intersecting planes. Then the dimensional design is done for the desired workspace and a simulation test is carried out to verify the kinematic formulations. Finally, the prototype of the final design is presented. (c) 2020 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In minimally invasive surgery applications, the use of robotic manipulators is becoming more and more common to enhance the precision of the operations and post-operative processes. Such operations are often performed through an incision port (a pivot point) on the patient's body. Since the end-effector (the handled surgical tool) move about the pivot point, the manipulator has to move about a remote center of motion. In this study, a 3-degrees-of-freedom parallel mechanism with 2R1T (R: rotation, T: translation) remote center of motion capability is presented for minimally invasive surgery applications. First, its kinematic structure is introduced. Then, its kinematic analysis is carried out by using a simplified kinematic model which consists of three intersecting planes. Then the dimensional design is done for the desired workspace and a simulation test is carried out to verify the kinematic formulations. Finally, the prototype of the final design is presented. (c) 2020 Elsevier Ltd. All rights reserved. |
Gorgulu, Ibrahimcan; Carbone, Giuseppe; Dede, Can M I Time efficient stiffness model computation for a parallel haptic mechanism via the virtual joint method Journal Article MECHANISM AND MACHINE THEORY, 143 , 2020, ISSN: 0094-114X. @article{ISI:000502050800019, title = {Time efficient stiffness model computation for a parallel haptic mechanism via the virtual joint method}, author = {Ibrahimcan Gorgulu and Giuseppe Carbone and Can M I Dede}, doi = {10.1016/j.mechmachtheory.2019.103614}, issn = {0094-114X}, year = {2020}, date = {2020-01-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {143}, abstract = {Haptic devices are used for displaying a range of mechanical impedance values to the user. This impedance is regulated by a real-time control loop depending on the position information of the end-effector, which is usually acquired indirectly by using forward kinematics equations. Nevertheless, the kinematic model is insufficient to obtain accurate values if there are non-negligible compliant displacements. This gives a strong motivation for implementing a real-time stiffness model in the haptic control loop for improving its accuracy. Additionally, stiffness performance indices can be used at the design stage for enhancing the haptic devices impedance range within optimal design procedures. Fast solutions of a stiffness model are required for a real-time control as well as for decreasing the optimization time during a design process with a trade-off between accuracy and computational costs. In this study, we propose a computation time-efficient stiffness analysis of a parallel haptic device mechanism. The accuracy and computational costs of the proposed model are calculated and compared with a model that is obtained via a finite element method to demonstrate the effectiveness of the proposed approach with the desired real-time and accuracy performance. (C) 2019 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Haptic devices are used for displaying a range of mechanical impedance values to the user. This impedance is regulated by a real-time control loop depending on the position information of the end-effector, which is usually acquired indirectly by using forward kinematics equations. Nevertheless, the kinematic model is insufficient to obtain accurate values if there are non-negligible compliant displacements. This gives a strong motivation for implementing a real-time stiffness model in the haptic control loop for improving its accuracy. Additionally, stiffness performance indices can be used at the design stage for enhancing the haptic devices impedance range within optimal design procedures. Fast solutions of a stiffness model are required for a real-time control as well as for decreasing the optimization time during a design process with a trade-off between accuracy and computational costs. In this study, we propose a computation time-efficient stiffness analysis of a parallel haptic device mechanism. The accuracy and computational costs of the proposed model are calculated and compared with a model that is obtained via a finite element method to demonstrate the effectiveness of the proposed approach with the desired real-time and accuracy performance. (C) 2019 Elsevier Ltd. All rights reserved. |
2017 |
Uzunoglu, Emre; Dede, Mehmet Ismet Can Extending model-mediation method to multi-degree-of-freedom teleoperation systems experiencing time delays in communication Journal Article ROBOTICA, 35 (5), pp. 1121-1136, 2017, ISSN: 0263-5747. @article{ISI:000399043500007, title = {Extending model-mediation method to multi-degree-of-freedom teleoperation systems experiencing time delays in communication}, author = {Emre Uzunoglu and Mehmet Ismet Can Dede}, doi = {10.1017/S0263574715001010}, issn = {0263-5747}, year = {2017}, date = {2017-05-01}, journal = {ROBOTICA}, volume = {35}, number = {5}, pages = {1121-1136}, abstract = {In this study, a bilateral teleoperation control algorithm is developed in which the model-mediation method is integrated with an impedance controller. The model-mediation method is also extended to three-degrees-of-freedom teleoperation. The aim of this controller is to compensate for instability issues and excessive forcing applied to the slave environment stemming from time delays in communication. The proposed control method is experimentally tested with two haptic desktop devices. Test results indicate that stability and passivity of the bilateral teleoperation system is preserved under variable time delays in communication. It is also observed that safer interactions of the slave system with its environment can be achieved by utilizing an extended version of the model-mediation method with an impedance controller.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, a bilateral teleoperation control algorithm is developed in which the model-mediation method is integrated with an impedance controller. The model-mediation method is also extended to three-degrees-of-freedom teleoperation. The aim of this controller is to compensate for instability issues and excessive forcing applied to the slave environment stemming from time delays in communication. The proposed control method is experimentally tested with two haptic desktop devices. Test results indicate that stability and passivity of the bilateral teleoperation system is preserved under variable time delays in communication. It is also observed that safer interactions of the slave system with its environment can be achieved by utilizing an extended version of the model-mediation method with an impedance controller. |
Kiper, Gokhan; Dede, Mehmet Ismet Can; Maaroof, Omar W; Ozkahya, Merve Function generation with two loop mechanisms using decomposition and correction method Journal Article MECHANISM AND MACHINE THEORY, 110 , pp. 16-26, 2017, ISSN: 0094-114X. @article{ISI:000394063500002, title = {Function generation with two loop mechanisms using decomposition and correction method}, author = {Gokhan Kiper and Mehmet Ismet Can Dede and Omar W Maaroof and Merve Ozkahya}, doi = {10.1016/j.mechmachtheory.2016.12.004}, issn = {0094-114X}, year = {2017}, date = {2017-04-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {110}, pages = {16-26}, abstract = {Method of decomposition has been successfully applied to function generation with multi-loop mechanisms. For a two-loop mechanism, a function y = f(x) can be decomposed into two as w = g(x) and y = h(w) = h(g(x)) = f(x). This study makes use of the method of decomposition for two loop mechanisms, where the errors from each loop are forced to match each other. In the first loop, which includes the input of the mechanism, the decomposed function (g) is generated and the resulting structural error is determined. Then, for the second loop, the desired output of the function (f) is considered as an input and the structural error of the decomposed function (g) is determined. By matching the obtained structural errors, the final error in the output of the mechanism is reduced. Three different correction methods are proposed. The first method has three precision points per loop, while the second method has four. In the third method, the extrema of the errors from both loops are matched. The methods are applied to a Watt II type planar six-bar linkage for demonstration. Several numerical examples are worked out and the results are compared with the results in the literature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Method of decomposition has been successfully applied to function generation with multi-loop mechanisms. For a two-loop mechanism, a function y = f(x) can be decomposed into two as w = g(x) and y = h(w) = h(g(x)) = f(x). This study makes use of the method of decomposition for two loop mechanisms, where the errors from each loop are forced to match each other. In the first loop, which includes the input of the mechanism, the decomposed function (g) is generated and the resulting structural error is determined. Then, for the second loop, the desired output of the function (f) is considered as an input and the structural error of the decomposed function (g) is determined. By matching the obtained structural errors, the final error in the output of the mechanism is reduced. Three different correction methods are proposed. The first method has three precision points per loop, while the second method has four. In the third method, the extrema of the errors from both loops are matched. The methods are applied to a Watt II type planar six-bar linkage for demonstration. Several numerical examples are worked out and the results are compared with the results in the literature. |
Sahin, Osman Nuri; Uzunoglu, Emre; Tatlicioglu, Enver; Dede, Can M I Design and Development of an Educational Desktop Robot (RD)-D-3 Journal Article COMPUTER APPLICATIONS IN ENGINEERING EDUCATION, 25 (2), pp. 222-229, 2017, ISSN: 1061-3773. @article{ISI:000401196200006, title = {Design and Development of an Educational Desktop Robot (RD)-D-3}, author = {Osman Nuri Sahin and Emre Uzunoglu and Enver Tatlicioglu and Can M I Dede}, doi = {10.1002/cae.21792}, issn = {1061-3773}, year = {2017}, date = {2017-03-01}, journal = {COMPUTER APPLICATIONS IN ENGINEERING EDUCATION}, volume = {25}, number = {2}, pages = {222-229}, abstract = {Robotic desktop devices have been used for academic purposes for a variety of investigation and development studies. Desktop devices for academic/educational purposes have been highly anticipated especially in the fields of haptics, teleoperation systems, and control studies. This paper's motivation is to present the steps of designing, manufacturing, and implementing of Educational Desktop Robot (RD)-D-3 to be used for haptics, teleoperation, and redundancy control studies. The design, manufacturing details, kinematic, and dynamic model of the robot are described in the manuscript. Additionally, a case study is carried out for end effector control in task space is given and the results are shared. (C) 2017 Wiley Periodicals, Inc.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Robotic desktop devices have been used for academic purposes for a variety of investigation and development studies. Desktop devices for academic/educational purposes have been highly anticipated especially in the fields of haptics, teleoperation systems, and control studies. This paper's motivation is to present the steps of designing, manufacturing, and implementing of Educational Desktop Robot (RD)-D-3 to be used for haptics, teleoperation, and redundancy control studies. The design, manufacturing details, kinematic, and dynamic model of the robot are described in the manuscript. Additionally, a case study is carried out for end effector control in task space is given and the results are shared. (C) 2017 Wiley Periodicals, Inc. |
2016 |
Gundogdu, Hilal Tolasa; Dede, Mehmet Ismet Can; Taner, Baris; Ridolfi, Alessandro; Costanzi, Riccardo; Allotta, Benedetto Design and testing of an innovative cleaning tool for underwater applications Journal Article PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART M-JOURNAL OF ENGINEERING FOR THE MARITIME ENVIRONMENT, 230 (4), pp. 579-590, 2016, ISSN: 1475-0902. @article{ISI:000392916800003, title = {Design and testing of an innovative cleaning tool for underwater applications}, author = {Hilal Tolasa Gundogdu and Mehmet Ismet Can Dede and Baris Taner and Alessandro Ridolfi and Riccardo Costanzi and Benedetto Allotta}, doi = {10.1177/1475090215610599}, issn = {1475-0902}, year = {2016}, date = {2016-11-01}, journal = {PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART M-JOURNAL OF ENGINEERING FOR THE MARITIME ENVIRONMENT}, volume = {230}, number = {4}, pages = {579-590}, abstract = {The aim of this work is to describe the development of an innovative cleaning tool for underwater applications, to be used in particular in the field of underwater archaeology. This work takes place in the framework of the EU FP7-funded ARROWS project. ARROWS adapts and develops low-cost autonomous underwater vehicle technologies to significantly reduce the costs of underwater archaeological operations, covering the full extent of archaeological campaigns. The project deals with underwater mapping, diagnosis and cleaning tasks. During the first half of the project, a cleaning tool prototype, able to be mounted on underwater vehicles, has been worked out: this cleaning tool will be exploited not only during research missions but also for the periodic monitoring, controlling and maintenance activities of well-known underwater archaeological sites (e.g. periodic cleaning operations).}, keywords = {}, pubstate = {published}, tppubtype = {article} } The aim of this work is to describe the development of an innovative cleaning tool for underwater applications, to be used in particular in the field of underwater archaeology. This work takes place in the framework of the EU FP7-funded ARROWS project. ARROWS adapts and develops low-cost autonomous underwater vehicle technologies to significantly reduce the costs of underwater archaeological operations, covering the full extent of archaeological campaigns. The project deals with underwater mapping, diagnosis and cleaning tasks. During the first half of the project, a cleaning tool prototype, able to be mounted on underwater vehicles, has been worked out: this cleaning tool will be exploited not only during research missions but also for the periodic monitoring, controlling and maintenance activities of well-known underwater archaeological sites (e.g. periodic cleaning operations). |
Dede, Mehmet Ismet Can; Maaroof, Omar W; Tatlicioglu, Enver A New Objective Function for Obstacle Avoidance by Redundant Service Robot Arms Journal Article INTERNATIONAL JOURNAL OF ADVANCED ROBOTIC SYSTEMS, 13 , 2016, ISSN: 1729-8806. @article{ISI:000372038700001, title = {A New Objective Function for Obstacle Avoidance by Redundant Service Robot Arms}, author = {Mehmet Ismet Can Dede and Omar W Maaroof and Enver Tatlicioglu}, doi = {10.5772/62471}, issn = {1729-8806}, year = {2016}, date = {2016-03-01}, journal = {INTERNATIONAL JOURNAL OF ADVANCED ROBOTIC SYSTEMS}, volume = {13}, abstract = {The performance of task-space tracking control of kinematically redundant robots regulating self-motion to ensure obstacle avoidance is studied and discussed. As the sub-task objective, the links of the kinematically redundant assistive robot should avoid any collisions with the patient that is being assisted. The shortcomings of the obstacle avoidance algorithms are discussed and a new obstacle avoidance algorithm is proposed. The performance of the proposed algorithm is validated with tests that were carried out using the virtual model of a seven degrees-of-freedom robot arm. The test results indicate that the developed controller for the robot manipulator is successful in both accomplishing the main-task and the sub-task objectives.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The performance of task-space tracking control of kinematically redundant robots regulating self-motion to ensure obstacle avoidance is studied and discussed. As the sub-task objective, the links of the kinematically redundant assistive robot should avoid any collisions with the patient that is being assisted. The shortcomings of the obstacle avoidance algorithms are discussed and a new obstacle avoidance algorithm is proposed. The performance of the proposed algorithm is validated with tests that were carried out using the virtual model of a seven degrees-of-freedom robot arm. The test results indicate that the developed controller for the robot manipulator is successful in both accomplishing the main-task and the sub-task objectives. |
Uzunoglu, Emre; Dede, Mehmet Ismet Can; Kiper, Gokhan Trajectory planning for a planar macro-micro manipulator of a laser-cutting machine Journal Article INDUSTRIAL ROBOT-THE INTERNATIONAL JOURNAL OF ROBOTICS RESEARCH AND APPLICATION, 43 (5, SI), pp. 513-523, 2016, ISSN: 0143-991X. @article{ISI:000386142100009, title = {Trajectory planning for a planar macro-micro manipulator of a laser-cutting machine}, author = {Emre Uzunoglu and Mehmet Ismet Can Dede and Gokhan Kiper}, doi = {10.1108/IR-02-2016-0057}, issn = {0143-991X}, year = {2016}, date = {2016-01-01}, journal = {INDUSTRIAL ROBOT-THE INTERNATIONAL JOURNAL OF ROBOTICS RESEARCH AND APPLICATION}, volume = {43}, number = {5, SI}, pages = {513-523}, abstract = {Purpose - In the industry, there is always a demand to shorten the task completion durations to maximize the efficiency of the operation. This work focuses on making use of a special type of kinematic redundancy, macro-micro manipulation, to minimize the task completion duration. The purpose of this paper is to develop the most convenient trajectory planner to be integrated with industrial computerized numerical control (CNC) systems to resolve kinematic redundancy for task duration minimization. Design/methodology/approach - A special type of kinematic redundancy is devised by using two kinematically different mechanisms that have different advantages, which are named as macro and micro mechanisms. In this case, the control design including the trajectory planning should be devised taking into account the distinct advantages of both mechanisms. A new trajectory planning algorithm is designed and used for the constructed planar laser-cutting machine, and some benchmark pieces are cut. Findings - Offline method has practical limitations for employment in a real case scenario such as assuming infinite jerk limits for each axis motion. This limitation was removed by using an online trajectory generation technique. Experimental test results indicate that the online trajectory planning technique developed for the macro-micro mechanism to shorten the task duration was successful. Practical implications - Although the new trajectory planning algorithm is implemented for a laser-cutting machine, it can also be used for other manufacturing systems that require higher acceleration and accuracy levels than the conventional machines. The new algorithm is compatible with the commercially available CNC systems. Originality/value - In this work, a new approach to reducing the task duration for planar machining operations was introduced by making use of macro-micro manipulation concept. The core novelty of the work is devising trajectory planning algorithms to get the most efficiency in terms of acceleration limits from a macro-micro manipulation while making these algorithms deployable to most of the CNC systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Purpose - In the industry, there is always a demand to shorten the task completion durations to maximize the efficiency of the operation. This work focuses on making use of a special type of kinematic redundancy, macro-micro manipulation, to minimize the task completion duration. The purpose of this paper is to develop the most convenient trajectory planner to be integrated with industrial computerized numerical control (CNC) systems to resolve kinematic redundancy for task duration minimization. Design/methodology/approach - A special type of kinematic redundancy is devised by using two kinematically different mechanisms that have different advantages, which are named as macro and micro mechanisms. In this case, the control design including the trajectory planning should be devised taking into account the distinct advantages of both mechanisms. A new trajectory planning algorithm is designed and used for the constructed planar laser-cutting machine, and some benchmark pieces are cut. Findings - Offline method has practical limitations for employment in a real case scenario such as assuming infinite jerk limits for each axis motion. This limitation was removed by using an online trajectory generation technique. Experimental test results indicate that the online trajectory planning technique developed for the macro-micro mechanism to shorten the task duration was successful. Practical implications - Although the new trajectory planning algorithm is implemented for a laser-cutting machine, it can also be used for other manufacturing systems that require higher acceleration and accuracy levels than the conventional machines. The new algorithm is compatible with the commercially available CNC systems. Originality/value - In this work, a new approach to reducing the task duration for planar machining operations was introduced by making use of macro-micro manipulation concept. The core novelty of the work is devising trajectory planning algorithms to get the most efficiency in terms of acceleration limits from a macro-micro manipulation while making these algorithms deployable to most of the CNC systems. |
2014 |
Alizade, Rasim I; Kiper, Gokhan; Bagdadioglu, Baris; Dede, Can M I Function synthesis of Bennett 6R mechanisms using Chebyshev approximation Journal Article MECHANISM AND MACHINE THEORY, 81 , pp. 62-78, 2014, ISSN: 0094-114X. @article{ISI:000341141400006, title = {Function synthesis of Bennett 6R mechanisms using Chebyshev approximation}, author = {Rasim I Alizade and Gokhan Kiper and Baris Bagdadioglu and Can M I Dede}, doi = {10.1016/j.mechmachtheory.2014.06.010}, issn = {0094-114X}, year = {2014}, date = {2014-11-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {81}, pages = {62-78}, abstract = {This study focuses on approximate function synthesis of the three types of overconstrained Bennett 6R mechanisms using Chebyshev approximation. The three mechanisms are the double-planar, double-spherical and the plano-spherical 6R linkages. The single-loop 6R mechanisms are dissected into two imaginary loops and function synthesis is performed for both loops. First, the link lengths are employed as construction parameters of the mechanism. Then extra construction parameters for the input or output joint variables are introduced in order to increase the design points and hence enhance the accuracy of approximation. The synthesis formulations are applied computationally as case studies. The case studies illustrate how a designer can compare the three types of Bennett 6R mechanisms for the same function. Also we present a comparison of the spherical four-bar with the double-spherical 6R mechanism and show that the accuracy is improved when the 6R linkage is used. (C) 2014 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study focuses on approximate function synthesis of the three types of overconstrained Bennett 6R mechanisms using Chebyshev approximation. The three mechanisms are the double-planar, double-spherical and the plano-spherical 6R linkages. The single-loop 6R mechanisms are dissected into two imaginary loops and function synthesis is performed for both loops. First, the link lengths are employed as construction parameters of the mechanism. Then extra construction parameters for the input or output joint variables are introduced in order to increase the design points and hence enhance the accuracy of approximation. The synthesis formulations are applied computationally as case studies. The case studies illustrate how a designer can compare the three types of Bennett 6R mechanisms for the same function. Also we present a comparison of the spherical four-bar with the double-spherical 6R mechanism and show that the accuracy is improved when the 6R linkage is used. (C) 2014 Elsevier Ltd. All rights reserved. |
Maaroof, Omar W; Dede, Mehmet Ismet Can Kinematic synthesis of over-constrained double-spherical six-bar mechanism Journal Article MECHANISM AND MACHINE THEORY, 73 , pp. 154-168, 2014, ISSN: 0094-114X. @article{ISI:000332399300011, title = {Kinematic synthesis of over-constrained double-spherical six-bar mechanism}, author = {Omar W Maaroof and Mehmet Ismet Can Dede}, doi = {10.1016/j.mechmachtheory.2013.10.013}, issn = {0094-114X}, year = {2014}, date = {2014-03-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {73}, pages = {154-168}, abstract = {The main problem in the synthesis of any mechanism is the fact that the objective function of the mechanism, which will be synthesized, should be found and simplified by using appropriate algebraic method. Finding objective function and calculation process can become complicated especially when the number of design parameters is increased for the over-constrained mechanisms. A new technique for solving the kinematic synthesis of over-constrained double-spherical six-bar mechanism is developed and applied in this work. Interpolation approximation is used during synthesis procedure. A numerical example for the kinematic synthesis procedure is given to validate the theory in application. (C) 2013 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The main problem in the synthesis of any mechanism is the fact that the objective function of the mechanism, which will be synthesized, should be found and simplified by using appropriate algebraic method. Finding objective function and calculation process can become complicated especially when the number of design parameters is increased for the over-constrained mechanisms. A new technique for solving the kinematic synthesis of over-constrained double-spherical six-bar mechanism is developed and applied in this work. Interpolation approximation is used during synthesis procedure. A numerical example for the kinematic synthesis procedure is given to validate the theory in application. (C) 2013 Elsevier Ltd. All rights reserved. |
2013 |
Kiper, Gökhan; Bilgincan, Tunç; Dede, Mehmet İsmet Can Function generation synthesis of planar 5R mechanism Journal Article 2013. @article{kiper2013function, title = {Function generation synthesis of planar 5R mechanism}, author = {Gökhan Kiper and Tunç Bilgincan and Mehmet İsmet Can Dede}, url = {http://hdl.handle.net/11147/4217}, year = {2013}, date = {2013-01-01}, publisher = {IFToMM}, abstract = {This paper deals with the function generation problem for a planar five-bar mechanism. The inputs to the mechanism are selected as one of the fixed joints and the mid-joint, whereas the remaining fixed joint represents the output. Synthesis problem of the five-bar mechanism is analytically formulated and an objective function is expressed in polynomial form. Function generation synthesis is performed with equal spacing and Chebyshev approximation method. The four unknown construction parameters and the error are evaluated by means of five design points and the coefficients of the objective function are determined by numerical iteration using four stationary and one moving design point. Stationary points are placed at the boundaries of the motion and the moving point is re-selected at each iteration as the point corresponding to the extremum error. Iterations are repeated until the values are stabilized. The stabilization usually occurs at the third iteration. By this method, the maximum error values are approximately equated, hence the total error is bounded at certain limits. Finally the construction parameters of the mechanism are determined.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper deals with the function generation problem for a planar five-bar mechanism. The inputs to the mechanism are selected as one of the fixed joints and the mid-joint, whereas the remaining fixed joint represents the output. Synthesis problem of the five-bar mechanism is analytically formulated and an objective function is expressed in polynomial form. Function generation synthesis is performed with equal spacing and Chebyshev approximation method. The four unknown construction parameters and the error are evaluated by means of five design points and the coefficients of the objective function are determined by numerical iteration using four stationary and one moving design point. Stationary points are placed at the boundaries of the motion and the moving point is re-selected at each iteration as the point corresponding to the extremum error. Iterations are repeated until the values are stabilized. The stabilization usually occurs at the third iteration. By this method, the maximum error values are approximately equated, hence the total error is bounded at certain limits. Finally the construction parameters of the mechanism are determined. |
Prof. Dr. H. Seçil Artem
External Transfer Coordinator
Educational Background
B.Sc. Middle East Technical University, Turkey, Engineering Sciences, 1987
M.Sc. Middle East Technical University, Turkey, Engineering Sciences, 1990
Ph.D. Middle East Technical University, Turkey, Engineering Sciences, 1999
Research Interests
- Engineering Mathematics
- Numerical solutions for PDEs
- +90 232 750 6771
- +90 232 750 6701
- Mechanical Engineering Building (114)
Publications
Kangal, Serkan; Say, Harun A; Ayakda, Ozan; Kartav, Osman; Aydin, Levent; Artem, Secil H; Aktas, Engin; Yuceturk, Kutay; Tanoglu, Metin; Kandemir, Sinan; Beylergil, Bertan A Comprehensive Study on Burst Pressure Performance of Aluminum Liner for Hydrogen Storage Vessels Journal Article JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME, 143 (4), 2021. @article{WOS:000669955100012, title = {A Comprehensive Study on Burst Pressure Performance of Aluminum Liner for Hydrogen Storage Vessels}, author = {Serkan Kangal and Harun A Say and Ozan Ayakda and Osman Kartav and Levent Aydin and Secil H Artem and Engin Aktas and Kutay Yuceturk and Metin Tanoglu and Sinan Kandemir and Bertan Beylergil}, doi = {10.1115/1.4049644}, year = {2021}, date = {2021-08-01}, journal = {JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, volume = {143}, number = {4}, abstract = {This paper presents a comparative study on the burst pressure performance of aluminum (Al) liner for type-III composite overwrapped pressure vessels (COPVs). In the analysis, the vessels were loaded with increasing internal pressure up to the burst pressure level. In the analytical part of the study, the burst pressure of the cylindrical part was predicted based on the modified von Mises, Tresca, and average shear stress criterion (ASSC). In the numerical analysis, a finite element (FE) model was established in order to predict the behavior of the vessel as a function of increasing internal pressure and determine the final burst. The Al pressure vessels made of Al-6061-T6 alloy with a capacity of 5 L were designed. The manufacturing of the metallic vessels was purchased from a metal forming company. The experimental study was conducted by pressurizing the Al vessels until the burst failure occurred. The radial and axial strain behaviors were monitored at various locations on the vessels during loading. The results obtained through analytical, numerical, and experimental work were compared. The average experimental burst pressure of the vessels was found to be 279 bar. The experimental strain data were compared with the results of the FE analysis. The results indicated that the FE analysis and ASSC-based elastoplastic analytical approaches yielded the best predictions which are within 2.2% of the experimental burst failure values. It was also found that the elastic analysis underestimated the burst failure results; however, it was effective for determining the critical regions over the vessel structure. The strain behavior of the vessels obtained through experimental investigations was well correlated with those predicted through FE analysis.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper presents a comparative study on the burst pressure performance of aluminum (Al) liner for type-III composite overwrapped pressure vessels (COPVs). In the analysis, the vessels were loaded with increasing internal pressure up to the burst pressure level. In the analytical part of the study, the burst pressure of the cylindrical part was predicted based on the modified von Mises, Tresca, and average shear stress criterion (ASSC). In the numerical analysis, a finite element (FE) model was established in order to predict the behavior of the vessel as a function of increasing internal pressure and determine the final burst. The Al pressure vessels made of Al-6061-T6 alloy with a capacity of 5 L were designed. The manufacturing of the metallic vessels was purchased from a metal forming company. The experimental study was conducted by pressurizing the Al vessels until the burst failure occurred. The radial and axial strain behaviors were monitored at various locations on the vessels during loading. The results obtained through analytical, numerical, and experimental work were compared. The average experimental burst pressure of the vessels was found to be 279 bar. The experimental strain data were compared with the results of the FE analysis. The results indicated that the FE analysis and ASSC-based elastoplastic analytical approaches yielded the best predictions which are within 2.2% of the experimental burst failure values. It was also found that the elastic analysis underestimated the burst failure results; however, it was effective for determining the critical regions over the vessel structure. The strain behavior of the vessels obtained through experimental investigations was well correlated with those predicted through FE analysis. |
Aydin, L; Artem, H S; Deveci, H A Single- and Multiobjective Optimizations of Dimensionally Stable Composites Using Genetic Algorithms Journal Article Mechanics of Composite Materials, 57 (3), pp. 321-336, 2021. @article{Aydin2021321, title = {Single- and Multiobjective Optimizations of Dimensionally Stable Composites Using Genetic Algorithms}, author = {L Aydin and H S Artem and H A Deveci}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85110920003&doi=10.1007%2fs11029-021-09957-y&partnerID=40&md5=c69289acc580f74cfaae88cb543a9cef}, doi = {10.1007/s11029-021-09957-y}, year = {2021}, date = {2021-01-01}, journal = {Mechanics of Composite Materials}, volume = {57}, number = {3}, pages = {321-336}, abstract = {The present study aims to design stacking sequences of dimensionally stable symmetric balanced laminated carbon/epoxy composites, with different numbers of layers, with a low coefficient of thermal expansion and high elastic moduli. To avoid excessive interlaminar stresses in the composites, the contiguity constraint for plies is also taken into consideration. In the design process, both single- and multiobjective optimization approaches, including genetic algorithms, are utilized. Results showed that stacking sequences ensuring lower thermal expansion coefficients and higher elastic moduli than those of traditional laminate designs can be obtained. © 2021, Springer Science+Business Media, LLC, part of Springer Nature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The present study aims to design stacking sequences of dimensionally stable symmetric balanced laminated carbon/epoxy composites, with different numbers of layers, with a low coefficient of thermal expansion and high elastic moduli. To avoid excessive interlaminar stresses in the composites, the contiguity constraint for plies is also taken into consideration. In the design process, both single- and multiobjective optimization approaches, including genetic algorithms, are utilized. Results showed that stacking sequences ensuring lower thermal expansion coefficients and higher elastic moduli than those of traditional laminate designs can be obtained. © 2021, Springer Science+Business Media, LLC, part of Springer Nature. |
Kartav, O; Kangal, S; Yücetürk, K; Tanoğlu, M; Aktaş, E; Artem, H S Development and analysis of composite overwrapped pressure vessels for hydrogen storage Journal Article Journal of Composite Materials, 55 (28), pp. 4141-4155, 2021. @article{Kartav20214141, title = {Development and analysis of composite overwrapped pressure vessels for hydrogen storage}, author = {O Kartav and S Kangal and K Yücetürk and M Tanoğlu and E Aktaş and H S Artem}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85110939454&doi=10.1177%2f00219983211033568&partnerID=40&md5=c31db8e0f0de63135bf2da9bf634900d}, doi = {10.1177/00219983211033568}, year = {2021}, date = {2021-01-01}, journal = {Journal of Composite Materials}, volume = {55}, number = {28}, pages = {4141-4155}, abstract = {In this study, composite overwrapped pressure vessels (COPVs) for high-pressure hydrogen storage were designed, modeled by finite element (FE) method, manufactured by filament winding technique and tested for burst pressure. Aluminum 6061-T6 was selected as a metallic liner material. Epoxy impregnated carbon filaments were overwrapped over the liner with a winding angle of ±14° to obtain fully overwrapped composite reinforced vessels with non-identical front and back dome layers. The COPVs were loaded with increasing internal pressure up to the burst pressure level. During loading, deformation of the vessels was measured locally with strain gauges. The mechanical performances of COPVs designed with various number of helical, hoop and doily layers were investigated by both experimental and numerical methods. In numerical method, FE analysis containing a simple progressive damage model available in ANSYS software package for the composite section was performed. The results revealed that the FE model provides a good correlation as compared to experimental strain results for the developed COPVs. The burst pressure test results showed that integration of doily layers to the filament winding process resulted with an improvement of the COPVs performance. © The Author(s) 2021.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, composite overwrapped pressure vessels (COPVs) for high-pressure hydrogen storage were designed, modeled by finite element (FE) method, manufactured by filament winding technique and tested for burst pressure. Aluminum 6061-T6 was selected as a metallic liner material. Epoxy impregnated carbon filaments were overwrapped over the liner with a winding angle of ±14° to obtain fully overwrapped composite reinforced vessels with non-identical front and back dome layers. The COPVs were loaded with increasing internal pressure up to the burst pressure level. During loading, deformation of the vessels was measured locally with strain gauges. The mechanical performances of COPVs designed with various number of helical, hoop and doily layers were investigated by both experimental and numerical methods. In numerical method, FE analysis containing a simple progressive damage model available in ANSYS software package for the composite section was performed. The results revealed that the FE model provides a good correlation as compared to experimental strain results for the developed COPVs. The burst pressure test results showed that integration of doily layers to the filament winding process resulted with an improvement of the COPVs performance. © The Author(s) 2021. |
Kangal, S; Kartav, O; Tanoğlu, M; Aktaş, E; Artem, H S Journal of Composite Materials, 54 (7), pp. 961-980, 2020. @article{Kangal2020961, title = {Investigation of interlayer hybridization effect on burst pressure performance of composite overwrapped pressure vessels with load-sharing metallic liner}, author = {S Kangal and O Kartav and M Tanoğlu and E Aktaş and H S Artem}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85071956589&doi=10.1177%2f0021998319870588&partnerID=40&md5=90d8ba513531b1cd09c963d447aebf4a}, doi = {10.1177/0021998319870588}, year = {2020}, date = {2020-01-01}, journal = {Journal of Composite Materials}, volume = {54}, number = {7}, pages = {961-980}, abstract = {In this study, multi-layered composite overwrapped pressure vessels for high-pressure gaseous storage were designed, modeled by finite element method and manufactured by filament winding technique. 34CrMo4 steel was selected as a load-sharing metallic liner. Glass and carbon filaments were overwrapped on the liner with a winding angle of [±11°/90°2]3 to obtain fully overwrapped composite reinforced vessel with non-identical front and back dome endings. The vessels were loaded with increasing internal pressure up to the burst pressure level. The mechanical performances of pressure vessels, (i) fully overwrapped with glass fibers and (ii) with additional two carbon hoop layers on the cylindrical section, were investigated by both experimental and numerical approaches. In numerical approaches, finite element analysis was performed featuring a simple progressive damage model available in ANSYS software package for the composite section. The metal liner was modeled as elastic–plastic material. The results reveal that the finite element model provides a good correlation between experimental and numerical strain results for the vessels, together with the indication of the positive effect on radial deformation of the COPVs due to the composite interlayer hybridization. The constructed model was also able to predict experimental burst pressures within a range of 8%. However, the experimental and finite element analysis results showed that hybridization of hoop layers did not have any significant impact on the burst pressure performance of the vessels. This finding was attributed to the change of load-sharing capacity of composite layers due to the stiffness difference of carbon and glass fibers. © The Author(s) 2019.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, multi-layered composite overwrapped pressure vessels for high-pressure gaseous storage were designed, modeled by finite element method and manufactured by filament winding technique. 34CrMo4 steel was selected as a load-sharing metallic liner. Glass and carbon filaments were overwrapped on the liner with a winding angle of [±11°/90°2]3 to obtain fully overwrapped composite reinforced vessel with non-identical front and back dome endings. The vessels were loaded with increasing internal pressure up to the burst pressure level. The mechanical performances of pressure vessels, (i) fully overwrapped with glass fibers and (ii) with additional two carbon hoop layers on the cylindrical section, were investigated by both experimental and numerical approaches. In numerical approaches, finite element analysis was performed featuring a simple progressive damage model available in ANSYS software package for the composite section. The metal liner was modeled as elastic–plastic material. The results reveal that the finite element model provides a good correlation between experimental and numerical strain results for the vessels, together with the indication of the positive effect on radial deformation of the COPVs due to the composite interlayer hybridization. The constructed model was also able to predict experimental burst pressures within a range of 8%. However, the experimental and finite element analysis results showed that hybridization of hoop layers did not have any significant impact on the burst pressure performance of the vessels. This finding was attributed to the change of load-sharing capacity of composite layers due to the stiffness difference of carbon and glass fibers. © The Author(s) 2019. |
Deveci, Arda H; Artem, Secil H Optimum design of fatigue-resistant composite laminates using hybrid algorithm Journal Article COMPOSITE STRUCTURES, 168 , pp. 178-188, 2017, ISSN: 0263-8223. @article{ISI:000398014200017, title = {Optimum design of fatigue-resistant composite laminates using hybrid algorithm}, author = {Arda H Deveci and Secil H Artem}, doi = {10.1016/j.compstruct.2017.01.064}, issn = {0263-8223}, year = {2017}, date = {2017-05-01}, journal = {COMPOSITE STRUCTURES}, volume = {168}, pages = {178-188}, abstract = {In this study, a fatigue life prediction model termed as Failure Tensor Polynomial in Fatigue (FTPF) is applied to the optimum stacking sequence design of laminated composites under various in-plane cyclic loadings to obtain maximum fatigue life. The validity of the model is investigated with an experimental correlation using the data available in the literature. The correlation study indicates the reliability of FTPF, and its applicability to different composite materials and multidirectional laminates. In the optimization, a hybrid algorithm combining genetic algorithm and generalized pattern search algorithm is used. It is found by test problems that the hybrid algorithm shows superior performance in finding global optima compared to the so far best results in the literature. After the verifications, a number of problems including different design cases are solved, and the optimum designs constituted of discrete fiber angles which give the maximum possible fatigue lives are proposed to discuss. A comparison study is also performed with selected design cases to demonstrate potential advantages of using non-conventional fiber angles in design. (C) 2017 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, a fatigue life prediction model termed as Failure Tensor Polynomial in Fatigue (FTPF) is applied to the optimum stacking sequence design of laminated composites under various in-plane cyclic loadings to obtain maximum fatigue life. The validity of the model is investigated with an experimental correlation using the data available in the literature. The correlation study indicates the reliability of FTPF, and its applicability to different composite materials and multidirectional laminates. In the optimization, a hybrid algorithm combining genetic algorithm and generalized pattern search algorithm is used. It is found by test problems that the hybrid algorithm shows superior performance in finding global optima compared to the so far best results in the literature. After the verifications, a number of problems including different design cases are solved, and the optimum designs constituted of discrete fiber angles which give the maximum possible fatigue lives are proposed to discuss. A comparison study is also performed with selected design cases to demonstrate potential advantages of using non-conventional fiber angles in design. (C) 2017 Elsevier Ltd. All rights reserved. |
Deveci, Arda H; Aydin, Levent; Artem, Secil H Buckling optimization of composite laminates using a hybrid algorithm under Puck failure criterion constraint Journal Article JOURNAL OF REINFORCED PLASTICS AND COMPOSITES, 35 (16), pp. 1233-1247, 2016, ISSN: 0731-6844. @article{ISI:000382493000002, title = {Buckling optimization of composite laminates using a hybrid algorithm under Puck failure criterion constraint}, author = {Arda H Deveci and Levent Aydin and Secil H Artem}, doi = {10.1177/0731684416646860}, issn = {0731-6844}, year = {2016}, date = {2016-08-01}, journal = {JOURNAL OF REINFORCED PLASTICS AND COMPOSITES}, volume = {35}, number = {16}, pages = {1233-1247}, abstract = {In this study, an optimization procedure is proposed to find the optimum stacking sequence designs of laminated composite plates in different fiber angle domains for maximum buckling resistance. A hybrid algorithm combining genetic algorithm and trust region reflective algorithm is used in the optimization to obtain higher performance and improve the quality of solutions. As a novelty, Puck fiber and inter-fiber failure criteria are directly implemented to the optimization problems as nonlinear function constraints, which have allowed more consistent and feasible results. The performance of the hybrid algorithm is demonstrated by comparing with the individual performances of genetic and trust region reflective algorithms via test problems from the literature. Also, a study is performed to exhibit the effectiveness of the selected failure criterion as constraint among the other common criteria. The proposed procedure is used to solve many problems including various design considerations. The results indicate that reliable stacking sequence designs can be achieved in specific configurations even for the composite plates subjected to superior buckling loads when Puck physically based (3D) failure theory is considered as a first ply failure constraint in the buckling optimization.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, an optimization procedure is proposed to find the optimum stacking sequence designs of laminated composite plates in different fiber angle domains for maximum buckling resistance. A hybrid algorithm combining genetic algorithm and trust region reflective algorithm is used in the optimization to obtain higher performance and improve the quality of solutions. As a novelty, Puck fiber and inter-fiber failure criteria are directly implemented to the optimization problems as nonlinear function constraints, which have allowed more consistent and feasible results. The performance of the hybrid algorithm is demonstrated by comparing with the individual performances of genetic and trust region reflective algorithms via test problems from the literature. Also, a study is performed to exhibit the effectiveness of the selected failure criterion as constraint among the other common criteria. The proposed procedure is used to solve many problems including various design considerations. The results indicate that reliable stacking sequence designs can be achieved in specific configurations even for the composite plates subjected to superior buckling loads when Puck physically based (3D) failure theory is considered as a first ply failure constraint in the buckling optimization. |
Aydin, Levent; Artem, Secil Altundag H Axisymmetric crack problem of thick-walled cylinder with loadings on crack surfaces Journal Article ENGINEERING FRACTURE MECHANICS, 75 (6), pp. 1294-1309, 2008, ISSN: 0013-7944. @article{ISI:000253751900002, title = {Axisymmetric crack problem of thick-walled cylinder with loadings on crack surfaces}, author = {Levent Aydin and Secil Altundag H Artem}, doi = {10.1016/j.engfracmech.2007.07.016}, issn = {0013-7944}, year = {2008}, date = {2008-04-01}, journal = {ENGINEERING FRACTURE MECHANICS}, volume = {75}, number = {6}, pages = {1294-1309}, abstract = {This study is concerned with the fracture of an infinite thick-walled cylinder. The inner surface of the cylinder is stress free and the outer is rigidly fixed. The cylinder having a ring-shaped crack located at the symmetry plane is subjected to distributed compressive load on its surfaces. The Hankel and Fourier transform techniques are used for the solution of the field equations. By applying the boundary conditions, the singular integral equation in terms of crack surface displacement derivative is derived. By using an appropriate quadrature formula, the integral equation is reduced to a system of linear algebraic equations. Numerical results are obtained for the stress intensity factors at the edges of the crack, surfaces of which are subjected to uniform, linear and parabolic load distributions. (C) 2007 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study is concerned with the fracture of an infinite thick-walled cylinder. The inner surface of the cylinder is stress free and the outer is rigidly fixed. The cylinder having a ring-shaped crack located at the symmetry plane is subjected to distributed compressive load on its surfaces. The Hankel and Fourier transform techniques are used for the solution of the field equations. By applying the boundary conditions, the singular integral equation in terms of crack surface displacement derivative is derived. By using an appropriate quadrature formula, the integral equation is reduced to a system of linear algebraic equations. Numerical results are obtained for the stress intensity factors at the edges of the crack, surfaces of which are subjected to uniform, linear and parabolic load distributions. (C) 2007 Elsevier Ltd. All rights reserved. |
Artem, HSA; Gecit, MR An elastic hollow cylinder under axial tension containing a crack and two rigid inclusions of ring shape Journal Article COMPUTERS & STRUCTURES, 80 (27-30), pp. 2277-2287, 2002, ISSN: 0045-7949, (5th International Conference on Computational Structures Technology/2nd International Conference on Engineering Computational Technology, LEUVEN, BELGIUM, SEP 06-08, 2000). @article{ISI:000179864300028, title = {An elastic hollow cylinder under axial tension containing a crack and two rigid inclusions of ring shape}, author = {HSA Artem and MR Gecit}, doi = {10.1016/S0045-7949(02)00236-5}, issn = {0045-7949}, year = {2002}, date = {2002-11-01}, journal = {COMPUTERS & STRUCTURES}, volume = {80}, number = {27-30}, pages = {2277-2287}, abstract = {This paper is concerned with the fracture of an axisymmetric hollow cylindrical bar containing rigid inclusions. The cylinder is under the action of uniformly distributed axial tension applied at infinity. The bar contains a ring-shaped crack at the symmetry plane whose surfaces are free of tractions and two ring-shaped rigid inclusions with negligible thickness symmetrically located on both sides of the crack. It is assumed that the material of the cylinder is linearly elastic and isotropic. The mixed boundary conditions of the problem lead the analysis to a system of three singular integral equations for crack surface displacement derivative and normal and shearing stress jumps on rigid inclusions. These integral equations are solved numerically and the stress intensity factors are calculated. (C) 2002 Civil-Comp Ltd. and Elsevier Science Ltd. All rights reserved.}, note = {5th International Conference on Computational Structures Technology/2nd International Conference on Engineering Computational Technology, LEUVEN, BELGIUM, SEP 06-08, 2000}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper is concerned with the fracture of an axisymmetric hollow cylindrical bar containing rigid inclusions. The cylinder is under the action of uniformly distributed axial tension applied at infinity. The bar contains a ring-shaped crack at the symmetry plane whose surfaces are free of tractions and two ring-shaped rigid inclusions with negligible thickness symmetrically located on both sides of the crack. It is assumed that the material of the cylinder is linearly elastic and isotropic. The mixed boundary conditions of the problem lead the analysis to a system of three singular integral equations for crack surface displacement derivative and normal and shearing stress jumps on rigid inclusions. These integral equations are solved numerically and the stress intensity factors are calculated. (C) 2002 Civil-Comp Ltd. and Elsevier Science Ltd. All rights reserved. |
Prof. Dr. Erdal Çetkin
Vice Chair
Educational Background
B.Sc. Kocaeli University, Turkey, Mechanical Engineering, 2007
M.Sc. Duke University, USA, Mechanical Engineering and Materials Science, 2010
Ph.D. Duke University, USA, Mechanical Engineering and Materials Science, 2013
Research Interests
- Vascular structures
- Self-cooling
- Self-healing
- Constructal theory
- Heat transfer enhancement
- Electronic cooling
- +90 232 750 6713
- +90 232 750 6701
- Mechanical Engineering Building (119)
Publications
2023 |
Gocmen, Sinan; Cetkin, Erdal Experimental Investigation of Air Cooling With/Out Tab Cooling in Cell and Module Levels for Thermal Uniformity in Battery Packs Journal Article Journal of Heat Transfer, 145 (2), 2023. @article{Gocmen2023, title = {Experimental Investigation of Air Cooling With/Out Tab Cooling in Cell and Module Levels for Thermal Uniformity in Battery Packs}, author = {Sinan Gocmen and Erdal Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85143991374&doi=10.1115%2f1.4055939&partnerID=40&md5=efb2c14fb28632d261da28c8f71ad9c5}, doi = {10.1115/1.4055939}, year = {2023}, date = {2023-01-01}, journal = {Journal of Heat Transfer}, volume = {145}, number = {2}, abstract = {Catastrophic effects of global warming and environmental pollution are becoming more evident each day, and reduction in fossil fuel consumption is an urgent need. Thus, electric vehicles powered by sustainable energy sources are becoming a major interest. However, there are some challenges such as safety, limited range, long charging times, and battery life which are inhibitory to the adaptation of them. One of the biggest reasons for these challenges is the relationship between battery degradation and temperature which can be eliminated if batteries can be kept at the optimum temperature range. Here, the effects of three distinct (natural convection, forced convection, and tab cooling) methodology were experimentally compared at both the cell and module levels (six serial 7.5 Ah Kokam pouch cells, 1P6S) for thermal management of lithium-ion cells. The experiments were conducted at a discharge rate of 3C with ambient temperatures of 24 ◦C and 29 ◦C. The cell-level test results show that the tab cooling yields 32.5% better thermal uniformity in comparison to the other techniques. Furthermore, tab cooling yields better temperature uniformity with and without air convection as the hot spots occurring near the tabs is eliminated. For the module level, the forced air convection method stands out as the best option with a 4.3% temperature deviation between cells and maximum cell temperature of 39 ◦C. Overall, the results show that a hybrid approach with tab cooling would be beneficial in terms of temperature homogeneity especially in high capacity electric vehicle battery cells. Copyright © 2023 by ASME.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Catastrophic effects of global warming and environmental pollution are becoming more evident each day, and reduction in fossil fuel consumption is an urgent need. Thus, electric vehicles powered by sustainable energy sources are becoming a major interest. However, there are some challenges such as safety, limited range, long charging times, and battery life which are inhibitory to the adaptation of them. One of the biggest reasons for these challenges is the relationship between battery degradation and temperature which can be eliminated if batteries can be kept at the optimum temperature range. Here, the effects of three distinct (natural convection, forced convection, and tab cooling) methodology were experimentally compared at both the cell and module levels (six serial 7.5 Ah Kokam pouch cells, 1P6S) for thermal management of lithium-ion cells. The experiments were conducted at a discharge rate of 3C with ambient temperatures of 24 ◦C and 29 ◦C. The cell-level test results show that the tab cooling yields 32.5% better thermal uniformity in comparison to the other techniques. Furthermore, tab cooling yields better temperature uniformity with and without air convection as the hot spots occurring near the tabs is eliminated. For the module level, the forced air convection method stands out as the best option with a 4.3% temperature deviation between cells and maximum cell temperature of 39 ◦C. Overall, the results show that a hybrid approach with tab cooling would be beneficial in terms of temperature homogeneity especially in high capacity electric vehicle battery cells. Copyright © 2023 by ASME. |
Gungor, Sahin; Gocmen, Sinan; Cetkin, Erdal A review on battery thermal management strategies in lithium-ion and post-lithium batteries for electric vehicles Journal Article Journal of Thermal Engineering, 9 (4), pp. 1078 – 1099, 2023, (All Open Access, Gold Open Access, Green Open Access). @article{Gungor20231078, title = {A review on battery thermal management strategies in lithium-ion and post-lithium batteries for electric vehicles}, author = {Sahin Gungor and Sinan Gocmen and Erdal Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85169015170&doi=10.18186%2fthermal.1334238&partnerID=40&md5=263294fb861dd4fbc4a7751e2bb7079d}, doi = {10.18186/thermal.1334238}, year = {2023}, date = {2023-01-01}, journal = {Journal of Thermal Engineering}, volume = {9}, number = {4}, pages = {1078 – 1099}, abstract = {Electrification on transportation and electricity generation via renewable sources play a vital role to diminish the effects of energy usage on the environment. Transition from the conventional fuels to renewables for transportation and electricity generation demands the storage of electricity in great capacities with desired power densities and relatively high C-rate values. Yet, thermal and electrical characteristics vary greatly depending on the chemistry and structure of battery cells. At this point, lithium-ion (Li-ion) batteries are more suitable in most applications due to their superiorities such as long lifetime, high recyclability, and capacities. However, exothermic electrochemical reactions yield temperature to increase suddenly which affects the degradation in cells, ageing, and electrochemical reaction kinetics. Therefore, strict temperature control increases battery lifetime and eliminates undesired situations such as layer degradation and thermal runaway. In the literature, there are many distinct battery thermal management strategies to effectively control battery cell temperatures. These strategies vary based on the geometrical form, size, capacity, and chemistry of the battery cells. Here, we focus on proposed battery thermal management strategies and current applications in the electric vehicle (EV) industry. In this review, various battery thermal management strategies are documented and compared in detail with respect to geometry, thermal uniformity, coolant type and heat transfer methodology for Li-ion and post-lithium batteries. © Copyright 2021, Yıldız Technical University. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).}, note = {All Open Access, Gold Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electrification on transportation and electricity generation via renewable sources play a vital role to diminish the effects of energy usage on the environment. Transition from the conventional fuels to renewables for transportation and electricity generation demands the storage of electricity in great capacities with desired power densities and relatively high C-rate values. Yet, thermal and electrical characteristics vary greatly depending on the chemistry and structure of battery cells. At this point, lithium-ion (Li-ion) batteries are more suitable in most applications due to their superiorities such as long lifetime, high recyclability, and capacities. However, exothermic electrochemical reactions yield temperature to increase suddenly which affects the degradation in cells, ageing, and electrochemical reaction kinetics. Therefore, strict temperature control increases battery lifetime and eliminates undesired situations such as layer degradation and thermal runaway. In the literature, there are many distinct battery thermal management strategies to effectively control battery cell temperatures. These strategies vary based on the geometrical form, size, capacity, and chemistry of the battery cells. Here, we focus on proposed battery thermal management strategies and current applications in the electric vehicle (EV) industry. In this review, various battery thermal management strategies are documented and compared in detail with respect to geometry, thermal uniformity, coolant type and heat transfer methodology for Li-ion and post-lithium batteries. © Copyright 2021, Yıldız Technical University. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/). |
Coşkun, Turgay; Çetkin, Erdal Vascularized mini cooling channels to achieve temperature uniformity: Battery thermal management and electronic cooling Journal Article Research on Engineering Structures and Materials, 9 (3), pp. 375 – 385, 2023, (All Open Access, Bronze Open Access). @article{Coşkun2023375, title = {Vascularized mini cooling channels to achieve temperature uniformity: Battery thermal management and electronic cooling}, author = {Turgay Coşkun and Erdal Çetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85172141689&doi=10.17515%2fresm2022.585ma1121&partnerID=40&md5=9ad60c3fb4eeb671fd48e7749faec21d}, doi = {10.17515/resm2022.585ma1121}, year = {2023}, date = {2023-01-01}, journal = {Research on Engineering Structures and Materials}, volume = {9}, number = {3}, pages = {375 – 385}, abstract = {Here we propose to use of distinct vascularized plates to be used in the applications of battery thermal management and electronic cooling. The temperatures of battery cells increase during charge and discharge; and elevated temperature values in them accelerated degradation and even may trigger battery fire because of the thermal runaway. Therefore, thermal management system is a necessity for battery packs to increase the battery performance and diminish the risk factors in the electric vehicles. Generally, high amount of heat is released in the high capacity (>15 Ah) cells in short time interval under fast charge/discharge conditions; thus, thermal management of the battery system can be achieved with liquid cooling in that situation. A silicon heater system which represents the thermal behavior of a battery cell is manufactured based on the literature and it is used in experiments. Such a method has not proposed up to now in the literature, so the study may be creating a new experimental procedure for future studies without the risk of battery fire/degradation to uncover even extreme conditions experimentally. Electronic cooling is also in prime importance due to enhanced computing requirement of current systems, and vascularized plates can solve the hot spot problems occurring with decreased energy consumption. According to the results, the cooling capacity of the vascularized plates are calculated as 20W, and a battery cell can be kept within its optimal operating temperature range when the heat loads up to 30W. Also, the temperature uniformity along the surface of mimic of the battery is satisfied by vascularized plates. © 2023 MIM Research Group. All rights reserved.}, note = {All Open Access, Bronze Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here we propose to use of distinct vascularized plates to be used in the applications of battery thermal management and electronic cooling. The temperatures of battery cells increase during charge and discharge; and elevated temperature values in them accelerated degradation and even may trigger battery fire because of the thermal runaway. Therefore, thermal management system is a necessity for battery packs to increase the battery performance and diminish the risk factors in the electric vehicles. Generally, high amount of heat is released in the high capacity (>15 Ah) cells in short time interval under fast charge/discharge conditions; thus, thermal management of the battery system can be achieved with liquid cooling in that situation. A silicon heater system which represents the thermal behavior of a battery cell is manufactured based on the literature and it is used in experiments. Such a method has not proposed up to now in the literature, so the study may be creating a new experimental procedure for future studies without the risk of battery fire/degradation to uncover even extreme conditions experimentally. Electronic cooling is also in prime importance due to enhanced computing requirement of current systems, and vascularized plates can solve the hot spot problems occurring with decreased energy consumption. According to the results, the cooling capacity of the vascularized plates are calculated as 20W, and a battery cell can be kept within its optimal operating temperature range when the heat loads up to 30W. Also, the temperature uniformity along the surface of mimic of the battery is satisfied by vascularized plates. © 2023 MIM Research Group. All rights reserved. |
Naseri, F; Gil, S; Barbu, C; Cetkin, E; Yarimca, G; Jensen, A C; Larsen, P G; Gomes, C Digital twin of electric vehicle battery systems: Comprehensive review of the use cases, requirements, and platforms Journal Article Renewable and Sustainable Energy Reviews, 179 , 2023, (All Open Access, Green Open Access, Hybrid Gold Open Access). @article{Naseri2023, title = {Digital twin of electric vehicle battery systems: Comprehensive review of the use cases, requirements, and platforms}, author = {F Naseri and S Gil and C Barbu and E Cetkin and G Yarimca and A C Jensen and P G Larsen and C Gomes}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85152416376&doi=10.1016%2fj.rser.2023.113280&partnerID=40&md5=cecb165a2389d2006c18cb72ba49eb6e}, doi = {10.1016/j.rser.2023.113280}, year = {2023}, date = {2023-01-01}, journal = {Renewable and Sustainable Energy Reviews}, volume = {179}, abstract = {Transportation electrification has been fueled by recent advancements in the technology and manufacturing of battery systems, but the industry yet is facing serious challenges that could be addressed using cutting-edge digital technologies. One such novel technology is based on the digital twining of battery systems. Digital twins (DTs) of batteries utilize advanced multi-layer models, artificial intelligence, advanced sensing units, Internet-of-Things technologies, and cloud computing techniques to provide a virtual live representation of the real battery system (the physical twin) to improve the performance, safety, and cost-effectiveness. Furthermore, they orchestrate the operation of the entire battery value chain offering great advantages, such as improving the economy of manufacturing, re-purposing, and recycling processes. In this context, various studies have been carried out discussing the DT applications and use cases from cloud-enabled battery management systems to the digitalization of battery testing. This work provides a comprehensive review of different possible use cases, key enabling technologies, and requirements for battery DTs. The review inclusively discusses the use cases, development/integration platforms, as well as hardware and software requirements for implementation of the battery DTs, including electrical topics related to the modeling and algorithmic approaches, software architectures, and digital platforms for DT development and integration. The existing challenges are identified and circumstances that will create enough value to justify these challenges, such as the added costs, are discussed. © 2023 The Authors}, note = {All Open Access, Green Open Access, Hybrid Gold Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Transportation electrification has been fueled by recent advancements in the technology and manufacturing of battery systems, but the industry yet is facing serious challenges that could be addressed using cutting-edge digital technologies. One such novel technology is based on the digital twining of battery systems. Digital twins (DTs) of batteries utilize advanced multi-layer models, artificial intelligence, advanced sensing units, Internet-of-Things technologies, and cloud computing techniques to provide a virtual live representation of the real battery system (the physical twin) to improve the performance, safety, and cost-effectiveness. Furthermore, they orchestrate the operation of the entire battery value chain offering great advantages, such as improving the economy of manufacturing, re-purposing, and recycling processes. In this context, various studies have been carried out discussing the DT applications and use cases from cloud-enabled battery management systems to the digitalization of battery testing. This work provides a comprehensive review of different possible use cases, key enabling technologies, and requirements for battery DTs. The review inclusively discusses the use cases, development/integration platforms, as well as hardware and software requirements for implementation of the battery DTs, including electrical topics related to the modeling and algorithmic approaches, software architectures, and digital platforms for DT development and integration. The existing challenges are identified and circumstances that will create enough value to justify these challenges, such as the added costs, are discussed. © 2023 The Authors |
Coşkun, Turgay; Çetkin, Erdal Cold plate enabling air and liquid cooling simultaneously: Experimental study for battery pack thermal management and electronic cooling Journal Article International Journal of Heat and Mass Transfer, 217 , 2023. @article{Coşkun2023b, title = {Cold plate enabling air and liquid cooling simultaneously: Experimental study for battery pack thermal management and electronic cooling}, author = {Turgay Coşkun and Erdal Çetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85171470128&doi=10.1016%2fj.ijheatmasstransfer.2023.124702&partnerID=40&md5=1857b720cbfc7b433f17d682d0c99b3a}, doi = {10.1016/j.ijheatmasstransfer.2023.124702}, year = {2023}, date = {2023-01-01}, journal = {International Journal of Heat and Mass Transfer}, volume = {217}, abstract = {The temperature of cells varies greatly during dis/charge while their performance and lifetime are greatly affected by this fluctuation. Elevated temperatures may yield battery fire due to thermal runaway as well they accelerate ageing and capacity fade of cells. Thermal management systems are a necessity for electric vehicles to extend the lifetime of battery cells and eliminate any fire risks, especially for fast dis/charging applications. Here, we document a hybrid cold plate with a working fluid(s) of sole air or liquid as well as both of them. Hybridization of air and liquid cooling promises to minimize energy consumption requirements during a charge/discharge cycle by combining the benefits of both thermal management strategies if energy management is controlled accordingly. The temperature of each cell can be kept below 30°C with the proposed hybrid cooling heat exchanger, and the temperature difference between the cells is reduced by 30 % relative to liquid cooling. The maximum temperatures are decreased by 18 % and 3 % in hybrid cooling when compared to air and water cooling, respectively. Furthermore, a step function combining various discharge rates (1C and 3C) was employed in experiments to mimic a realistic situation, i.e. variable C-rate rather than constant. The results show that the temperature of the battery cells can be kept below 30°C with air cooling for variable discharge rate and the effect of contact resistance should not be overlooked for liquid cooling. Furthermore, the possible use of the proposed hybrid cold plates is surveyed in the cooling of electronic devices which produce more and continuous heat than cells. Therefore, three resistance heaters with a capacity of 50W are used in experiments as well. The results show that the proposed cold plates could be used in both electronics cooling and battery thermal management with a control algorithm to switch between sole working fluid and combination modes which could be developed based on the results of this paper. © 2023}, keywords = {}, pubstate = {published}, tppubtype = {article} } The temperature of cells varies greatly during dis/charge while their performance and lifetime are greatly affected by this fluctuation. Elevated temperatures may yield battery fire due to thermal runaway as well they accelerate ageing and capacity fade of cells. Thermal management systems are a necessity for electric vehicles to extend the lifetime of battery cells and eliminate any fire risks, especially for fast dis/charging applications. Here, we document a hybrid cold plate with a working fluid(s) of sole air or liquid as well as both of them. Hybridization of air and liquid cooling promises to minimize energy consumption requirements during a charge/discharge cycle by combining the benefits of both thermal management strategies if energy management is controlled accordingly. The temperature of each cell can be kept below 30°C with the proposed hybrid cooling heat exchanger, and the temperature difference between the cells is reduced by 30 % relative to liquid cooling. The maximum temperatures are decreased by 18 % and 3 % in hybrid cooling when compared to air and water cooling, respectively. Furthermore, a step function combining various discharge rates (1C and 3C) was employed in experiments to mimic a realistic situation, i.e. variable C-rate rather than constant. The results show that the temperature of the battery cells can be kept below 30°C with air cooling for variable discharge rate and the effect of contact resistance should not be overlooked for liquid cooling. Furthermore, the possible use of the proposed hybrid cold plates is surveyed in the cooling of electronic devices which produce more and continuous heat than cells. Therefore, three resistance heaters with a capacity of 50W are used in experiments as well. The results show that the proposed cold plates could be used in both electronics cooling and battery thermal management with a control algorithm to switch between sole working fluid and combination modes which could be developed based on the results of this paper. © 2023 |
2022 |
Gungor, Sahin; Cetkin, Erdal; Lorente, Sylvie Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 182 , 2022. @article{WOS:000709733600003, title = {Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach}, author = {Sahin Gungor and Erdal Cetkin and Sylvie Lorente}, doi = {10.1016/j.ijheatmasstransfer.2021.121918}, year = {2022}, date = {2022-01-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {182}, abstract = {With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate. (c) 2021 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate. (c) 2021 Elsevier Ltd. All rights reserved. |
Sahin, R C; Gocmen, S; Cetkin, E Thermal management system for air-cooled battery packs with flow-disturbing structures Journal Article Journal of Power Sources, 551 , 2022. @article{Sahin2022b, title = {Thermal management system for air-cooled battery packs with flow-disturbing structures}, author = {R C Sahin and S Gocmen and E Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85140273371&doi=10.1016%2fj.jpowsour.2022.232214&partnerID=40&md5=b488f0477918b1e6b4dd91f0627d4578}, doi = {10.1016/j.jpowsour.2022.232214}, year = {2022}, date = {2022-01-01}, journal = {Journal of Power Sources}, volume = {551}, abstract = {Lithium-ion battery packs are preferred in electrical vehicles (EVs) due to their efficient and stable characteristics. Battery thermal management systems (BTMS) have vital importance in EVs to keep batteries in the desired temperature range to maximize performance and lifetime. BTMS with air cooling is simpler and lighter relative to competing methods; however, low thermal conductivity and heat capacity of air necessitate thermal performance and pressure drop adjustments. This work offers a novel design method for cylindrical cells by evaluating the effect of various baffles (cylindrical, triangular, diamond and winglet) on the cooling performance and pressure drop of an air-cooled battery module with 12 21700 cylindrical cells. Thermal characteristics are simulated by the electrochemical-thermal battery model, the P3D multiscale model (modelling parameters for a commercial 21700 cell are documented) in COMSOL Multiphysics 5.5 and their accuracy is validated by experiments. As a result, baffles reduce the maximum temperature and temperature difference by 5% (1.8 °C) and 40% (1.7 °C), respectively, consuming 3.5 times more power than the base design. Delta winglets offer the optimum solution, reducing the maximum temperature and temperature difference by 2% (0.6 °C) and 15% (0.7 °C), respectively, with a 44% (0.12 W) rise in parasitic power consumption. © 2022 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Lithium-ion battery packs are preferred in electrical vehicles (EVs) due to their efficient and stable characteristics. Battery thermal management systems (BTMS) have vital importance in EVs to keep batteries in the desired temperature range to maximize performance and lifetime. BTMS with air cooling is simpler and lighter relative to competing methods; however, low thermal conductivity and heat capacity of air necessitate thermal performance and pressure drop adjustments. This work offers a novel design method for cylindrical cells by evaluating the effect of various baffles (cylindrical, triangular, diamond and winglet) on the cooling performance and pressure drop of an air-cooled battery module with 12 21700 cylindrical cells. Thermal characteristics are simulated by the electrochemical-thermal battery model, the P3D multiscale model (modelling parameters for a commercial 21700 cell are documented) in COMSOL Multiphysics 5.5 and their accuracy is validated by experiments. As a result, baffles reduce the maximum temperature and temperature difference by 5% (1.8 °C) and 40% (1.7 °C), respectively, consuming 3.5 times more power than the base design. Delta winglets offer the optimum solution, reducing the maximum temperature and temperature difference by 2% (0.6 °C) and 15% (0.7 °C), respectively, with a 44% (0.12 W) rise in parasitic power consumption. © 2022 Elsevier B.V. |
Gungor, S; Cetkin, E Enhanced temperature uniformity with minimized pressure drop in electric vehicle battery packs at elevated C-rates Journal Article Heat Transfer, 51 (8), pp. 7540-7561, 2022. @article{Gungor20227540, title = {Enhanced temperature uniformity with minimized pressure drop in electric vehicle battery packs at elevated C-rates}, author = {S Gungor and E Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85135263580&doi=10.1002%2fhtj.22654&partnerID=40&md5=3b91b531fb44340686649125afd2a02a}, doi = {10.1002/htj.22654}, year = {2022}, date = {2022-01-01}, journal = {Heat Transfer}, volume = {51}, number = {8}, pages = {7540-7561}, abstract = {The trend of transition from fossil fuel to electrification in transportation is a result of no carbon emission produced by electric vehicles (EVs) during their daily operations. Furthermore, the global carbon footprint of EVs can be minimized if the electricity is generated from renewable sources such as wind and solar. On the other hand, there are some drawbacks of these vehicles such as charging time being very long and the mileage range of vehicles not at the desired level. Battery cells are being charged at relatively high C-rates to eliminate these problems, yet high current rates accelerate the aging of batteries and capacity losses due to the generated heat. Generated heat causes overheating, and excess temperature triggers degradation and thermal runaway risks. This paper uncovers how the battery pack temperature uniformity and strict thermal control can be achieved with heat transfer enhancement by conduction (cold plates) and convection (vascular channels). We aimed to reduce the energy consumption of the EV battery pack system while increasing the thermal performance. The impact of the thermal contact resistance is also considered for many realistic scenarios. The results indicate that an integrated system with cold plates and vascular channels satisfies the temperature uniformity requirement (over 81%) with comparatively less pumping power (∼72%) of advanced electric vehicles for relatively high C-rates. Furthermore, findings show the temperature level can increase up to 4°C as thermal contact resistance increases. The proposed cooling technique, which has low cost, easy application, and lower energy consumption superiorities, can be implemented in palpable EV battery packs. © 2022 Wiley Periodicals LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The trend of transition from fossil fuel to electrification in transportation is a result of no carbon emission produced by electric vehicles (EVs) during their daily operations. Furthermore, the global carbon footprint of EVs can be minimized if the electricity is generated from renewable sources such as wind and solar. On the other hand, there are some drawbacks of these vehicles such as charging time being very long and the mileage range of vehicles not at the desired level. Battery cells are being charged at relatively high C-rates to eliminate these problems, yet high current rates accelerate the aging of batteries and capacity losses due to the generated heat. Generated heat causes overheating, and excess temperature triggers degradation and thermal runaway risks. This paper uncovers how the battery pack temperature uniformity and strict thermal control can be achieved with heat transfer enhancement by conduction (cold plates) and convection (vascular channels). We aimed to reduce the energy consumption of the EV battery pack system while increasing the thermal performance. The impact of the thermal contact resistance is also considered for many realistic scenarios. The results indicate that an integrated system with cold plates and vascular channels satisfies the temperature uniformity requirement (over 81%) with comparatively less pumping power (∼72%) of advanced electric vehicles for relatively high C-rates. Furthermore, findings show the temperature level can increase up to 4°C as thermal contact resistance increases. The proposed cooling technique, which has low cost, easy application, and lower energy consumption superiorities, can be implemented in palpable EV battery packs. © 2022 Wiley Periodicals LLC. |
Gungor, S; Cetkin, E; Lorente, S Thermal and electrical characterization of an electric vehicle battery cell, an experimental investigation Journal Article Applied Thermal Engineering, 212 , 2022. @article{Gungor2022b, title = {Thermal and electrical characterization of an electric vehicle battery cell, an experimental investigation}, author = {S Gungor and E Cetkin and S Lorente}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85129534427&doi=10.1016%2fj.applthermaleng.2022.118530&partnerID=40&md5=fe9a51259b3473a5b8a99fc67ed0043c}, doi = {10.1016/j.applthermaleng.2022.118530}, year = {2022}, date = {2022-01-01}, journal = {Applied Thermal Engineering}, volume = {212}, abstract = {This paper documents the experimental characterization of a Li-ion battery cell during charging/discharging cyclic operations. The study of the battery cell is conducted in the absence of cooling aid system, and provides thermal and electrical insights. After describing the experimental set-up, the changes in temperature are presented and highlight the nonuniform distribution of the temperature on the battery cell surface. The findings indicate that the maximum temperature difference on the investigated battery cell surface may reach up to 11 C at 3C and 17 ⁰C at 5C, at the end of the discharge in the natural convection case. These changes in space come with temporal variations that are also documented. Voltage curves are provided during charging and discharging operations. The impact of the discharge rate, ambient temperature are then investigated together with the capacity fade after 500 cycles, and results showed that ventilation and low ambient temperatures allow to alleviate the battery capacity fade by 3%. © 2022 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper documents the experimental characterization of a Li-ion battery cell during charging/discharging cyclic operations. The study of the battery cell is conducted in the absence of cooling aid system, and provides thermal and electrical insights. After describing the experimental set-up, the changes in temperature are presented and highlight the nonuniform distribution of the temperature on the battery cell surface. The findings indicate that the maximum temperature difference on the investigated battery cell surface may reach up to 11 C at 3C and 17 ⁰C at 5C, at the end of the discharge in the natural convection case. These changes in space come with temporal variations that are also documented. Voltage curves are provided during charging and discharging operations. The impact of the discharge rate, ambient temperature are then investigated together with the capacity fade after 500 cycles, and results showed that ventilation and low ambient temperatures allow to alleviate the battery capacity fade by 3%. © 2022 Elsevier Ltd |
Demirkıran, İ G; Rocha, L A O; Cetkin, E Emergence of asymmetric straight and branched fins in horizontally oriented latent heat thermal energy storage units Journal Article International Journal of Heat and Mass Transfer, 189 , 2022. @article{Demirkıran2022, title = {Emergence of asymmetric straight and branched fins in horizontally oriented latent heat thermal energy storage units}, author = {İ G Demirkıran and L A O Rocha and E Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85125777922&doi=10.1016%2fj.ijheatmasstransfer.2022.122726&partnerID=40&md5=dfad7a7519437326f78acb3461cbaa3d}, doi = {10.1016/j.ijheatmasstransfer.2022.122726}, year = {2022}, date = {2022-01-01}, journal = {International Journal of Heat and Mass Transfer}, volume = {189}, abstract = {Mobilized thermal energy storage units have a vital role in reducing energy consumption in buildings by enabling industrial waste heat to be used in buildings. High conductive fins can enhance the heat transfer performance of mobilized thermal energy storage tanks which suffer significantly from the low thermal conductivity of phase change materials. On the other hand, investment costs of the mobilized thermal energy storage tanks need to be decreased to compete with fossil fuel-driven systems in buildings. The present study numerically investigates the effect of innovative fin structures on the melting performance for fixed fin material volume to disable cost increase. Two-dimensional models with phase change were simulated for shell-and-tube heat exchangers. The shell geometry was designed sufficiently large to observe the melting growth of phase change material independent from shell walls within the given charging time. Straight and Branched type fin structures with the fin numbers of Nfin=2, 4, and 6 were simulated to uncover the effect of shape and length scale of fins on natural convection-driven melting. It was found that Straight fin type is more suited than Branched fins as they do not show significant melting enhancement with increased complexity and cost. The fin structures in all cases performed better when located at the top of the heat transfer fluid tube, even though the literature considers that top-located fins inhibit natural convection circulations. Varying the number of fins from (2-fin) to (4-fin) causes 15.8% increase in melting ratio, but further increase in the fin number (6-fin) reduces melting ratio below the (4-fin) case. Within (4-fin) structures located at the top, using distinct fin lengths yields melting ratio to increase 28.1%. Overall, the results show that heat transfer could be improved by varying the fin structure without increasing total fin volume and cost. The melting region growth shape with optimized fin structure forms the basis for the multitube arrangement of mobilized thermal energy storage units to enhance heat transfer performance with low cost. © 2022 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } Mobilized thermal energy storage units have a vital role in reducing energy consumption in buildings by enabling industrial waste heat to be used in buildings. High conductive fins can enhance the heat transfer performance of mobilized thermal energy storage tanks which suffer significantly from the low thermal conductivity of phase change materials. On the other hand, investment costs of the mobilized thermal energy storage tanks need to be decreased to compete with fossil fuel-driven systems in buildings. The present study numerically investigates the effect of innovative fin structures on the melting performance for fixed fin material volume to disable cost increase. Two-dimensional models with phase change were simulated for shell-and-tube heat exchangers. The shell geometry was designed sufficiently large to observe the melting growth of phase change material independent from shell walls within the given charging time. Straight and Branched type fin structures with the fin numbers of Nfin=2, 4, and 6 were simulated to uncover the effect of shape and length scale of fins on natural convection-driven melting. It was found that Straight fin type is more suited than Branched fins as they do not show significant melting enhancement with increased complexity and cost. The fin structures in all cases performed better when located at the top of the heat transfer fluid tube, even though the literature considers that top-located fins inhibit natural convection circulations. Varying the number of fins from (2-fin) to (4-fin) causes 15.8% increase in melting ratio, but further increase in the fin number (6-fin) reduces melting ratio below the (4-fin) case. Within (4-fin) structures located at the top, using distinct fin lengths yields melting ratio to increase 28.1%. Overall, the results show that heat transfer could be improved by varying the fin structure without increasing total fin volume and cost. The melting region growth shape with optimized fin structure forms the basis for the multitube arrangement of mobilized thermal energy storage units to enhance heat transfer performance with low cost. © 2022 Elsevier Ltd |
Demirkıran, İ G; Cetkin, E Computation time reduction of PCM melting process by changing modeling parameters Journal Article Numerical Heat Transfer; Part A: Applications, 83 (1), pp. 50-67, 2022. @article{Demirkıran202250, title = {Computation time reduction of PCM melting process by changing modeling parameters}, author = {İ G Demirkıran and E Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85142904241&doi=10.1080%2f10407782.2022.2149229&partnerID=40&md5=9060437b1c078c4230068c898ce0213f}, doi = {10.1080/10407782.2022.2149229}, year = {2022}, date = {2022-01-01}, journal = {Numerical Heat Transfer; Part A: Applications}, volume = {83}, number = {1}, pages = {50-67}, abstract = {This study can be considered as a helpful reference for whom endeavor to boost the computation efficiency of the PCM melting process. Researchers sacrifice accuracy to decrease computation time since computational fluid dynamics (CFD) solutions of PCM melting processes require comparatively very long time, i.e., from hours to days or weeks, depending on the system geometry. The present study compares the approaches recommended in the literature in terms of their influence on computation time reduction and accuracy. A horizontally finned tube LHTES unit is modeled in 2-D space using ANSYS Fluent, the most common commercial CFD software for the considered problem in the literature. The outcomes obtained from the attempts to boost the computation efficiency are as follows: adaptive time step size approach causes 72% enhancement in computation time (from 90 hours to 25 hours), frozen flux algorithm and constant thermophysical properties have almost no influence on computation time. Even though low convergence criteria and neglecting natural convection reduces computation time drastically, the errors in accuracy are not in acceptable level. © 2022 Taylor & Francis Group, LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study can be considered as a helpful reference for whom endeavor to boost the computation efficiency of the PCM melting process. Researchers sacrifice accuracy to decrease computation time since computational fluid dynamics (CFD) solutions of PCM melting processes require comparatively very long time, i.e., from hours to days or weeks, depending on the system geometry. The present study compares the approaches recommended in the literature in terms of their influence on computation time reduction and accuracy. A horizontally finned tube LHTES unit is modeled in 2-D space using ANSYS Fluent, the most common commercial CFD software for the considered problem in the literature. The outcomes obtained from the attempts to boost the computation efficiency are as follows: adaptive time step size approach causes 72% enhancement in computation time (from 90 hours to 25 hours), frozen flux algorithm and constant thermophysical properties have almost no influence on computation time. Even though low convergence criteria and neglecting natural convection reduces computation time drastically, the errors in accuracy are not in acceptable level. © 2022 Taylor & Francis Group, LLC. |
Gocmen, S; Cetkin, E Emergence of elevated battery positioning in air cooled battery packs for temperature uniformity in ultra-fast dis/charging applications Journal Article Journal of Energy Storage, 45 , 2022. @article{Gocmen2022, title = {Emergence of elevated battery positioning in air cooled battery packs for temperature uniformity in ultra-fast dis/charging applications}, author = {S Gocmen and E Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85118748009&doi=10.1016%2fj.est.2021.103516&partnerID=40&md5=736e4f4ff2d5aeb573d8473e4039ed23}, doi = {10.1016/j.est.2021.103516}, year = {2022}, date = {2022-01-01}, journal = {Journal of Energy Storage}, volume = {45}, abstract = {Pure electric vehicles (EVs) are gradually becoming major interest of research in worldwide. Battery cells in EV battery packs must be kept in between the desired operational temperature range (∼30°C) and temperature should be homogeneous in packs to eliminate safety risks and prolong battery life. In this study, performance of a novel BTMS design was studied at various discharge conditions with fast and ultra-fast C-rate values. Cooling with natural convection exceeds desired operational temperature in the pack as well as forced air convection in Z-type manifold. Elevated battery positions yield flow resistance along the air channels in between battery cells to be uniform which yields flow rate sweeping the surface of each cell to be the same. Therefore, the maximum temperature in between cells decreases to less than 0.3K from the order of 12K. The temperature uniformity is essential for ageing and electrical resistance of cells to be homogeneous in a pack. In addition, heat transfer enhancement with various fin designs is documented as well as its effect on the temperature distribution. The accuracy of numerical studies is validated by experimental work. The results show that the peak temperature can be kept under the desired operational temperature with minimum deviation in the temperature difference for distinct operation conditions required for advanced electric vehicles (cars, airplanes, helicopters) with extreme charging and discharging capability. © 2021 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } Pure electric vehicles (EVs) are gradually becoming major interest of research in worldwide. Battery cells in EV battery packs must be kept in between the desired operational temperature range (∼30°C) and temperature should be homogeneous in packs to eliminate safety risks and prolong battery life. In this study, performance of a novel BTMS design was studied at various discharge conditions with fast and ultra-fast C-rate values. Cooling with natural convection exceeds desired operational temperature in the pack as well as forced air convection in Z-type manifold. Elevated battery positions yield flow resistance along the air channels in between battery cells to be uniform which yields flow rate sweeping the surface of each cell to be the same. Therefore, the maximum temperature in between cells decreases to less than 0.3K from the order of 12K. The temperature uniformity is essential for ageing and electrical resistance of cells to be homogeneous in a pack. In addition, heat transfer enhancement with various fin designs is documented as well as its effect on the temperature distribution. The accuracy of numerical studies is validated by experimental work. The results show that the peak temperature can be kept under the desired operational temperature with minimum deviation in the temperature difference for distinct operation conditions required for advanced electric vehicles (cars, airplanes, helicopters) with extreme charging and discharging capability. © 2021 Elsevier Ltd |
Gungor, S; Cetkin, E; Lorente, S Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach Journal Article International Journal of Heat and Mass Transfer, 182 , 2022. @article{Gungor2022c, title = {Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach}, author = {S Gungor and E Cetkin and S Lorente}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85114670203&doi=10.1016%2fj.ijheatmasstransfer.2021.121918&partnerID=40&md5=705da93dfe3b91f9ec006e9534aa4333}, doi = {10.1016/j.ijheatmasstransfer.2021.121918}, year = {2022}, date = {2022-01-01}, journal = {International Journal of Heat and Mass Transfer}, volume = {182}, abstract = {With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate. © 2021}, keywords = {}, pubstate = {published}, tppubtype = {article} } With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate. © 2021 |
2021 |
Cetkin, E; Miguel, A F Asymmetric Y-shaped Micromixers with Spherical Mixing Chamber for Enhanced Mixing Efficiency and Reduced Flow Impedance Journal Article JOURNAL OF APPLIED FLUID MECHANICS, 14 (5), pp. 1389-1397, 2021. @article{WOS:000658420100009, title = {Asymmetric Y-shaped Micromixers with Spherical Mixing Chamber for Enhanced Mixing Efficiency and Reduced Flow Impedance}, author = {E Cetkin and A F Miguel}, doi = {10.47176/jafm.14.05.32317}, year = {2021}, date = {2021-09-01}, journal = {JOURNAL OF APPLIED FLUID MECHANICS}, volume = {14}, number = {5}, pages = {1389-1397}, abstract = {Microfluidic devices have many attractive qualities such as low cost, small size, and in-field use. Micromixers are very important components of these devices because affect their efficiency. In a passive mixer, the structural characteristics of the mixer are crucial and must be analyzed. This paper presents a numerical study of the mixing in passive Y-shaped micromixers with a spherical mixing chamber for a volume constrained system. The effect of asymmetric bifurcated ducts, the angle in between the inflow ducts, eccentricity and, obstacles inserted in the mixing sphere, on the mixing efficiency and flow impedance is evaluated. Vortical structures characteristics and the possible occurrence of engulfment are also identified. The results show that flow impedance (pressure drop for unit volumetric flow rate) can be decreased greatly for the same mixing efficiency as the volume of the spherical mixing chamber is 20% of the total volume. Insertion of the obstacles into the sphere mixing chamber decreases the mixing efficiency while they increase the flow impedance. The results also show that spherical mixing chamber enhances mixing efficiency while decreasing flow impedance if the volume reserved for it is greater than a limit value which depends on the diameter and length scale ratios in between the mother and daughter ducts as well as the total volume. Overall, the paper documents the variation of mixing efficiency and flow impedance based on the geometrical parameters of three-dimensional asymmetric passive micromixer with sphere mixing chamber.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Microfluidic devices have many attractive qualities such as low cost, small size, and in-field use. Micromixers are very important components of these devices because affect their efficiency. In a passive mixer, the structural characteristics of the mixer are crucial and must be analyzed. This paper presents a numerical study of the mixing in passive Y-shaped micromixers with a spherical mixing chamber for a volume constrained system. The effect of asymmetric bifurcated ducts, the angle in between the inflow ducts, eccentricity and, obstacles inserted in the mixing sphere, on the mixing efficiency and flow impedance is evaluated. Vortical structures characteristics and the possible occurrence of engulfment are also identified. The results show that flow impedance (pressure drop for unit volumetric flow rate) can be decreased greatly for the same mixing efficiency as the volume of the spherical mixing chamber is 20% of the total volume. Insertion of the obstacles into the sphere mixing chamber decreases the mixing efficiency while they increase the flow impedance. The results also show that spherical mixing chamber enhances mixing efficiency while decreasing flow impedance if the volume reserved for it is greater than a limit value which depends on the diameter and length scale ratios in between the mother and daughter ducts as well as the total volume. Overall, the paper documents the variation of mixing efficiency and flow impedance based on the geometrical parameters of three-dimensional asymmetric passive micromixer with sphere mixing chamber. |
Demirkiran, Ismail Gurkan; Cetkin, Erdal Emergence of rectangular shell shape in thermal energy storage applications: Fitting melted phase changing material in a fixed space Journal Article JOURNAL OF ENERGY STORAGE, 37 , 2021. @article{WOS:000641410200002, title = {Emergence of rectangular shell shape in thermal energy storage applications: Fitting melted phase changing material in a fixed space}, author = {Ismail Gurkan Demirkiran and Erdal Cetkin}, doi = {10.1016/j.est.2021.102455}, year = {2021}, date = {2021-05-01}, journal = {JOURNAL OF ENERGY STORAGE}, volume = {37}, abstract = {Here we document the effect of heat transfer fluid (HTF) tube position and shell shape on the melting time and sensible energy requirement for melting a phase change material (PCM) in a multitube latent heat thermal energy storage (LHTES) application. Tube location and shell shape are essential as the shape of the melted region, i.e. similar to the boundary layer, affects convective heat transfer performance. HTF tube total area is fixed in all cases to have the same amount of PCM. In order to eliminate the effect of heat transfer surface area variation, results of two- and four-tube configurations were compared within themselves. Liquid fraction, sensible enthalpy content, and latent/sensible enthalpy ratio relative to time were documented for two and four HTF configurations in various shell shape and tube locations. Results show that eccentric two tubes with rectangular shell decreases melting time and sensible energy requirement from 67 min to 32 min and from 161.8 kJ/kg to 136.3 kJ/kg for 72.3% liquid fraction, respectively, in comparison to the concentric tubes with the circular shell. When the number of HTF tubes increases to four, then the required melting time and sensible energy decrease 80% and 3.8%, respectively, for PCM to melt completely as the concentric tubes and circular shell is replaced with eccentric tubes and rectangular shell. Results of liquid fraction variation relative to time show that S-curve of melting becomes steeper if PCM distribution is such that the intersection of melted regions is delayed. Therefore, melted PCM regions could be packed into a shell that minimizes melting time and required sensible energy. Even rectangular shell shape increases the heat transfer surface (increased heat loss rate) because melting time has decreased greatly, total energy lost to the ambient from the surfaces of shell decreases. Eccentricity slows down the solidification process but due to increased heat loss rate from the surface, rectangular shell enables faster solidification than circular shell shape. There is a trade off in between solidification time and heat loss energy for rectangular channels which can be optimized by selecting proper insulation thickness. Overall, the results show that without any thermal conductivity enhancement (TCE) method, melting performance and latent heat storage capability can be significantly enhanced as decreasing the sensible heat storage by fitting the melted PCM regions into a fixed space for the applications where charging speed is lot faster than discharging.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here we document the effect of heat transfer fluid (HTF) tube position and shell shape on the melting time and sensible energy requirement for melting a phase change material (PCM) in a multitube latent heat thermal energy storage (LHTES) application. Tube location and shell shape are essential as the shape of the melted region, i.e. similar to the boundary layer, affects convective heat transfer performance. HTF tube total area is fixed in all cases to have the same amount of PCM. In order to eliminate the effect of heat transfer surface area variation, results of two- and four-tube configurations were compared within themselves. Liquid fraction, sensible enthalpy content, and latent/sensible enthalpy ratio relative to time were documented for two and four HTF configurations in various shell shape and tube locations. Results show that eccentric two tubes with rectangular shell decreases melting time and sensible energy requirement from 67 min to 32 min and from 161.8 kJ/kg to 136.3 kJ/kg for 72.3% liquid fraction, respectively, in comparison to the concentric tubes with the circular shell. When the number of HTF tubes increases to four, then the required melting time and sensible energy decrease 80% and 3.8%, respectively, for PCM to melt completely as the concentric tubes and circular shell is replaced with eccentric tubes and rectangular shell. Results of liquid fraction variation relative to time show that S-curve of melting becomes steeper if PCM distribution is such that the intersection of melted regions is delayed. Therefore, melted PCM regions could be packed into a shell that minimizes melting time and required sensible energy. Even rectangular shell shape increases the heat transfer surface (increased heat loss rate) because melting time has decreased greatly, total energy lost to the ambient from the surfaces of shell decreases. Eccentricity slows down the solidification process but due to increased heat loss rate from the surface, rectangular shell enables faster solidification than circular shell shape. There is a trade off in between solidification time and heat loss energy for rectangular channels which can be optimized by selecting proper insulation thickness. Overall, the results show that without any thermal conductivity enhancement (TCE) method, melting performance and latent heat storage capability can be significantly enhanced as decreasing the sensible heat storage by fitting the melted PCM regions into a fixed space for the applications where charging speed is lot faster than discharging. |
2020 |
Coskun, Turgay; Cetkin, Erdal A review of heat and fluid flow characteristics in microchannel heat sinks Journal Article HEAT TRANSFER, 49 (8), pp. 4109-4133, 2020, ISSN: 2688-4534. @article{ISI:000595699600002, title = {A review of heat and fluid flow characteristics in microchannel heat sinks}, author = {Turgay Coskun and Erdal Cetkin}, doi = {10.1002/htj.21819}, issn = {2688-4534}, year = {2020}, date = {2020-12-01}, journal = {HEAT TRANSFER}, volume = {49}, number = {8}, pages = {4109-4133}, abstract = {Heat transfer and flow characteristic in microchannel heat sinks (MCHS) are extensively studied in the literature due to high heat transfer rate capability by increased heat transfer surface area relative to the macroscale heat sinks. However, heat transfer and fluid flow characteristics in MCHS differ from conventional ones because of the scaling effects. This review summarizes the studies that are mainly based on heat transfer and fluid flow characteristic in MCHS. There is no consistency among the published results; however, everyone agrees on that there is no new physical phenomenon in microscale that does not exist at macroscale. Only difference between them is that the effect of some physical phenomena such as viscous dissipation, axial heat conduction, entrance effect, rarefaction, and so forth, is negligibly small at macroscale, whereas it is not at microscale. The effect of these physical phenomena on the heat transfer and flow characteristics becomes significant with respect to specified conditions such as Reynolds number, Peclet number, hydraulic diameter, and heat transfer boundary conditions. Here, the literature was reviewed to document when these physical phenomena become significant and insignificant.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Heat transfer and flow characteristic in microchannel heat sinks (MCHS) are extensively studied in the literature due to high heat transfer rate capability by increased heat transfer surface area relative to the macroscale heat sinks. However, heat transfer and fluid flow characteristics in MCHS differ from conventional ones because of the scaling effects. This review summarizes the studies that are mainly based on heat transfer and fluid flow characteristic in MCHS. There is no consistency among the published results; however, everyone agrees on that there is no new physical phenomenon in microscale that does not exist at macroscale. Only difference between them is that the effect of some physical phenomena such as viscous dissipation, axial heat conduction, entrance effect, rarefaction, and so forth, is negligibly small at macroscale, whereas it is not at microscale. The effect of these physical phenomena on the heat transfer and flow characteristics becomes significant with respect to specified conditions such as Reynolds number, Peclet number, hydraulic diameter, and heat transfer boundary conditions. Here, the literature was reviewed to document when these physical phenomena become significant and insignificant. |
Gocmen, Sinan; Gungor, Sahin; Cetkin, Erdal Thermal management of electric vehicle battery cells with homogeneous coolant and temperature distribution Journal Article JOURNAL OF APPLIED PHYSICS, 127 (23), 2020, ISSN: 0021-8979. @article{ISI:000542961200001, title = {Thermal management of electric vehicle battery cells with homogeneous coolant and temperature distribution}, author = {Sinan Gocmen and Sahin Gungor and Erdal Cetkin}, doi = {10.1063/5.0004453}, issn = {0021-8979}, year = {2020}, date = {2020-06-01}, journal = {JOURNAL OF APPLIED PHYSICS}, volume = {127}, number = {23}, abstract = {Electric vehicles play an integral role in eliminating pollution related to transportation, especially if the electricity is generated via renewable sources. However, storing electricity onboard requires many battery cells. If the temperature of the cells is not strictly regulated, their capacity decreases in time, and they may burn or explode due to thermal runaway. Battery thermal management systems emerged for safe operations by keeping the battery cell temperatures under limit values. However, the current solutions do not yield uniform temperature distribution for all the cells in a pack. Here, we document that constant temperature distribution can be achieved with uniform coolant distribution to the channels located between batteries. The design process of the developed battery pack begins with a design used in current packs. Later, how the shape of the distributor channel affects flow uniformity is documented. Then, the design complexity was increased to satisfy the flow uniformity condition, which is essential for temperature uniformity. The design was altered based on a constructal design methodology with an iterative exhaustive search approach. The uncovered constructal design yields a uniform coolant distribution with a maximum of 0.81% flow rate deviation along channels. The developed design is palpable and easy to manufacture relative to the tapered manifold designs. The results also document that the peak temperature difference between the cells decreases from a maximum of 12K to 0.4K. Furthermore, homogenous distribution of air is one of the limiting factors of the development of metal-air batteries. This paper also documents how air can be distributed uniformly to metal-air battery cells in a battery pack.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electric vehicles play an integral role in eliminating pollution related to transportation, especially if the electricity is generated via renewable sources. However, storing electricity onboard requires many battery cells. If the temperature of the cells is not strictly regulated, their capacity decreases in time, and they may burn or explode due to thermal runaway. Battery thermal management systems emerged for safe operations by keeping the battery cell temperatures under limit values. However, the current solutions do not yield uniform temperature distribution for all the cells in a pack. Here, we document that constant temperature distribution can be achieved with uniform coolant distribution to the channels located between batteries. The design process of the developed battery pack begins with a design used in current packs. Later, how the shape of the distributor channel affects flow uniformity is documented. Then, the design complexity was increased to satisfy the flow uniformity condition, which is essential for temperature uniformity. The design was altered based on a constructal design methodology with an iterative exhaustive search approach. The uncovered constructal design yields a uniform coolant distribution with a maximum of 0.81% flow rate deviation along channels. The developed design is palpable and easy to manufacture relative to the tapered manifold designs. The results also document that the peak temperature difference between the cells decreases from a maximum of 12K to 0.4K. Furthermore, homogenous distribution of air is one of the limiting factors of the development of metal-air batteries. This paper also documents how air can be distributed uniformly to metal-air battery cells in a battery pack. |
2017 |
Cetin, Eylem; Cetkin, Erdal The effect of cavities and T-shaped assembly of fins on overall thermal resistances Journal Article INTERNATIONAL JOURNAL OF HEAT AND TECHNOLOGY, 35 (4), pp. 944-952, 2017, ISSN: 0392-8764. @article{ISI:000429132900030, title = {The effect of cavities and T-shaped assembly of fins on overall thermal resistances}, author = {Eylem Cetin and Erdal Cetkin}, doi = {10.18280/ijht.350430}, issn = {0392-8764}, year = {2017}, date = {2017-12-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND TECHNOLOGY}, volume = {35}, number = {4}, pages = {944-952}, abstract = {In this study, authors show that maximum excess temperature on a heat generating cylindrical solid domain can be minimized with numerically optimized rectangular cavities and T-shaped fins. The effect of the cavities and the fins on overall thermal resistances were compared while their volume fraction in a unit volume element is fixed. Furthermore, the designs correspond to the minimum thermal resistance were uncovered for two types of flows; parallel and cross-flow. The governing equations of the heat transfer and the fluid flow were solved simultaneously in order to show the effects of design on the flow characteristics and the thermal performance. Two-dimensional solution domain was used to uncover the thermal performance in cross-flow case because the flow direction is perpendicular to the heat transfer surface area of the heat generating domain. However, three-dimensional domain was used in parallel flow case because the fluid flows along the outer surface of the heat generating domain. For the cross-flow case, the results show that T-shaped assembly of fins with longer stem and shorter tributaries correspond to the lower peak temperature. In addition, the results also show that there is an optimal cavity shape that minimizes the peak temperature. This optimal shape becomes thinner when the number of the cavities increase. In parallel flow case, fins with thicker and shorter stem and longer tributaries correspond to the minimum excess temperature. In addition, the longer and thinner cavities increase the thermal performance in parallel flow case.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, authors show that maximum excess temperature on a heat generating cylindrical solid domain can be minimized with numerically optimized rectangular cavities and T-shaped fins. The effect of the cavities and the fins on overall thermal resistances were compared while their volume fraction in a unit volume element is fixed. Furthermore, the designs correspond to the minimum thermal resistance were uncovered for two types of flows; parallel and cross-flow. The governing equations of the heat transfer and the fluid flow were solved simultaneously in order to show the effects of design on the flow characteristics and the thermal performance. Two-dimensional solution domain was used to uncover the thermal performance in cross-flow case because the flow direction is perpendicular to the heat transfer surface area of the heat generating domain. However, three-dimensional domain was used in parallel flow case because the fluid flows along the outer surface of the heat generating domain. For the cross-flow case, the results show that T-shaped assembly of fins with longer stem and shorter tributaries correspond to the lower peak temperature. In addition, the results also show that there is an optimal cavity shape that minimizes the peak temperature. This optimal shape becomes thinner when the number of the cavities increase. In parallel flow case, fins with thicker and shorter stem and longer tributaries correspond to the minimum excess temperature. In addition, the longer and thinner cavities increase the thermal performance in parallel flow case. |
Cetkin, Erdal JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME, 139 (8), 2017, ISSN: 0022-1481. @article{ISI:000426124400018, title = {Constructal Microdevice Manifold Design With Uniform Flow Rate Distribution by Consideration of the Tree-Branching Rule of Leonardo da Vinci and Hess-Murray Rule}, author = {Erdal Cetkin}, doi = {10.1115/1.4036089}, issn = {0022-1481}, year = {2017}, date = {2017-08-01}, journal = {JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME}, volume = {139}, number = {8}, abstract = {In this paper, we show how the design of a microdevice manifold should be tapered for uniform flow rate distribution. The designs based on the tree-branching rule of Leonardo da Vinci and the Hess-Murray rule were considered in addition to the constructal design. Both da Vinci and Hess-Murray designs are insensitive to the inlet velocity, and they provide better flow uniformity than the base (not tapered) design. However, the results of this paper uncover that not only pressure drop but also velocity distribution in the microdevice play an integral role in the flow uniformity. Therefore, an iterative approach was adopted with five degrees-of-freedom (inclined wall positions) and one constraint (constant distribution channel thickness) in order to uncover the constructal design which conforms the uniform flow rate distribution. In addition, the effect of slenderness of the microchannels (Svelteness) and inlet velocity on the flow rate distribution to the microchannels has been documented. This paper also uncovers that the design of a manifold should be designed with not only the consideration of pressure distribution but also dynamic pressure distribution especially for non-Svelte microdevices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, we show how the design of a microdevice manifold should be tapered for uniform flow rate distribution. The designs based on the tree-branching rule of Leonardo da Vinci and the Hess-Murray rule were considered in addition to the constructal design. Both da Vinci and Hess-Murray designs are insensitive to the inlet velocity, and they provide better flow uniformity than the base (not tapered) design. However, the results of this paper uncover that not only pressure drop but also velocity distribution in the microdevice play an integral role in the flow uniformity. Therefore, an iterative approach was adopted with five degrees-of-freedom (inclined wall positions) and one constraint (constant distribution channel thickness) in order to uncover the constructal design which conforms the uniform flow rate distribution. In addition, the effect of slenderness of the microchannels (Svelteness) and inlet velocity on the flow rate distribution to the microchannels has been documented. This paper also uncovers that the design of a manifold should be designed with not only the consideration of pressure distribution but also dynamic pressure distribution especially for non-Svelte microdevices. |
Cetkin, E VASCULAR STRUCTURES FOR SMART FEATURES: SELF-COOLING AND SELF-HEALING Journal Article JOURNAL OF THERMAL ENGINEERING, 3 (4, 5), pp. 1338-1345, 2017, ISSN: 2148-7847. @article{ISI:000407804200004, title = {VASCULAR STRUCTURES FOR SMART FEATURES: SELF-COOLING AND SELF-HEALING}, author = {E Cetkin}, doi = {10.18186/journal-of-thermal-engineering.330185}, issn = {2148-7847}, year = {2017}, date = {2017-08-01}, journal = {JOURNAL OF THERMAL ENGINEERING}, volume = {3}, number = {4, 5}, pages = {1338-1345}, abstract = {Here we show how smart features of self-cooling and self-healing can be gained to mechanical systems with embedded vascular structures. Vascular structures mimic the circulatory system of animals. Similar to blood distribution from heart to the animal body, vascular channels provide the distribution of coolant and/or healing agent from a point to the entire body of a mechanic system. Thus the mechanic system becomes capable of cooling itself under unpredictable heat attacks and capable of healing itself as cracks occur due to applied mechanical loads. These smart features are necessary for advanced devices, equipment and vehicles. The essential design parameter is vascularization in order to provide smart features. There are distinct configurations for vascularization such as radial, tree-shaped, grid and hybrids of these designs. In addition, several theories are available for the shape optimization of vascular structures such as fractal theory and constructal theory. Unlike fractal theory, constructal theory does not include constraints based on generic algorithms and dictated assumptions. Therefore, constructal theory approach is discussed in this paper. This paper shows how smart features can be gained to a mechanical system while its weight decreases and its mechanical strength increases simultaneously.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here we show how smart features of self-cooling and self-healing can be gained to mechanical systems with embedded vascular structures. Vascular structures mimic the circulatory system of animals. Similar to blood distribution from heart to the animal body, vascular channels provide the distribution of coolant and/or healing agent from a point to the entire body of a mechanic system. Thus the mechanic system becomes capable of cooling itself under unpredictable heat attacks and capable of healing itself as cracks occur due to applied mechanical loads. These smart features are necessary for advanced devices, equipment and vehicles. The essential design parameter is vascularization in order to provide smart features. There are distinct configurations for vascularization such as radial, tree-shaped, grid and hybrids of these designs. In addition, several theories are available for the shape optimization of vascular structures such as fractal theory and constructal theory. Unlike fractal theory, constructal theory does not include constraints based on generic algorithms and dictated assumptions. Therefore, constructal theory approach is discussed in this paper. This paper shows how smart features can be gained to a mechanical system while its weight decreases and its mechanical strength increases simultaneously. |
2016 |
Yenigun, O; Cetkin, E Experimental and numerical investigation of constructal vascular channels for self-cooling: Parallel channels, tree-shaped and hybrid designs Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 103 , pp. 1155-1165, 2016, ISSN: 0017-9310. @article{ISI:000384777800107b, title = {Experimental and numerical investigation of constructal vascular channels for self-cooling: Parallel channels, tree-shaped and hybrid designs}, author = {O Yenigun and E Cetkin}, doi = {10.1016/j.ijheatmasstransfer.2016.08.074}, issn = {0017-9310}, year = {2016}, date = {2016-12-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {103}, pages = {1155-1165}, abstract = {In this paper, we show experimentally and numerically how a plate which is subjected to a constant heat load can be kept under an allowable temperature limit. Vascular channels in which coolant fluid flows have been embedded in the plate. Three types of vascular channel designs were compared: parallel channels, tree-shaped and their hybrid. The effects of channel design on the thermal performance for different volume fractions (the fluid volume over the solid volume) are documented. In addition, the effects of the number of channels on cooling performance have been documented. Changing the design from parallel channels to tree-shaped designs decreases the order of pressure drop. Hence increase in the order of the convective heat transfer coefficient is achieved. However, tree-shaped designs do not bathe the entire domain, which increases the conductive resistances. Therefore, additional channels were inserted at the uncooled regions in the tree-shaped design (hybrid design). The best features of both parallel channels and tree-shaped designs are combined in the hybrid of them: the flow resistances to the fluid and heat flow become almost as low as the tree-shaped and parallel channels designs, respectively. The effect of design on the maximum temperature shows that there should be an optimum design for a distinct set of boundary conditions, and this design should be varied as the boundary conditions change. This result is in accord with the constructal law, i.e. the shape should be varied in order to minimize resistances to the flows. (C) 2016 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, we show experimentally and numerically how a plate which is subjected to a constant heat load can be kept under an allowable temperature limit. Vascular channels in which coolant fluid flows have been embedded in the plate. Three types of vascular channel designs were compared: parallel channels, tree-shaped and their hybrid. The effects of channel design on the thermal performance for different volume fractions (the fluid volume over the solid volume) are documented. In addition, the effects of the number of channels on cooling performance have been documented. Changing the design from parallel channels to tree-shaped designs decreases the order of pressure drop. Hence increase in the order of the convective heat transfer coefficient is achieved. However, tree-shaped designs do not bathe the entire domain, which increases the conductive resistances. Therefore, additional channels were inserted at the uncooled regions in the tree-shaped design (hybrid design). The best features of both parallel channels and tree-shaped designs are combined in the hybrid of them: the flow resistances to the fluid and heat flow become almost as low as the tree-shaped and parallel channels designs, respectively. The effect of design on the maximum temperature shows that there should be an optimum design for a distinct set of boundary conditions, and this design should be varied as the boundary conditions change. This result is in accord with the constructal law, i.e. the shape should be varied in order to minimize resistances to the flows. (C) 2016 Elsevier Ltd. All rights reserved. |
2015 |
Cetkin, Erdal Constructal Vascular Structures With High-Conductivity Inserts for Self-Cooling Journal Article JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME, 137 (11), 2015, ISSN: 0022-1481. @article{ISI:000362512900008, title = {Constructal Vascular Structures With High-Conductivity Inserts for Self-Cooling}, author = {Erdal Cetkin}, doi = {10.1115/1.4030906}, issn = {0022-1481}, year = {2015}, date = {2015-11-01}, journal = {JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME}, volume = {137}, number = {11}, abstract = {In this paper, we show how a heat-generating domain can be cooled with embedded cooling channels and high-conductivity inserts. The volume of cooling channels and high-conductivity inserts is fixed, so is the volume of the heat-generating domain. The maximum temperature in the domain decreases with high-conductivity inserts even though the coolant volume decreases. The locations and the shapes of high-conductivity inserts corresponding to the smallest peak temperatures for different number of inserts are documented}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, we show how a heat-generating domain can be cooled with embedded cooling channels and high-conductivity inserts. The volume of cooling channels and high-conductivity inserts is fixed, so is the volume of the heat-generating domain. The maximum temperature in the domain decreases with high-conductivity inserts even though the coolant volume decreases. The locations and the shapes of high-conductivity inserts corresponding to the smallest peak temperatures for different number of inserts are documented |
Cetkin, Erdal; Oliani, Alessandro The natural emergence of asymmetric tree-shaped pathways for cooling of a non-uniformly heated domain Journal Article JOURNAL OF APPLIED PHYSICS, 118 (2), 2015, ISSN: 0021-8979. @article{ISI:000357961000033, title = {The natural emergence of asymmetric tree-shaped pathways for cooling of a non-uniformly heated domain}, author = {Erdal Cetkin and Alessandro Oliani}, doi = {10.1063/1.4926620}, issn = {0021-8979}, year = {2015}, date = {2015-07-01}, journal = {JOURNAL OF APPLIED PHYSICS}, volume = {118}, number = {2}, abstract = {Here, we show that the peak temperature on a non-uniformly heated domain can be decreased by embedding a high-conductivity insert in it. The trunk of the high-conductivity insert is in contact with a heat sink. The heat is generated non-uniformly throughout the domain or concentrated in a square spot of length scale 0.1 L-0, where L-0 is the length scale of the non-uniformly heated domain. Peak and average temperatures are affected by the volume fraction of the high-conductivity material and by the shape of the high-conductivity pathways. This paper uncovers how varying the shape of the symmetric and asymmetric high-conductivity trees affects the overall thermal conductance of the heat generating domain. The tree-shaped high-conductivity inserts tend to grow toward where the heat generation is concentrated in order to minimize the peak temperature, i.e., in order to minimize the resistances to the heat flow. This behaviour of high-conductivity trees is alike with the root growth of the plants and trees. They also tend to grow towards sunlight, and their roots tend to grow towards water and nutrients. This paper uncovers the similarity between biological trees and high-conductivity trees, which is that trees should grow asymmetrically when the boundary conditions are non-uniform. We show here even though all the trees have the same objectives (minimum flow resistance), their shape should not be the same because of the variation in boundary conditions. To sum up, this paper shows that there is a high-conductivity tree design corresponding to minimum peak temperature with fixed constraints and conditions. This result is in accord with the constructal law which states that there should be an optimal design for a given set of conditions and constraints, and this design should be morphed in order to ensure minimum flow resistances as conditions and constraints change. (c) 2015 AIP Publishing LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here, we show that the peak temperature on a non-uniformly heated domain can be decreased by embedding a high-conductivity insert in it. The trunk of the high-conductivity insert is in contact with a heat sink. The heat is generated non-uniformly throughout the domain or concentrated in a square spot of length scale 0.1 L-0, where L-0 is the length scale of the non-uniformly heated domain. Peak and average temperatures are affected by the volume fraction of the high-conductivity material and by the shape of the high-conductivity pathways. This paper uncovers how varying the shape of the symmetric and asymmetric high-conductivity trees affects the overall thermal conductance of the heat generating domain. The tree-shaped high-conductivity inserts tend to grow toward where the heat generation is concentrated in order to minimize the peak temperature, i.e., in order to minimize the resistances to the heat flow. This behaviour of high-conductivity trees is alike with the root growth of the plants and trees. They also tend to grow towards sunlight, and their roots tend to grow towards water and nutrients. This paper uncovers the similarity between biological trees and high-conductivity trees, which is that trees should grow asymmetrically when the boundary conditions are non-uniform. We show here even though all the trees have the same objectives (minimum flow resistance), their shape should not be the same because of the variation in boundary conditions. To sum up, this paper shows that there is a high-conductivity tree design corresponding to minimum peak temperature with fixed constraints and conditions. This result is in accord with the constructal law which states that there should be an optimal design for a given set of conditions and constraints, and this design should be morphed in order to ensure minimum flow resistances as conditions and constraints change. (c) 2015 AIP Publishing LLC. |
Cetkin, Erdal CONSTRUCTAL STRUCTURES FOR SELF-COOLING: MICROVASCULAR WAVY AND STRAIGHT CHANNELS Journal Article JOURNAL OF THERMAL ENGINEERING, 1 (5, 1), pp. 166-174, 2015, ISSN: 2148-7847. @article{ISI:000434616100004, title = {CONSTRUCTAL STRUCTURES FOR SELF-COOLING: MICROVASCULAR WAVY AND STRAIGHT CHANNELS}, author = {Erdal Cetkin}, doi = {10.18186/jte.10873}, issn = {2148-7847}, year = {2015}, date = {2015-02-01}, journal = {JOURNAL OF THERMAL ENGINEERING}, volume = {1}, number = {5, 1}, pages = {166-174}, abstract = {This paper shows that a conductive domain which is subjected to heating from its bottom can be cooled with embedded microvascular cooling channels in it. The volume of the domain and the coolant are fixed. The actively cooled domain is mimicked from the human skin (which regulates temperature with microvascular blood vessels). The effect of the shape of cooling channels (sinusoidal or straight) and their locations in the direction perpendicular to the bottom surface on the peak and average temperatures are studied. In addition, the effect of pressure difference in between the inlet and outlet is varied. The pressure drop in the sinusoidal channel configurations is greater than the straight channel configurations for a fixed cooling channel volume. The peak and average temperatures are the smallest with straight cooling channels located at y = 0.7 mm. Furthermore, how the cooling channel configuration should change when the heat is generated throughout the volume is studied. The peak and average temperatures are smaller with straight channels than the sinusoidal ones when the pressure drop is less than 420 Pa, and they become smaller with sinusoidal channel configurations when the pressure drop is greater than 420 Pa. In addition, the peak and average temperatures are the smallest with sinusoidal channels for a fixed flow rate. Furthermore, the peak temperatures for multiple cooling channels is documented, and the multiple channel configurations promise to the smallest peak temperature for a fixed pressure drop value. This paper uncovers that there is no optimal cooling channel design for any condition, but there is one for specific objectives and conditions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper shows that a conductive domain which is subjected to heating from its bottom can be cooled with embedded microvascular cooling channels in it. The volume of the domain and the coolant are fixed. The actively cooled domain is mimicked from the human skin (which regulates temperature with microvascular blood vessels). The effect of the shape of cooling channels (sinusoidal or straight) and their locations in the direction perpendicular to the bottom surface on the peak and average temperatures are studied. In addition, the effect of pressure difference in between the inlet and outlet is varied. The pressure drop in the sinusoidal channel configurations is greater than the straight channel configurations for a fixed cooling channel volume. The peak and average temperatures are the smallest with straight cooling channels located at y = 0.7 mm. Furthermore, how the cooling channel configuration should change when the heat is generated throughout the volume is studied. The peak and average temperatures are smaller with straight channels than the sinusoidal ones when the pressure drop is less than 420 Pa, and they become smaller with sinusoidal channel configurations when the pressure drop is greater than 420 Pa. In addition, the peak and average temperatures are the smallest with sinusoidal channels for a fixed flow rate. Furthermore, the peak temperatures for multiple cooling channels is documented, and the multiple channel configurations promise to the smallest peak temperature for a fixed pressure drop value. This paper uncovers that there is no optimal cooling channel design for any condition, but there is one for specific objectives and conditions. |
Cetkin, E; Lorente, S; Bejan, A Vascularization for cooling and reduced thermal stresses Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 80 , pp. 858-864, 2015, ISSN: 0017-9310. @article{ISI:000345202100080, title = {Vascularization for cooling and reduced thermal stresses}, author = {E Cetkin and S Lorente and A Bejan}, doi = {10.1016/j.ijheatmasstransfer.2014.09.027}, issn = {0017-9310}, year = {2015}, date = {2015-01-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {80}, pages = {858-864}, abstract = {This paper documents the effect of thermal expansion on a vascularized plate that is heated and loaded mechanically. Vascular cooling channels embedded in a circular plate provide cooling and mechanical strength. The coolant enters the plate from the center and leaves after it cools the plate to an allowable temperature limit. The mechanical strength of the plate decreases because of the embedded cooling channels. However, cooling the plate under an allowable temperature level decreases the thermal stresses. The mechanical strength of the plate which is heated and loaded mechanically at the same time can be increased by inserting cooling channels in it. The mechanical and thermofluid behavior of a vascularized plate was simulated numerically. The cooling channel configurations that provide the smallest peak temperature and von Mises stress are documented. There is one cooling channel configuration that is the best for the given set of boundary conditions and constraints; however, there is no single configuration that is best for all conditions. (C) 2014 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper documents the effect of thermal expansion on a vascularized plate that is heated and loaded mechanically. Vascular cooling channels embedded in a circular plate provide cooling and mechanical strength. The coolant enters the plate from the center and leaves after it cools the plate to an allowable temperature limit. The mechanical strength of the plate decreases because of the embedded cooling channels. However, cooling the plate under an allowable temperature level decreases the thermal stresses. The mechanical strength of the plate which is heated and loaded mechanically at the same time can be increased by inserting cooling channels in it. The mechanical and thermofluid behavior of a vascularized plate was simulated numerically. The cooling channel configurations that provide the smallest peak temperature and von Mises stress are documented. There is one cooling channel configuration that is the best for the given set of boundary conditions and constraints; however, there is no single configuration that is best for all conditions. (C) 2014 Elsevier Ltd. All rights reserved. |
Cetkin, Erdal Constructal vascularized structures Journal Article OPEN ENGINEERING, 5 (1), pp. 220-228, 2015, ISSN: 2391-5439. @article{ISI:000218406100024, title = {Constructal vascularized structures}, author = {Erdal Cetkin}, doi = {10.1515/eng-2015-0017}, issn = {2391-5439}, year = {2015}, date = {2015-01-01}, journal = {OPEN ENGINEERING}, volume = {5}, number = {1}, pages = {220-228}, abstract = {Smart features such as self-healing and selfcooling require bathing the entire volume with a coolant or/and healing agent. Bathing the entire volume is an example of point to area (or volume) flows. Point to area flows cover all the distributing and collecting kinds of flows, i.e. inhaling and exhaling, mining, river deltas, energy distribution, distribution of products on the landscape and so on. The flow resistances of a point to area flow can be decreased by changing the design with the guidance of the constructal law, which is the law of the design evolution in time. In this paper, how the flow resistances (heat, fluid and stress) can be decreased by using the constructal law is shown with examples. First, the validity of two assumptions is surveyed: using temperature independent Hess-Murray rule and using constant diameter ducts where the duct discharges fluid along its edge. Then, point to area types of flows are explained by illustrating the results of two examples: fluid networks and heating an area. Last, how the structures should be vascularized for cooling and mechanical strength is documented. This paper shows that flow resistances can be decreased by morphing the shape freely without any restrictions or generic algorithms.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Smart features such as self-healing and selfcooling require bathing the entire volume with a coolant or/and healing agent. Bathing the entire volume is an example of point to area (or volume) flows. Point to area flows cover all the distributing and collecting kinds of flows, i.e. inhaling and exhaling, mining, river deltas, energy distribution, distribution of products on the landscape and so on. The flow resistances of a point to area flow can be decreased by changing the design with the guidance of the constructal law, which is the law of the design evolution in time. In this paper, how the flow resistances (heat, fluid and stress) can be decreased by using the constructal law is shown with examples. First, the validity of two assumptions is surveyed: using temperature independent Hess-Murray rule and using constant diameter ducts where the duct discharges fluid along its edge. Then, point to area types of flows are explained by illustrating the results of two examples: fluid networks and heating an area. Last, how the structures should be vascularized for cooling and mechanical strength is documented. This paper shows that flow resistances can be decreased by morphing the shape freely without any restrictions or generic algorithms. |
Cetkin, Erdal INVERTED FINS FOR COOLING OF A NON-UNIFORMLY HEATED DOMAIN Journal Article JOURNAL OF THERMAL ENGINEERING, 1 (1), pp. 1-9, 2015, ISSN: 2148-7847. @article{ISI:000434614600001, title = {INVERTED FINS FOR COOLING OF A NON-UNIFORMLY HEATED DOMAIN}, author = {Erdal Cetkin}, doi = {10.18186/jte.12488}, issn = {2148-7847}, year = {2015}, date = {2015-01-01}, journal = {JOURNAL OF THERMAL ENGINEERING}, volume = {1}, number = {1}, pages = {1-9}, abstract = {This paper shows that the peak temperature of a non-uniformly heated region can be decreased by embedding high-conductivity tree-shaped inserts which is in contact with a heat sink from its stem. The volume fraction of the high-conductivity material is fixed, and so is the volume of the solid region. The length scale of the solid domain is L. Inside there is a cube-shaped region with length scale of 0.1L and heat production 100 times greater than the rest of the domain. The location of this hot spot was varied to uncover how its location affects the peak temperature and the design of inverted fins, i.e. highconductivity tree-shaped inserts. The volume fraction of the high-conductivity tree was varied for number of bifurcation levels of 0, 1 and 2. This showed that increasing the number of the bifurcation levels decreases the peak temperature when the volume fraction decreases. The optimal diameter ratios and optimal bifurcation angles at the each junction level are also documented. Y-shaped trees promise smaller peak temperatures than T-shaped trees. The location of the vascular tree in the z direction also affects the peak temperature when the heat generation is non-uniform. In addition, the peak temperature is minimum when z = 0.65L even though the hot spot is located on z = 0.75L.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper shows that the peak temperature of a non-uniformly heated region can be decreased by embedding high-conductivity tree-shaped inserts which is in contact with a heat sink from its stem. The volume fraction of the high-conductivity material is fixed, and so is the volume of the solid region. The length scale of the solid domain is L. Inside there is a cube-shaped region with length scale of 0.1L and heat production 100 times greater than the rest of the domain. The location of this hot spot was varied to uncover how its location affects the peak temperature and the design of inverted fins, i.e. highconductivity tree-shaped inserts. The volume fraction of the high-conductivity tree was varied for number of bifurcation levels of 0, 1 and 2. This showed that increasing the number of the bifurcation levels decreases the peak temperature when the volume fraction decreases. The optimal diameter ratios and optimal bifurcation angles at the each junction level are also documented. Y-shaped trees promise smaller peak temperatures than T-shaped trees. The location of the vascular tree in the z direction also affects the peak temperature when the heat generation is non-uniform. In addition, the peak temperature is minimum when z = 0.65L even though the hot spot is located on z = 0.75L. |
2014 |
Cetkin, Erdal Three-dimensional high-conductivity trees for volumetric cooling Journal Article INTERNATIONAL JOURNAL OF ENERGY RESEARCH, 38 (12), pp. 1571-1577, 2014, ISSN: 0363-907X. @article{ISI:000342133500008, title = {Three-dimensional high-conductivity trees for volumetric cooling}, author = {Erdal Cetkin}, doi = {10.1002/er.3176}, issn = {0363-907X}, year = {2014}, date = {2014-10-01}, journal = {INTERNATIONAL JOURNAL OF ENERGY RESEARCH}, volume = {38}, number = {12}, pages = {1571-1577}, abstract = {Here, we show how the cooling performance of a volumetrically heated solid can be increased by embedding high-conductivity tree-shaped designs in it. The volume fraction occupied by the high-conductivity material is fixed. Embedding the high-conductivity material as trees in the solid decreases the maximum temperature more than three times compared with distributing the high-conductivity material uniformly throughout the solid. The maximum temperature decreases as the number of the bifurcation levels and the volume fraction of the highly conductive material increase. The thermal resistance of the cube is the lowest when the diameter ratio of the mother and daughter branches at each pairing junction is 2. Changing from T-shaped to Y-shaped designs and from two-dimensional to three-dimensional designs decrease the maximum and the volume averaged temperatures. The peak temperature is the lowest in three-dimensional and Y-shaped designs. This paper shows that the peak temperature of the heated solid can be decreased by only varying the shape of the high-conductivity tree embedded in it. Copyright (c) 2014 John Wiley & Sons, Ltd.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here, we show how the cooling performance of a volumetrically heated solid can be increased by embedding high-conductivity tree-shaped designs in it. The volume fraction occupied by the high-conductivity material is fixed. Embedding the high-conductivity material as trees in the solid decreases the maximum temperature more than three times compared with distributing the high-conductivity material uniformly throughout the solid. The maximum temperature decreases as the number of the bifurcation levels and the volume fraction of the highly conductive material increase. The thermal resistance of the cube is the lowest when the diameter ratio of the mother and daughter branches at each pairing junction is 2. Changing from T-shaped to Y-shaped designs and from two-dimensional to three-dimensional designs decrease the maximum and the volume averaged temperatures. The peak temperature is the lowest in three-dimensional and Y-shaped designs. This paper shows that the peak temperature of the heated solid can be decreased by only varying the shape of the high-conductivity tree embedded in it. Copyright (c) 2014 John Wiley & Sons, Ltd. |
Cetkin, Erdal EMERGENCE OF TAPERED DUCTS IN VASCULAR DESIGNS WITH LAMINAR AND TURBULENT FLOWS Journal Article JOURNAL OF POROUS MEDIA, 17 (8), pp. 715-722, 2014, ISSN: 1091-028X. @article{ISI:000342967400005, title = {EMERGENCE OF TAPERED DUCTS IN VASCULAR DESIGNS WITH LAMINAR AND TURBULENT FLOWS}, author = {Erdal Cetkin}, doi = {10.1615/JPorMedia.v17.i8.50}, issn = {1091-028X}, year = {2014}, date = {2014-01-01}, journal = {JOURNAL OF POROUS MEDIA}, volume = {17}, number = {8}, pages = {715-722}, abstract = {Here we show that tapered ducts emerge in volumetrically bathed porous materials to decrease the resistance to the flow in laminar and turbulent flow regimes. The fluid enters the volume from one point and it is distributed to the entire volume. After bathing the volume, it is collected and leaves the volume from another point, i.e., two trees matched canopy to canopy. This paper shows that the flow architecture (i.e., design of the void spaces in a porous material) should be changed to obtain the minimum resistance to the flow as its size increases. Tapering the ducts decreases the order of the transition size, i.e., the size for changing from one construct to another to obtain the minimum pressure drop. The decrease in the pressure drop is 16% and 38% with the tapered ducts when the flow is laminar and turbulent, respectively. In addition, the volume ratios and the shape of the tapered ducts are documented. There is no design existing in nature with diameters of constant size in order to distribute and/or collect heat, fluid, and/or stress such as bones, rivers, veins, and tree branches. The emergence of the tapered ducts in designed porous materials is natural.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here we show that tapered ducts emerge in volumetrically bathed porous materials to decrease the resistance to the flow in laminar and turbulent flow regimes. The fluid enters the volume from one point and it is distributed to the entire volume. After bathing the volume, it is collected and leaves the volume from another point, i.e., two trees matched canopy to canopy. This paper shows that the flow architecture (i.e., design of the void spaces in a porous material) should be changed to obtain the minimum resistance to the flow as its size increases. Tapering the ducts decreases the order of the transition size, i.e., the size for changing from one construct to another to obtain the minimum pressure drop. The decrease in the pressure drop is 16% and 38% with the tapered ducts when the flow is laminar and turbulent, respectively. In addition, the volume ratios and the shape of the tapered ducts are documented. There is no design existing in nature with diameters of constant size in order to distribute and/or collect heat, fluid, and/or stress such as bones, rivers, veins, and tree branches. The emergence of the tapered ducts in designed porous materials is natural. |
2013 |
Cetkin, E; Lorente, S; Bejan, A Constructal paddle design with ``fingers'' Journal Article JOURNAL OF APPLIED PHYSICS, 113 (19), 2013, ISSN: 0021-8979. @article{ISI:000319295200065, title = {Constructal paddle design with ``fingers''}, author = {E Cetkin and S Lorente and A Bejan}, doi = {10.1063/1.4804961}, issn = {0021-8979}, year = {2013}, date = {2013-05-01}, journal = {JOURNAL OF APPLIED PHYSICS}, volume = {113}, number = {19}, abstract = {Here, we show how the performance of a paddle that pushes a fluid can be increased by making parallel slits through it. The slit spacing is varied to see its effect on the drag force and the maximum stress in the paddle. The effect of water speed and paddle dimensions is documented. Designs with one or more slits are investigated. The drag force is maximum when the slit spacing matches the boundary layer thickness of the flow through the slit. Furthermore, the drag force is greater when the slit spacing is nonuniform: larger in the central slits than in the peripheral slits. The paddle with slits of one size performs almost as well as the best design with nonuniform spacings. The paddle design with slits achieves the same drag force and maximum stress with less material compared with a paddle without slits. (C) 2013 AIP Publishing LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here, we show how the performance of a paddle that pushes a fluid can be increased by making parallel slits through it. The slit spacing is varied to see its effect on the drag force and the maximum stress in the paddle. The effect of water speed and paddle dimensions is documented. Designs with one or more slits are investigated. The drag force is maximum when the slit spacing matches the boundary layer thickness of the flow through the slit. Furthermore, the drag force is greater when the slit spacing is nonuniform: larger in the central slits than in the peripheral slits. The paddle with slits of one size performs almost as well as the best design with nonuniform spacings. The paddle design with slits achieves the same drag force and maximum stress with less material compared with a paddle without slits. (C) 2013 AIP Publishing LLC. |
2012 |
Cetkin, E; Lorente, S; Bejan, A Vascularization for cooling a plate heated by a randomly moving source Journal Article JOURNAL OF APPLIED PHYSICS, 112 (8), 2012, ISSN: 0021-8979. @article{ISI:000310597500155, title = {Vascularization for cooling a plate heated by a randomly moving source}, author = {E Cetkin and S Lorente and A Bejan}, doi = {10.1063/1.4759290}, issn = {0021-8979}, year = {2012}, date = {2012-10-01}, journal = {JOURNAL OF APPLIED PHYSICS}, volume = {112}, number = {8}, abstract = {Here, we show that a plate heated by a moving beam can be cooled effectively by fluid that flows through a vasculature of channels embedded in the plate. The vascular designs studied are radial, grid and hybrid (radial + grid). The peak temperature of the plate changes with the path and direction of the moving beam. The strength, size and speed of the beam vary. The peak temperature increases as the beam strength and size increase and as the speed of the beam decreases. The grid and hybrid designs are robust because of loops present in the flow structure. The pressure difference that drives the fluid flow varied. The channel diameter ratios that provide greatest flow access are reported. The cooling performance of the multiscale grid structures is less sensitive to the changes in beam path than the cooling performance of the other structures studied. The effect of adding a vascular structure to the design is dramatic. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4759290]}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here, we show that a plate heated by a moving beam can be cooled effectively by fluid that flows through a vasculature of channels embedded in the plate. The vascular designs studied are radial, grid and hybrid (radial + grid). The peak temperature of the plate changes with the path and direction of the moving beam. The strength, size and speed of the beam vary. The peak temperature increases as the beam strength and size increase and as the speed of the beam decreases. The grid and hybrid designs are robust because of loops present in the flow structure. The pressure difference that drives the fluid flow varied. The channel diameter ratios that provide greatest flow access are reported. The cooling performance of the multiscale grid structures is less sensitive to the changes in beam path than the cooling performance of the other structures studied. The effect of adding a vascular structure to the design is dramatic. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4759290] |
Lorente, S; Cetkin, E; Bello-Ochende, T; Meyer, J P; Bejan, A The constructal-law physics of why swimmers must spread their fingers and toes Journal Article JOURNAL OF THEORETICAL BIOLOGY, 308 , pp. 141-146, 2012, ISSN: 0022-5193. @article{ISI:000307030100015, title = {The constructal-law physics of why swimmers must spread their fingers and toes}, author = {S Lorente and E Cetkin and T Bello-Ochende and J P Meyer and A Bejan}, doi = {10.1016/j.jtbi.2012.05.033}, issn = {0022-5193}, year = {2012}, date = {2012-09-01}, journal = {JOURNAL OF THEORETICAL BIOLOGY}, volume = {308}, pages = {141-146}, abstract = {Here we show theoretically that swimming animals and athletes gain an advantage in force and speed by spreading their fingers and toes optimally. The larger force means larger body mass lifted and greater speed, in accord with the constructal theory of all animal locomotion. The spacing between fingers must be twice the thickness of the boundary layer around one finger. This theoretical prediction is confirmed by computational fluid dynamics simulations of flow across two and four cylinders of diameter D. The optimal spacing is in the range 0.2D-0.4D, and decreases slightly as the Reynolds number (Re) increases from 20 to 100. For example, the total force exerted by two optimally spaced cylinders exceeds by 53% the total force of two cylinders with no spacing when Re=20. These design features hold for both time-dependent and steady-state flows. (C) 2012 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here we show theoretically that swimming animals and athletes gain an advantage in force and speed by spreading their fingers and toes optimally. The larger force means larger body mass lifted and greater speed, in accord with the constructal theory of all animal locomotion. The spacing between fingers must be twice the thickness of the boundary layer around one finger. This theoretical prediction is confirmed by computational fluid dynamics simulations of flow across two and four cylinders of diameter D. The optimal spacing is in the range 0.2D-0.4D, and decreases slightly as the Reynolds number (Re) increases from 20 to 100. For example, the total force exerted by two optimally spaced cylinders exceeds by 53% the total force of two cylinders with no spacing when Re=20. These design features hold for both time-dependent and steady-state flows. (C) 2012 Elsevier Ltd. All rights reserved. |
Assoc. Prof. Dr. Mehmet Dördüncü
Educational Background
B.Sc. Erciyes University, Turkey, Mechanical Engineering, 2011
M.Sc. Erciyes University, Turkey, Mechanical Engineering, 2013
Ph.D. University of Arizona, USA, Mechanical Engineering, 2018
Research Interests
- Mechanical Behaviors of Materials, Computational Mechanics
- Peridynamics
- Fracture Mechanics
- Composite Materials
- +90 232 750 6784
- +90 232 750 6701
- Mechanical Engineering Building (Z17)
Publications
Res. Assist. Dr. Timuçin Eriş
Educational Background
B.Sc. Gazi University, Mechanical Engineering, 1991
M.Sc. Illinois Institute of Technology, Mechanical Engineering, 1997
Ph.D. Dokuz Eylül University, Mechanical Engineering, 2008
Research Interests
- Control Systems
- Artificial Neural Networks
- Finite Elements
- +90 232 750 6790
- +90 232 750 6701
- Mechanical Engineering Building (203, 2nd floor)
Publications
Prof. Dr. Mustafa Güden
Educational Background
B.Sc. Middle East Technical University, Turkey, Metallurgical and Materials Engineering, 1989
M.Sc. Middle East Technical University, Turkey, Metallurgical and Materials Engineering, 1992
Ph.D. University of Delaware, USA, Materials Science and Engineering, 1999
Research Interests
- Composite materials (Carbon and glass fiber reinforced and nano silica reinforced epoxy matrix composites, ceramic fiber and particulate reinforced aluminum and magnesium matrix composites, ceramic-ceramic composites): processing, static and dynamic testing and dynamic mechanical deformation numerical modelling (Ls-DYNA, Mat 162)
- Cellular and lattice structures (Aluminum foams, honeycomb and corrugated structures, Titanium foams, cellular concrete and glass foams): processing, dynamic testing and dynamic mechanical deformation numerical modelling
- Additive manufacturing (316 L Stainless Steel and Ti64)
- (4) Dynamic testing (Split Hopkinson Pressure Bar and Direct impact and Taylor impact tests): test and numerical and analytical modelling;
- Mechanical behavior of materials and
- Microstructure-mechanical property relations
- +90 232 750 6779
- +90 232 750 6701
- Mechanical Engineering Building (Z10)
Publications
2023 |
Enser, Samed; Guden, Mustafa; Tasdemirci, Alper; Davut, Kemal The strain rate history effect in a selective-laser-melt 316L stainless steel Journal Article MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 862 , 2023. @article{WOS:000905147200003, title = {The strain rate history effect in a selective-laser-melt 316L stainless steel}, author = {Samed Enser and Mustafa Guden and Alper Tasdemirci and Kemal Davut}, doi = {10.1016/j.msea.2022.144439}, year = {2023}, date = {2023-01-01}, journal = {MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, volume = {862}, abstract = {The strain rate history effect in a selective laser melt 316L (SLM-316L) alloy was investigated through quasi -static (10-3 s- 1) and high strain rate (1600-3200 s-1) interrupted and reloading compression tests. The speci-mens pre-tested until about prescribed strains at quasi-static and high strain rates were reloaded dynamically and quasi-statically, respectively. The results revealed that the flow stress depended on strain and strain rate as well as strain-rate history. Quasi-static reloading the dynamically pre-tested specimens until about prescribed strains induced a higher flow stress than the specimens tested quasi-statically. The strengthening was-70 MPa at 0.11 pre-strain and decreased as the dynamic test pre-strain was increased due to adiabatic heating. On the other side, reloading the quasi-statically pre-tested specimens dynamically at 0.11 pre-strain resulted in-60 MPa lower flow stress than the specimens tested dynamically. The grains of the quasi-statically tested specimens until 0.11 strain were shown to have a lower Taylor factor for twinning and geometrically necessary dislocation density, indicating more potential for twinning than dynamically tested specimen. Although, quasi-statically and dynamically tested specimens were deformed predominantly by the twinning induced plasticity, a higher frac-tion of twin boundaries was shown microscopically in the dynamically pre-tested specimens until 0.11 pre-strain. This phenomenon of boundary strengthening could be used as a tool of strengthening of SLM-316L alloy at low strains.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The strain rate history effect in a selective laser melt 316L (SLM-316L) alloy was investigated through quasi -static (10-3 s- 1) and high strain rate (1600-3200 s-1) interrupted and reloading compression tests. The speci-mens pre-tested until about prescribed strains at quasi-static and high strain rates were reloaded dynamically and quasi-statically, respectively. The results revealed that the flow stress depended on strain and strain rate as well as strain-rate history. Quasi-static reloading the dynamically pre-tested specimens until about prescribed strains induced a higher flow stress than the specimens tested quasi-statically. The strengthening was-70 MPa at 0.11 pre-strain and decreased as the dynamic test pre-strain was increased due to adiabatic heating. On the other side, reloading the quasi-statically pre-tested specimens dynamically at 0.11 pre-strain resulted in-60 MPa lower flow stress than the specimens tested dynamically. The grains of the quasi-statically tested specimens until 0.11 strain were shown to have a lower Taylor factor for twinning and geometrically necessary dislocation density, indicating more potential for twinning than dynamically tested specimen. Although, quasi-statically and dynamically tested specimens were deformed predominantly by the twinning induced plasticity, a higher frac-tion of twin boundaries was shown microscopically in the dynamically pre-tested specimens until 0.11 pre-strain. This phenomenon of boundary strengthening could be used as a tool of strengthening of SLM-316L alloy at low strains. |
Tuncer, C; Güden, M; Orhan, M; Sarıkaya, M K; Taşdemirci, A Quasi-static and dynamic Brazilian testing and failure analysis of a deer antler in the transverse to the osteon growth direction Journal Article Journal of the Mechanical Behavior of Biomedical Materials, 138 , 2023. @article{Tuncer2023, title = {Quasi-static and dynamic Brazilian testing and failure analysis of a deer antler in the transverse to the osteon growth direction}, author = {C Tuncer and M Güden and M Orhan and M K Sarıkaya and A Taşdemirci}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85145658319&doi=10.1016%2fj.jmbbm.2023.105648&partnerID=40&md5=f2b3c0121aa41d2857249a24554f05da}, doi = {10.1016/j.jmbbm.2023.105648}, year = {2023}, date = {2023-01-01}, journal = {Journal of the Mechanical Behavior of Biomedical Materials}, volume = {138}, abstract = {The transverse tensile strength of a naturally fallen red deer antler (Cervus Elaphus) was determined through indirect Brazilian tests using dry disc-shape specimens at quasi-static and high strain rates. Dynamic Brazilian tests were performed in a compression Split-Hopkinson Pressure Bar. Quasi-static tensile and indirect Brazilian tests were also performed along the osteon growth direction for comparison. The quasi-static transverse tensile strength ranged 31.5–44.5 MPa. The strength increased to 83 MPa on the average in the dynamic Brazilian tests, proving a rate sensitive transverse strength. The quasi-static tensile strength in the osteon growth direction was however found comparably higher, 192 MPa. A Weibull analysis indicated a higher tensile ductility in the osteon growth direction than in the transverse to the osteon growth direction. The microscopic analysis of the quasi-static Brazilian test specimens (tensile strain along the osteon growth direction) revealed a micro-cracking mechanism operating by the crack deflection/twisting at the lacunae in the concentric lamellae region and at the interface between concentric lamellae and interstitial lamellae. On the other side, the specimens in the transverse direction fractured in a more brittle manner by the separation/delamination of the concentric lamellae and pulling of the interstitial lamellae. The detected increase in the transverse strength in the high strain rate tests was further ascribed to the pull and fracture of the visco-plastic collagen fibers in the interstitial lamellae. This was also confirmed microscopically; the dynamically tested specimens exhibited flatter fracture surfaces. © 2023 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The transverse tensile strength of a naturally fallen red deer antler (Cervus Elaphus) was determined through indirect Brazilian tests using dry disc-shape specimens at quasi-static and high strain rates. Dynamic Brazilian tests were performed in a compression Split-Hopkinson Pressure Bar. Quasi-static tensile and indirect Brazilian tests were also performed along the osteon growth direction for comparison. The quasi-static transverse tensile strength ranged 31.5–44.5 MPa. The strength increased to 83 MPa on the average in the dynamic Brazilian tests, proving a rate sensitive transverse strength. The quasi-static tensile strength in the osteon growth direction was however found comparably higher, 192 MPa. A Weibull analysis indicated a higher tensile ductility in the osteon growth direction than in the transverse to the osteon growth direction. The microscopic analysis of the quasi-static Brazilian test specimens (tensile strain along the osteon growth direction) revealed a micro-cracking mechanism operating by the crack deflection/twisting at the lacunae in the concentric lamellae region and at the interface between concentric lamellae and interstitial lamellae. On the other side, the specimens in the transverse direction fractured in a more brittle manner by the separation/delamination of the concentric lamellae and pulling of the interstitial lamellae. The detected increase in the transverse strength in the high strain rate tests was further ascribed to the pull and fracture of the visco-plastic collagen fibers in the interstitial lamellae. This was also confirmed microscopically; the dynamically tested specimens exhibited flatter fracture surfaces. © 2023 Elsevier Ltd |
Enser, S; Güden, M; Taşdemirci, A; Davut, K The strain rate history effect in a selective-laser-melt 316L stainless steel Journal Article Materials Science and Engineering A, 862 , 2023. @article{Enser2023, title = {The strain rate history effect in a selective-laser-melt 316L stainless steel}, author = {S Enser and M Güden and A Taşdemirci and K Davut}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85143677799&doi=10.1016%2fj.msea.2022.144439&partnerID=40&md5=d3e4693f86b0e95c1ee6eb89a46551aa}, doi = {10.1016/j.msea.2022.144439}, year = {2023}, date = {2023-01-01}, journal = {Materials Science and Engineering A}, volume = {862}, abstract = {The strain rate history effect in a selective laser melt 316L (SLM-316L) alloy was investigated through quasi-static (10−3 s−1) and high strain rate (1600-3200 s−1) interrupted and reloading compression tests. The specimens pre-tested until about prescribed strains at quasi-static and high strain rates were reloaded dynamically and quasi-statically, respectively. The results revealed that the flow stress depended on strain and strain rate as well as strain-rate history. Quasi-static reloading the dynamically pre-tested specimens until about prescribed strains induced a higher flow stress than the specimens tested quasi-statically. The strengthening was ∼70 MPa at 0.11 pre-strain and decreased as the dynamic test pre-strain was increased due to adiabatic heating. On the other side, reloading the quasi-statically pre-tested specimens dynamically at 0.11 pre-strain resulted in ∼60 MPa lower flow stress than the specimens tested dynamically. The grains of the quasi-statically tested specimens until 0.11 strain were shown to have a lower Taylor factor for twinning and geometrically necessary dislocation density, indicating more potential for twinning than dynamically tested specimen. Although, quasi-statically and dynamically tested specimens were deformed predominantly by the twinning induced plasticity, a higher fraction of twin boundaries was shown microscopically in the dynamically pre-tested specimens until 0.11 pre-strain. This phenomenon of boundary strengthening could be used as a tool of strengthening of SLM-316L alloy at low strains. © 2022 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The strain rate history effect in a selective laser melt 316L (SLM-316L) alloy was investigated through quasi-static (10−3 s−1) and high strain rate (1600-3200 s−1) interrupted and reloading compression tests. The specimens pre-tested until about prescribed strains at quasi-static and high strain rates were reloaded dynamically and quasi-statically, respectively. The results revealed that the flow stress depended on strain and strain rate as well as strain-rate history. Quasi-static reloading the dynamically pre-tested specimens until about prescribed strains induced a higher flow stress than the specimens tested quasi-statically. The strengthening was ∼70 MPa at 0.11 pre-strain and decreased as the dynamic test pre-strain was increased due to adiabatic heating. On the other side, reloading the quasi-statically pre-tested specimens dynamically at 0.11 pre-strain resulted in ∼60 MPa lower flow stress than the specimens tested dynamically. The grains of the quasi-statically tested specimens until 0.11 strain were shown to have a lower Taylor factor for twinning and geometrically necessary dislocation density, indicating more potential for twinning than dynamically tested specimen. Although, quasi-statically and dynamically tested specimens were deformed predominantly by the twinning induced plasticity, a higher fraction of twin boundaries was shown microscopically in the dynamically pre-tested specimens until 0.11 pre-strain. This phenomenon of boundary strengthening could be used as a tool of strengthening of SLM-316L alloy at low strains. © 2022 Elsevier B.V. |
Zeybek, M K; Güden, M; Taşdemirci, A Journal of Materials Engineering and Performance, 2023. @article{Zeybek2023, title = {The Effect of Strain Rate on the Compression Behavior of Additively Manufactured Short Carbon Fiber-Reinforced Polyamide Composites with Different Layer Heights, Infill Patterns, and Built Angles}, author = {M K Zeybek and M Güden and A Taşdemirci}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85147762551&doi=10.1007%2fs11665-023-07918-1&partnerID=40&md5=e7bbc8949f442fcf22b8812d43a6fa1e}, doi = {10.1007/s11665-023-07918-1}, year = {2023}, date = {2023-01-01}, journal = {Journal of Materials Engineering and Performance}, abstract = {Previous studies on the fused deposition modelling (FDM) processed short carbon fiber/Polyamide 6 (PA6) matrix composites and neat PA6 have mostly concentrated on the quasi-static mechanical properties. Present study focused on the strain rate-dependent deformation behavior of a short carbon fiber-reinforced PA6 (Onyx) and neat PA6, produced in different layer heights, infill patterns and built angles. As compared with PA6, Onyx showed a higher compression stress at all strain rates investigated. A layer height of 0.2 mm in PA6 specimens promoted a better bonding between [0/90°] infill layers; hence, a higher flow stress than 0.2 mm layer height specimens, while 0.2 mm layer height induced a higher porosity in Onyx specimens, leading to a lower flow stress. The porosities in Onyx [0/90°] infill specimens were due to the constraining effect of 0/90° fiber layers. Changing infill pattern from a [0/90°] to a concentric one decreased porosity at the same layer height and hence increased the compressive flow stress. The highest compressive strength was found in the specimens with the loading axis 90 and 0° to [0/90°] infill plane. The lowest strength was, however, determined in the specimens with the loading axis 30 and 60o to [0/90°] infill plane in quasi-static loading. However, the specimens with the loading axis of 60, 45, 30 and 0° exhibited a brittle behavior in high strain rate loading (1500 s−1). The specimens with the loading axis of 45° had the lowest fracture stress and strain in the high strain rate loading. This signified the importance of loading angle at high strain rates. Finally, the rate sensitivities of PA6 and Onyx specimens were shown to be similar, showing a matrix dominated deformation. However, the strain rate jump tests indicated a slightly higher rate sensitivity of Onyx specimens at quasi-static strain rates (10−3-10−1 s−1). © 2023, ASM International.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Previous studies on the fused deposition modelling (FDM) processed short carbon fiber/Polyamide 6 (PA6) matrix composites and neat PA6 have mostly concentrated on the quasi-static mechanical properties. Present study focused on the strain rate-dependent deformation behavior of a short carbon fiber-reinforced PA6 (Onyx) and neat PA6, produced in different layer heights, infill patterns and built angles. As compared with PA6, Onyx showed a higher compression stress at all strain rates investigated. A layer height of 0.2 mm in PA6 specimens promoted a better bonding between [0/90°] infill layers; hence, a higher flow stress than 0.2 mm layer height specimens, while 0.2 mm layer height induced a higher porosity in Onyx specimens, leading to a lower flow stress. The porosities in Onyx [0/90°] infill specimens were due to the constraining effect of 0/90° fiber layers. Changing infill pattern from a [0/90°] to a concentric one decreased porosity at the same layer height and hence increased the compressive flow stress. The highest compressive strength was found in the specimens with the loading axis 90 and 0° to [0/90°] infill plane. The lowest strength was, however, determined in the specimens with the loading axis 30 and 60o to [0/90°] infill plane in quasi-static loading. However, the specimens with the loading axis of 60, 45, 30 and 0° exhibited a brittle behavior in high strain rate loading (1500 s−1). The specimens with the loading axis of 45° had the lowest fracture stress and strain in the high strain rate loading. This signified the importance of loading angle at high strain rates. Finally, the rate sensitivities of PA6 and Onyx specimens were shown to be similar, showing a matrix dominated deformation. However, the strain rate jump tests indicated a slightly higher rate sensitivity of Onyx specimens at quasi-static strain rates (10−3-10−1 s−1). © 2023, ASM International. |
Turan, A K; Tasdemirci, A; Kara, A; Sahin, S; Guden, M Thin-Walled Structures, 182 , 2023. @article{Turan2023, title = {Investigation of penetration behavior of combined geometry shells at quasi-static and intermediate strain rates: An experimental and numerical study}, author = {A K Turan and A Tasdemirci and A Kara and S Sahin and M Guden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85140804922&doi=10.1016%2fj.tws.2022.110261&partnerID=40&md5=a68187ac67baf30b83898f98789e157e}, doi = {10.1016/j.tws.2022.110261}, year = {2023}, date = {2023-01-01}, journal = {Thin-Walled Structures}, volume = {182}, abstract = {In this study, the penetration/perforation behavior of a core material with previously determined static and dynamic crushing characteristics was investigated both experimentally and numerically. Penetration/perforation problems occur due to shrapnel effect when sandwich structures containing energy-absorbing core materials by crushing are exposed to blast loads. The penetration behavior of combined geometry shells consisting of a hemispherical cap and a cylindrical segment was investigated experimentally using blunt, conical and hemispherical penetrator tips. The quasi-static penetration tests were performed in a universal test machine, and the intermediate strain rate penetration tests were performed in a drop weight test device. The numerical models of penetration tests were implemented in LS-DYNA at the test strain rates as well as at the higher strain rates. Results showed that different penetrator geometries induced damage forms of symmetrical tearing, petaling, plugging and inversely formed hemispherical domed cone. The increase in the thickness of core geometry resulted in a decent increase in force–displacement curves, as average of force levels increased around 140%, 200% and 220% for blunt, conical and hemispherical tip penetrators, respectively. Numerical results indicated very good correlation with experimental work and enabled to investigate effect of strain rate and micro-inertia over numerical models at elevated penetrator velocities. Penetration behavior was found to be affected from micro-inertia effects up to a threshold displacement of 4 mm for thicker and 5 mm for thinner core units and strain rate effects were found to be dominant beyond that point. © 2022 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, the penetration/perforation behavior of a core material with previously determined static and dynamic crushing characteristics was investigated both experimentally and numerically. Penetration/perforation problems occur due to shrapnel effect when sandwich structures containing energy-absorbing core materials by crushing are exposed to blast loads. The penetration behavior of combined geometry shells consisting of a hemispherical cap and a cylindrical segment was investigated experimentally using blunt, conical and hemispherical penetrator tips. The quasi-static penetration tests were performed in a universal test machine, and the intermediate strain rate penetration tests were performed in a drop weight test device. The numerical models of penetration tests were implemented in LS-DYNA at the test strain rates as well as at the higher strain rates. Results showed that different penetrator geometries induced damage forms of symmetrical tearing, petaling, plugging and inversely formed hemispherical domed cone. The increase in the thickness of core geometry resulted in a decent increase in force–displacement curves, as average of force levels increased around 140%, 200% and 220% for blunt, conical and hemispherical tip penetrators, respectively. Numerical results indicated very good correlation with experimental work and enabled to investigate effect of strain rate and micro-inertia over numerical models at elevated penetrator velocities. Penetration behavior was found to be affected from micro-inertia effects up to a threshold displacement of 4 mm for thicker and 5 mm for thinner core units and strain rate effects were found to be dominant beyond that point. © 2022 Elsevier Ltd |
Güden, Mustafa; Ülker, Sevkan; Movahedi, Nima Epoxy matrix nano composites: modulus, strength and ductility enhancement through auxeticity of α-Cristobalite filler Journal Article Materials Letters, 349 , 2023. @article{Güden2023, title = {Epoxy matrix nano composites: modulus, strength and ductility enhancement through auxeticity of α-Cristobalite filler}, author = {Mustafa Güden and Sevkan Ülker and Nima Movahedi}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85162134261&doi=10.1016%2fj.matlet.2023.134759&partnerID=40&md5=34d79791a88c5b5655fa411fe0895b99}, doi = {10.1016/j.matlet.2023.134759}, year = {2023}, date = {2023-01-01}, journal = {Materials Letters}, volume = {349}, abstract = {The negative Poisson's ratio (NPR) nano-size α-Cristobalite particle/epoxy composites were prepared and tensile tested. The elastic modulus and strength of the composites were improved as the particle volume fraction increased from 0 to 0.02. Unlike the conventional particle reinforced composites, the fracture strain increased with the nano α-Cristobalite addition, an effect which was ascribed to the intrinsic NPR behavior of the filler. © 2023 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The negative Poisson's ratio (NPR) nano-size α-Cristobalite particle/epoxy composites were prepared and tensile tested. The elastic modulus and strength of the composites were improved as the particle volume fraction increased from 0 to 0.02. Unlike the conventional particle reinforced composites, the fracture strain increased with the nano α-Cristobalite addition, an effect which was ascribed to the intrinsic NPR behavior of the filler. © 2023 Elsevier B.V. |
Güden, Mustafa; Riaz, Arslan Bin; Toksoy, Ahmet Kaan; Yıldıztekin, Murat; Erten, Hacer İrem; Çimen, Gülden; Hızlı, Burak; Çellek, Burçin Seven; Güleç, Efe; Taşdemirci, Alper; Yavaş, Hakan; Altınok, Sertaç Materials Science and Engineering: A, 885 , 2023. @article{Güden2023b, title = {Investigation and validation of the flow stress equation and damage model parameters of an electron beam melted Ti6Al4V alloy with a martensitic phase}, author = {Mustafa Güden and Arslan Bin Riaz and Ahmet Kaan Toksoy and Murat Yıldıztekin and Hacer İrem Erten and Gülden Çimen and Burak Hızlı and Burçin Seven Çellek and Efe Güleç and Alper Taşdemirci and Hakan Yavaş and Sertaç Altınok}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85171624739&doi=10.1016%2fj.msea.2023.145590&partnerID=40&md5=206e908384653029d335d5611a983306}, doi = {10.1016/j.msea.2023.145590}, year = {2023}, date = {2023-01-01}, journal = {Materials Science and Engineering: A}, volume = {885}, abstract = {The Johnson and Cook flow stress and damage model parameters of an electron beam melt (EBM)-Ti64 alloy composed of α' (martensite) and α+β and an extruded-annealed conventional Ti64 alloy were determined experimentally. The validities of the determined flow stress equations and damage model parameters were then verified by the numerical simulations of the compression tests on the Body Centered Cubic lattices produced using the same EBM parameters with the solid EBM samples. In addition, a compression flow stress equation was extracted from the small-size test specimens (1 and 2 mm diameter) taken directly from the struts of the as-built lattices. The microscopic observations, XRD analyses and hardness tests confirmed the presence of α′ phase in the EBM solid samples and in the struts of the BCC lattices, which reduced the ductility of the EBM solid specimens and struts compared to the conventional Ti64. Furthermore, the partially melt particles on the surfaces of the struts acted as the stress concentration sides for micro-cracking; hence, the compression flow stresses of the struts were found to be significantly lower than those of the as-built EBM solid specimens. The flow stress equation derived from the struts predicted more accurately the compression behavior of the lattices. The compression tests and models showed that early damage formation in the lattices was noted to decrease the initial peak and post-peak stresses. As with the experiments, the initial damage occurred in the models with the separation of the nodes at the lattice cell surface edges. This resulted in an abrupt reduction in the stresses after the peak stress. The numerical lattices without damage showed a localized lattice deformation at the mid-sections and the stress increased continuously as a function of normal strain. © 2023 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The Johnson and Cook flow stress and damage model parameters of an electron beam melt (EBM)-Ti64 alloy composed of α' (martensite) and α+β and an extruded-annealed conventional Ti64 alloy were determined experimentally. The validities of the determined flow stress equations and damage model parameters were then verified by the numerical simulations of the compression tests on the Body Centered Cubic lattices produced using the same EBM parameters with the solid EBM samples. In addition, a compression flow stress equation was extracted from the small-size test specimens (1 and 2 mm diameter) taken directly from the struts of the as-built lattices. The microscopic observations, XRD analyses and hardness tests confirmed the presence of α′ phase in the EBM solid samples and in the struts of the BCC lattices, which reduced the ductility of the EBM solid specimens and struts compared to the conventional Ti64. Furthermore, the partially melt particles on the surfaces of the struts acted as the stress concentration sides for micro-cracking; hence, the compression flow stresses of the struts were found to be significantly lower than those of the as-built EBM solid specimens. The flow stress equation derived from the struts predicted more accurately the compression behavior of the lattices. The compression tests and models showed that early damage formation in the lattices was noted to decrease the initial peak and post-peak stresses. As with the experiments, the initial damage occurred in the models with the separation of the nodes at the lattice cell surface edges. This resulted in an abrupt reduction in the stresses after the peak stress. The numerical lattices without damage showed a localized lattice deformation at the mid-sections and the stress increased continuously as a function of normal strain. © 2023 Elsevier B.V. |
Çelik, Muhammet; Güden, Mustafa; Sarıkaya, Mustafa; Taşdemirci, Alper; Genç, Cem; Ersoy, Kurtuluş; Serin, Özgür Composite Structures, 320 , 2023. @article{Çelik2023, title = {The impact response of a Nomex® honeycomb core/E-glass/epoxy composite sandwich structure to increasing velocities: Experimental and numerical analysis}, author = {Muhammet Çelik and Mustafa Güden and Mustafa Sarıkaya and Alper Taşdemirci and Cem Genç and Kurtuluş Ersoy and Özgür Serin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85162005169&doi=10.1016%2fj.compstruct.2023.117205&partnerID=40&md5=fb47471b22e7653bc2d670c7a45b347b}, doi = {10.1016/j.compstruct.2023.117205}, year = {2023}, date = {2023-01-01}, journal = {Composite Structures}, volume = {320}, abstract = {The impact response of an E-glass fiber reinforced epoxy/Nomex® honeycomb core sandwich was investigated both experimentally and numerically at increasing velocities through concentrated quasi-static indentation force (CQIF), low velocity impact (LVI) and high velocity impact (HVI) tests. The composite face sheets and core were modelled using MAT_162 and MAT_026 homogenized material model in LS-DYNA, respectively. The experimental and numerical LVI test forces corresponding to core crushing and face sheet penetration were shown to be higher than those of the CQIF tests and increased as the impactor velocity increased. The increase of the impact forces at increasing velocities was largely ascribed to the inertia and the strain rate sensitive fracture strength of the composite sheets. The core shearing was detected in the CQIF and LVI tests both experimentally and numerically. It was also detected in the HVI tests at the velocities less than 20 m s−1. The deformation in the HVI tests at and above ∼ 29.4 m s−1 was highly localized in the impact area with no core shearing and a large delamination damage area at the front face sheet. The force enhancement due to the micro-inertia of the core deformation was shown to be not significant at the studied velocities. © 2023 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The impact response of an E-glass fiber reinforced epoxy/Nomex® honeycomb core sandwich was investigated both experimentally and numerically at increasing velocities through concentrated quasi-static indentation force (CQIF), low velocity impact (LVI) and high velocity impact (HVI) tests. The composite face sheets and core were modelled using MAT_162 and MAT_026 homogenized material model in LS-DYNA, respectively. The experimental and numerical LVI test forces corresponding to core crushing and face sheet penetration were shown to be higher than those of the CQIF tests and increased as the impactor velocity increased. The increase of the impact forces at increasing velocities was largely ascribed to the inertia and the strain rate sensitive fracture strength of the composite sheets. The core shearing was detected in the CQIF and LVI tests both experimentally and numerically. It was also detected in the HVI tests at the velocities less than 20 m s−1. The deformation in the HVI tests at and above ∼ 29.4 m s−1 was highly localized in the impact area with no core shearing and a large delamination damage area at the front face sheet. The force enhancement due to the micro-inertia of the core deformation was shown to be not significant at the studied velocities. © 2023 Elsevier Ltd |
Sarıkaya, Mustafa; Güden, Mustafa; Kambur, Çağdaş; Özbek, Sevim Çankaya; Taşdemirci, Alper Development of the Johnson-Cook flow stress and damage parameters for the impact response of polycarbonate: Experimental and numerical approach Journal Article International Journal of Impact Engineering, 179 , 2023. @article{Sarıkaya2023, title = {Development of the Johnson-Cook flow stress and damage parameters for the impact response of polycarbonate: Experimental and numerical approach}, author = {Mustafa Sarıkaya and Mustafa Güden and Çağdaş Kambur and Sevim Çankaya Özbek and Alper Taşdemirci}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85160689008&doi=10.1016%2fj.ijimpeng.2023.104674&partnerID=40&md5=26109d206458c5db0dfc878ae314e9b4}, doi = {10.1016/j.ijimpeng.2023.104674}, year = {2023}, date = {2023-01-01}, journal = {International Journal of Impact Engineering}, volume = {179}, abstract = {The Johnson and Cook (JC) flow stress and damage model parameters of a polycarbonate (PC) plate were determined by the mechanical tests and numerical simulations of the tests. The experimental tests included quasi-static and high strain rate tension and compression, quasi-static notched-specimen tension, quasi-static indentation (QSI), low velocity impact (LVI) and projectile impact (PI). Initially, five different quasi-static flow stress-strain equations were extracted from the experimental and numerical tests. The flow stress equation determined from the experimental average true stress-true strain curve well agreed with the effective stress-strain obtained from the quasi-static numerical tension test. The numerical QSI force-displacement curve based on the experimental average true stress-true strain equation was further shown to be very similar to that of the experiment. The LVI and PI test simulations were then continued with the experimental average true stress-true strain equation using five different flow stress-strain rate relations: JC, Huh and Kang (HK), Allen-Rule and Jones (ARJ), Cowper-Symonds (CS) and the nonlinear rate approach (NLA). The rate sensitivity parameters of these relations were extracted from the quasi-static and high strain rate tests. The LVI test simulations using the stress-strain rate relations exhibited force-displacement curves higher than those of the experiments. The detected almost no strain rate sensitivity in the LVI tests was ascribed to low strain rate dependency of the flow stress at these intermediate strain rates and large strains involved. On the other side, all the stress-strain rate relations investigated nearly predicted the experimental damage types: dishing at 100 and 140 m s−1 and petalling at 160 m s−1, except the CS relation which predicted the fracture of the plate at 140 m s−1. The experimental average projectile exit velocity at 160 m s−1 was further well predicted by the used stress-strain rate relations while the experimental average petal thicknesses were under estimated by the models. The absorbed energy at 160 m s−1 PI test was determined 1.6 times that of the QSI test, which proved an increased energy absorption capability of the tested PC at the investigated impact velocities. © 2023 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The Johnson and Cook (JC) flow stress and damage model parameters of a polycarbonate (PC) plate were determined by the mechanical tests and numerical simulations of the tests. The experimental tests included quasi-static and high strain rate tension and compression, quasi-static notched-specimen tension, quasi-static indentation (QSI), low velocity impact (LVI) and projectile impact (PI). Initially, five different quasi-static flow stress-strain equations were extracted from the experimental and numerical tests. The flow stress equation determined from the experimental average true stress-true strain curve well agreed with the effective stress-strain obtained from the quasi-static numerical tension test. The numerical QSI force-displacement curve based on the experimental average true stress-true strain equation was further shown to be very similar to that of the experiment. The LVI and PI test simulations were then continued with the experimental average true stress-true strain equation using five different flow stress-strain rate relations: JC, Huh and Kang (HK), Allen-Rule and Jones (ARJ), Cowper-Symonds (CS) and the nonlinear rate approach (NLA). The rate sensitivity parameters of these relations were extracted from the quasi-static and high strain rate tests. The LVI test simulations using the stress-strain rate relations exhibited force-displacement curves higher than those of the experiments. The detected almost no strain rate sensitivity in the LVI tests was ascribed to low strain rate dependency of the flow stress at these intermediate strain rates and large strains involved. On the other side, all the stress-strain rate relations investigated nearly predicted the experimental damage types: dishing at 100 and 140 m s−1 and petalling at 160 m s−1, except the CS relation which predicted the fracture of the plate at 140 m s−1. The experimental average projectile exit velocity at 160 m s−1 was further well predicted by the used stress-strain rate relations while the experimental average petal thicknesses were under estimated by the models. The absorbed energy at 160 m s−1 PI test was determined 1.6 times that of the QSI test, which proved an increased energy absorption capability of the tested PC at the investigated impact velocities. © 2023 Elsevier Ltd |
Mauko, Anja; Sarıkaya, Mustafa; Güden, Mustafa; Duarte, Isabel; Borovinšek, Matej; Vesenjak, Matej; Ren, Zoran High strain-rate deformation analysis of open-cell aluminium foam Journal Article Journal of Materials Research and Technology, 25 , pp. 1208 – 1221, 2023, (All Open Access, Gold Open Access, Green Open Access). @article{Mauko20231208, title = {High strain-rate deformation analysis of open-cell aluminium foam}, author = {Anja Mauko and Mustafa Sarıkaya and Mustafa Güden and Isabel Duarte and Matej Borovinšek and Matej Vesenjak and Zoran Ren}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85162885101&doi=10.1016%2fj.jmrt.2023.05.280&partnerID=40&md5=a55525f2fe8789924a5b73ce11d13a7a}, doi = {10.1016/j.jmrt.2023.05.280}, year = {2023}, date = {2023-01-01}, journal = {Journal of Materials Research and Technology}, volume = {25}, pages = {1208 – 1221}, abstract = {This study investigated the high-strain rate mechanical properties of open-cell aluminium foam M-pore®. While previous research has examined the response of this type of foam under quasi-static and transitional dynamic loading conditions, there is a lack of knowledge about its behaviour under higher strain rates (transitional and shock loading regimes). To address this gap in understanding, cylindrical open-cell foam specimens were tested using a modified Direct Impact Hopkinson Bar (DIHB) apparatus over a wide range of strain rates, up to 93 m/s. The results showed a strong dependency of the foam's behaviour on the loading rate, with increased plateau stress and changes in deformation front formation and propagation at higher strain rates. The internal structure of the specimens was examined using X-ray micro-computed tomography (mCT). The mCT images were used to build simplified 3D numerical models of analysed aluminium foam specimens that were used in computational simulations of their behaviour under all experimentally tested loading regimes using LS-DYNA software. The overall agreement between the experimental and computational results was good enough to validate the built numerical models capable of correctly simulating the mechanical response of analysed aluminium foam at different loading rates. © 2023 The Authors}, note = {All Open Access, Gold Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study investigated the high-strain rate mechanical properties of open-cell aluminium foam M-pore®. While previous research has examined the response of this type of foam under quasi-static and transitional dynamic loading conditions, there is a lack of knowledge about its behaviour under higher strain rates (transitional and shock loading regimes). To address this gap in understanding, cylindrical open-cell foam specimens were tested using a modified Direct Impact Hopkinson Bar (DIHB) apparatus over a wide range of strain rates, up to 93 m/s. The results showed a strong dependency of the foam's behaviour on the loading rate, with increased plateau stress and changes in deformation front formation and propagation at higher strain rates. The internal structure of the specimens was examined using X-ray micro-computed tomography (mCT). The mCT images were used to build simplified 3D numerical models of analysed aluminium foam specimens that were used in computational simulations of their behaviour under all experimentally tested loading regimes using LS-DYNA software. The overall agreement between the experimental and computational results was good enough to validate the built numerical models capable of correctly simulating the mechanical response of analysed aluminium foam at different loading rates. © 2023 The Authors |
2022 |
Ulker, Sevkan; Guden, Mustafa MATERIALS EXPRESS, 12 (8), pp. 1094-1107, 2022. @article{WOS:000897716200001, title = {The effect of the temperature of heat treatment process and the concentration and duration of acid leaching on the size and crystallinity of nano-silica powders formed by the dissociation of natural diatom frustule}, author = {Sevkan Ulker and Mustafa Guden}, doi = {10.1166/mex.2022.2251}, year = {2022}, date = {2022-08-01}, journal = {MATERIALS EXPRESS}, volume = {12}, number = {8}, pages = {1094-1107}, abstract = {The present study focused on the processing of nano-silica powders in varying sizes and crystallinities through IP: 846247.10 On: Wed, 14 Dec 2022 07:29:25 heat treatment (900-1200 degrees C), hydrofluoric acid leaching (1-7 N), and ball milling (1 h, 500 rpm) of natural Copyright American Scentfic P blishers diatom frustules. The starting natural frustules were determined to be composed of amorphous silica (88%) Delivered by Ingenta and quartz. The partially ordered crystalline low-quartz and or precursor to low-cristobalite started to form at-900 degrees C. As the heat treatment temperature increased, the crystallinity of the frustules increased from 9.3% at 25 degrees C to 46% at 1200 degrees C. Applying a ball milling reduced the mean particle sizes of the as-received and heat-treated frustules from 15.6-13.7 mu m to 7.2-6.7 mu m, respectively. Acid leaching of the as-received and heat-treated frustules resulted in a further increase in the crystallinity. Furthermore, a ball milling applied after an acid leaching was very effective in reducing the particle size of the as-received and heat-treated frustules. The mean particle size of the acid-leached frustules decreased to 774-547 nm with a crystallinity varying between 12 and 48% after ball milling. A partially dissolved amorphous phase was observed in between crystalline silica grains after acid leaching, which resulted in a rapid fracture/separation of the frustules in ball milling.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The present study focused on the processing of nano-silica powders in varying sizes and crystallinities through IP: 846247.10 On: Wed, 14 Dec 2022 07:29:25 heat treatment (900-1200 degrees C), hydrofluoric acid leaching (1-7 N), and ball milling (1 h, 500 rpm) of natural Copyright American Scentfic P blishers diatom frustules. The starting natural frustules were determined to be composed of amorphous silica (88%) Delivered by Ingenta and quartz. The partially ordered crystalline low-quartz and or precursor to low-cristobalite started to form at-900 degrees C. As the heat treatment temperature increased, the crystallinity of the frustules increased from 9.3% at 25 degrees C to 46% at 1200 degrees C. Applying a ball milling reduced the mean particle sizes of the as-received and heat-treated frustules from 15.6-13.7 mu m to 7.2-6.7 mu m, respectively. Acid leaching of the as-received and heat-treated frustules resulted in a further increase in the crystallinity. Furthermore, a ball milling applied after an acid leaching was very effective in reducing the particle size of the as-received and heat-treated frustules. The mean particle size of the acid-leached frustules decreased to 774-547 nm with a crystallinity varying between 12 and 48% after ball milling. A partially dissolved amorphous phase was observed in between crystalline silica grains after acid leaching, which resulted in a rapid fracture/separation of the frustules in ball milling. |
Tuzgel, F; Akbulut, E F; Guzel, E; Yucesoy, A; Sahin, S; Tasdemirci, A; Guden, M Testing and modeling blast loading of a sandwich structure cored with a bio-inspired (balanus) core Journal Article Thin-Walled Structures, 175 , 2022. @article{Tuzgel2022, title = {Testing and modeling blast loading of a sandwich structure cored with a bio-inspired (balanus) core}, author = {F Tuzgel and E F Akbulut and E Guzel and A Yucesoy and S Sahin and A Tasdemirci and M Guden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85127099692&doi=10.1016%2fj.tws.2022.109185&partnerID=40&md5=598aa9ba4baa82852c1ddd0b8676727c}, doi = {10.1016/j.tws.2022.109185}, year = {2022}, date = {2022-01-01}, journal = {Thin-Walled Structures}, volume = {175}, abstract = {The blast loading response of a sandwich structure consisted of bio-inspired (balanus) cores/units was investigated experimentally and numerically. A Direct Pressure Pulse (DPP) set-up was used to impose a blast-like loading. The equivalent blast conditions corresponding to the used impact velocities were implemented in the models. A benchmark study was performed by using three different methods namely pure Lagrangian, Arbitrary Lagrangian Eulerian, and hybrid. Dynamic crushing behavior was analyzed and exhibited a higher specific energy absorption capacity than its constituents (core and shell). Among the core configurations, all-front configuration was found the most efficient configuration regarding the specific energy absorption. © 2022 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The blast loading response of a sandwich structure consisted of bio-inspired (balanus) cores/units was investigated experimentally and numerically. A Direct Pressure Pulse (DPP) set-up was used to impose a blast-like loading. The equivalent blast conditions corresponding to the used impact velocities were implemented in the models. A benchmark study was performed by using three different methods namely pure Lagrangian, Arbitrary Lagrangian Eulerian, and hybrid. Dynamic crushing behavior was analyzed and exhibited a higher specific energy absorption capacity than its constituents (core and shell). Among the core configurations, all-front configuration was found the most efficient configuration regarding the specific energy absorption. © 2022 Elsevier Ltd |
Güden, M; Alpkaya, A T; Hamat, B A; Hızlı, B; Taşdemirci, A; Tanrıkulu, A A; Yavaş, H Strain, 58 (3), 2022. @article{Güden2022, title = {The quasi-static crush response of electron-beam-melt Ti6Al4V body-centred-cubic lattices: The effect of the number of cells, strut diameter and face sheet}, author = {M Güden and A T Alpkaya and B A Hamat and B Hızlı and A Taşdemirci and A A Tanrıkulu and H Yavaş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85125105289&doi=10.1111%2fstr.12411&partnerID=40&md5=e6515c23c4247096157d4bec2da4a9f3}, doi = {10.1111/str.12411}, year = {2022}, date = {2022-01-01}, journal = {Strain}, volume = {58}, number = {3}, abstract = {The effect of the number of cells, strut diameter and face sheet on the compression of electron-beam-melt (EBM) Ti6Al4V (Ti64) body-centred-cubic (BCC) lattices was investigated experimentally and numerically. The lattices with the same relative density (~0.182) were fabricated with and without 2-mm-thick face sheets in 10 and 5 mm cell size, 8–125 unit cell (two to five cells/edge) and 2 and 1 mm strut diameter. The experimental compression tests were further numerically simulated in the LS-DYNA. Experimentally two bending-dominated crushing modes, namely, lateral and diagonal layer crushing, were determined. The numerical models however exhibited merely a bending-dominated lateral layer crushing mode when the erosion strain was 0.4 and without face-sheet models showed a diagonal layer crushing mode when the erosion strain was 0.3. Lower erosion strains promoted a diagonal layer crushing mode by introducing geometrical inhomogeneity to the lattice, leading to strain localisation as similar to the face sheets which introduced extensive strut bending in the layers adjacent to the face sheets. The face-sheet model showed a higher but decreasing collapse strength at an increasing number of cells, just as opposite to the without face-sheet model, and the collapse strength of both models converged when the number of cells was higher than five-cell/edge. The decrease/increase of the collapse strengths of lattices before the critical number of cells was claimed mainly due to the size-imposed lattice boundary condition, rather than the specimen volume. The difference in the experimental collapse strengths between the 5- and the 10-mm cell-size lattices was ascribed to the variations in the microstructures—hence the material model parameters between the small-diameter and the large-diameter EBM-Ti64 strut lattices. © 2022 John Wiley & Sons Ltd.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of the number of cells, strut diameter and face sheet on the compression of electron-beam-melt (EBM) Ti6Al4V (Ti64) body-centred-cubic (BCC) lattices was investigated experimentally and numerically. The lattices with the same relative density (~0.182) were fabricated with and without 2-mm-thick face sheets in 10 and 5 mm cell size, 8–125 unit cell (two to five cells/edge) and 2 and 1 mm strut diameter. The experimental compression tests were further numerically simulated in the LS-DYNA. Experimentally two bending-dominated crushing modes, namely, lateral and diagonal layer crushing, were determined. The numerical models however exhibited merely a bending-dominated lateral layer crushing mode when the erosion strain was 0.4 and without face-sheet models showed a diagonal layer crushing mode when the erosion strain was 0.3. Lower erosion strains promoted a diagonal layer crushing mode by introducing geometrical inhomogeneity to the lattice, leading to strain localisation as similar to the face sheets which introduced extensive strut bending in the layers adjacent to the face sheets. The face-sheet model showed a higher but decreasing collapse strength at an increasing number of cells, just as opposite to the without face-sheet model, and the collapse strength of both models converged when the number of cells was higher than five-cell/edge. The decrease/increase of the collapse strengths of lattices before the critical number of cells was claimed mainly due to the size-imposed lattice boundary condition, rather than the specimen volume. The difference in the experimental collapse strengths between the 5- and the 10-mm cell-size lattices was ascribed to the variations in the microstructures—hence the material model parameters between the small-diameter and the large-diameter EBM-Ti64 strut lattices. © 2022 John Wiley & Sons Ltd. |
Movahedi, N; Fiedler, T; Taşdemirci, A; Murch, G E; Belova, I V; Güden, M Impact loading of functionally graded metal syntactic foams Journal Article Materials Science and Engineering A, 839 , 2022. @article{Movahedi2022, title = {Impact loading of functionally graded metal syntactic foams}, author = {N Movahedi and T Fiedler and A Taşdemirci and G E Murch and I V Belova and M Güden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85124878036&doi=10.1016%2fj.msea.2022.142831&partnerID=40&md5=7c2f5ff50091f5c640df480605838c8c}, doi = {10.1016/j.msea.2022.142831}, year = {2022}, date = {2022-01-01}, journal = {Materials Science and Engineering A}, volume = {839}, abstract = {The present study addresses the impact loading of functionally graded metal syntactic foams (FG-MSF). For comparison, samples of the same material were also compression loaded at quasi-static velocities. Samples of A356 aluminium FG-MSF were produced using counter-gravity infiltration casting with combination of equal-sized layers of expanded perlite (EP) and activated carbon (AC) particles. A modified Split Hopkinson Pressure Bar test set-up was used to impact the FG-MSFs from their EP or AC layers at 55 m/s or 175 m/s impact velocities. A high-speed camera captured the deformation of the samples during testing. It was shown that increasing the loading velocity enhanced both the compressive proof strength and energy absorption of the impacted FG-MSF from both layers, confirming a dynamic strengthening effect of the foam. The samples impacted from both layers at 55 and 175 m/s showed a transition and a shock mode of deformation, respectively. The impacted samples at 55 m/s experienced lower final average strain values compared to 175 m/s. © 2022 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The present study addresses the impact loading of functionally graded metal syntactic foams (FG-MSF). For comparison, samples of the same material were also compression loaded at quasi-static velocities. Samples of A356 aluminium FG-MSF were produced using counter-gravity infiltration casting with combination of equal-sized layers of expanded perlite (EP) and activated carbon (AC) particles. A modified Split Hopkinson Pressure Bar test set-up was used to impact the FG-MSFs from their EP or AC layers at 55 m/s or 175 m/s impact velocities. A high-speed camera captured the deformation of the samples during testing. It was shown that increasing the loading velocity enhanced both the compressive proof strength and energy absorption of the impacted FG-MSF from both layers, confirming a dynamic strengthening effect of the foam. The samples impacted from both layers at 55 and 175 m/s showed a transition and a shock mode of deformation, respectively. The impacted samples at 55 m/s experienced lower final average strain values compared to 175 m/s. © 2022 Elsevier B.V. |
Güden, M; Enser, S; Bayhan, M; Taşdemirci, A; Yavaş, H Materials Science and Engineering A, 838 , 2022. @article{Güden2022b, title = {The strain rate sensitive flow stresses and constitutive equations of a selective-laser-melt and an annealed-rolled 316L stainless steel: A comparative study}, author = {M Güden and S Enser and M Bayhan and A Taşdemirci and H Yavaş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85124262590&doi=10.1016%2fj.msea.2022.142743&partnerID=40&md5=c9a9ea5a5d2240e3b1fb245fdb7f8e27}, doi = {10.1016/j.msea.2022.142743}, year = {2022}, date = {2022-01-01}, journal = {Materials Science and Engineering A}, volume = {838}, abstract = {The strain rate dependent compressive flow stresses of a Selective-Laser-Melt 316L (SLM-316L) alloy and a commercial (annealed-extruded) 316L (C-316L) alloy were determined, for comparison, between 1x10-4 and ∼2500 s-1 and between 1x10-4 and ∼2800 s-1, respectively. The Johnson and Cook flow stress material model parameters of both alloys were also determined. The microstructural examinations of the deformed cross-sections of tested specimens (interrupted tests) showed a twinning-induced-plasticity in SLM-316L alloy and a martensitic transformation-induced-plasticity in C-316L alloy. Twin and martensite formations were detected microscopically higher in the dynamically tested specimens until about 0.22 strain, while the twin and martensite formations decreased at increasing strains due to adiabatic heating. The rate sensitivity of SLM-316L was determined slightly higher than that of C-316L within the quasi-static strain rate range (1x10-4 and 1x10-2 s-1), while the rate sensitivities of both alloys were similar in the quasi-static-high strain rate range (1x10-4 and ∼2500-2800 s-1) at low strains. A more rapid decrease in the rate sensitivity of C-316L at increasing strains was found in the quasi-static-high strain rate range. The similar activation volumes of both alloys, corresponding to the dislocation intersections, indicated a similar thermally activated deformation process involvement in both alloys. © 2022 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The strain rate dependent compressive flow stresses of a Selective-Laser-Melt 316L (SLM-316L) alloy and a commercial (annealed-extruded) 316L (C-316L) alloy were determined, for comparison, between 1x10-4 and ∼2500 s-1 and between 1x10-4 and ∼2800 s-1, respectively. The Johnson and Cook flow stress material model parameters of both alloys were also determined. The microstructural examinations of the deformed cross-sections of tested specimens (interrupted tests) showed a twinning-induced-plasticity in SLM-316L alloy and a martensitic transformation-induced-plasticity in C-316L alloy. Twin and martensite formations were detected microscopically higher in the dynamically tested specimens until about 0.22 strain, while the twin and martensite formations decreased at increasing strains due to adiabatic heating. The rate sensitivity of SLM-316L was determined slightly higher than that of C-316L within the quasi-static strain rate range (1x10-4 and 1x10-2 s-1), while the rate sensitivities of both alloys were similar in the quasi-static-high strain rate range (1x10-4 and ∼2500-2800 s-1) at low strains. A more rapid decrease in the rate sensitivity of C-316L at increasing strains was found in the quasi-static-high strain rate range. The similar activation volumes of both alloys, corresponding to the dislocation intersections, indicated a similar thermally activated deformation process involvement in both alloys. © 2022 Elsevier B.V. |
2021 |
Aydin, Murat; Bulut, Tugrul; Guden, Mustafa; Erel, Nuri Transdiscal screw fixation in L5-S1 spondylolysis: A biomechanical study Transdiscal screw fixation in L5-51 spondylolysis Journal Article ANNALS OF CLINICAL AND ANALYTICAL MEDICINE, 12 (9), pp. 1055-1057, 2021. @article{WOS:000732457800019, title = {Transdiscal screw fixation in L5-S1 spondylolysis: A biomechanical study Transdiscal screw fixation in L5-51 spondylolysis}, author = {Murat Aydin and Tugrul Bulut and Mustafa Guden and Nuri Erel}, doi = {10.4328/ACAM.20586}, year = {2021}, date = {2021-09-01}, journal = {ANNALS OF CLINICAL AND ANALYTICAL MEDICINE}, volume = {12}, number = {9}, pages = {1055-1057}, abstract = {Aim: This study aimed to investigate whether the L5-S1 transdiscal screw fixation is biomechanically sufficient against axial loads and the resulting shear forces. Material and Methods: Eighteen fresh calf spines under 1 year of age were used in this study. Two randomly selected spines were used as test materials. The inferior facet and ligamentum flavum were removed in 7 randomly selected spines. In these spines (transdiscal screw group), two transdiscal screws were placed bilaterally between 15 and S1. Tests were performed on the remaining 9 spines, while the spines were initially intact (intact group) and after creating a listhesis model (injury group). The extent of displacement occurring as a result of axial loading was noted in all groups in order to calculate the load-displacement curves. Results: The mean displacement as a result of successive axial loadings of 5000 N was as follows: 3 mm (range: 2.4 - 4 mm) in the intact group, 3.5 mm (range: 3 - 4.5 mm) in the transdiscal screw group and 4.5 mm (range: 3.9 - 5 mm) In the group with injury. The difference was statistically significant (p<0.05). None of the samples exhibited broken screws, screw deformation or dislocation, even in failure tests, in the transdiscal screw group. Discussion: These findings have shown that transdiscal screw fixation can be biomechanically sufficient against the shear forces occurring as a result of axial loading. We believe that this technique can be a good alternative as a fixation method for the L5-S1 spondylolisthesis.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Aim: This study aimed to investigate whether the L5-S1 transdiscal screw fixation is biomechanically sufficient against axial loads and the resulting shear forces. Material and Methods: Eighteen fresh calf spines under 1 year of age were used in this study. Two randomly selected spines were used as test materials. The inferior facet and ligamentum flavum were removed in 7 randomly selected spines. In these spines (transdiscal screw group), two transdiscal screws were placed bilaterally between 15 and S1. Tests were performed on the remaining 9 spines, while the spines were initially intact (intact group) and after creating a listhesis model (injury group). The extent of displacement occurring as a result of axial loading was noted in all groups in order to calculate the load-displacement curves. Results: The mean displacement as a result of successive axial loadings of 5000 N was as follows: 3 mm (range: 2.4 - 4 mm) in the intact group, 3.5 mm (range: 3 - 4.5 mm) in the transdiscal screw group and 4.5 mm (range: 3.9 - 5 mm) In the group with injury. The difference was statistically significant (p<0.05). None of the samples exhibited broken screws, screw deformation or dislocation, even in failure tests, in the transdiscal screw group. Discussion: These findings have shown that transdiscal screw fixation can be biomechanically sufficient against the shear forces occurring as a result of axial loading. We believe that this technique can be a good alternative as a fixation method for the L5-S1 spondylolisthesis. |
Enser, S; Yavas, H; Hamat, B A; Aydın, H; Kafadar, G; Tanrıkulu, A A; Kazdal, H Z; Ozturk, F; Güden, M Comparing Compression Deformation and Rate Sensitivity of Additively Manufactured and Extruded-Annealed 316L Alloys Journal Article Journal of Materials Engineering and Performance, 30 (12), pp. 8831-8840, 2021. @article{Enser20218831, title = {Comparing Compression Deformation and Rate Sensitivity of Additively Manufactured and Extruded-Annealed 316L Alloys}, author = {S Enser and H Yavas and B A Hamat and H Aydın and G Kafadar and A A Tanrıkulu and H Z Kazdal and F Ozturk and M Güden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85118462128&doi=10.1007%2fs11665-021-06340-9&partnerID=40&md5=d25a9a6e9c2f3be728f463e1a9b2e3a0}, doi = {10.1007/s11665-021-06340-9}, year = {2021}, date = {2021-01-01}, journal = {Journal of Materials Engineering and Performance}, volume = {30}, number = {12}, pages = {8831-8840}, abstract = {The deformation behavior of a selective-laser-melt-processed 316-L alloy (SLM-316L) under compression was determined together with a commercial annealed-extruded 316L alloy bar (C-316L) for comparison. Strain rate jump tests and hardness tests on the untested and compression tested samples were also performed. Extensive microscopic observations on the deformed and undeformed samples showed a twinning-dominated deformation in SLM-316L, similar to twinning-induced-plasticity steels, while a martensitic transformation-dominated deformation in C-316L alloy, similar to transformation-induced-plasticity steels. Within the studied quasi-static strain rate regime, the measured higher strain rate sensitivity of SLM-316L was ascribed to the lower distances between the nano-twins, in the level of 100 nm, than the distances between martensite plates, in the level of 1000 nm. A higher hardness increase in the martensite transformation region as compared with the twinned region proved the higher work hardening of C-316L. The hardness tests in the micron and sub-micron levels further confirmed the previously determined relatively low resistances of the dislocation cell walls (sub-grain) to the dislocation motion in SLM-316L alloy. © 2021, ASM International.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The deformation behavior of a selective-laser-melt-processed 316-L alloy (SLM-316L) under compression was determined together with a commercial annealed-extruded 316L alloy bar (C-316L) for comparison. Strain rate jump tests and hardness tests on the untested and compression tested samples were also performed. Extensive microscopic observations on the deformed and undeformed samples showed a twinning-dominated deformation in SLM-316L, similar to twinning-induced-plasticity steels, while a martensitic transformation-dominated deformation in C-316L alloy, similar to transformation-induced-plasticity steels. Within the studied quasi-static strain rate regime, the measured higher strain rate sensitivity of SLM-316L was ascribed to the lower distances between the nano-twins, in the level of 100 nm, than the distances between martensite plates, in the level of 1000 nm. A higher hardness increase in the martensite transformation region as compared with the twinned region proved the higher work hardening of C-316L. The hardness tests in the micron and sub-micron levels further confirmed the previously determined relatively low resistances of the dislocation cell walls (sub-grain) to the dislocation motion in SLM-316L alloy. © 2021, ASM International. |
Polat, D; Güden, M Processing and characterization of geopolymer and sintered geopolymer foams of waste glass powders Journal Article Construction and Building Materials, 300 , 2021. @article{Polat2021, title = {Processing and characterization of geopolymer and sintered geopolymer foams of waste glass powders}, author = {D Polat and M Güden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85110473118&doi=10.1016%2fj.conbuildmat.2021.124259&partnerID=40&md5=0d7a948bc247b782e77d4b5908d062f3}, doi = {10.1016/j.conbuildmat.2021.124259}, year = {2021}, date = {2021-01-01}, journal = {Construction and Building Materials}, volume = {300}, abstract = {Geopolymer foams of fine and coarse waste glass (WG) powders were prepared using an activation solution of NaOH (8 M) and Na2SiO3. The effects of WG powder particle size, solid/liquid ratio (S/L = 1, 1.5, and 2) and Al foaming agent content (2–20 wt%) on the expansion and temperature behavior of the slurries were determined in-situ using a laser sensor and a thermocouple, respectively. The geopolymer foams processed using a coarse WG powder slurry, S/L = 2, and 2 wt% Al, were further sintered at 600, 700, 725, and 750 °C. The compression strengths and thermal conductivities of the geopolymer and sintered geopolymer foams were also determined. The slurry expansions continued until about a maximum, and the temperatures of the slurries increased to a maximum, 85–88 °C. At the maximum temperature, the slurry evaporation and the resultant increase in the S/L ratio limited the slurry expansion. Increasing the Al content decreased the final density of the foams (238–555 kg m−3), while the coarse powder slurries resulted in lower densities than the fine powder slurries. Three crystal phases, muscovite, sodium aluminum silicate hydrate, and thermonitrite, were determined in the geopolymer foams. The muscovite formation was noted to be favored at high S/L ratios. During sintering, the partial melting of glass particles started after about 700 °C, while sintering above this temperature decreased the final density of the foams. The reduced density above 700 °C was ascribed to the release of CO2 due to the decomposition of thermonitrite. Both the compressive strength and thermal conductivity of the geopolymer and sintered geopolymer foams increased with increasing foam density. The highest increase in the compressive strength and reduction in the density were seen in the geopolymer foams sintered at 750 °C. © 2021 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } Geopolymer foams of fine and coarse waste glass (WG) powders were prepared using an activation solution of NaOH (8 M) and Na2SiO3. The effects of WG powder particle size, solid/liquid ratio (S/L = 1, 1.5, and 2) and Al foaming agent content (2–20 wt%) on the expansion and temperature behavior of the slurries were determined in-situ using a laser sensor and a thermocouple, respectively. The geopolymer foams processed using a coarse WG powder slurry, S/L = 2, and 2 wt% Al, were further sintered at 600, 700, 725, and 750 °C. The compression strengths and thermal conductivities of the geopolymer and sintered geopolymer foams were also determined. The slurry expansions continued until about a maximum, and the temperatures of the slurries increased to a maximum, 85–88 °C. At the maximum temperature, the slurry evaporation and the resultant increase in the S/L ratio limited the slurry expansion. Increasing the Al content decreased the final density of the foams (238–555 kg m−3), while the coarse powder slurries resulted in lower densities than the fine powder slurries. Three crystal phases, muscovite, sodium aluminum silicate hydrate, and thermonitrite, were determined in the geopolymer foams. The muscovite formation was noted to be favored at high S/L ratios. During sintering, the partial melting of glass particles started after about 700 °C, while sintering above this temperature decreased the final density of the foams. The reduced density above 700 °C was ascribed to the release of CO2 due to the decomposition of thermonitrite. Both the compressive strength and thermal conductivity of the geopolymer and sintered geopolymer foams increased with increasing foam density. The highest increase in the compressive strength and reduction in the density were seen in the geopolymer foams sintered at 750 °C. © 2021 Elsevier Ltd |
Shi, C; Guo, B; Sarıkaya, M; Çelik, M; Chen, P; Güden, M International Journal of Impact Engineering, 149 , 2021. @article{Shi2021, title = {Determination of the material model and damage parameters of a carbon fiber reinforced laminated epoxy composite for high strain rate planar compression}, author = {C Shi and B Guo and M Sarıkaya and M Çelik and P Chen and M Güden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85097220985&doi=10.1016%2fj.ijimpeng.2020.103771&partnerID=40&md5=eecdd1023b76f40453f6cd5e379c9ec8}, doi = {10.1016/j.ijimpeng.2020.103771}, year = {2021}, date = {2021-01-01}, journal = {International Journal of Impact Engineering}, volume = {149}, abstract = {The progressive failure of a 0°/90° laminated carbon fiber reinforced epoxy composite was modeled in LS-DYNA using the MAT_162 material model, including the strain rate, damage progression and anisotropy effects. In addition to conventional standard and non-standard tests, double-shear and Brazilian tests were applied to determine the through-thickness shear modulus and the through-thickness tensile strength of the composite, respectively. The modulus reduction and strain softening for shear and delamination parameters were calibrated by low velocity drop-weight impact tests. The rate sensitivities of the modulus and strength of in-plane and through-thickness direction were determined by the compression tests at quasi-static and high strain rates. The fidelity of the determined model parameters was finally verified in the in-plane and through-thickness direction by the 3D numerical models of the Split Hopkinson Pressure Bar compression tests. The numerical bar stresses and damage progressions modes showed acceptable correlations with those of the experiments in both directions. The composite failed both numerically and experimentally by the fiber buckling induced fiber-matrix axial splitting in the in-plane and the matrix shear fracture in the through-thickness direction. © 2020}, keywords = {}, pubstate = {published}, tppubtype = {article} } The progressive failure of a 0°/90° laminated carbon fiber reinforced epoxy composite was modeled in LS-DYNA using the MAT_162 material model, including the strain rate, damage progression and anisotropy effects. In addition to conventional standard and non-standard tests, double-shear and Brazilian tests were applied to determine the through-thickness shear modulus and the through-thickness tensile strength of the composite, respectively. The modulus reduction and strain softening for shear and delamination parameters were calibrated by low velocity drop-weight impact tests. The rate sensitivities of the modulus and strength of in-plane and through-thickness direction were determined by the compression tests at quasi-static and high strain rates. The fidelity of the determined model parameters was finally verified in the in-plane and through-thickness direction by the 3D numerical models of the Split Hopkinson Pressure Bar compression tests. The numerical bar stresses and damage progressions modes showed acceptable correlations with those of the experiments in both directions. The composite failed both numerically and experimentally by the fiber buckling induced fiber-matrix axial splitting in the in-plane and the matrix shear fracture in the through-thickness direction. © 2020 |
Güden, M; Canbaz, İ International Journal of Crashworthiness, 26 (1), pp. 38-52, 2021. @article{Güden202138, title = {The effect of cell wall material strain and strain-rate hardening behaviour on the dynamic crush response of an aluminium multi-layered corrugated core}, author = {M Güden and İ Canbaz}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85074867388&doi=10.1080%2f13588265.2019.1682351&partnerID=40&md5=4c12613ac0ed4e34ef1ed09c892300c6}, doi = {10.1080/13588265.2019.1682351}, year = {2021}, date = {2021-01-01}, journal = {International Journal of Crashworthiness}, volume = {26}, number = {1}, pages = {38-52}, abstract = {The effect of the parameters of the Johnson and Cook material model on the direct impact crushing behaviour of a layered 1050 H14 aluminium corrugated structure was investigated numerically in LS-DYNA at quasi-static (0.0048 m s−1) and dynamic (20, 60, 150 and 250 m s−1) velocities. Numerical and experimental direct impact tests were performed by lunching a striker bar onto corrugated samples attached to the end of the incident bar of a Split Hopkinson Pressure Bar set-up. The numerical impact-end stress-time and velocity-time curves were further compared with those of rigid-perfectly-plastic-locking (r-p-p-l) model. Numerical and r-p-p-l model impact-end stress analysis revealed a shock mode at 150 and 250 m s−1, transition mode at 60 m s−1 and quasi-static homogenous mode at 20 m s−1. The increase of velocity from quasi-static to 20 m s−1 increased the numerical distal-end initial peak-stress, while it almost stayed constant between 20 and 250 m s−1 for all material models. The increased distal-end initial peak-stress of strain rate insensitive models from quasi-static to 20 m s−1 confirmed the effect of micro-inertia. The numerical models further indicated a negligible effect of used material models on the impact-end stress of investigated structure. Finally, the contribution of strain rate to the distal-end initial peak-stress of cellular structures made of low strain rate sensitive Al alloys was shown to be relatively low as compared with that of strain hardening and micro-inertia, but it might be substantial for the structures constructed using relatively high strain rate sensitive alloys. © 2019 Informa UK Limited, trading as Taylor & Francis Group.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of the parameters of the Johnson and Cook material model on the direct impact crushing behaviour of a layered 1050 H14 aluminium corrugated structure was investigated numerically in LS-DYNA at quasi-static (0.0048 m s−1) and dynamic (20, 60, 150 and 250 m s−1) velocities. Numerical and experimental direct impact tests were performed by lunching a striker bar onto corrugated samples attached to the end of the incident bar of a Split Hopkinson Pressure Bar set-up. The numerical impact-end stress-time and velocity-time curves were further compared with those of rigid-perfectly-plastic-locking (r-p-p-l) model. Numerical and r-p-p-l model impact-end stress analysis revealed a shock mode at 150 and 250 m s−1, transition mode at 60 m s−1 and quasi-static homogenous mode at 20 m s−1. The increase of velocity from quasi-static to 20 m s−1 increased the numerical distal-end initial peak-stress, while it almost stayed constant between 20 and 250 m s−1 for all material models. The increased distal-end initial peak-stress of strain rate insensitive models from quasi-static to 20 m s−1 confirmed the effect of micro-inertia. The numerical models further indicated a negligible effect of used material models on the impact-end stress of investigated structure. Finally, the contribution of strain rate to the distal-end initial peak-stress of cellular structures made of low strain rate sensitive Al alloys was shown to be relatively low as compared with that of strain hardening and micro-inertia, but it might be substantial for the structures constructed using relatively high strain rate sensitive alloys. © 2019 Informa UK Limited, trading as Taylor & Francis Group. |
Güden, M; Yavaş, H; Tanrıkulu, A A; Taşdemirci, A; Akın, B; Enser, S; Karakuş, A; Hamat, B A Orientation dependent tensile properties of a selective-laser-melt 316L stainless steel Journal Article Materials Science and Engineering A, 824 , 2021. @article{Güden2021b, title = {Orientation dependent tensile properties of a selective-laser-melt 316L stainless steel}, author = {M Güden and H Yavaş and A A Tanrıkulu and A Taşdemirci and B Akın and S Enser and A Karakuş and B A Hamat}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85111194339&doi=10.1016%2fj.msea.2021.141808&partnerID=40&md5=d838bade5a0604998ddd4cb8ecce7457}, doi = {10.1016/j.msea.2021.141808}, year = {2021}, date = {2021-01-01}, journal = {Materials Science and Engineering A}, volume = {824}, abstract = {The effect of specimen inclination angle with respect to building direction on the tensile properties of a selective laser melt 316L alloy was investigated. Tensile test specimens were fabricated with the angles between 0° to 90° at 15° intervals using a rotation scanning. In addition, 316L alloy test specimens were generated in the ANSYS 2020R1 additive module and tensile tested in LS-DYNA in order to determine the effect of residual stresses on the tensile strengths. The microscopic analysis revealed a strong ⟨110⟩ fiber texture orientation along the building direction (the loading axis of 0° inclined specimens) and a weak <111> texture or nearly random distribution of directions in the normal to the building direction (tensile loading axis of 90° inclined specimens). The yield and tensile strength increased and ductility decreased with increasing inclination angle. The strength variation with the inclination angle was shown well-fitted with the Tsai-Hill failure criterion. Although, the used numerical models indicated an inclination-dependent residual stress, the difference in the residual stresses was much lower than the difference in the strengths between 0° and 90° inclined specimens. Predictions showed a lower twinning stress in 0° inclined specimens due to ⟨110⟩ fiber texture orientation in the tensile axis. The fiber texture resulted in extensive twinning; hence, higher ductility and tension-compression asymmetry in 0° inclined specimens. Based on these results, the variations in the strength and ductility of tested SLM-316L specimens with the inclination angle was ascribed to the variations in the angle between the fiber texture orientation and loading axis. © 2021 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of specimen inclination angle with respect to building direction on the tensile properties of a selective laser melt 316L alloy was investigated. Tensile test specimens were fabricated with the angles between 0° to 90° at 15° intervals using a rotation scanning. In addition, 316L alloy test specimens were generated in the ANSYS 2020R1 additive module and tensile tested in LS-DYNA in order to determine the effect of residual stresses on the tensile strengths. The microscopic analysis revealed a strong ⟨110⟩ fiber texture orientation along the building direction (the loading axis of 0° inclined specimens) and a weak <111> texture or nearly random distribution of directions in the normal to the building direction (tensile loading axis of 90° inclined specimens). The yield and tensile strength increased and ductility decreased with increasing inclination angle. The strength variation with the inclination angle was shown well-fitted with the Tsai-Hill failure criterion. Although, the used numerical models indicated an inclination-dependent residual stress, the difference in the residual stresses was much lower than the difference in the strengths between 0° and 90° inclined specimens. Predictions showed a lower twinning stress in 0° inclined specimens due to ⟨110⟩ fiber texture orientation in the tensile axis. The fiber texture resulted in extensive twinning; hence, higher ductility and tension-compression asymmetry in 0° inclined specimens. Based on these results, the variations in the strength and ductility of tested SLM-316L specimens with the inclination angle was ascribed to the variations in the angle between the fiber texture orientation and loading axis. © 2021 Elsevier B.V. |
Seven, S B; Çankaya, M A; Uysal, Ç; Tasdemirci, A; Saatçi, S; Güden, M Constitutive equation determination and dynamic numerical modelling of the compression deformation of concrete Journal Article Strain, 57 (2), 2021. @article{Seven2021, title = {Constitutive equation determination and dynamic numerical modelling of the compression deformation of concrete}, author = {S B Seven and M A Çankaya and Ç Uysal and A Tasdemirci and S Saatçi and M Güden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85099175099&doi=10.1111%2fstr.12377&partnerID=40&md5=4651c623ee9ea5323e2e6b03771b2c5f}, doi = {10.1111/str.12377}, year = {2021}, date = {2021-01-01}, journal = {Strain}, volume = {57}, number = {2}, abstract = {The dynamic compression deformation of an in-house cast concrete (average aggregate size of 2–2.5 mm) was modelled using the finite element (FE), element-free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values. © 2021 John Wiley & Sons Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The dynamic compression deformation of an in-house cast concrete (average aggregate size of 2–2.5 mm) was modelled using the finite element (FE), element-free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values. © 2021 John Wiley & Sons Ltd |
2020 |
Zeren, Dogus; Senturk, Ufuk; Guden, Mustafa The expansion behavior of slurries containing recycled glass powder carboxymethyl cellulose, lime and aluminum powder Journal Article CONSTRUCTION AND BUILDING MATERIALS, 240 , 2020, ISSN: 0950-0618. @article{ISI:000527362400021, title = {The expansion behavior of slurries containing recycled glass powder carboxymethyl cellulose, lime and aluminum powder}, author = {Dogus Zeren and Ufuk Senturk and Mustafa Guden}, doi = {10.1016/j.conbuildmat.2019.117898}, issn = {0950-0618}, year = {2020}, date = {2020-04-01}, journal = {CONSTRUCTION AND BUILDING MATERIALS}, volume = {240}, abstract = {The rheology and foaming/expansion of the slurries of a waste/recycled glass powder with 50, 55 and 60 wt% of solid (glass powder) were experimentally investigated. The glass powder slurries were foamed using aluminum powder as foaming agent (0.75 wt%) and calcium hydroxide as activator (1 wt%). Sodium carboxymethyl cellulose (CMC) was added to the slurries as a binder with the amounts between 0 and 4 wt%. The expansions of the slurries were measured in-situ using a laser sensor and reported as percent volume expansion. The CMC-addition increased the viscosities of the slurries, particularly the fine size powder slurries. The slurries with the relatively low-viscosity exhibited lower initial expansion rates compared to the slurries with the relatively high-viscosity. The maximum expansions of the slurries increased from 300 to 350%, when the viscosity increased to 5 Pa s and reached a steady value around 400% between 5 and 50 Pa s. The expansions of the slurries could not be achieved above 50 Pa s since they became too thick to be foamed. The foam samples made from the slurries with 55 and 60 wt% of solid and sintered at 700 and 750 degrees C for 30 min had the average densities between 355 and 530 kg m(-3) and the average compressive strengths between 0.2 and 0.5 MPa. Increasing sintering time to 60 min at 750 degrees C increased the average compressive strength from 0.5 to 1.5 MPa for the foam samples made from the slurry with 60 wt% of solid. These proved that both sintering temperature and time were effective in increasing the compressive strengths of the foamed structures. The thermal conductivities of the sintered foam samples with the densities of 355 and 504 kg m(-3) were measured 0.042 and 0.057 W m(-1) K-1, respectively. (C) 2019 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The rheology and foaming/expansion of the slurries of a waste/recycled glass powder with 50, 55 and 60 wt% of solid (glass powder) were experimentally investigated. The glass powder slurries were foamed using aluminum powder as foaming agent (0.75 wt%) and calcium hydroxide as activator (1 wt%). Sodium carboxymethyl cellulose (CMC) was added to the slurries as a binder with the amounts between 0 and 4 wt%. The expansions of the slurries were measured in-situ using a laser sensor and reported as percent volume expansion. The CMC-addition increased the viscosities of the slurries, particularly the fine size powder slurries. The slurries with the relatively low-viscosity exhibited lower initial expansion rates compared to the slurries with the relatively high-viscosity. The maximum expansions of the slurries increased from 300 to 350%, when the viscosity increased to 5 Pa s and reached a steady value around 400% between 5 and 50 Pa s. The expansions of the slurries could not be achieved above 50 Pa s since they became too thick to be foamed. The foam samples made from the slurries with 55 and 60 wt% of solid and sintered at 700 and 750 degrees C for 30 min had the average densities between 355 and 530 kg m(-3) and the average compressive strengths between 0.2 and 0.5 MPa. Increasing sintering time to 60 min at 750 degrees C increased the average compressive strength from 0.5 to 1.5 MPa for the foam samples made from the slurry with 60 wt% of solid. These proved that both sintering temperature and time were effective in increasing the compressive strengths of the foamed structures. The thermal conductivities of the sintered foam samples with the densities of 355 and 504 kg m(-3) were measured 0.042 and 0.057 W m(-1) K-1, respectively. (C) 2019 Elsevier Ltd. All rights reserved. |
Kilicaslan, Cenk; Guden, Mustafa The effect of core height on energy absorbing capacity in aluminum corrugated sandwich panels Journal Article JOURNAL OF THE FACULTY OF ENGINEERING AND ARCHITECTURE OF GAZI UNIVERSITY, 35 (1), pp. 17-26, 2020, ISSN: 1300-1884. @article{ISI:000520598100002, title = {The effect of core height on energy absorbing capacity in aluminum corrugated sandwich panels}, author = {Cenk Kilicaslan and Mustafa Guden}, doi = {10.17341/gazimmfd.639834}, issn = {1300-1884}, year = {2020}, date = {2020-01-01}, journal = {JOURNAL OF THE FACULTY OF ENGINEERING AND ARCHITECTURE OF GAZI UNIVERSITY}, volume = {35}, number = {1}, pages = {17-26}, abstract = {In this study, energy absorbing capacity of brazed and polyurethane adhesively bonded corrugated aluminum sandwich panels were investigated. In sandwich panels, Al 1050 H14 trapezoidal zig-zag corrugated cores and face and interlayer sheets were used. Each sandwich panel has core orientation of 0 degrees/0 degrees or 0 degrees/90 degrees. The cores used in these panels were smaller, core height is about 3 mm, in contrast to conventional sandwich cores. Impact tests were conducted at 3 and 6 m/s with spherical projectors. Adhesively bonded sandwich panels were also tested at 6 m/s with flat and conical projectors. Numerical models were prepared in LSDYNA to investigated the deformation behavior of cores. Panels tested with flat and conical projectors experienced complete perforation and absorbed more energy at configuration of 0 degrees/0 degrees core orientation. However, panels tested with spherical projectors were not perforated and they absorbed more energy at configuration of 0 degrees/90 degrees core orientation. Energy absorbing capacity of the panels were also compared to the panels having 9 mm height corrugated cores. The results showed that effective collapsing length was seen to increase due to increase in core height and impact energy distributed the whole panel surface more homogenous manner.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, energy absorbing capacity of brazed and polyurethane adhesively bonded corrugated aluminum sandwich panels were investigated. In sandwich panels, Al 1050 H14 trapezoidal zig-zag corrugated cores and face and interlayer sheets were used. Each sandwich panel has core orientation of 0 degrees/0 degrees or 0 degrees/90 degrees. The cores used in these panels were smaller, core height is about 3 mm, in contrast to conventional sandwich cores. Impact tests were conducted at 3 and 6 m/s with spherical projectors. Adhesively bonded sandwich panels were also tested at 6 m/s with flat and conical projectors. Numerical models were prepared in LSDYNA to investigated the deformation behavior of cores. Panels tested with flat and conical projectors experienced complete perforation and absorbed more energy at configuration of 0 degrees/0 degrees core orientation. However, panels tested with spherical projectors were not perforated and they absorbed more energy at configuration of 0 degrees/90 degrees core orientation. Energy absorbing capacity of the panels were also compared to the panels having 9 mm height corrugated cores. The results showed that effective collapsing length was seen to increase due to increase in core height and impact energy distributed the whole panel surface more homogenous manner. |
Seven, Semih Berk; Cankaya, Alper M; Uysal, Cetin; Tasdemirci, Alper; Saatci, Selcuk; Guden, Mustafa Constitutive equation determination and dynamic numerical modelling of the compression deformation of concrete Journal Article STRAIN, 2020, ISSN: 0039-2103. @article{ISI:000605351700001, title = {Constitutive equation determination and dynamic numerical modelling of the compression deformation of concrete}, author = {Semih Berk Seven and Alper M Cankaya and Cetin Uysal and Alper Tasdemirci and Selcuk Saatci and Mustafa Guden}, doi = {10.1111/str.12377, Early Access Date = JAN 2021}, issn = {0039-2103}, year = {2020}, date = {2020-00-00}, journal = {STRAIN}, abstract = {The dynamic compression deformation of an in-house cast concrete (average aggregate size of 2-2.5 mm) was modelled using the finite element (FE), element-free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The dynamic compression deformation of an in-house cast concrete (average aggregate size of 2-2.5 mm) was modelled using the finite element (FE), element-free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values. |
2017 |
Odac, Ismet Kutlay; Guden, Mustafa; Klcaslan, Cenk; Tasdemirci, Alper The varying densification strain in a multi-layer aluminum corrugate structure: Direct impact testing and layer-wise numerical modelling Journal Article INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, 103 , pp. 64-75, 2017, ISSN: 0734-743X. @article{ISI:000395844400006, title = {The varying densification strain in a multi-layer aluminum corrugate structure: Direct impact testing and layer-wise numerical modelling}, author = {Ismet Kutlay Odac and Mustafa Guden and Cenk Klcaslan and Alper Tasdemirci}, doi = {10.1016/j.ijimpeng.2016.10.014}, issn = {0734-743X}, year = {2017}, date = {2017-05-01}, journal = {INTERNATIONAL JOURNAL OF IMPACT ENGINEERING}, volume = {103}, pages = {64-75}, abstract = {An aluminum (1050 H14) multi-layer corrugated structure composed of brazed 16 trapezoidal zig-zig fin layers was direct impact tested above the critical velocities for shock formation using a modified Split Hopkinson Pressure Bar. The experimentally measured stress-time histories of the cylindrical test samples in the direct impact tests were verified with the simulations implemented in the explicit finite element code of LS-DYNA. The quasi-static experimental and simulation deformation of the corrugated samples proceeded with the discrete, non-contiguous bands of crushed fin layers, while the dynamic crushing started from the proximal impact end and proceeded with a sequential and in-planar manner, showing shock type deformation characteristic. The experimental and numerical crushing stresses and the numerically determined densification strains of the fin layers increased with increasing impact velocity above the critical velocities. When the numerically determined densification strain at a specific velocity above the critical velocities was incorporated, the rigid-perfectly-plastic-locking idealized model resulted in peak stresses similar to the experimental and simulation mean crushing stresses. However, the model underestimated the experimental and simulation peak stresses below 200 m s(-1). It was proposed, while the micro inertial effects were responsible for the increase of the crushing stresses at and below subcritical velocities, the shock deformation became dominant above the critical velocities. (C) 2016 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } An aluminum (1050 H14) multi-layer corrugated structure composed of brazed 16 trapezoidal zig-zig fin layers was direct impact tested above the critical velocities for shock formation using a modified Split Hopkinson Pressure Bar. The experimentally measured stress-time histories of the cylindrical test samples in the direct impact tests were verified with the simulations implemented in the explicit finite element code of LS-DYNA. The quasi-static experimental and simulation deformation of the corrugated samples proceeded with the discrete, non-contiguous bands of crushed fin layers, while the dynamic crushing started from the proximal impact end and proceeded with a sequential and in-planar manner, showing shock type deformation characteristic. The experimental and numerical crushing stresses and the numerically determined densification strains of the fin layers increased with increasing impact velocity above the critical velocities. When the numerically determined densification strain at a specific velocity above the critical velocities was incorporated, the rigid-perfectly-plastic-locking idealized model resulted in peak stresses similar to the experimental and simulation mean crushing stresses. However, the model underestimated the experimental and simulation peak stresses below 200 m s(-1). It was proposed, while the micro inertial effects were responsible for the increase of the crushing stresses at and below subcritical velocities, the shock deformation became dominant above the critical velocities. (C) 2016 Elsevier Ltd. All rights reserved. |
Zeren, Dogus; Guden, Mustafa The increased compression strength of an epoxy resin with the addition of heat-treated natural nano-structured diatom frustules Journal Article JOURNAL OF COMPOSITE MATERIALS, 51 (12), pp. 1681-1691, 2017, ISSN: 0021-9983. @article{ISI:000401035100002, title = {The increased compression strength of an epoxy resin with the addition of heat-treated natural nano-structured diatom frustules}, author = {Dogus Zeren and Mustafa Guden}, doi = {10.1177/0021998316669855}, issn = {0021-9983}, year = {2017}, date = {2017-05-01}, journal = {JOURNAL OF COMPOSITE MATERIALS}, volume = {51}, number = {12}, pages = {1681-1691}, abstract = {Natural diatom frustules composing nanometer size silica particles were heat-treated at temperatures between 600 and 1200 degrees C for 2h and used as filler/reinforcing agent (15wt%) in an epoxy resin. The opal structure of as-received natural diatom frustules was transformed into cristobalite after the heat-treatment above 900 degrees C The epoxy resin test samples reinforced with heat-treated and as-received frustules and neat epoxy test samples were compression tested at the quasi-static strain rate of 7x10(-3)s(-1). The results showed that the inclusion of the frustules heat-treated at 1000 degrees C increased the compressive yield strength of the resin by 50%, while the addition of the diatom frustules heat-treated above and below 1000 degrees C and the as-received frustules increased the strength by similar to 25% and 16%, respectively. The heat treatment above 1000 degrees C decreased the surface area of the frustules from 8.23m(2)g(-1) to 3.46m(2)g(-1). The cristobalite grains of the frustules heat-treated at 1000 degrees C was smaller than 100nm, while the grain size increased to similar to 500nm at 1200 degrees C. The increased compressive stresses of the resin at the specific heat treatment temperature (1000 degrees C) were ascribed to nano size crystalline cristobalite grains. The relatively lower compressive stresses of the epoxy resin filled with frustules heat-treated above 1000 degrees C were attributed to the micro-cracking of the frustules that might be resulted from higher density of the cristobalite than that of the opal and accompanying reduction of the surface area and the surface pore sizes that might impair the resin-frustule interlocking and intrusion.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Natural diatom frustules composing nanometer size silica particles were heat-treated at temperatures between 600 and 1200 degrees C for 2h and used as filler/reinforcing agent (15wt%) in an epoxy resin. The opal structure of as-received natural diatom frustules was transformed into cristobalite after the heat-treatment above 900 degrees C The epoxy resin test samples reinforced with heat-treated and as-received frustules and neat epoxy test samples were compression tested at the quasi-static strain rate of 7x10(-3)s(-1). The results showed that the inclusion of the frustules heat-treated at 1000 degrees C increased the compressive yield strength of the resin by 50%, while the addition of the diatom frustules heat-treated above and below 1000 degrees C and the as-received frustules increased the strength by similar to 25% and 16%, respectively. The heat treatment above 1000 degrees C decreased the surface area of the frustules from 8.23m(2)g(-1) to 3.46m(2)g(-1). The cristobalite grains of the frustules heat-treated at 1000 degrees C was smaller than 100nm, while the grain size increased to similar to 500nm at 1200 degrees C. The increased compressive stresses of the resin at the specific heat treatment temperature (1000 degrees C) were ascribed to nano size crystalline cristobalite grains. The relatively lower compressive stresses of the epoxy resin filled with frustules heat-treated above 1000 degrees C were attributed to the micro-cracking of the frustules that might be resulted from higher density of the cristobalite than that of the opal and accompanying reduction of the surface area and the surface pore sizes that might impair the resin-frustule interlocking and intrusion. |
2016 |
Turkan, Ugur; Guden, Mustafa; Sudagidan, Mert Staphylococcus epidermidis adhesion on surface-treated open-cell Ti6Al4V foams Journal Article BIOMEDICAL ENGINEERING-BIOMEDIZINISCHE TECHNIK, 61 (3), pp. 299-307, 2016, ISSN: 0013-5585. @article{ISI:000377547000006, title = {Staphylococcus epidermidis adhesion on surface-treated open-cell Ti6Al4V foams}, author = {Ugur Turkan and Mustafa Guden and Mert Sudagidan}, doi = {10.1515/bmt-2015-0007}, issn = {0013-5585}, year = {2016}, date = {2016-06-01}, journal = {BIOMEDICAL ENGINEERING-BIOMEDIZINISCHE TECHNIK}, volume = {61}, number = {3}, pages = {299-307}, abstract = {The effect of alkali and nitric acid surface treatments on the adhesion of Staphylococcus epidermidis to the surface of 60% porous open-cell Ti6Al4V foam was investigated. The resultant surface roughness of foam particles was determined from the ground flat surfaces of thin foam specimens. Alkali treatment formed a porous, rough Na2Ti5O11 surface layer on Ti6Al4V particles, while nitric acid treatment increased the number of undulations on foam flat and particle surfaces, leading to the development of finer surface topographical features. Both surface treatments increased the nanometric-scale surface roughness of particles and the number of bacteria adhering to the surface, while the adhesion was found to be significantly higher in alkali-treated foam sample. The significant increase in the number of bacterial attachment on the alkali-treated sample was attributed to the formation of a highly porous and nanorough Na2Ti5O11 surface layer.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of alkali and nitric acid surface treatments on the adhesion of Staphylococcus epidermidis to the surface of 60% porous open-cell Ti6Al4V foam was investigated. The resultant surface roughness of foam particles was determined from the ground flat surfaces of thin foam specimens. Alkali treatment formed a porous, rough Na2Ti5O11 surface layer on Ti6Al4V particles, while nitric acid treatment increased the number of undulations on foam flat and particle surfaces, leading to the development of finer surface topographical features. Both surface treatments increased the nanometric-scale surface roughness of particles and the number of bacteria adhering to the surface, while the adhesion was found to be significantly higher in alkali-treated foam sample. The significant increase in the number of bacterial attachment on the alkali-treated sample was attributed to the formation of a highly porous and nanorough Na2Ti5O11 surface layer. |
Tasdemirci, Alper; Kara, Ali; Turan, Kivanc; Sahin, Selim; Guden, Mustafa Effect of heat treatment on the blast loading response of combined geometry shell core sandwich structures Journal Article THIN-WALLED STRUCTURES, 100 , pp. 180-191, 2016, ISSN: 0263-8231. @article{ISI:000369463600016, title = {Effect of heat treatment on the blast loading response of combined geometry shell core sandwich structures}, author = {Alper Tasdemirci and Ali Kara and Kivanc Turan and Selim Sahin and Mustafa Guden}, doi = {10.1016/j.tws.2015.12.012}, issn = {0263-8231}, year = {2016}, date = {2016-03-01}, journal = {THIN-WALLED STRUCTURES}, volume = {100}, pages = {180-191}, abstract = {The effect of heat treatment on the dynamic crushing and energy absorption behavior of combined geometry shell cores (hemisphere and cylinder) of sandwich structures were investigated both experimentally and numerically. The applied heat treatment on the combined geometry shell cores relieved the stress caused by deep drawing, diminishing the peak transmitted forces. The verified numerical models of the as-received and heat-treated combined geometry shells were used to model blast loading of various sandwich configurations and the additional sandwich configurations of reversing the cylindrical side of the cores to the impacted side. Both the applied heat-treatment and the reversing process decreased the magnitude of the force transmitted to the protected structure. The applied heat treatment increased the arrival time of blast force wave to the protected structure, while the reversing resulted in opposite. (C) 2015 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of heat treatment on the dynamic crushing and energy absorption behavior of combined geometry shell cores (hemisphere and cylinder) of sandwich structures were investigated both experimentally and numerically. The applied heat treatment on the combined geometry shell cores relieved the stress caused by deep drawing, diminishing the peak transmitted forces. The verified numerical models of the as-received and heat-treated combined geometry shells were used to model blast loading of various sandwich configurations and the additional sandwich configurations of reversing the cylindrical side of the cores to the impacted side. Both the applied heat-treatment and the reversing process decreased the magnitude of the force transmitted to the protected structure. The applied heat treatment increased the arrival time of blast force wave to the protected structure, while the reversing resulted in opposite. (C) 2015 Elsevier Ltd. All rights reserved. |
2014 |
Demir, Mustafa M; Horzum, Nesrin; Tasdemirci, Alper; Turan, Kivanc; Guden, Mustafa Mechanical Interlocking between Porous Electrospun Polystyrene Fibers and an Epoxy Matrix Journal Article ACS APPLIED MATERIALS & INTERFACES, 6 (24), pp. 21901-21905, 2014, ISSN: 1944-8244. @article{ISI:000347139400018, title = {Mechanical Interlocking between Porous Electrospun Polystyrene Fibers and an Epoxy Matrix}, author = {Mustafa M Demir and Nesrin Horzum and Alper Tasdemirci and Kivanc Turan and Mustafa Guden}, doi = {10.1021/am507029c}, issn = {1944-8244}, year = {2014}, date = {2014-12-01}, journal = {ACS APPLIED MATERIALS & INTERFACES}, volume = {6}, number = {24}, pages = {21901-21905}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Kilicaslan, C; Odaci, I K; Tasdemirci, A; Guden, M STRAIN, 50 (3), pp. 236-249, 2014, ISSN: 1475-1305. @article{ISI:000336487800004, title = {Experimental Testing and Full and Homogenized Numerical Models of the Low Velocity and Dynamic Deformation of the Trapezoidal Aluminium Corrugated Core Sandwich}, author = {C Kilicaslan and I K Odaci and A Tasdemirci and M Guden}, doi = {10.1111/str.12085}, issn = {1475-1305}, year = {2014}, date = {2014-06-01}, journal = {STRAIN}, volume = {50}, number = {3}, pages = {236-249}, abstract = {The simulations of the low velocity and dynamic deformation of a multi-layer 1050-H14 Al trapezoidal zig-zag corrugated core sandwich were investigated using the homogenized models (solid models) of a single core layer (without face sheets). In the first part of the study, the LS-DYNA MAT-26 material model parameters of a single core layer were developed through experimental and numerical compression tests on the single core layer. In the second part, the fidelities of the developed numerical models were checked by the split-Hopkinson pressure bar direct impact, low velocity compression and indentation and projectile impact tests. The results indicated that the element size had a significant effect on the initial peak and post-peak stresses of the homogenized models of the direct impact testing of the single-layer corrugated sandwich. This was attributed to the lack of the inertial effects in the homogenized models, which resulted in reduced initial peak stresses as compared with the full model and experiment. However, the homogenized models based on the experimental stress-strain curve of the single core layer predicted the low velocity compression and indentation and projectile impact tests of the multi-layer corrugated sandwich with an acceptable accuracy and reduced the computational time of the models significantly.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The simulations of the low velocity and dynamic deformation of a multi-layer 1050-H14 Al trapezoidal zig-zag corrugated core sandwich were investigated using the homogenized models (solid models) of a single core layer (without face sheets). In the first part of the study, the LS-DYNA MAT-26 material model parameters of a single core layer were developed through experimental and numerical compression tests on the single core layer. In the second part, the fidelities of the developed numerical models were checked by the split-Hopkinson pressure bar direct impact, low velocity compression and indentation and projectile impact tests. The results indicated that the element size had a significant effect on the initial peak and post-peak stresses of the homogenized models of the direct impact testing of the single-layer corrugated sandwich. This was attributed to the lack of the inertial effects in the homogenized models, which resulted in reduced initial peak stresses as compared with the full model and experiment. However, the homogenized models based on the experimental stress-strain curve of the single core layer predicted the low velocity compression and indentation and projectile impact tests of the multi-layer corrugated sandwich with an acceptable accuracy and reduced the computational time of the models significantly. |
Ozyildiz, Figen; Uzel, Atac; Hazar, Ayse Serpil; Guden, Mustafa; Olmez, Sultan; Aras, Isil; Karaboz, Ismail Photocatalytic antimicrobial effect of TiO2 anatase thin-film-coated orthodontic arch wires on 3 oral pathogens Journal Article TURKISH JOURNAL OF BIOLOGY, 38 (2), pp. 289-295, 2014, ISSN: 1300-0152. @article{ISI:000332944300015, title = {Photocatalytic antimicrobial effect of TiO2 anatase thin-film-coated orthodontic arch wires on 3 oral pathogens}, author = {Figen Ozyildiz and Atac Uzel and Ayse Serpil Hazar and Mustafa Guden and Sultan Olmez and Isil Aras and Ismail Karaboz}, doi = {10.3906/biy-1308-43}, issn = {1300-0152}, year = {2014}, date = {2014-01-01}, journal = {TURKISH JOURNAL OF BIOLOGY}, volume = {38}, number = {2}, pages = {289-295}, abstract = {The aim of this study was to introduce antimicrobial activity to stainless steel orthodontic arch wires by coating them with TiO2 in anatase form. Stainless steel (0.016 x 0.022 inch), D-rect (0.016 x 0.022 inch), and multistranded hammered retainer wires (0.014 x 0.018 inch) were coated with TiO2 anatase by the sol-gel dip coating method. The wires were assessed for their photocatalytic antimicrobial activity against Streptococcus mutans, Candida albicans, and Enterococcus faecalis. After illumination under UVA (315400 nm) at 1.0 mW/cm(2) for 1 h, the reduction efficiencies of the anatase-coated arch wires were calculated by using colony-forming unit counts. All anatase-coated arch wires showed remarkable inhibitor effects against the test microorganisms under UVA. The most efficient wire on S. mutans was the stainless steel wire, with a 99.99% reduction in growth, but multistranded hammered retainer wire was the most active against both C. albicans and E. faecalis, with 98.0% and 91.68% reduction rates, respectively. TiO2-coated arch wires exposed to UVA illumination showed significant antimicrobial activity when compared with uncoated samples and coated, but not UVA-exposed, samples. Our results suggest that the antimicrobial effect of TiO2-coated arch wires in long-lasting orthodontic treatments would be beneficial for the prophylaxis of caries.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The aim of this study was to introduce antimicrobial activity to stainless steel orthodontic arch wires by coating them with TiO2 in anatase form. Stainless steel (0.016 x 0.022 inch), D-rect (0.016 x 0.022 inch), and multistranded hammered retainer wires (0.014 x 0.018 inch) were coated with TiO2 anatase by the sol-gel dip coating method. The wires were assessed for their photocatalytic antimicrobial activity against Streptococcus mutans, Candida albicans, and Enterococcus faecalis. After illumination under UVA (315400 nm) at 1.0 mW/cm(2) for 1 h, the reduction efficiencies of the anatase-coated arch wires were calculated by using colony-forming unit counts. All anatase-coated arch wires showed remarkable inhibitor effects against the test microorganisms under UVA. The most efficient wire on S. mutans was the stainless steel wire, with a 99.99% reduction in growth, but multistranded hammered retainer wire was the most active against both C. albicans and E. faecalis, with 98.0% and 91.68% reduction rates, respectively. TiO2-coated arch wires exposed to UVA illumination showed significant antimicrobial activity when compared with uncoated samples and coated, but not UVA-exposed, samples. Our results suggest that the antimicrobial effect of TiO2-coated arch wires in long-lasting orthodontic treatments would be beneficial for the prophylaxis of caries. |
2013 |
Attila, Yigit; Guden, Mustafa; Tasdemirci, Alper Foam glass processing using a polishing glass powder residue Journal Article CERAMICS INTERNATIONAL, 39 (5), pp. 5869-5877, 2013, ISSN: 0272-8842. @article{ISI:000318577600141, title = {Foam glass processing using a polishing glass powder residue}, author = {Yigit Attila and Mustafa Guden and Alper Tasdemirci}, doi = {10.1016/j.ceramint.2012.12.104}, issn = {0272-8842}, year = {2013}, date = {2013-07-01}, journal = {CERAMICS INTERNATIONAL}, volume = {39}, number = {5}, pages = {5869-5877}, abstract = {The foaming behavior of a powder residue/waste of a soda-lime window glass polishing facility was investigated at the temperatures between 700 and 950 degrees C. The results showed that the foaming of the glass powder started at a characteristic temperature between 670 and 680 degrees C. The maximum volume expansions of the glass powder and the density of the foams varied between 600% and 750% and 0.206 and 0.378 g cm(-3), respectively. The expansion of the studied glass powder residue resulted from the decomposition of the organic compounds on the surfaces of the glass powder particles, derived from an oil-based coolant used in the polishing. The collapse stress of the foams ranged between similar to 1 and 4 MPa and the thermal conductivity between 0.048 and 0.079 W K-1 m(-1). Both the collapse stress and thermal conductivity increased with increasing the foam density. The foams showed the characteristics of the compression deformation of the open cell brittle foams, which was attributed to the relatively thick cell edges. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The foaming behavior of a powder residue/waste of a soda-lime window glass polishing facility was investigated at the temperatures between 700 and 950 degrees C. The results showed that the foaming of the glass powder started at a characteristic temperature between 670 and 680 degrees C. The maximum volume expansions of the glass powder and the density of the foams varied between 600% and 750% and 0.206 and 0.378 g cm(-3), respectively. The expansion of the studied glass powder residue resulted from the decomposition of the organic compounds on the surfaces of the glass powder particles, derived from an oil-based coolant used in the polishing. The collapse stress of the foams ranged between similar to 1 and 4 MPa and the thermal conductivity between 0.048 and 0.079 W K-1 m(-1). Both the collapse stress and thermal conductivity increased with increasing the foam density. The foams showed the characteristics of the compression deformation of the open cell brittle foams, which was attributed to the relatively thick cell edges. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. |
Cakircali, Metin; Kilicaslan, Cenk; Guden, Mustafa; Kiranli, Engin; Shchukin, Valery Y; Petronko, Vladimir V Cross wedge rolling of a Ti6Al4V (ELI) alloy: the experimental studies and the finite element simulation of the deformation and failure Journal Article INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, 65 (9-12), pp. 1273-1287, 2013, ISSN: 0268-3768. @article{ISI:000316364000007, title = {Cross wedge rolling of a Ti6Al4V (ELI) alloy: the experimental studies and the finite element simulation of the deformation and failure}, author = {Metin Cakircali and Cenk Kilicaslan and Mustafa Guden and Engin Kiranli and Valery Y Shchukin and Vladimir V Petronko}, doi = {10.1007/s00170-012-4256-3}, issn = {0268-3768}, year = {2013}, date = {2013-04-01}, journal = {INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY}, volume = {65}, number = {9-12}, pages = {1273-1287}, abstract = {The cross wedge rolling (CWR) deformation and fracture of a Ti6Al4Al (ELI) alloy were investigated experimentally and numerically using a coupled thermo-mechanical finite element model analysis. The experimentally determined flow stress and damage model parameters were verified by tension split Hopkinson pressure bar testing of notched samples. The simulation and experimental CWR forces showed well agreements except near the end of the stretching zone. The model analysis showed that the temperature distribution in the work piece was non-uniform during the CWR. When the initial temperature of the work piece was relatively low, the work piece temperature increased, a heating effect of the plastic deformation, while relatively high initial work piece temperatures resulted in cooling the work piece, caused by the work piece contact with the tools. The cracks were shown numerically to initiate in the midsections of the work piece during the guiding action and elongated in a direction normal to the maximum tensile stress triaxiality, resulting in cruciform-shaped crack formation, which was well agreed with the previously observed crack shape.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The cross wedge rolling (CWR) deformation and fracture of a Ti6Al4Al (ELI) alloy were investigated experimentally and numerically using a coupled thermo-mechanical finite element model analysis. The experimentally determined flow stress and damage model parameters were verified by tension split Hopkinson pressure bar testing of notched samples. The simulation and experimental CWR forces showed well agreements except near the end of the stretching zone. The model analysis showed that the temperature distribution in the work piece was non-uniform during the CWR. When the initial temperature of the work piece was relatively low, the work piece temperature increased, a heating effect of the plastic deformation, while relatively high initial work piece temperatures resulted in cooling the work piece, caused by the work piece contact with the tools. The cracks were shown numerically to initiate in the midsections of the work piece during the guiding action and elongated in a direction normal to the maximum tensile stress triaxiality, resulting in cruciform-shaped crack formation, which was well agreed with the previously observed crack shape. |
Kesici, Kutsal; Tuney, Inci; Zeren, Dogus; Guden, Mustafa; Sukatar, Atakan Morphological and molecular identification of pennate diatoms isolated from Urla, Izmir, coast of the Aegean Sea Journal Article TURKISH JOURNAL OF BIOLOGY, 37 (5), pp. 530-537, 2013, ISSN: 1300-0152. @article{ISI:000325300500004, title = {Morphological and molecular identification of pennate diatoms isolated from Urla, Izmir, coast of the Aegean Sea}, author = {Kutsal Kesici and Inci Tuney and Dogus Zeren and Mustafa Guden and Atakan Sukatar}, doi = {10.3906/biy-1205-40}, issn = {1300-0152}, year = {2013}, date = {2013-01-01}, journal = {TURKISH JOURNAL OF BIOLOGY}, volume = {37}, number = {5}, pages = {530-537}, abstract = {Diatoms represent an important class of aquatic phototrophs. They are not only one of the major contributors to global carbon fixation, but they also play a key role in the biogeochemical cycling of silica. Molecular identification methods based on conserved DNA sequences, such as internal transcribed spacer (ITS) have revolutionized our knowledge and understanding of conventional taxonomy. In this study, we aimed to compare the conventional identification methods with molecular identification methods. To do so, we isolated 4 diatom samples from the coast at Urla and characterized them Using light microscopy (LM) and scanning electron microscopy (SEM) according to morphological features. Then we amplified ITS regions using a conventional polymerase chain reaction (PCR), sequenced the PCR products, and analyzed the sequences using bioinformatic tools. Bioinformatic analysis indicated that the isolated species had high sequence similarity to Pseudo-nitzschia delicatissima, Achnanthes taeniata, Amphora coffeaeformis, and Cylindrotheca closterium. We think that molecular identification methods enable rapid and more reliable identification of diatom species and are crucial for monitoring harmful algal blooms.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Diatoms represent an important class of aquatic phototrophs. They are not only one of the major contributors to global carbon fixation, but they also play a key role in the biogeochemical cycling of silica. Molecular identification methods based on conserved DNA sequences, such as internal transcribed spacer (ITS) have revolutionized our knowledge and understanding of conventional taxonomy. In this study, we aimed to compare the conventional identification methods with molecular identification methods. To do so, we isolated 4 diatom samples from the coast at Urla and characterized them Using light microscopy (LM) and scanning electron microscopy (SEM) according to morphological features. Then we amplified ITS regions using a conventional polymerase chain reaction (PCR), sequenced the PCR products, and analyzed the sequences using bioinformatic tools. Bioinformatic analysis indicated that the isolated species had high sequence similarity to Pseudo-nitzschia delicatissima, Achnanthes taeniata, Amphora coffeaeformis, and Cylindrotheca closterium. We think that molecular identification methods enable rapid and more reliable identification of diatom species and are crucial for monitoring harmful algal blooms. |
Gulturk, E A; Guden, M; Tasdemirci, A Calcined and natural frustules filled epoxy matrices: The effect of volume fraction on the tensile and compression behavior Journal Article COMPOSITES PART B-ENGINEERING, 44 (1), pp. 491-500, 2013, ISSN: 1359-8368. @article{ISI:000313854200059, title = {Calcined and natural frustules filled epoxy matrices: The effect of volume fraction on the tensile and compression behavior}, author = {E A Gulturk and M Guden and A Tasdemirci}, doi = {10.1016/j.compositesb.2012.03.022}, issn = {1359-8368}, year = {2013}, date = {2013-01-01}, journal = {COMPOSITES PART B-ENGINEERING}, volume = {44}, number = {1}, pages = {491-500}, abstract = {The effects of calcined diatom (CD) and natural diatom (ND) frustules filling (0-12 vol.%) on the quasi-static tensile and quasi-static and high strain rate compression behavior of an epoxy matrix were investigated experimentally. The high strain rate testing of frustules-filled and neat epoxy samples was performed in a compression Split Hopkinson Pressure Bar set-up. The frustules filling increased the stress values at a constant strain and decreased the tensile failure strains of the epoxy matrix. Compression tests results showed that frustules filling of epoxy increased both elastic modulus and yield strength values at quasi-static and high strain rates. While, a higher strengthening effect and strain rate sensitivity were found with ND frustules filling. Microscopic observations revealed two main compression deformation modes at quasi-static strain rates: the debonding of the frustules from the epoxy and/or crushing of the frustules. However, the failure of the filled composites at high strain rates was dominated by the fracture of epoxy matrix. (C) 2012 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effects of calcined diatom (CD) and natural diatom (ND) frustules filling (0-12 vol.%) on the quasi-static tensile and quasi-static and high strain rate compression behavior of an epoxy matrix were investigated experimentally. The high strain rate testing of frustules-filled and neat epoxy samples was performed in a compression Split Hopkinson Pressure Bar set-up. The frustules filling increased the stress values at a constant strain and decreased the tensile failure strains of the epoxy matrix. Compression tests results showed that frustules filling of epoxy increased both elastic modulus and yield strength values at quasi-static and high strain rates. While, a higher strengthening effect and strain rate sensitivity were found with ND frustules filling. Microscopic observations revealed two main compression deformation modes at quasi-static strain rates: the debonding of the frustules from the epoxy and/or crushing of the frustules. However, the failure of the filled composites at high strain rates was dominated by the fracture of epoxy matrix. (C) 2012 Elsevier Ltd. All rights reserved. |
2012 |
Tasdemirci, A; Turan, A K; Guden, M The effect of strain rate on the mechanical behavior of Teflon foam Journal Article POLYMER TESTING, 31 (6), pp. 723-727, 2012, ISSN: 0142-9418. @article{ISI:000307614000002, title = {The effect of strain rate on the mechanical behavior of Teflon foam}, author = {A Tasdemirci and A K Turan and M Guden}, doi = {10.1016/j.polymertesting.2012.05.004}, issn = {0142-9418}, year = {2012}, date = {2012-09-01}, journal = {POLYMER TESTING}, volume = {31}, number = {6}, pages = {723-727}, abstract = {The quasi-static (1 x 10(-3), 1 x 10(-2) and 1 x 10(-1) s(-1)) and high strain rate (7200 and 9500 s(-1)) experimental and high strain rate numerical compression deformation of a Gore Polarchip (TM) CP7003 heat insulating Teflon foam was investigated. High strain rate tests were conducted with the insertion of quartz crystal piezoelectric transducers at the end of the transmitter bar of a compression Split Hopkinson Pressure Bar (SHPB) set-up in order to measure the force at the back face of the specimen. A fully developed numerical model of the SHPB test on Teflon was also implemented using LS-DYNA. The simulation stresses showed close correlations with the experimentally measured stresses on the bars. The developed model successfully simulated the high strain rate loading. The damage initiation and progression of experimental high strain rate tests were further recorded using a high speed camera and found to be very similar to those of the simulation high strain rate tests. (C) 2012 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The quasi-static (1 x 10(-3), 1 x 10(-2) and 1 x 10(-1) s(-1)) and high strain rate (7200 and 9500 s(-1)) experimental and high strain rate numerical compression deformation of a Gore Polarchip (TM) CP7003 heat insulating Teflon foam was investigated. High strain rate tests were conducted with the insertion of quartz crystal piezoelectric transducers at the end of the transmitter bar of a compression Split Hopkinson Pressure Bar (SHPB) set-up in order to measure the force at the back face of the specimen. A fully developed numerical model of the SHPB test on Teflon was also implemented using LS-DYNA. The simulation stresses showed close correlations with the experimentally measured stresses on the bars. The developed model successfully simulated the high strain rate loading. The damage initiation and progression of experimental high strain rate tests were further recorded using a high speed camera and found to be very similar to those of the simulation high strain rate tests. (C) 2012 Elsevier Ltd. All rights reserved. |
Savaci, Umut; Yilmaz, Sinan; Guden, Mustafa Open cell lead foams: processing, microstructure, and mechanical properties Journal Article JOURNAL OF MATERIALS SCIENCE, 47 (15), pp. 5646-5654, 2012, ISSN: 0022-2461. @article{ISI:000304110400004, title = {Open cell lead foams: processing, microstructure, and mechanical properties}, author = {Umut Savaci and Sinan Yilmaz and Mustafa Guden}, doi = {10.1007/s10853-012-6496-x}, issn = {0022-2461}, year = {2012}, date = {2012-08-01}, journal = {JOURNAL OF MATERIALS SCIENCE}, volume = {47}, number = {15}, pages = {5646-5654}, abstract = {Open cell lead foams with the porosities between 48 and 74 % were prepared by means of powder metallurgical and casting routes, using ammonium bicarbonate particles, silica beads, and sodium chloride salt particles as space holder. The resulting foam samples structure closely resembled open cell foam structure: each cell had few interconnections with neighboring cells. Small-sized lead (II) fluoride precipitates were microscopically observed in the interior of cells in the foam samples prepared using silica beads as space holder, resulting from the reaction between silica and hydrofluoric acid in the space holder dissolution step. The compression stress-strain curve of foam samples prepared by powder metallurgical route showed brittle deformation behavior following the initial elastic deformation region, while the foam samples prepared by casting route showed characteristic foam deformation behavior: cell edge crushing on the bent cell walls, and cell wall tearing. The collapse stresses, densification strains, and elastic moduli of the prepared foams were further fitted with scaling relations.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Open cell lead foams with the porosities between 48 and 74 % were prepared by means of powder metallurgical and casting routes, using ammonium bicarbonate particles, silica beads, and sodium chloride salt particles as space holder. The resulting foam samples structure closely resembled open cell foam structure: each cell had few interconnections with neighboring cells. Small-sized lead (II) fluoride precipitates were microscopically observed in the interior of cells in the foam samples prepared using silica beads as space holder, resulting from the reaction between silica and hydrofluoric acid in the space holder dissolution step. The compression stress-strain curve of foam samples prepared by powder metallurgical route showed brittle deformation behavior following the initial elastic deformation region, while the foam samples prepared by casting route showed characteristic foam deformation behavior: cell edge crushing on the bent cell walls, and cell wall tearing. The collapse stresses, densification strains, and elastic moduli of the prepared foams were further fitted with scaling relations. |
Tasdemirci, A; Tunusoglu, G; Guden, M The effect of the interlayer on the ballistic performance of ceramic/composite armors: Experimental and numerical study Journal Article INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, 44 , pp. 1-9, 2012, ISSN: 0734-743X. @article{ISI:000301473600001, title = {The effect of the interlayer on the ballistic performance of ceramic/composite armors: Experimental and numerical study}, author = {A Tasdemirci and G Tunusoglu and M Guden}, doi = {10.1016/j.ijimpeng.2011.12.005}, issn = {0734-743X}, year = {2012}, date = {2012-06-01}, journal = {INTERNATIONAL JOURNAL OF IMPACT ENGINEERING}, volume = {44}, pages = {1-9}, abstract = {The effect of rubber, Teflon and aluminum foam interlayer material on the ballistic performance of composite armor was investigated both experimentally and numerically. Although, rubber interlayer did not cause any significant delay in the initial stress build-up in the composite layer, Teflon and aluminum foam interlayer caused a significant delay and reduction in the magnitude of the stress transmitted to the composite backing plate. Damage in the ceramic layer was found to be highly localized around the projectile impact zone for the configuration without interlayer and rubber interlayer while aluminum foam and Teflon interlayer spread the damage zone in the radial direction. Relatively large pieces of the ceramic around the impact axis in the rubber interlayer configuration were observed while the ceramic layer was efficiently fragmented in aluminum foam and Teflon interlayer configuration. (C) 2011 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of rubber, Teflon and aluminum foam interlayer material on the ballistic performance of composite armor was investigated both experimentally and numerically. Although, rubber interlayer did not cause any significant delay in the initial stress build-up in the composite layer, Teflon and aluminum foam interlayer caused a significant delay and reduction in the magnitude of the stress transmitted to the composite backing plate. Damage in the ceramic layer was found to be highly localized around the projectile impact zone for the configuration without interlayer and rubber interlayer while aluminum foam and Teflon interlayer spread the damage zone in the radial direction. Relatively large pieces of the ceramic around the impact axis in the rubber interlayer configuration were observed while the ceramic layer was efficiently fragmented in aluminum foam and Teflon interlayer configuration. (C) 2011 Elsevier Ltd. All rights reserved. |
Odaci, Ismet Kutlay; Kilicaslan, Cenk; Tasdemirci, Alper; Guden, Mustafa INTERNATIONAL JOURNAL OF CRASHWORTHINESS, 17 (5), pp. 508-518, 2012, ISSN: 1358-8265. @article{ISI:000308991800004, title = {Projectile impact testing of glass fiber-reinforced composite and layered corrugated aluminium and aluminium foam core sandwich panels: a comparative study}, author = {Ismet Kutlay Odaci and Cenk Kilicaslan and Alper Tasdemirci and Mustafa Guden}, doi = {10.1080/13588265.2012.690215}, issn = {1358-8265}, year = {2012}, date = {2012-01-01}, journal = {INTERNATIONAL JOURNAL OF CRASHWORTHINESS}, volume = {17}, number = {5}, pages = {508-518}, abstract = {E-glass/polyester composite and layered corrugated aluminium and aluminium foam core sandwich panels were projectile impact tested between 127 m/s and 190 m/s using a hardened steel sphere projectile. The corrugated aluminium cores, constructed from aluminium fin layers and aluminium interlayers and face sheets, exhibited relatively lower-plateau stresses and higher stress oscillations in the plateau region than aluminium foam cores. The applied brazing process resulted in reductions in the plateau stresses of the corrugated aluminium cores. The sandwich panels with 2- and 3-mm-thick composite face sheets and the epoxy-bonded corrugated aluminium sheet cores were perforated, while the sandwich panels with 5-mm-thick composite face sheets were penetrated in the projectile impact tests. On the other hand, the sandwich panels with aluminium foam cores were only penetrated. A simple comparison between the ballistic limits of the sandwich panels as a function of total weight revealed significant increases in the ballistic limits of the cores with the inclusion of composite face sheets. The determined higher impact resistance of the foam core sandwich panels was attributed to the relatively higher strength of the foam cores investigated and the ability to distribute the incident impulse to a relatively large area of the backing composite plate.}, keywords = {}, pubstate = {published}, tppubtype = {article} } E-glass/polyester composite and layered corrugated aluminium and aluminium foam core sandwich panels were projectile impact tested between 127 m/s and 190 m/s using a hardened steel sphere projectile. The corrugated aluminium cores, constructed from aluminium fin layers and aluminium interlayers and face sheets, exhibited relatively lower-plateau stresses and higher stress oscillations in the plateau region than aluminium foam cores. The applied brazing process resulted in reductions in the plateau stresses of the corrugated aluminium cores. The sandwich panels with 2- and 3-mm-thick composite face sheets and the epoxy-bonded corrugated aluminium sheet cores were perforated, while the sandwich panels with 5-mm-thick composite face sheets were penetrated in the projectile impact tests. On the other hand, the sandwich panels with aluminium foam cores were only penetrated. A simple comparison between the ballistic limits of the sandwich panels as a function of total weight revealed significant increases in the ballistic limits of the cores with the inclusion of composite face sheets. The determined higher impact resistance of the foam core sandwich panels was attributed to the relatively higher strength of the foam cores investigated and the ability to distribute the incident impulse to a relatively large area of the backing composite plate. |
2011 |
Turkan, Ugur; Guden, Mustafa The effect of surface treatment on CaP deposition of Ti6Al4V open cell foams in SBF solution (vol 39, pg 1805, 2010) Journal Article CERAMICS INTERNATIONAL, 37 (2), pp. 693, 2011, ISSN: 0272-8842. @article{ISI:000286957900040, title = {The effect of surface treatment on CaP deposition of Ti6Al4V open cell foams in SBF solution (vol 39, pg 1805, 2010)}, author = {Ugur Turkan and Mustafa Guden}, doi = {10.1016/j.ceramint.2010.07.002}, issn = {0272-8842}, year = {2011}, date = {2011-03-01}, journal = {CERAMICS INTERNATIONAL}, volume = {37}, number = {2}, pages = {693}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Durmus, A; Guden, M; Gulcimen, B; Ulku, S; Musa, E Experimental investigations on the ballistic impact performances of cold rolled sheet metals Journal Article MATERIALS & DESIGN, 32 (3), pp. 1356-1366, 2011, ISSN: 0261-3069. @article{ISI:000286904200033, title = {Experimental investigations on the ballistic impact performances of cold rolled sheet metals}, author = {A Durmus and M Guden and B Gulcimen and S Ulku and E Musa}, doi = {10.1016/j.matdes.2010.09.016}, issn = {0261-3069}, year = {2011}, date = {2011-03-01}, journal = {MATERIALS & DESIGN}, volume = {32}, number = {3}, pages = {1356-1366}, abstract = {This study focuses on the ballistic performances of 1 and 2 mm-thick and 2 x 1 mm-thick cold rolled sheet metal plates against 9 mm standard NATO projectile. The velocity of the projectile before and after perforation, the diameter of the front face deformation, the depth of the crater and the diameter of the hole were measured. The fracture surfaces of the plates near the ballistic limit were also microscopically analyzed. The highest ballistic limit was found in 2 mm-thick plate (332 m s(-1)) and the lowest in 1 mm-thick plate (97 m s(-1)). While, the ballistic limit of 2 x 1 mm-thick plate decreased to 306 m s(-1). Typical failure mechanism of the projectile was the flattening and mushrooming at relatively low velocities and the separation from the jacket at relatively high velocities. In accord with the ballistic limits, 2 mm-thick target plate exhibited the highest hardness value. Microscopic investigations showed the significant reductions in the grain size of the targets after the test. (C) 2010 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study focuses on the ballistic performances of 1 and 2 mm-thick and 2 x 1 mm-thick cold rolled sheet metal plates against 9 mm standard NATO projectile. The velocity of the projectile before and after perforation, the diameter of the front face deformation, the depth of the crater and the diameter of the hole were measured. The fracture surfaces of the plates near the ballistic limit were also microscopically analyzed. The highest ballistic limit was found in 2 mm-thick plate (332 m s(-1)) and the lowest in 1 mm-thick plate (97 m s(-1)). While, the ballistic limit of 2 x 1 mm-thick plate decreased to 306 m s(-1). Typical failure mechanism of the projectile was the flattening and mushrooming at relatively low velocities and the separation from the jacket at relatively high velocities. In accord with the ballistic limits, 2 mm-thick target plate exhibited the highest hardness value. Microscopic investigations showed the significant reductions in the grain size of the targets after the test. (C) 2010 Elsevier Ltd. All rights reserved. |
Toksoy, A K; Guden, M The optimisation of the energy absorption of partially Al foam-filled commercial 1050H14 and 6061T4 Al crash boxes Journal Article INTERNATIONAL JOURNAL OF CRASHWORTHINESS, 16 (1), pp. 97-109, 2011, ISSN: 1358-8265. @article{ISI:000288960900009, title = {The optimisation of the energy absorption of partially Al foam-filled commercial 1050H14 and 6061T4 Al crash boxes}, author = {A K Toksoy and M Guden}, doi = {10.1080/13588265.2010.514774}, issn = {1358-8265}, year = {2011}, date = {2011-01-01}, journal = {INTERNATIONAL JOURNAL OF CRASHWORTHINESS}, volume = {16}, number = {1}, pages = {97-109}, abstract = {Partially Alulight and Hydro Al closed-cell foam-filled commercial 1050H14 Al and 6061T4 Al crash boxes were optimised using the response surface methodology in order to maximise specific energy absorption (SEA). The quasi-static crushing of empty and filled crash boxes was simulated using LS-DYNA, and the results were further confirmed with experimental quasi-static crushing testing of empty and Alulight foam-filled commercial 1050H14 Al crash boxes. Results showed that partial foam filling of commercial crash boxes increased both SEA and mean load because of foam filler axial and lateral deformation in between the progressing folds of the crash box. Within the studied constraint range of box mean load, box wall thickness and foam filler density, the optimised Alulight and Hydro foam-filled 1050H14 and 6061T4 crash boxes resulted in 26%-40% increase in total energy absorption as compared with empty crash boxes. Considering the same weight basis, the use of a higher yield strength box wall material and higher plateau stresses of Al foam filler resulted in higher energy absorptions in partial foam-filled boxes at relatively low displacements.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Partially Alulight and Hydro Al closed-cell foam-filled commercial 1050H14 Al and 6061T4 Al crash boxes were optimised using the response surface methodology in order to maximise specific energy absorption (SEA). The quasi-static crushing of empty and filled crash boxes was simulated using LS-DYNA, and the results were further confirmed with experimental quasi-static crushing testing of empty and Alulight foam-filled commercial 1050H14 Al crash boxes. Results showed that partial foam filling of commercial crash boxes increased both SEA and mean load because of foam filler axial and lateral deformation in between the progressing folds of the crash box. Within the studied constraint range of box mean load, box wall thickness and foam filler density, the optimised Alulight and Hydro foam-filled 1050H14 and 6061T4 crash boxes resulted in 26%-40% increase in total energy absorption as compared with empty crash boxes. Considering the same weight basis, the use of a higher yield strength box wall material and higher plateau stresses of Al foam filler resulted in higher energy absorptions in partial foam-filled boxes at relatively low displacements. |
2010 |
Turkan, U; Guden, M The effect of nitric acid surface treatment on CaP deposition of Ti6Al4V open-cell foams in SBF solution Journal Article SURFACE & COATINGS TECHNOLOGY, 205 (7), pp. 1904-1916, 2010, ISSN: 0257-8972. @article{ISI:000286343100017, title = {The effect of nitric acid surface treatment on CaP deposition of Ti6Al4V open-cell foams in SBF solution}, author = {U Turkan and M Guden}, doi = {10.1016/j.surfcoat.2010.08.071}, issn = {0257-8972}, year = {2010}, date = {2010-12-01}, journal = {SURFACE & COATINGS TECHNOLOGY}, volume = {205}, number = {7}, pages = {1904-1916}, abstract = {The effect of nitric acid surface treatment on CaP deposition of an open-cell Ti6Al4V foam (60% porous and 300-500 m in pore size), prepared by means of the space holder method using 94 and 66 mu m average particle size powders, was investigated in a simulated body fluid (SBF) solution up to 14 days. Although, nitric acid surface treatment did not change the foam flat surface roughness values significantly, it increased surface area difference greatly by introducing nano scale undulations on the surface. The increased surface area difference was found to be more pronounced in smaller particle size foam samples. A continuous relatively thin CaP coating layer formed after 5 and 14 days of SBF immersion in nitric acid surface treated small and larger average particle size foam specimens, respectively. Whereas, the cells of untreated foam specimen were observed to be filled with CaP precipitates and a continuous CaP layer development was found after 14 days of SBF immersion. These results were also confirmed with the grazing incidence XRD and FTIR analysis of SBF immersed specimens. (C) 2010 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of nitric acid surface treatment on CaP deposition of an open-cell Ti6Al4V foam (60% porous and 300-500 m in pore size), prepared by means of the space holder method using 94 and 66 mu m average particle size powders, was investigated in a simulated body fluid (SBF) solution up to 14 days. Although, nitric acid surface treatment did not change the foam flat surface roughness values significantly, it increased surface area difference greatly by introducing nano scale undulations on the surface. The increased surface area difference was found to be more pronounced in smaller particle size foam samples. A continuous relatively thin CaP coating layer formed after 5 and 14 days of SBF immersion in nitric acid surface treated small and larger average particle size foam specimens, respectively. Whereas, the cells of untreated foam specimen were observed to be filled with CaP precipitates and a continuous CaP layer development was found after 14 days of SBF immersion. These results were also confirmed with the grazing incidence XRD and FTIR analysis of SBF immersed specimens. (C) 2010 Elsevier B.V. All rights reserved. |
Turkan, Ugur; Guden, Mustafa The effect of surface treatment on CaP deposition of Ti6Al4V open cell foams in SBF solution Journal Article CERAMICS INTERNATIONAL, 36 (6), pp. 1805-1816, 2010, ISSN: 0272-8842. @article{ISI:000280027800008, title = {The effect of surface treatment on CaP deposition of Ti6Al4V open cell foams in SBF solution}, author = {Ugur Turkan and Mustafa Guden}, doi = {10.1016/j.ceramint.2010.03.030}, issn = {0272-8842}, year = {2010}, date = {2010-08-01}, journal = {CERAMICS INTERNATIONAL}, volume = {36}, number = {6}, pages = {1805-1816}, abstract = {The effects of alkali and nitric acid surface treatment and acid etching on the CaP deposition of an open cell Ti6Al4V foam (60% porous and 300-500 mu m in pore size) developed for biomedical applications were investigated in a simulated body fluid (SBF) solution for 14-day. The surface roughness of the foam specimens ground flat surfaces was measured in nano-metric scale before and after SBF immersion using an atomic force microscope (AFM). A significant increase in the surface roughness of alkali treated foam specimen after SBF immersion indicated a smaller crystal size CaP deposition, which was also confirmed by the AFM micrographs. The microscopic evaluation clearly showed that alkali treatment and nitric acid treatment induced a continuous, uniform CaP deposition on the cell wall surfaces of the foam (interior of cells). While in untreated foam specimen the cells are filled with CaP precipitates and acid etching did not produce a continuous coating layer on particles interior of the cells. The coating layer thickness was similar to 3 mu m in alkali treated foam specimens after 14-day of SBF immersion, while nitric acid treatment induced relatively thinner coating layer, 0.6 mu m. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effects of alkali and nitric acid surface treatment and acid etching on the CaP deposition of an open cell Ti6Al4V foam (60% porous and 300-500 mu m in pore size) developed for biomedical applications were investigated in a simulated body fluid (SBF) solution for 14-day. The surface roughness of the foam specimens ground flat surfaces was measured in nano-metric scale before and after SBF immersion using an atomic force microscope (AFM). A significant increase in the surface roughness of alkali treated foam specimen after SBF immersion indicated a smaller crystal size CaP deposition, which was also confirmed by the AFM micrographs. The microscopic evaluation clearly showed that alkali treatment and nitric acid treatment induced a continuous, uniform CaP deposition on the cell wall surfaces of the foam (interior of cells). While in untreated foam specimen the cells are filled with CaP precipitates and acid etching did not produce a continuous coating layer on particles interior of the cells. The coating layer thickness was similar to 3 mu m in alkali treated foam specimens after 14-day of SBF immersion, while nitric acid treatment induced relatively thinner coating layer, 0.6 mu m. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved. |
Ozyildiz, E; Guden, M; Uzel, A; Karaboz, I; Akil, O; Bulut, H Antimicrobial Activity of TiO2-coated Orthodontic Ceramic Brackets against Streptococcus mutans and Candida albicans Journal Article BIOTECHNOLOGY AND BIOPROCESS ENGINEERING, 15 (4), pp. 680-685, 2010, ISSN: 1226-8372. @article{ISI:000281514400022, title = {Antimicrobial Activity of TiO2-coated Orthodontic Ceramic Brackets against Streptococcus mutans and Candida albicans}, author = {E Ozyildiz and M Guden and A Uzel and I Karaboz and O Akil and H Bulut}, doi = {10.1007/s12257-009-3005-4}, issn = {1226-8372}, year = {2010}, date = {2010-07-01}, journal = {BIOTECHNOLOGY AND BIOPROCESS ENGINEERING}, volume = {15}, number = {4}, pages = {680-685}, abstract = {Polycrystalline alumina ceramic orthodontic brackets were coated with anatase TiO2 film via a sol-gel dip-coating method. The surface structure morphology and composition of the films were evaluated via scanning electron microscopy, atomic force microscopy, and X-ray diffraction. The antimicrobial activity of the ceramic brackets was assessed against two oral pathogens, S. mutans and C. albicans. The results demonstrated that TiO2-coated brackets exposed to low energy UV-A illumination efficiently reduced the populations of test microorganisms relative to the uncoated brackets. The reduction efficiencies were 98% for S. mutans ATCC 10449 and 93% for C. albicans ATCC 60193.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Polycrystalline alumina ceramic orthodontic brackets were coated with anatase TiO2 film via a sol-gel dip-coating method. The surface structure morphology and composition of the films were evaluated via scanning electron microscopy, atomic force microscopy, and X-ray diffraction. The antimicrobial activity of the ceramic brackets was assessed against two oral pathogens, S. mutans and C. albicans. The results demonstrated that TiO2-coated brackets exposed to low energy UV-A illumination efficiently reduced the populations of test microorganisms relative to the uncoated brackets. The reduction efficiencies were 98% for S. mutans ATCC 10449 and 93% for C. albicans ATCC 60193. |
Toksoy, A K; Guden, M Partial Al foam filling of commercial 1050H14 Al crash boxes: The effect of box column thickness and foam relative density on energy absorption Journal Article THIN-WALLED STRUCTURES, 48 (7), pp. 482-494, 2010, ISSN: 0263-8231. @article{ISI:000278670400002, title = {Partial Al foam filling of commercial 1050H14 Al crash boxes: The effect of box column thickness and foam relative density on energy absorption}, author = {A K Toksoy and M Guden}, doi = {10.1016/j.tws.2010.02.002}, issn = {0263-8231}, year = {2010}, date = {2010-07-01}, journal = {THIN-WALLED STRUCTURES}, volume = {48}, number = {7}, pages = {482-494}, abstract = {The crushing behavior of partially Al closed-cell foam filled commercial 1050H14 Al crash boxes was determined at quasi-static and dynamic deformation velocities. The quasi-static and dynamic crushing of the boxes were simulated using the LS-DYNA. The results showed that partial foam filling tended to change the deformation mode of empty boxes from a non-sequential to a sequential folding mode. In general, the experimental and simulation results showed similar mean load values and deformation modes. The SEA values of empty, partially and fully foam filled boxes were predicted as function of box wall thickness between 1 and 3 mm and foam filler relative density between 0 and 0.2, using the analytical equations developed for the mean crushing loads. The analysis indicated that both fully and partially foam filled boxes were energetically more efficient than empty boxes above a critical foam filler relative density. Partial foam filling, however, decreases the critical foam filler density at increasing box wall thicknesses. (C) 2010 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The crushing behavior of partially Al closed-cell foam filled commercial 1050H14 Al crash boxes was determined at quasi-static and dynamic deformation velocities. The quasi-static and dynamic crushing of the boxes were simulated using the LS-DYNA. The results showed that partial foam filling tended to change the deformation mode of empty boxes from a non-sequential to a sequential folding mode. In general, the experimental and simulation results showed similar mean load values and deformation modes. The SEA values of empty, partially and fully foam filled boxes were predicted as function of box wall thickness between 1 and 3 mm and foam filler relative density between 0 and 0.2, using the analytical equations developed for the mean crushing loads. The analysis indicated that both fully and partially foam filled boxes were energetically more efficient than empty boxes above a critical foam filler relative density. Partial foam filling, however, decreases the critical foam filler density at increasing box wall thicknesses. (C) 2010 Elsevier Ltd. All rights reserved. |
Tasdemirci, A; Ergonenc, C; Guden, M Split Hopkinson pressure bar multiple reloading and modeling of a 316 L stainless steel metallic hollow sphere structure Journal Article INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, 37 (3), pp. 250-259, 2010, ISSN: 0734-743X. @article{ISI:000273106000003, title = {Split Hopkinson pressure bar multiple reloading and modeling of a 316 L stainless steel metallic hollow sphere structure}, author = {A Tasdemirci and C Ergonenc and M Guden}, doi = {10.1016/j.ijimpeng.2009.06.010}, issn = {0734-743X}, year = {2010}, date = {2010-03-01}, journal = {INTERNATIONAL JOURNAL OF IMPACT ENGINEERING}, volume = {37}, number = {3}, pages = {250-259}, abstract = {The high strain rate (600 s(-1)) compression deformation of a 316 L metallic hollow sphere (MHS) structure (density: 500 kg m(-3): average outer hollow sphere diameter: 2 mm and wall thickness: 45 mu m) was determined both numerically and experimentally. The experimental compressive stress-strain behavior at high strain rates until about large strains was obtained with multiple reloading tests using a large-diameter compression type aluminum Split Hopkinson Pressure Bar (SHPB) test apparatus. The multiple reloading of MHS samples in SHPB was analyzed with a 3D finite element model using the commercial explicit finite element code LS-DYNA. The tested MHS samples showed increased crushing stress values, when the strain rate increased from quasi-static (0.8 x 10(-4) s(-1)) to high strain rate (600 s(-1)). Experimentally and numerically deformed sections of MHS samples tested showed very similar crushing characteristics; plastic hinge formation, the indentation of the spheres at the contact regions and sphere wall buckling at intermediate strains. The extent of micro-inertial effects was further predicted with the strain rate insensitive cell wall material model and with the strain rate sensitive behavior of MHS structure similar to that of the cell wall material. Based on the predictions, the strain rate sensitivity of the studied 316 L MHS sample was attributed to the strain rate sensitivity of the cell wall material and the micro-inertia. (C) 2009 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The high strain rate (600 s(-1)) compression deformation of a 316 L metallic hollow sphere (MHS) structure (density: 500 kg m(-3): average outer hollow sphere diameter: 2 mm and wall thickness: 45 mu m) was determined both numerically and experimentally. The experimental compressive stress-strain behavior at high strain rates until about large strains was obtained with multiple reloading tests using a large-diameter compression type aluminum Split Hopkinson Pressure Bar (SHPB) test apparatus. The multiple reloading of MHS samples in SHPB was analyzed with a 3D finite element model using the commercial explicit finite element code LS-DYNA. The tested MHS samples showed increased crushing stress values, when the strain rate increased from quasi-static (0.8 x 10(-4) s(-1)) to high strain rate (600 s(-1)). Experimentally and numerically deformed sections of MHS samples tested showed very similar crushing characteristics; plastic hinge formation, the indentation of the spheres at the contact regions and sphere wall buckling at intermediate strains. The extent of micro-inertial effects was further predicted with the strain rate insensitive cell wall material model and with the strain rate sensitive behavior of MHS structure similar to that of the cell wall material. Based on the predictions, the strain rate sensitivity of the studied 316 L MHS sample was attributed to the strain rate sensitivity of the cell wall material and the micro-inertia. (C) 2009 Elsevier Ltd. All rights reserved. |
2008 |
Tirtom, Ismail; Guden, Mustafa; Yilidz, Hasan Simulation of the strain rate sensitive flow behavior of SiC-particulate reinforced aluminum metal matrix composites Journal Article COMPUTATIONAL MATERIALS SCIENCE, 42 (4), pp. 570-578, 2008, ISSN: 0927-0256. @article{ISI:000256777300005, title = {Simulation of the strain rate sensitive flow behavior of SiC-particulate reinforced aluminum metal matrix composites}, author = {Ismail Tirtom and Mustafa Guden and Hasan Yilidz}, doi = {10.1016/j.commatsci.2007.09.005}, issn = {0927-0256}, year = {2008}, date = {2008-06-01}, journal = {COMPUTATIONAL MATERIALS SCIENCE}, volume = {42}, number = {4}, pages = {570-578}, abstract = {Strain rate dependent compression mechanical behavior of an SiC-particulate reinforced Al (2024-O) metal matrix composite (MMC) with different particle volume fractions was numerically investigated at various strain rates. Calculations were performed using axisymmetric finite element unit cell model, in which an elastic SiC particle was embedded inside a strain rate sensitive viscoplastic Al matrix. Stress-strain curves of Al matrix material were derived from Split Hopkinson Pressure Bar experiments at various strain rates and used as inputs in the FEM model. Numerically computed stress-strain curves and strain rate sensitivity were compared with those of experiments for a 15% SiC-particulate reinforced MMC. Computed strain rate sensitivity of the MMC was found to be higher than that of the matrix alloy and increased with increasing strain contrary to the strain independent matrix strain rate sensitivity. The strain rate sensitivity of the MMC was also found to increase with increasing particle volume fraction at the same particle size. Finally, several possible reasons including assumptions used in the model, adiabatic heating, microstructural variations between the composite matrix and matrix alloy, particle shape and distribution and damage accumulation for the small discrepancy found between computed and experimental stress-strain curves and strain rate sensitivity of the composite were discussed. (C) 2007 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Strain rate dependent compression mechanical behavior of an SiC-particulate reinforced Al (2024-O) metal matrix composite (MMC) with different particle volume fractions was numerically investigated at various strain rates. Calculations were performed using axisymmetric finite element unit cell model, in which an elastic SiC particle was embedded inside a strain rate sensitive viscoplastic Al matrix. Stress-strain curves of Al matrix material were derived from Split Hopkinson Pressure Bar experiments at various strain rates and used as inputs in the FEM model. Numerically computed stress-strain curves and strain rate sensitivity were compared with those of experiments for a 15% SiC-particulate reinforced MMC. Computed strain rate sensitivity of the MMC was found to be higher than that of the matrix alloy and increased with increasing strain contrary to the strain independent matrix strain rate sensitivity. The strain rate sensitivity of the MMC was also found to increase with increasing particle volume fraction at the same particle size. Finally, several possible reasons including assumptions used in the model, adiabatic heating, microstructural variations between the composite matrix and matrix alloy, particle shape and distribution and damage accumulation for the small discrepancy found between computed and experimental stress-strain curves and strain rate sensitivity of the composite were discussed. (C) 2007 Elsevier B.V. All rights reserved. |
Tasdemirci, A; Yuksel, S; Karsu, D; Gulturk, E; Hall, I W; Guden, M Diatom frustule-filled epoxy: Experimental and numerical study of the quasi-static and high strain rate compression behavior Journal Article MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 480 (1-2), pp. 373-382, 2008, ISSN: 0921-5093. @article{ISI:000255881300049, title = {Diatom frustule-filled epoxy: Experimental and numerical study of the quasi-static and high strain rate compression behavior}, author = {A Tasdemirci and S Yuksel and D Karsu and E Gulturk and I W Hall and M Guden}, doi = {10.1016/j.msea.2007.07.037}, issn = {0921-5093}, year = {2008}, date = {2008-05-01}, journal = {MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, volume = {480}, number = {1-2}, pages = {373-382}, abstract = {In this study, centric type diatom frustules obtained from a diatomaceous earth filter material were used as filler in an epoxy resin with a weight percentage of 15% in order to assess the possible effects on the compressive behavior at quasi-static and high strain rates. The high strain rate testing of frustule-filled and neat epoxy samples was performed in a split-Hopkinson pressure bar (SHPB) set-up and modeled using the commercial explicit finite element code LS-DYNA 970. Result has shown that 15% frustule filling of epoxy increased both modulus and yield strength values at quasi-static and high strain rates without significantly reducing the failure strain. Microscopic observations revealed two main deformation modes: the debonding of the frustules from the epoxy and crushing/fracture of the frustules. The modeling results have further confirmed the attainment of stress equilibrium in the samples in SHPB testing following the initial elastic region and showed good agreement with the experimental stress-time response and deformation sequence of the samples in high strain rate testing. (C) 2007 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, centric type diatom frustules obtained from a diatomaceous earth filter material were used as filler in an epoxy resin with a weight percentage of 15% in order to assess the possible effects on the compressive behavior at quasi-static and high strain rates. The high strain rate testing of frustule-filled and neat epoxy samples was performed in a split-Hopkinson pressure bar (SHPB) set-up and modeled using the commercial explicit finite element code LS-DYNA 970. Result has shown that 15% frustule filling of epoxy increased both modulus and yield strength values at quasi-static and high strain rates without significantly reducing the failure strain. Microscopic observations revealed two main deformation modes: the debonding of the frustules from the epoxy and crushing/fracture of the frustules. The modeling results have further confirmed the attainment of stress equilibrium in the samples in SHPB testing following the initial elastic region and showed good agreement with the experimental stress-time response and deformation sequence of the samples in high strain rate testing. (C) 2007 Elsevier B.V. All rights reserved. |
Lecturer Dr. Özgür Günelsu
Educational Background
B.Sc. Middle East Technical University, Turkey, Mechanical Engineering, 2003
M.Sc. İstanbul Technical University, Turkey, Automotive Engineering, 2006
Ph.D. İstanbul Technical University, Turkey, Automotive Engineering, 2006
Research Interests
- Piston Secondary Dynamics and Lubrication
- +90 232 750 6762
- +90 232 750 6701
- Mechanical Engineering Building (101)
Publications
2014 |
Gunelsu, Ozgur; Akalin, Ozgen The Effects of Piston Skirt Profiles on Secondary Motion and Friction Journal Article JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME, 136 (6), 2014, ISSN: 0742-4795. @article{ISI:000337939500013, title = {The Effects of Piston Skirt Profiles on Secondary Motion and Friction}, author = {Ozgur Gunelsu and Ozgen Akalin}, doi = {10.1115/1.4026486}, issn = {0742-4795}, year = {2014}, date = {2014-06-01}, journal = {JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME}, volume = {136}, number = {6}, abstract = {Piston skirt form deviating from a perfect cylinder is investigated numerically for an improved frictional performance. Three features defining the barrel and oval form of the skirt are compared in the search for lower friction power loss. Radius of curvature around the bulge of the barrel is changed to obtain a flatter or more-rounded lubricated area with respect to a hot-piston profile as well as the axial location of this bulge. On the other hand, the circumferential variation in the separation between the skirt and cylinder wall is represented by an elliptical piston and the aspect ratio is varied for comparison. These different skirt profiles are used in a developed piston secondary dynamics model solving for the lateral movement of the piston by calculating the hydrodynamic and boundary normal forces acting on the piston together with friction. Finally, an improved skirt profile is suggested to obtain better frictional efficiency.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Piston skirt form deviating from a perfect cylinder is investigated numerically for an improved frictional performance. Three features defining the barrel and oval form of the skirt are compared in the search for lower friction power loss. Radius of curvature around the bulge of the barrel is changed to obtain a flatter or more-rounded lubricated area with respect to a hot-piston profile as well as the axial location of this bulge. On the other hand, the circumferential variation in the separation between the skirt and cylinder wall is represented by an elliptical piston and the aspect ratio is varied for comparison. These different skirt profiles are used in a developed piston secondary dynamics model solving for the lateral movement of the piston by calculating the hydrodynamic and boundary normal forces acting on the piston together with friction. Finally, an improved skirt profile is suggested to obtain better frictional efficiency. |
Assoc. Prof. Dr. Sinan Kandemir
Educational Background
B.Sc. Balıkesir University, Turkey, Mechanical Engineering, 2006
M.Sc. University of Leicester, UK, Mechanical Engineering, 2009
Ph.D. University of Leicester, UK, Mechanical Engineering, 2013
Research Interests
- Light alloys
- Composite materials
- Metal matrix composites/nanomaterials
- Manufacturing processes (casting, semi-solid metal forming)
- Mechanical testing
- Materials Characterization
- Advanced electron microscopy
- Tribology
- +90 232 750 6787
- +90 232 750 6701
- Mechanical Engineering Building (Z16)
Publications
2023 |
Kandemir, Sinan; Bohlen, Jan; Dieringa, Hajo Influence of recycled carbon fiber addition on the microstructure and creep response of extruded AZ91 magnesium alloy Journal Article Journal of Magnesium and Alloys, 11 (7), pp. 2518 – 2529, 2023, (All Open Access, Gold Open Access). @article{Kandemir20232518, title = {Influence of recycled carbon fiber addition on the microstructure and creep response of extruded AZ91 magnesium alloy}, author = {Sinan Kandemir and Jan Bohlen and Hajo Dieringa}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85166356480&doi=10.1016%2fj.jma.2023.06.004&partnerID=40&md5=c08bdbb377339cd4ef3e7fcae68561d5}, doi = {10.1016/j.jma.2023.06.004}, year = {2023}, date = {2023-01-01}, journal = {Journal of Magnesium and Alloys}, volume = {11}, number = {7}, pages = {2518 – 2529}, abstract = {In this study, the recycled short carbon fiber (CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion. The objective was to investigate the impact of CF content (2.5 and 5.0 wt.%) and fiber length (100 and 500 µm) on the microstructure, mechanical properties, and creep behavior of AZ91 alloy matrix. The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy. In comparison to the unreinforced AZ91 alloy, the composites with 2.5 wt.% CF exhibited an increase in hardness by 16–20% and yield strength by 5–15%, depending on the fiber length, while experiencing a reduction in ductility. When the reinforcement content was increased from 2.5 to 5.0 wt.%, strength values exhibited fluctuations and decline, accompanied by decreased ductility. These divergent outcomes were discussed in relation to fiber length, clustering tendency due to higher reinforcement content, and the presence of interfacial products with micro-cracks at the CF-matrix interface. Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy, suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep. © 2023}, note = {All Open Access, Gold Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, the recycled short carbon fiber (CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion. The objective was to investigate the impact of CF content (2.5 and 5.0 wt.%) and fiber length (100 and 500 µm) on the microstructure, mechanical properties, and creep behavior of AZ91 alloy matrix. The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy. In comparison to the unreinforced AZ91 alloy, the composites with 2.5 wt.% CF exhibited an increase in hardness by 16–20% and yield strength by 5–15%, depending on the fiber length, while experiencing a reduction in ductility. When the reinforcement content was increased from 2.5 to 5.0 wt.%, strength values exhibited fluctuations and decline, accompanied by decreased ductility. These divergent outcomes were discussed in relation to fiber length, clustering tendency due to higher reinforcement content, and the presence of interfacial products with micro-cracks at the CF-matrix interface. Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy, suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep. © 2023 |
2021 |
Kangal, Serkan; Say, Harun A; Ayakda, Ozan; Kartav, Osman; Aydin, Levent; Artem, Secil H; Aktas, Engin; Yuceturk, Kutay; Tanoglu, Metin; Kandemir, Sinan; Beylergil, Bertan A Comprehensive Study on Burst Pressure Performance of Aluminum Liner for Hydrogen Storage Vessels Journal Article JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME, 143 (4), 2021. @article{WOS:000669955100012, title = {A Comprehensive Study on Burst Pressure Performance of Aluminum Liner for Hydrogen Storage Vessels}, author = {Serkan Kangal and Harun A Say and Ozan Ayakda and Osman Kartav and Levent Aydin and Secil H Artem and Engin Aktas and Kutay Yuceturk and Metin Tanoglu and Sinan Kandemir and Bertan Beylergil}, doi = {10.1115/1.4049644}, year = {2021}, date = {2021-08-01}, journal = {JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, volume = {143}, number = {4}, abstract = {This paper presents a comparative study on the burst pressure performance of aluminum (Al) liner for type-III composite overwrapped pressure vessels (COPVs). In the analysis, the vessels were loaded with increasing internal pressure up to the burst pressure level. In the analytical part of the study, the burst pressure of the cylindrical part was predicted based on the modified von Mises, Tresca, and average shear stress criterion (ASSC). In the numerical analysis, a finite element (FE) model was established in order to predict the behavior of the vessel as a function of increasing internal pressure and determine the final burst. The Al pressure vessels made of Al-6061-T6 alloy with a capacity of 5 L were designed. The manufacturing of the metallic vessels was purchased from a metal forming company. The experimental study was conducted by pressurizing the Al vessels until the burst failure occurred. The radial and axial strain behaviors were monitored at various locations on the vessels during loading. The results obtained through analytical, numerical, and experimental work were compared. The average experimental burst pressure of the vessels was found to be 279 bar. The experimental strain data were compared with the results of the FE analysis. The results indicated that the FE analysis and ASSC-based elastoplastic analytical approaches yielded the best predictions which are within 2.2% of the experimental burst failure values. It was also found that the elastic analysis underestimated the burst failure results; however, it was effective for determining the critical regions over the vessel structure. The strain behavior of the vessels obtained through experimental investigations was well correlated with those predicted through FE analysis.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper presents a comparative study on the burst pressure performance of aluminum (Al) liner for type-III composite overwrapped pressure vessels (COPVs). In the analysis, the vessels were loaded with increasing internal pressure up to the burst pressure level. In the analytical part of the study, the burst pressure of the cylindrical part was predicted based on the modified von Mises, Tresca, and average shear stress criterion (ASSC). In the numerical analysis, a finite element (FE) model was established in order to predict the behavior of the vessel as a function of increasing internal pressure and determine the final burst. The Al pressure vessels made of Al-6061-T6 alloy with a capacity of 5 L were designed. The manufacturing of the metallic vessels was purchased from a metal forming company. The experimental study was conducted by pressurizing the Al vessels until the burst failure occurred. The radial and axial strain behaviors were monitored at various locations on the vessels during loading. The results obtained through analytical, numerical, and experimental work were compared. The average experimental burst pressure of the vessels was found to be 279 bar. The experimental strain data were compared with the results of the FE analysis. The results indicated that the FE analysis and ASSC-based elastoplastic analytical approaches yielded the best predictions which are within 2.2% of the experimental burst failure values. It was also found that the elastic analysis underestimated the burst failure results; however, it was effective for determining the critical regions over the vessel structure. The strain behavior of the vessels obtained through experimental investigations was well correlated with those predicted through FE analysis. |
Kandemir, S; Gavras, S; Dieringa, H Journal of Magnesium and Alloys, 9 (5), pp. 1753-1767, 2021. @article{Kandemir20211753, title = {High temperature tensile, compression and creep behavior of recycled short carbon fibre reinforced AZ91 magnesium alloy fabricated by a high shearing dispersion technique}, author = {S Kandemir and S Gavras and H Dieringa}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85106274015&doi=10.1016%2fj.jma.2021.03.029&partnerID=40&md5=33482583e6489310dc991aed7c7b0793}, doi = {10.1016/j.jma.2021.03.029}, year = {2021}, date = {2021-01-01}, journal = {Journal of Magnesium and Alloys}, volume = {9}, number = {5}, pages = {1753-1767}, abstract = {The present study seeks the feasibility of using short carbon fibres recycled from polymer matrix composites as alternative to virgin carbon fibres in the reinforcement of magnesium alloys. The microstructures, high temperature mechanical and creep properties of AZ91 alloy and its composites with various recycled carbon fibre contents (2.5 and 5 wt.%) and lengths (100 and 500 μm) were investigated in the temperature range of 25–200 °C. The microstructural characterization showed that the high shear dispersion technique provided the cast composites with finer grains and relatively homogenous distribution of fibres. The materials tested displayed different behaviour depending on the type of loading. In general, while enhancements in the mechanical properties of composites is attributed to the load bearing and grain refinement effects of fibres, the fluctuations in the properties were discussed on the basis of porosity formation, relatively high reinforcement content leading to fibre clustering and interlayer found between the matrix and reinforcement compared to those of AZ91 alloy. The compressive creep tests revealed similar or higher minimum creep rates in the recycled carbon fibre reinforced AZ91 in comparison to the unreinforced AZ91. © 2021}, keywords = {}, pubstate = {published}, tppubtype = {article} } The present study seeks the feasibility of using short carbon fibres recycled from polymer matrix composites as alternative to virgin carbon fibres in the reinforcement of magnesium alloys. The microstructures, high temperature mechanical and creep properties of AZ91 alloy and its composites with various recycled carbon fibre contents (2.5 and 5 wt.%) and lengths (100 and 500 μm) were investigated in the temperature range of 25–200 °C. The microstructural characterization showed that the high shear dispersion technique provided the cast composites with finer grains and relatively homogenous distribution of fibres. The materials tested displayed different behaviour depending on the type of loading. In general, while enhancements in the mechanical properties of composites is attributed to the load bearing and grain refinement effects of fibres, the fluctuations in the properties were discussed on the basis of porosity formation, relatively high reinforcement content leading to fibre clustering and interlayer found between the matrix and reinforcement compared to those of AZ91 alloy. The compressive creep tests revealed similar or higher minimum creep rates in the recycled carbon fibre reinforced AZ91 in comparison to the unreinforced AZ91. © 2021 |
Martin, S; Kandemir, S; Antonov, M Investigation of the high temperature dry sliding wear behavior of graphene nanoplatelets reinforced aluminum matrix composites Journal Article Journal of Composite Materials, 55 (13), pp. 1769-1782, 2021. @article{Martin20211769, title = {Investigation of the high temperature dry sliding wear behavior of graphene nanoplatelets reinforced aluminum matrix composites}, author = {S Martin and S Kandemir and M Antonov}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85097279024&doi=10.1177%2f0021998320979037&partnerID=40&md5=554c5ed3fcc37de88e360d033402ed4b}, doi = {10.1177/0021998320979037}, year = {2021}, date = {2021-01-01}, journal = {Journal of Composite Materials}, volume = {55}, number = {13}, pages = {1769-1782}, abstract = {In this study, graphene nanoplatelets (GNPs) with a thickness of 50-100 nm have been utilized to improve the mechanical and tribological properties of A360 alloy due to their extraordinary mechanical properties and solid lubricant nature. For the investigation of tribological properties, ball-on disc tests were carried out at various temperatures including room temperature (RT), 150 °C, and 300 °C. According to the hardness and ball-on-disc test results, the nanocomposite samples reinforced with GNPs exhibited improved hardness and wear resistance. The improvement in the wear behavior of nanocomposites was referred to the temporarily formed solid lubricant film of harder GNPs during the wear, and hence coefficient of friction (COF) and volume loss were considerably reduced. Abrasive-adhesive, oxidative, and mild-to-severe were found to be main wear mechanisms at RT, 150 °C, and 300 °C, respectively. Overall, the results show that the nanocomposites fabricated by casting method combined with mechanical stirring and ultrasonication have promising wear performance, especially at elevated temperatures. This may suggest that these developed materials could be potential candidates to be used in the engineering applications requiring high temperature wear performance. © The Author(s) 2020.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, graphene nanoplatelets (GNPs) with a thickness of 50-100 nm have been utilized to improve the mechanical and tribological properties of A360 alloy due to their extraordinary mechanical properties and solid lubricant nature. For the investigation of tribological properties, ball-on disc tests were carried out at various temperatures including room temperature (RT), 150 °C, and 300 °C. According to the hardness and ball-on-disc test results, the nanocomposite samples reinforced with GNPs exhibited improved hardness and wear resistance. The improvement in the wear behavior of nanocomposites was referred to the temporarily formed solid lubricant film of harder GNPs during the wear, and hence coefficient of friction (COF) and volume loss were considerably reduced. Abrasive-adhesive, oxidative, and mild-to-severe were found to be main wear mechanisms at RT, 150 °C, and 300 °C, respectively. Overall, the results show that the nanocomposites fabricated by casting method combined with mechanical stirring and ultrasonication have promising wear performance, especially at elevated temperatures. This may suggest that these developed materials could be potential candidates to be used in the engineering applications requiring high temperature wear performance. © The Author(s) 2020. |
2018 |
Kandemir, S Development of Graphene Nanoplatelet-Reinforced AZ91 Magnesium Alloy by Solidification Processing Journal Article Journal of Materials Engineering and Performance, 27 (6), pp. 3014-3023, 2018. @article{Kandemir20183014, title = {Development of Graphene Nanoplatelet-Reinforced AZ91 Magnesium Alloy by Solidification Processing}, author = {S Kandemir}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85046038152&doi=10.1007%2fs11665-018-3391-x&partnerID=40&md5=1915050ebdd364d0e0e99a6144a89c16}, doi = {10.1007/s11665-018-3391-x}, year = {2018}, date = {2018-01-01}, journal = {Journal of Materials Engineering and Performance}, volume = {27}, number = {6}, pages = {3014-3023}, abstract = {It is a challenging task to effectively incorporate graphene nanoplatelets (GNPs) which have recently emerged as potential reinforcement for strengthening metals into magnesium-based matrices by conventional solidification processes due to their large surface areas and poor wettability. A solidification processing which combines mechanical stirring and ultrasonic dispersion of reinforcements in liquid matrix was employed to develop AZ91 magnesium alloy matrix composites reinforced with 0.25 and 0.5 wt.% GNPs. The microstructural studies conducted with scanning and transmission electron microscopes revealed that fairly uniform distribution and dispersion of GNPs through the matrix were achieved due to effective combination of mechanical and ultrasonic stirring. The GNPs embedded into the magnesium matrix led to significant enhancement in the hardness, tensile strength and ductility of the composites compared to those of unreinforced AZ91 alloy. The strength enhancement was predominantly attributed to the grain refinement by the GNP addition and dislocation generation strengthening due to the coefficient of thermal expansion mismatch between the matrix and reinforcement. The improved ductility was attributed to the refinement of β eutectics by transforming from lamellar to the divorced eutectics due to the GNP additions. In addition, the strengthening efficiency of the composite with 0.25 wt.% GNP was found to be higher than those of the composite with 0.5 wt.% GNP as the agglomeration tendency of GNPs is increased with increasing GNP content. These results were compared with those of the GNP-reinforced magnesium composites reported in the literature, indicating the potential of the process introduced in this study in terms of fabricating light and high-performance metal matrix composites. © 2018, ASM International.}, keywords = {}, pubstate = {published}, tppubtype = {article} } It is a challenging task to effectively incorporate graphene nanoplatelets (GNPs) which have recently emerged as potential reinforcement for strengthening metals into magnesium-based matrices by conventional solidification processes due to their large surface areas and poor wettability. A solidification processing which combines mechanical stirring and ultrasonic dispersion of reinforcements in liquid matrix was employed to develop AZ91 magnesium alloy matrix composites reinforced with 0.25 and 0.5 wt.% GNPs. The microstructural studies conducted with scanning and transmission electron microscopes revealed that fairly uniform distribution and dispersion of GNPs through the matrix were achieved due to effective combination of mechanical and ultrasonic stirring. The GNPs embedded into the magnesium matrix led to significant enhancement in the hardness, tensile strength and ductility of the composites compared to those of unreinforced AZ91 alloy. The strength enhancement was predominantly attributed to the grain refinement by the GNP addition and dislocation generation strengthening due to the coefficient of thermal expansion mismatch between the matrix and reinforcement. The improved ductility was attributed to the refinement of β eutectics by transforming from lamellar to the divorced eutectics due to the GNP additions. In addition, the strengthening efficiency of the composite with 0.25 wt.% GNP was found to be higher than those of the composite with 0.5 wt.% GNP as the agglomeration tendency of GNPs is increased with increasing GNP content. These results were compared with those of the GNP-reinforced magnesium composites reported in the literature, indicating the potential of the process introduced in this study in terms of fabricating light and high-performance metal matrix composites. © 2018, ASM International. |
Kandemir, S Development of Graphene Nanoplatelet-Reinforced AZ91 Magnesium Alloy by Solidification Processing Journal Article Journal of Materials Engineering and Performance, 27 (6), pp. 3014-3023, 2018. @article{Kandemir20183014b, title = {Development of Graphene Nanoplatelet-Reinforced AZ91 Magnesium Alloy by Solidification Processing}, author = {S Kandemir}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85046038152&doi=10.1007%2fs11665-018-3391-x&partnerID=40&md5=1915050ebdd364d0e0e99a6144a89c16}, doi = {10.1007/s11665-018-3391-x}, year = {2018}, date = {2018-01-01}, journal = {Journal of Materials Engineering and Performance}, volume = {27}, number = {6}, pages = {3014-3023}, abstract = {It is a challenging task to effectively incorporate graphene nanoplatelets (GNPs) which have recently emerged as potential reinforcement for strengthening metals into magnesium-based matrices by conventional solidification processes due to their large surface areas and poor wettability. A solidification processing which combines mechanical stirring and ultrasonic dispersion of reinforcements in liquid matrix was employed to develop AZ91 magnesium alloy matrix composites reinforced with 0.25 and 0.5 wt.% GNPs. The microstructural studies conducted with scanning and transmission electron microscopes revealed that fairly uniform distribution and dispersion of GNPs through the matrix were achieved due to effective combination of mechanical and ultrasonic stirring. The GNPs embedded into the magnesium matrix led to significant enhancement in the hardness, tensile strength and ductility of the composites compared to those of unreinforced AZ91 alloy. The strength enhancement was predominantly attributed to the grain refinement by the GNP addition and dislocation generation strengthening due to the coefficient of thermal expansion mismatch between the matrix and reinforcement. The improved ductility was attributed to the refinement of β eutectics by transforming from lamellar to the divorced eutectics due to the GNP additions. In addition, the strengthening efficiency of the composite with 0.25 wt.% GNP was found to be higher than those of the composite with 0.5 wt.% GNP as the agglomeration tendency of GNPs is increased with increasing GNP content. These results were compared with those of the GNP-reinforced magnesium composites reported in the literature, indicating the potential of the process introduced in this study in terms of fabricating light and high-performance metal matrix composites. © 2018, ASM International.}, keywords = {}, pubstate = {published}, tppubtype = {article} } It is a challenging task to effectively incorporate graphene nanoplatelets (GNPs) which have recently emerged as potential reinforcement for strengthening metals into magnesium-based matrices by conventional solidification processes due to their large surface areas and poor wettability. A solidification processing which combines mechanical stirring and ultrasonic dispersion of reinforcements in liquid matrix was employed to develop AZ91 magnesium alloy matrix composites reinforced with 0.25 and 0.5 wt.% GNPs. The microstructural studies conducted with scanning and transmission electron microscopes revealed that fairly uniform distribution and dispersion of GNPs through the matrix were achieved due to effective combination of mechanical and ultrasonic stirring. The GNPs embedded into the magnesium matrix led to significant enhancement in the hardness, tensile strength and ductility of the composites compared to those of unreinforced AZ91 alloy. The strength enhancement was predominantly attributed to the grain refinement by the GNP addition and dislocation generation strengthening due to the coefficient of thermal expansion mismatch between the matrix and reinforcement. The improved ductility was attributed to the refinement of β eutectics by transforming from lamellar to the divorced eutectics due to the GNP additions. In addition, the strengthening efficiency of the composite with 0.25 wt.% GNP was found to be higher than those of the composite with 0.5 wt.% GNP as the agglomeration tendency of GNPs is increased with increasing GNP content. These results were compared with those of the GNP-reinforced magnesium composites reported in the literature, indicating the potential of the process introduced in this study in terms of fabricating light and high-performance metal matrix composites. © 2018, ASM International. |
2017 |
Kandemir, Sinan Effects of TiB2 nanoparticle content on the microstructure and mechanical properties of aluminum matrix nanocomposites Journal Article MATERIALS TESTING, 59 (10), pp. 844-852, 2017, ISSN: 0025-5300. @article{ISI:000415695400003, title = {Effects of TiB2 nanoparticle content on the microstructure and mechanical properties of aluminum matrix nanocomposites}, author = {Sinan Kandemir}, doi = {10.3139/120.111079}, issn = {0025-5300}, year = {2017}, date = {2017-10-01}, journal = {MATERIALS TESTING}, volume = {59}, number = {10}, pages = {844-852}, abstract = {The present work reports the fabrication of A357 alloy matrix nanocomposites reinforced with 0.5, 1.0 and 2.0 wt.-% TiB2 nanoparticles (20-30 nm) by a novel method which is the combination of semi-solid mechanical mixing and ultrasonic dispersion of nanoparticles in liquid state. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicated that reasonably effective deagglomeration and uniform distribution of TiB2 nanoparticles into the matrix were achieved. Transmission electron microscopy studies also confirmed that the nanoparticles were embedded into the matrix and a good bonding was obtained between the matrix and the reinforcement. Increasing nanoparticle content led to grain refinement and significant enhancement in the mechanical properties of nanocomposites. The addition of 0.5, 1.0, and 2.0 wt.-% TiB2 nanoparticles increased the 0.2 % proof stress of matrix alloy by approximately 31, 48 and 61 %, respectively. The contribution of different mechanisms to the strength enhancement is discussed. It is proposed that the strengthening is mainly due to Orowan mechanism and dislocation generation effect by the coefficient of thermal expansion mismatch between the TiB2 nanoparticles and the matrix.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The present work reports the fabrication of A357 alloy matrix nanocomposites reinforced with 0.5, 1.0 and 2.0 wt.-% TiB2 nanoparticles (20-30 nm) by a novel method which is the combination of semi-solid mechanical mixing and ultrasonic dispersion of nanoparticles in liquid state. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicated that reasonably effective deagglomeration and uniform distribution of TiB2 nanoparticles into the matrix were achieved. Transmission electron microscopy studies also confirmed that the nanoparticles were embedded into the matrix and a good bonding was obtained between the matrix and the reinforcement. Increasing nanoparticle content led to grain refinement and significant enhancement in the mechanical properties of nanocomposites. The addition of 0.5, 1.0, and 2.0 wt.-% TiB2 nanoparticles increased the 0.2 % proof stress of matrix alloy by approximately 31, 48 and 61 %, respectively. The contribution of different mechanisms to the strength enhancement is discussed. It is proposed that the strengthening is mainly due to Orowan mechanism and dislocation generation effect by the coefficient of thermal expansion mismatch between the TiB2 nanoparticles and the matrix. |
Kandemir, Sinan JOURNAL OF COMPOSITE MATERIALS, 51 (3), pp. 395-404, 2017, ISSN: 0021-9983. @article{ISI:000394801300009, title = {Microstructure and mechanical properties of A357/SiC nanocomposites fabricated by ultrasonic cavitation-based dispersion of ball-milled nanoparticles}, author = {Sinan Kandemir}, doi = {10.1177/0021998316644850}, issn = {0021-9983}, year = {2017}, date = {2017-02-01}, journal = {JOURNAL OF COMPOSITE MATERIALS}, volume = {51}, number = {3}, pages = {395-404}, abstract = {In this work, A357/0.5wt.% SiC nanocomposites were fabricated with a combination of ultrasonic processing and a nanoparticle feeding mechanism that involves the introduction of a closed end aluminium tube filled with the ball-milled SiC nanoparticles (20-30nm) and aluminium powders (<75 mu m) into the melt for complete deagglomeration and uniform dispersion of nanoparticles through the matrix. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicate that relatively effective deagglomeration and uniform dispersion of SiC nanoparticles into the molten alloy were achieved. The hardness and tensile properties of the nanocomposites were notably improved compared to those of the ultrasonically processed A357 alloy without reinforcement, showing the strengthening potency of nanoparticles and the good bonding obtained at the particle-reinforcement interface.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this work, A357/0.5wt.% SiC nanocomposites were fabricated with a combination of ultrasonic processing and a nanoparticle feeding mechanism that involves the introduction of a closed end aluminium tube filled with the ball-milled SiC nanoparticles (20-30nm) and aluminium powders (<75 mu m) into the melt for complete deagglomeration and uniform dispersion of nanoparticles through the matrix. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicate that relatively effective deagglomeration and uniform dispersion of SiC nanoparticles into the molten alloy were achieved. The hardness and tensile properties of the nanocomposites were notably improved compared to those of the ultrasonically processed A357 alloy without reinforcement, showing the strengthening potency of nanoparticles and the good bonding obtained at the particle-reinforcement interface. |
Kandemir, S Journal of Composite Materials, 51 (3), pp. 395-404, 2017. @article{Kandemir2017395, title = {Microstructure and mechanical properties of A357/SiC nanocomposites fabricated by ultrasonic cavitation-based dispersion of ball-milled nanoparticles}, author = {S Kandemir}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85011573357&doi=10.1177%2f0021998316644850&partnerID=40&md5=1c26ba4dde5d58581fb0feb8fa56d880}, doi = {10.1177/0021998316644850}, year = {2017}, date = {2017-01-01}, journal = {Journal of Composite Materials}, volume = {51}, number = {3}, pages = {395-404}, abstract = {In this work, A357/0.5 wt.% SiC nanocomposites were fabricated with a combination of ultrasonic processing and a nanoparticle feeding mechanism that involves the introduction of a closed end aluminium tube filled with the ball-milled SiC nanoparticles (20-30 nm) and aluminium powders (<75 μm) into the melt for complete deagglomeration and uniform dispersion of nanoparticles through the matrix. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicate that relatively effective deagglomeration and uniform dispersion of SiC nanoparticles into the molten alloy were achieved. The hardness and tensile properties of the nanocomposites were notably improved compared to those of the ultrasonically processed A357 alloy without reinforcement, showing the strengthening potency of nanoparticles and the good bonding obtained at the particle-reinforcement interface. © The Author(s) 2016.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this work, A357/0.5 wt.% SiC nanocomposites were fabricated with a combination of ultrasonic processing and a nanoparticle feeding mechanism that involves the introduction of a closed end aluminium tube filled with the ball-milled SiC nanoparticles (20-30 nm) and aluminium powders (<75 μm) into the melt for complete deagglomeration and uniform dispersion of nanoparticles through the matrix. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicate that relatively effective deagglomeration and uniform dispersion of SiC nanoparticles into the molten alloy were achieved. The hardness and tensile properties of the nanocomposites were notably improved compared to those of the ultrasonically processed A357 alloy without reinforcement, showing the strengthening potency of nanoparticles and the good bonding obtained at the particle-reinforcement interface. © The Author(s) 2016. |
Kandemir, S Journal of Composite Materials, 51 (3), pp. 395-404, 2017. @article{Kandemir2017395b, title = {Microstructure and mechanical properties of A357/SiC nanocomposites fabricated by ultrasonic cavitation-based dispersion of ball-milled nanoparticles}, author = {S Kandemir}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85011573357&doi=10.1177%2f0021998316644850&partnerID=40&md5=1c26ba4dde5d58581fb0feb8fa56d880}, doi = {10.1177/0021998316644850}, year = {2017}, date = {2017-01-01}, journal = {Journal of Composite Materials}, volume = {51}, number = {3}, pages = {395-404}, abstract = {In this work, A357/0.5 wt.% SiC nanocomposites were fabricated with a combination of ultrasonic processing and a nanoparticle feeding mechanism that involves the introduction of a closed end aluminium tube filled with the ball-milled SiC nanoparticles (20-30 nm) and aluminium powders (<75 μm) into the melt for complete deagglomeration and uniform dispersion of nanoparticles through the matrix. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicate that relatively effective deagglomeration and uniform dispersion of SiC nanoparticles into the molten alloy were achieved. The hardness and tensile properties of the nanocomposites were notably improved compared to those of the ultrasonically processed A357 alloy without reinforcement, showing the strengthening potency of nanoparticles and the good bonding obtained at the particle-reinforcement interface. © The Author(s) 2016.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this work, A357/0.5 wt.% SiC nanocomposites were fabricated with a combination of ultrasonic processing and a nanoparticle feeding mechanism that involves the introduction of a closed end aluminium tube filled with the ball-milled SiC nanoparticles (20-30 nm) and aluminium powders (<75 μm) into the melt for complete deagglomeration and uniform dispersion of nanoparticles through the matrix. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicate that relatively effective deagglomeration and uniform dispersion of SiC nanoparticles into the molten alloy were achieved. The hardness and tensile properties of the nanocomposites were notably improved compared to those of the ultrasonically processed A357 alloy without reinforcement, showing the strengthening potency of nanoparticles and the good bonding obtained at the particle-reinforcement interface. © The Author(s) 2016. |
2014 |
Kandemir, Sinan; Atkinson, Helen V; Weston, David P; Hainsworth, Sarah V METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 45A (12), pp. 5782-5798, 2014, ISSN: 1073-5623. @article{ISI:000342443200049, title = {Thixoforming of A356/SiC and A356/TiB2 Nanocomposites Fabricated by a Combination of Green Compact Nanoparticle Incorporation and Ultrasonic Treatment of the Melted Compact}, author = {Sinan Kandemir and Helen V Atkinson and David P Weston and Sarah V Hainsworth}, doi = {10.1007/s11661-014-2501-0}, issn = {1073-5623}, year = {2014}, date = {2014-11-01}, journal = {METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE}, volume = {45A}, number = {12}, pages = {5782-5798}, abstract = {Thixoforming is a type of semi-solid processing which is based on forming metals in the semi-solid state rather than fully liquid or solid state. There have been no reports of the thixoforming of nanocomposites in the literature. The incorporation of ceramic nanoparticles into liquid metals is a challenging task for the fabrication of metal matrix nanocomposites due to their large surface-to-volume ratio and poor wettability. Previous research work by a number of workers has highlighted the challenges with the incorporation of nanoparticles into liquid aluminum alloy. In the present study, SiC and TiB2 nanoparticles with an average diameter between 20 and 30 nm were firstly incorporated into green compacts by a powder forming route, and then the compacts were melted and treated ultrasonically. The microstructural studies reveal that the engulfment and relatively effective distribution of the nanoparticles into the melt were achieved. The hardness was considerably improved with only 0.8 wt pct addition of the nanoparticles. The nanocomposites were successfully thixoformed at a solid fraction between 0.65 and 0.70. The microstructures, hardness, and tensile mechanical properties of the thixoformed nanocomposites were investigated and compared with those of the as-received A356 and thixoformed A356 alloys. The tensile properties of the thixoformed nanocomposites were significantly enhanced compared to thixoformed A356 alloy without reinforcement, indicating the strengthening effects of the nanoparticles.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Thixoforming is a type of semi-solid processing which is based on forming metals in the semi-solid state rather than fully liquid or solid state. There have been no reports of the thixoforming of nanocomposites in the literature. The incorporation of ceramic nanoparticles into liquid metals is a challenging task for the fabrication of metal matrix nanocomposites due to their large surface-to-volume ratio and poor wettability. Previous research work by a number of workers has highlighted the challenges with the incorporation of nanoparticles into liquid aluminum alloy. In the present study, SiC and TiB2 nanoparticles with an average diameter between 20 and 30 nm were firstly incorporated into green compacts by a powder forming route, and then the compacts were melted and treated ultrasonically. The microstructural studies reveal that the engulfment and relatively effective distribution of the nanoparticles into the melt were achieved. The hardness was considerably improved with only 0.8 wt pct addition of the nanoparticles. The nanocomposites were successfully thixoformed at a solid fraction between 0.65 and 0.70. The microstructures, hardness, and tensile mechanical properties of the thixoformed nanocomposites were investigated and compared with those of the as-received A356 and thixoformed A356 alloys. The tensile properties of the thixoformed nanocomposites were significantly enhanced compared to thixoformed A356 alloy without reinforcement, indicating the strengthening effects of the nanoparticles. |
Kandemir, S; Atkinson, H V; Weston, D P; Hainsworth, S V Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 45 (12), pp. 5782-5798, 2014. @article{Kandemir20145782, title = {Thixoforming of A356/SiC and A356/TiB2 Nanocomposites Fabricated by a Combination of Green Compact Nanoparticle Incorporation and Ultrasonic Treatment of the Melted Compact}, author = {S Kandemir and H V Atkinson and D P Weston and S V Hainsworth}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84920256211&doi=10.1007%2fs11661-014-2501-0&partnerID=40&md5=fc9071c132a6cd74edb6c9123fe89695}, doi = {10.1007/s11661-014-2501-0}, year = {2014}, date = {2014-01-01}, journal = {Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science}, volume = {45}, number = {12}, pages = {5782-5798}, abstract = {Thixoforming is a type of semi-solid processing which is based on forming metals in the semi-solid state rather than fully liquid or solid state. There have been no reports of the thixoforming of nanocomposites in the literature. The incorporation of ceramic nanoparticles into liquid metals is a challenging task for the fabrication of metal matrix nanocomposites due to their large surface-to-volume ratio and poor wettability. Previous research work by a number of workers has highlighted the challenges with the incorporation of nanoparticles into liquid aluminum alloy. In the present study, SiC and TiB2 nanoparticles with an average diameter between 20 and 30 nm were firstly incorporated into green compacts by a powder forming route, and then the compacts were melted and treated ultrasonically. The microstructural studies reveal that the engulfment and relatively effective distribution of the nanoparticles into the melt were achieved. The hardness was considerably improved with only 0.8 wt pct addition of the nanoparticles. The nanocomposites were successfully thixoformed at a solid fraction between 0.65 and 0.70. The microstructures, hardness, and tensile mechanical properties of the thixoformed nanocomposites were investigated and compared with those of the as-received A356 and thixoformed A356 alloys. The tensile properties of the thixoformed nanocomposites were significantly enhanced compared to thixoformed A356 alloy without reinforcement, indicating the strengthening effects of the nanoparticles. © 2014, The Minerals, Metals & Materials Society and ASM International.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Thixoforming is a type of semi-solid processing which is based on forming metals in the semi-solid state rather than fully liquid or solid state. There have been no reports of the thixoforming of nanocomposites in the literature. The incorporation of ceramic nanoparticles into liquid metals is a challenging task for the fabrication of metal matrix nanocomposites due to their large surface-to-volume ratio and poor wettability. Previous research work by a number of workers has highlighted the challenges with the incorporation of nanoparticles into liquid aluminum alloy. In the present study, SiC and TiB2 nanoparticles with an average diameter between 20 and 30 nm were firstly incorporated into green compacts by a powder forming route, and then the compacts were melted and treated ultrasonically. The microstructural studies reveal that the engulfment and relatively effective distribution of the nanoparticles into the melt were achieved. The hardness was considerably improved with only 0.8 wt pct addition of the nanoparticles. The nanocomposites were successfully thixoformed at a solid fraction between 0.65 and 0.70. The microstructures, hardness, and tensile mechanical properties of the thixoformed nanocomposites were investigated and compared with those of the as-received A356 and thixoformed A356 alloys. The tensile properties of the thixoformed nanocomposites were significantly enhanced compared to thixoformed A356 alloy without reinforcement, indicating the strengthening effects of the nanoparticles. © 2014, The Minerals, Metals & Materials Society and ASM International. |
Kandemir, S; Atkinson, H V; Weston, D P; Hainsworth, S V Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 45 (12), pp. 5782-5798, 2014. @article{Kandemir20145782b, title = {Thixoforming of A356/SiC and A356/TiB2 Nanocomposites Fabricated by a Combination of Green Compact Nanoparticle Incorporation and Ultrasonic Treatment of the Melted Compact}, author = {S Kandemir and H V Atkinson and D P Weston and S V Hainsworth}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84920256211&doi=10.1007%2fs11661-014-2501-0&partnerID=40&md5=fc9071c132a6cd74edb6c9123fe89695}, doi = {10.1007/s11661-014-2501-0}, year = {2014}, date = {2014-01-01}, journal = {Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science}, volume = {45}, number = {12}, pages = {5782-5798}, abstract = {Thixoforming is a type of semi-solid processing which is based on forming metals in the semi-solid state rather than fully liquid or solid state. There have been no reports of the thixoforming of nanocomposites in the literature. The incorporation of ceramic nanoparticles into liquid metals is a challenging task for the fabrication of metal matrix nanocomposites due to their large surface-to-volume ratio and poor wettability. Previous research work by a number of workers has highlighted the challenges with the incorporation of nanoparticles into liquid aluminum alloy. In the present study, SiC and TiB2 nanoparticles with an average diameter between 20 and 30 nm were firstly incorporated into green compacts by a powder forming route, and then the compacts were melted and treated ultrasonically. The microstructural studies reveal that the engulfment and relatively effective distribution of the nanoparticles into the melt were achieved. The hardness was considerably improved with only 0.8 wt pct addition of the nanoparticles. The nanocomposites were successfully thixoformed at a solid fraction between 0.65 and 0.70. The microstructures, hardness, and tensile mechanical properties of the thixoformed nanocomposites were investigated and compared with those of the as-received A356 and thixoformed A356 alloys. The tensile properties of the thixoformed nanocomposites were significantly enhanced compared to thixoformed A356 alloy without reinforcement, indicating the strengthening effects of the nanoparticles. © 2014, The Minerals, Metals & Materials Society and ASM International.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Thixoforming is a type of semi-solid processing which is based on forming metals in the semi-solid state rather than fully liquid or solid state. There have been no reports of the thixoforming of nanocomposites in the literature. The incorporation of ceramic nanoparticles into liquid metals is a challenging task for the fabrication of metal matrix nanocomposites due to their large surface-to-volume ratio and poor wettability. Previous research work by a number of workers has highlighted the challenges with the incorporation of nanoparticles into liquid aluminum alloy. In the present study, SiC and TiB2 nanoparticles with an average diameter between 20 and 30 nm were firstly incorporated into green compacts by a powder forming route, and then the compacts were melted and treated ultrasonically. The microstructural studies reveal that the engulfment and relatively effective distribution of the nanoparticles into the melt were achieved. The hardness was considerably improved with only 0.8 wt pct addition of the nanoparticles. The nanocomposites were successfully thixoformed at a solid fraction between 0.65 and 0.70. The microstructures, hardness, and tensile mechanical properties of the thixoformed nanocomposites were investigated and compared with those of the as-received A356 and thixoformed A356 alloys. The tensile properties of the thixoformed nanocomposites were significantly enhanced compared to thixoformed A356 alloy without reinforcement, indicating the strengthening effects of the nanoparticles. © 2014, The Minerals, Metals & Materials Society and ASM International. |
Lecturer Dr. Büşra Karaş
Erasmus Co-Coordinator
Educational Background
B.Sc. Eskisehir Osmangazi University, Turkey, Industrial Engineering, 2015
M.Sc. Newcastle University, United Kingdom, Design and Manufacturing Engineering, 2017
Ph.D. The University of Sheffield, United Kingdom, Mechanical Engineering, 2022
Research Interests
- Additive Manufacturing for Metals and Composites
- Manufacturing Processes
- Optimization of Production Systems
- Sustainability
- Cost Modelling
- +90 232 750 6783
- +90 232 750 6701
- Mechanical Engineering Building (Z15)
Publications
Prof. Dr. Gökhan Kiper
Minor Program Coordinator
Educational Background
B.Sc. Middle East Technical University, Turkey, Mechanical Engineering / Mathematics, 2004
M.Sc. Middle East Technical University, Turkey, Mechanical Engineering, 2006
Ph.D. Middle East Technical University, Turkey, Mechanical Engineering, 2011
Research Interests
- Mechanisms
- Deployable Structures
- Kinematics of Robotics
- Dynamics of Machinery
- +90 232 750 6777
- +90 232 750 6701
- Mechanical Engineering Building (Z14)
Publications
2024 |
Liao, Yuan; Kiper, Gokhan; Krishnan, Sudarshan Mobility analysis of tripod scissor structures using screw theory Journal Article MECHANISM AND MACHINE THEORY, 191 , 2024. @article{WOS:001081762000001, title = {Mobility analysis of tripod scissor structures using screw theory}, author = {Yuan Liao and Gokhan Kiper and Sudarshan Krishnan}, doi = {10.1016/j.mechmachtheory.2023.105468}, year = {2024}, date = {2024-01-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {191}, abstract = {Mechanisms consisting of spatial scissor units have different kinematic behaviors than those of planar scissors. However, their kinematics, especially the mobility analysis, has not received enough attention. Two types of deployable asseblies are analyzed in this paper, namely the translational and mirrored assemblies. Both the assemblies are made of tripod scissor units, and their instantaneous mobility are examined using screw theory. The study starts on the configuration where all the members have the identical deployment angle. Firstly, the geometric property of each assembly was studied. Then, screw-loop equations were developed based on graph theory and closure equations. Finally, the mobility of each assembly was computed using linear algebra. Following the analysis, physical prototypes were constructed to validate the results, and several different motion modes were obtained for the translational assembly. The analysis reveals different kinematic behaviors of the two assemblies. In the given configuration, the translational assemblies have four instantaneous degrees of freedom, while the mirrored assemblies have only a single instantaneous degree of freedom.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Mechanisms consisting of spatial scissor units have different kinematic behaviors than those of planar scissors. However, their kinematics, especially the mobility analysis, has not received enough attention. Two types of deployable asseblies are analyzed in this paper, namely the translational and mirrored assemblies. Both the assemblies are made of tripod scissor units, and their instantaneous mobility are examined using screw theory. The study starts on the configuration where all the members have the identical deployment angle. Firstly, the geometric property of each assembly was studied. Then, screw-loop equations were developed based on graph theory and closure equations. Finally, the mobility of each assembly was computed using linear algebra. Following the analysis, physical prototypes were constructed to validate the results, and several different motion modes were obtained for the translational assembly. The analysis reveals different kinematic behaviors of the two assemblies. In the given configuration, the translational assemblies have four instantaneous degrees of freedom, while the mirrored assemblies have only a single instantaneous degree of freedom. |
2023 |
Gorgulu, Ibrahimcan; Dede, Mehmet Ismet Can; Kiper, Gokhan Stiffness modeling of a 2-DoF over-constrained planar parallel mechanism Journal Article MECHANISM AND MACHINE THEORY, 185 , 2023. @article{WOS:000966404700001, title = {Stiffness modeling of a 2-DoF over-constrained planar parallel mechanism}, author = {Ibrahimcan Gorgulu and Mehmet Ismet Can Dede and Gokhan Kiper}, doi = {10.1016/j.mechmachtheory.2023.105343}, year = {2023}, date = {2023-07-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {185}, abstract = {Stiffness model acquisition of over-constrained parallel mechanisms is relatively difficult since they have more than necessary kinematic loops. In this study, a stiffness modeling solution for over-constrained parallel mechanisms is proposed while considering the computational cost efficiency. Three contributions of the paper are: (1) Presenting the stiffness modeling procedure for serially connected closed-loop structures by using the Virtual Joint Method (2) Considering the effect of dynamic auxiliary forces and dynamic external forces on the mobile platform's deflection and achieving a direct solution by using superposition principle (3) A model fitting procedure for modifying the stiffness coefficients to comply with the experimental data. A 2 degrees-of-freedom over-constrained parallel mechanism is investigated as a case study. However, the proposed stiffness model is 6-DoF since compliant deflections occur in any direction. A finite element analysis and an experimental study verify the model's results.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Stiffness model acquisition of over-constrained parallel mechanisms is relatively difficult since they have more than necessary kinematic loops. In this study, a stiffness modeling solution for over-constrained parallel mechanisms is proposed while considering the computational cost efficiency. Three contributions of the paper are: (1) Presenting the stiffness modeling procedure for serially connected closed-loop structures by using the Virtual Joint Method (2) Considering the effect of dynamic auxiliary forces and dynamic external forces on the mobile platform's deflection and achieving a direct solution by using superposition principle (3) A model fitting procedure for modifying the stiffness coefficients to comply with the experimental data. A 2 degrees-of-freedom over-constrained parallel mechanism is investigated as a case study. However, the proposed stiffness model is 6-DoF since compliant deflections occur in any direction. A finite element analysis and an experimental study verify the model's results. |
Aldanmaz, Ataol Behram; Ayit, Orhan; Kiper, Gökhan; Dede, Mehmet İsmet Can Gravity compensation of a 2R1T mechanism with remote center of motion for minimally invasive transnasal surgery applications Journal Article Robotica, 41 (3), pp. 807 – 820, 2023, (All Open Access, Green Open Access). @article{Aldanmaz2023807, title = {Gravity compensation of a 2R1T mechanism with remote center of motion for minimally invasive transnasal surgery applications}, author = {Ataol Behram Aldanmaz and Orhan Ayit and Gökhan Kiper and Mehmet İsmet Can Dede}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85148022623&doi=10.1017%2fS0263574722000534&partnerID=40&md5=d9e00d3ba2c7864df127963817903586}, doi = {10.1017/S0263574722000534}, year = {2023}, date = {2023-01-01}, journal = {Robotica}, volume = {41}, number = {3}, pages = {807 – 820}, abstract = {This work addresses the gravity balancing of a 2R1T (2 rotations - 1 translation) mechanism with remote center of motion. A previously developed balancing solution is modified and applied to a prototype, and test results are presented. The mechanism is an endoscope holder for minimally invasive transnasal pituitary gland surgery. In this surgery, the endoscope is inserted through a nostril of the patient through a natural path to the pituitary gland. During the surgery, it is vital for the manipulator to be statically balanced so that in case of a motor failure, the patient is protected against any harmful motion of the endoscope. Additionally, static balancing takes the gravitational load from the actuators and hence facilitates the control of the mechanism. The mechanism is a 2URRR-URR type parallel manipulator with three legs. The payload mass is distributed to the legs on the sides. By using counter-masses for two links of each leg, the center of mass of each leg is lumped on the proximal link which simplifies the problem of balancing of a two degree-of-freedom inverted pendulum. The two proximal links with the lumped mass are statically balanced via springs. Dynamic simulations indicate that when the mechanism is statically balanced, generated actuator torques are reduced by 93.5%. Finally, the balancing solution is implemented on the prototype of the manipulator. The tests indicate that the manipulator is statically balanced within its task space when the actuators are disconnected. When the actuators are connected, the torque requirements decrease by about 37.8% with balancing. © The Author(s), 2022. Published by Cambridge University Press.}, note = {All Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } This work addresses the gravity balancing of a 2R1T (2 rotations - 1 translation) mechanism with remote center of motion. A previously developed balancing solution is modified and applied to a prototype, and test results are presented. The mechanism is an endoscope holder for minimally invasive transnasal pituitary gland surgery. In this surgery, the endoscope is inserted through a nostril of the patient through a natural path to the pituitary gland. During the surgery, it is vital for the manipulator to be statically balanced so that in case of a motor failure, the patient is protected against any harmful motion of the endoscope. Additionally, static balancing takes the gravitational load from the actuators and hence facilitates the control of the mechanism. The mechanism is a 2URRR-URR type parallel manipulator with three legs. The payload mass is distributed to the legs on the sides. By using counter-masses for two links of each leg, the center of mass of each leg is lumped on the proximal link which simplifies the problem of balancing of a two degree-of-freedom inverted pendulum. The two proximal links with the lumped mass are statically balanced via springs. Dynamic simulations indicate that when the mechanism is statically balanced, generated actuator torques are reduced by 93.5%. Finally, the balancing solution is implemented on the prototype of the manipulator. The tests indicate that the manipulator is statically balanced within its task space when the actuators are disconnected. When the actuators are connected, the torque requirements decrease by about 37.8% with balancing. © The Author(s), 2022. Published by Cambridge University Press. |
Demirel, Murat; Kiper, Gökhan; Carbone, Giuseppe; Ceccarelli, Marco Design of a novel hybrid cable-constrained parallel leg mechanism for biped walking machines Journal Article Robotica, 41 (6), pp. 1778 – 1793, 2023, (All Open Access, Green Open Access). @article{Demirel20231778, title = {Design of a novel hybrid cable-constrained parallel leg mechanism for biped walking machines}, author = {Murat Demirel and Gökhan Kiper and Giuseppe Carbone and Marco Ceccarelli}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85182028851&doi=10.1017%2fS0263574723000140&partnerID=40&md5=60745b93d1c9dbaf0d172fdcc365338f}, doi = {10.1017/S0263574723000140}, year = {2023}, date = {2023-01-01}, journal = {Robotica}, volume = {41}, number = {6}, pages = {1778 – 1793}, abstract = {In this paper, a novel cable-constrained parallel mechanism is presented as a lightweight, low-cost leg mechanism design for walking machines to be used on flat surfaces. The proposed leg mechanism has three translational degrees of freedom. It is based on two specific hybrid kinematic topologies being herewith proposed. The paper reports the kinematic analysis formulation and a position performance evaluation to confirm the main characteristics of the proposed solutions. A 3D CAD model and simulations are carried out to demonstrate the feasibility of the proposed design for performing a human-like gait trajectory. A prototype has been built, and preliminarily tests have been conducted to confirm the motion capabilities of the proposed mechanism design. Then a second, enhanced prototype has been designed and built. An experimental validation is carried out for tracking a planar walking trajectory with the built prototypes by using a real-time PCI controller. Results are presented to validate the operation characteristics of the proposed mechanism and to prove its feasibility for legged walking machines. © The Author(s), 2023.}, note = {All Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, a novel cable-constrained parallel mechanism is presented as a lightweight, low-cost leg mechanism design for walking machines to be used on flat surfaces. The proposed leg mechanism has three translational degrees of freedom. It is based on two specific hybrid kinematic topologies being herewith proposed. The paper reports the kinematic analysis formulation and a position performance evaluation to confirm the main characteristics of the proposed solutions. A 3D CAD model and simulations are carried out to demonstrate the feasibility of the proposed design for performing a human-like gait trajectory. A prototype has been built, and preliminarily tests have been conducted to confirm the motion capabilities of the proposed mechanism design. Then a second, enhanced prototype has been designed and built. An experimental validation is carried out for tracking a planar walking trajectory with the built prototypes by using a real-time PCI controller. Results are presented to validate the operation characteristics of the proposed mechanism and to prove its feasibility for legged walking machines. © The Author(s), 2023. |
2022 |
Kiper, Gokhan; Korkmaz, Koray; Gur, Sebnem; Uncu, Mujde Yar; Maden, Feray; Akgun, Yenal; Karagoz, Cevahir Loop based classification of planar scissor linkages Journal Article SADHANA-ACADEMY PROCEEDINGS IN ENGINEERING SCIENCES, 47 (1), 2022. @article{WOS:000736787800002, title = {Loop based classification of planar scissor linkages}, author = {Gokhan Kiper and Koray Korkmaz and Sebnem Gur and Mujde Yar Uncu and Feray Maden and Yenal Akgun and Cevahir Karagoz}, doi = {10.1007/s12046-021-01783-1}, year = {2022}, date = {2022-03-01}, journal = {SADHANA-ACADEMY PROCEEDINGS IN ENGINEERING SCIENCES}, volume = {47}, number = {1}, abstract = {Scissor linkages have been used for several applications since ancient Greeks and Romans. In addition to simple scissor linkages with straight rods, linkages with angulated elements have been introduced in the last decades. In the related literature, two methods have been used to design scissor linkages, one of which is based on scissor elements, and the other is based on assembling loops. This study presents a systematic classification of scissor linkages as assemblies of rhombus, kite, dart, parallelogram and anti-parallelogram loops using frieze patterns and long-short diagonal connections. After the loops are replicated along a curve as a pattern, the linkages are obtained by selection of proper common link sections for adjacent loops. The resulting linkages are analyzed for their motions and they are classified as realizing scaling deployable, angular deployable or transformable motion. Some of the linkages obtained are novel. Totally 10 scalable deployable, 1 angular deployable and 8 transformable scissor linkages are listed. Designers in architecture and engineering can use this list of linkages as a library of scissor linkage topologies.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Scissor linkages have been used for several applications since ancient Greeks and Romans. In addition to simple scissor linkages with straight rods, linkages with angulated elements have been introduced in the last decades. In the related literature, two methods have been used to design scissor linkages, one of which is based on scissor elements, and the other is based on assembling loops. This study presents a systematic classification of scissor linkages as assemblies of rhombus, kite, dart, parallelogram and anti-parallelogram loops using frieze patterns and long-short diagonal connections. After the loops are replicated along a curve as a pattern, the linkages are obtained by selection of proper common link sections for adjacent loops. The resulting linkages are analyzed for their motions and they are classified as realizing scaling deployable, angular deployable or transformable motion. Some of the linkages obtained are novel. Totally 10 scalable deployable, 1 angular deployable and 8 transformable scissor linkages are listed. Designers in architecture and engineering can use this list of linkages as a library of scissor linkage topologies. |
Maral, M O; Korkmaz, K; Kiper, G A NOVEL DESIGN METHOD OF DEPLOYABLE SEMI-REGULAR TESSELLATED SURFACES WITH PLANO-SPHERICAL UNITS Journal Article Journal of the International Association for Shell and Spatial Structures, 63 (3), pp. 189-202, 2022. @article{Maral2022189, title = {A NOVEL DESIGN METHOD OF DEPLOYABLE SEMI-REGULAR TESSELLATED SURFACES WITH PLANO-SPHERICAL UNITS}, author = {M O Maral and K Korkmaz and G Kiper}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85141332813&doi=10.20898%2fj.iass.2022.005&partnerID=40&md5=00e88391f1aab60b0932e2d29bdd5db2}, doi = {10.20898/j.iass.2022.005}, year = {2022}, date = {2022-01-01}, journal = {Journal of the International Association for Shell and Spatial Structures}, volume = {63}, number = {3}, pages = {189-202}, abstract = {The design of movable systems gives an opportunity to create transformable designs which respond to the environmental, functional, cultural, and aesthetical needs of today's architecture. This paper proposes a method for designing a family of deployable structures which can be applied to semi-regular tessellated planar surfaces such as roofs, walls, and shading devices. The generated modular approach and adaptability provides a wide usage area and various combinations for these designs. The regular convex polygon modules are designed as a network of the triangular units. The triangular unit is designed using Bennett's overconstrained plano-spherical linkage topology. The polygonal modules are assembled to each other in one-uniform semi-regular tessellations. The assembly of adjacent regular convex polygons in each tessellation is examined to find a proper solution for no collision during deployment and to properly fit a surface without any gaps or overlaps in the deployed position. The assembly method for creating 1-DoF deployable surfaces and mobility calculations for a unit, the polygonal modules, and the assemblies are computed, and motion studies are demonstrated with CAD models and exemplified for a square module for motion tests in a prototype. © 2022 by Mesude Oraj Maral, Koray Korkmaz and Gökhan Kiper.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The design of movable systems gives an opportunity to create transformable designs which respond to the environmental, functional, cultural, and aesthetical needs of today's architecture. This paper proposes a method for designing a family of deployable structures which can be applied to semi-regular tessellated planar surfaces such as roofs, walls, and shading devices. The generated modular approach and adaptability provides a wide usage area and various combinations for these designs. The regular convex polygon modules are designed as a network of the triangular units. The triangular unit is designed using Bennett's overconstrained plano-spherical linkage topology. The polygonal modules are assembled to each other in one-uniform semi-regular tessellations. The assembly of adjacent regular convex polygons in each tessellation is examined to find a proper solution for no collision during deployment and to properly fit a surface without any gaps or overlaps in the deployed position. The assembly method for creating 1-DoF deployable surfaces and mobility calculations for a unit, the polygonal modules, and the assemblies are computed, and motion studies are demonstrated with CAD models and exemplified for a square module for motion tests in a prototype. © 2022 by Mesude Oraj Maral, Koray Korkmaz and Gökhan Kiper. |
Özen, G; Kiper, G; Korkmaz, K DESIGN OF DEMOUNTABLE RECIPROCAL FRAMES WITH NEW GEOMETRIC PROPERTIES Journal Article Journal of the International Association for Shell and Spatial Structures, 63 (3), pp. 203-212, 2022. @article{Özen2022203, title = {DESIGN OF DEMOUNTABLE RECIPROCAL FRAMES WITH NEW GEOMETRIC PROPERTIES}, author = {G Özen and G Kiper and K Korkmaz}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85141307917&doi=10.20898%2fj.iass.2022.013&partnerID=40&md5=a0f27a35c8299c76151cffcb848aa678}, doi = {10.20898/j.iass.2022.013}, year = {2022}, date = {2022-01-01}, journal = {Journal of the International Association for Shell and Spatial Structures}, volume = {63}, number = {3}, pages = {203-212}, abstract = {This study aims to develop missing geometric knowledge for demountable reciprocal frames (RF). While designing a demountable RF, one should know the initial, in-process and final form of the RF. These processes require some specific geometric knowledge. There are some deficiencies about geometric properties in the previous studies about demountable RFs. In this study, the positions and the orientations of the nexors are found by using the Denavit-Hartenberg parameters. This information gives where the joints are placed, how they are oriented and take position according to one another. Besides, the influence of engagement length on the fan height and the base edge are analyzed. Thereby one will be able to find out how much space the RF covers with the known base edge. With the geometric knowledge obtained from this study, demountable RFs having different engagement lengths can be produced with the same nexors. Copyright © 2022 by Gülçin Özen, Gökhan Kiper and Koray Korkmaz.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study aims to develop missing geometric knowledge for demountable reciprocal frames (RF). While designing a demountable RF, one should know the initial, in-process and final form of the RF. These processes require some specific geometric knowledge. There are some deficiencies about geometric properties in the previous studies about demountable RFs. In this study, the positions and the orientations of the nexors are found by using the Denavit-Hartenberg parameters. This information gives where the joints are placed, how they are oriented and take position according to one another. Besides, the influence of engagement length on the fan height and the base edge are analyzed. Thereby one will be able to find out how much space the RF covers with the known base edge. With the geometric knowledge obtained from this study, demountable RFs having different engagement lengths can be produced with the same nexors. Copyright © 2022 by Gülçin Özen, Gökhan Kiper and Koray Korkmaz. |
Boztaş, S; Kiper, G Enumeration and instantaneous mobility analysis of a class of 3-UPU parallel manipulators with equilateral triangular platforms Journal Article Robotica, 40 (5), pp. 1538-1569, 2022. @article{Boztaş20221538, title = {Enumeration and instantaneous mobility analysis of a class of 3-UPU parallel manipulators with equilateral triangular platforms}, author = {S Boztaş and G Kiper}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85117189706&doi=10.1017%2fS0263574721001259&partnerID=40&md5=1f5d59f04a34765e2bd8e7c9809d9606}, doi = {10.1017/S0263574721001259}, year = {2022}, date = {2022-01-01}, journal = {Robotica}, volume = {40}, number = {5}, pages = {1538-1569}, abstract = {In this study, several joint axis orientations on equilateral platforms and the limbs of 3-UPU parallel manipulators (PMs) are examined. The generated joint layouts for the platforms were matched with each other to generate and enumerate manipulator architectures based on certain assumptions. The structures of thus obtained manipulators are examined and limb types were determined. These limb types were analyzed using screw theory. The instantaneous mobility of the manipulators and the motion characteristics of the moving platforms are tabulated. The finite mobility analysis of one of the manipulators is performed using a software package as an example. Among several different 3-UPU PM architectures, 118 novel 3-UPU PMs with non-parasitic 3-degrees-of-freedom are significantly important. The classified 3-UPU PMs with determined motion characteristics can be used by researchers as a design alternative for their specific design task. ©}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, several joint axis orientations on equilateral platforms and the limbs of 3-UPU parallel manipulators (PMs) are examined. The generated joint layouts for the platforms were matched with each other to generate and enumerate manipulator architectures based on certain assumptions. The structures of thus obtained manipulators are examined and limb types were determined. These limb types were analyzed using screw theory. The instantaneous mobility of the manipulators and the motion characteristics of the moving platforms are tabulated. The finite mobility analysis of one of the manipulators is performed using a software package as an example. Among several different 3-UPU PM architectures, 118 novel 3-UPU PMs with non-parasitic 3-degrees-of-freedom are significantly important. The classified 3-UPU PMs with determined motion characteristics can be used by researchers as a design alternative for their specific design task. © |
2021 |
Kumtepe, Elvan Doğan; Kiper, Gökhan Design, prototyping and tests of a rollable ramp for temporary use Journal Article Sadhana - Academy Proceedings in Engineering Sciences, 46 (4), 2021. @article{DoğanKumtepe2021, title = {Design, prototyping and tests of a rollable ramp for temporary use}, author = {Elvan Doğan Kumtepe and Gökhan Kiper}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85118582555&doi=10.1007%2fs12046-021-01756-4&partnerID=40&md5=17fef753eb6120e9431bab50f4ce0492}, doi = {10.1007/s12046-021-01756-4}, year = {2021}, date = {2021-01-01}, journal = {Sadhana - Academy Proceedings in Engineering Sciences}, volume = {46}, number = {4}, abstract = {Portable ramps, used generally by wheelchair users, offer temporary solution to increase accessibility and mobility. Preferably these ramps should be compact and lightweight for ease of handling and storage. Different types of portable ramps in the market that are used by wheelchair users are generally made of aluminum and require several improvements, especially in terms of lightweight and compactness. Based on wheelchair users’ inclinations a compact and lightweight rollable ramp is designed in this study. A parametric model of the links of the ramp are derived and the rolled geometry is optimized using convex hull and smallest enclosing circle algorithms. The side bars of the links are designed and manufactured from aluminum and the load-bearing panels are manufactured from sandwich composite structures with honeycomb core. Strength calculations are performed analytically and also with finite-element analysis. After the design is finalized, a prototype is manufactured. The designed ramp is 15.4% more compact and has 18.9% less weight compared to the best rival product available in the market. Load tests and functional tests are performed with voluntary wheelchair users. Several positive feedbacks are received from the participants about the ramp being practical, easy to use and store, lightweight, advantage of the anti-slip surface. © 2021, Indian Academy of Sciences.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Portable ramps, used generally by wheelchair users, offer temporary solution to increase accessibility and mobility. Preferably these ramps should be compact and lightweight for ease of handling and storage. Different types of portable ramps in the market that are used by wheelchair users are generally made of aluminum and require several improvements, especially in terms of lightweight and compactness. Based on wheelchair users’ inclinations a compact and lightweight rollable ramp is designed in this study. A parametric model of the links of the ramp are derived and the rolled geometry is optimized using convex hull and smallest enclosing circle algorithms. The side bars of the links are designed and manufactured from aluminum and the load-bearing panels are manufactured from sandwich composite structures with honeycomb core. Strength calculations are performed analytically and also with finite-element analysis. After the design is finalized, a prototype is manufactured. The designed ramp is 15.4% more compact and has 18.9% less weight compared to the best rival product available in the market. Load tests and functional tests are performed with voluntary wheelchair users. Several positive feedbacks are received from the participants about the ramp being practical, easy to use and store, lightweight, advantage of the anti-slip surface. © 2021, Indian Academy of Sciences. |
Dede, M I C; Kiper, G; Ayav, T; Ozdemirel, B; Tatlıcıoglu, E; Hanalioglu, S; Işıkay, I; Berker, M Human–robot interfaces of the neuroboscope: A minimally invasive endoscopic pituitary tumor surgery robotic assistance system Journal Article Journal of Medical Devices, Transactions of the ASME, 15 (1), 2021. @article{Dede2021, title = {Human–robot interfaces of the neuroboscope: A minimally invasive endoscopic pituitary tumor surgery robotic assistance system}, author = {M I C Dede and G Kiper and T Ayav and B Ozdemirel and E Tatlıcıoglu and S Hanalioglu and I Işıkay and M Berker}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85107958529&doi=10.1115%2f1.4049394&partnerID=40&md5=975e1687eb1d91a0fe45def8948da24f}, doi = {10.1115/1.4049394}, year = {2021}, date = {2021-01-01}, journal = {Journal of Medical Devices, Transactions of the ASME}, volume = {15}, number = {1}, abstract = {Endoscopic endonasal surgery is a commonly practiced minimally invasive neurosurgical operation for the treatment of a wide range of skull base pathologies including pituitary tumors. A common shortcoming of this surgery is the necessity of a third hand when the endoscope has to be handled to allow active use of both hands of the main surgeon. The robot surgery assistant NeuRoboScope system has been developed to take over the endoscope from the main surgeon’s hand while providing the surgeon with the necessary means of controlling the location and direction of the endoscope. One of the main novelties of the NeuRoboScope system is its human–robot interface designs which regulate and facilitate the interaction between the surgeon and the robot assistant. The human–robot interaction design of the NeuRoboScope system is investigated in two domains: direct physical interaction (DPI) and master–slave teleoperation (MST). The user study indicating the learning curve and ease of use of the MST is given and this paper is concluded via providing the reader with an outlook of possible new human–robot interfaces for the robot assisted surgery systems. Copyright VC 2021 by ASME}, keywords = {}, pubstate = {published}, tppubtype = {article} } Endoscopic endonasal surgery is a commonly practiced minimally invasive neurosurgical operation for the treatment of a wide range of skull base pathologies including pituitary tumors. A common shortcoming of this surgery is the necessity of a third hand when the endoscope has to be handled to allow active use of both hands of the main surgeon. The robot surgery assistant NeuRoboScope system has been developed to take over the endoscope from the main surgeon’s hand while providing the surgeon with the necessary means of controlling the location and direction of the endoscope. One of the main novelties of the NeuRoboScope system is its human–robot interface designs which regulate and facilitate the interaction between the surgeon and the robot assistant. The human–robot interaction design of the NeuRoboScope system is investigated in two domains: direct physical interaction (DPI) and master–slave teleoperation (MST). The user study indicating the learning curve and ease of use of the MST is given and this paper is concluded via providing the reader with an outlook of possible new human–robot interfaces for the robot assisted surgery systems. Copyright VC 2021 by ASME |
2020 |
Yasir, Abdullah; Kiper, Gokhan; Dede, Can M I Kinematic design of a non-parasitic 2R1T parallel mechanism with remote center of motion to be used in minimally invasive surgery applications Journal Article MECHANISM AND MACHINE THEORY, 153 , 2020, ISSN: 0094-114X. @article{ISI:000566908100008, title = {Kinematic design of a non-parasitic 2R1T parallel mechanism with remote center of motion to be used in minimally invasive surgery applications}, author = {Abdullah Yasir and Gokhan Kiper and Can M I Dede}, doi = {10.1016/j.mechmachtheory.2020.104013}, issn = {0094-114X}, year = {2020}, date = {2020-11-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {153}, abstract = {In minimally invasive surgery applications, the use of robotic manipulators is becoming more and more common to enhance the precision of the operations and post-operative processes. Such operations are often performed through an incision port (a pivot point) on the patient's body. Since the end-effector (the handled surgical tool) move about the pivot point, the manipulator has to move about a remote center of motion. In this study, a 3-degrees-of-freedom parallel mechanism with 2R1T (R: rotation, T: translation) remote center of motion capability is presented for minimally invasive surgery applications. First, its kinematic structure is introduced. Then, its kinematic analysis is carried out by using a simplified kinematic model which consists of three intersecting planes. Then the dimensional design is done for the desired workspace and a simulation test is carried out to verify the kinematic formulations. Finally, the prototype of the final design is presented. (c) 2020 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In minimally invasive surgery applications, the use of robotic manipulators is becoming more and more common to enhance the precision of the operations and post-operative processes. Such operations are often performed through an incision port (a pivot point) on the patient's body. Since the end-effector (the handled surgical tool) move about the pivot point, the manipulator has to move about a remote center of motion. In this study, a 3-degrees-of-freedom parallel mechanism with 2R1T (R: rotation, T: translation) remote center of motion capability is presented for minimally invasive surgery applications. First, its kinematic structure is introduced. Then, its kinematic analysis is carried out by using a simplified kinematic model which consists of three intersecting planes. Then the dimensional design is done for the desired workspace and a simulation test is carried out to verify the kinematic formulations. Finally, the prototype of the final design is presented. (c) 2020 Elsevier Ltd. All rights reserved. |
2019 |
Gur, Sebnem; Korkmaz, Koray; Kiper, Gokhan DESIGN OF ANTI-PARALLELOGRAM LOOP ASSEMBLIES Journal Article JOURNAL OF THE INTERNATIONAL ASSOCIATION FOR SHELL AND SPATIAL STRUCTURES, 60 (3), pp. 232-240, 2019, ISSN: 1028-365X. @article{ISI:000488985500006, title = {DESIGN OF ANTI-PARALLELOGRAM LOOP ASSEMBLIES}, author = {Sebnem Gur and Koray Korkmaz and Gokhan Kiper}, doi = {10.20898/j.iass.2019.201.006}, issn = {1028-365X}, year = {2019}, date = {2019-09-01}, journal = {JOURNAL OF THE INTERNATIONAL ASSOCIATION FOR SHELL AND SPATIAL STRUCTURES}, volume = {60}, number = {3}, pages = {232-240}, abstract = {Scissor mechanisms are frequently used for deployable structures and many studies have been conducted on the subject. Most of the studies consider scissor units as modules in the design process. An alternative approach is to utilize loops as the modules for design. In this paper, the design alternatives of single degree-of-freedom planar linkages comprising anti-parallelogram loops using the loop assembly method is presented. First, scissor mechanisms are reviewed. Next, the types of four-bar loops and the resulting linkages in the literature are introduced and those which are yet to be explored, anti-parallelogram being one of them, are identified. Then the loop assembly method and the examples in the literature are reviewed. As a method to form as many alternatives as possible, symmetry operations are proposed. Suitable frieze symmetry groups utilized for obtaining the assemblies are explained and the anti-parallelogram loop patterns are derived. Next, the single degree-of-freedom linkages are obtained from the loop assemblies. Finally, a selection of the resulting linkages with novel properties are presented. This study shows that loop assemblies are efficient in systematic type synthesis of scissor linkages, some types of which could not be foreseen by using units as modules.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Scissor mechanisms are frequently used for deployable structures and many studies have been conducted on the subject. Most of the studies consider scissor units as modules in the design process. An alternative approach is to utilize loops as the modules for design. In this paper, the design alternatives of single degree-of-freedom planar linkages comprising anti-parallelogram loops using the loop assembly method is presented. First, scissor mechanisms are reviewed. Next, the types of four-bar loops and the resulting linkages in the literature are introduced and those which are yet to be explored, anti-parallelogram being one of them, are identified. Then the loop assembly method and the examples in the literature are reviewed. As a method to form as many alternatives as possible, symmetry operations are proposed. Suitable frieze symmetry groups utilized for obtaining the assemblies are explained and the anti-parallelogram loop patterns are derived. Next, the single degree-of-freedom linkages are obtained from the loop assemblies. Finally, a selection of the resulting linkages with novel properties are presented. This study shows that loop assemblies are efficient in systematic type synthesis of scissor linkages, some types of which could not be foreseen by using units as modules. |
Maden, Feray; Akgun, Yenal; Kiper, Gokhan; Gur, Sebnem; Yar, Mujde; Korkmaz, Koray A CRITICAL REVIEW ON CLASSIFICATION AND TERMINOLOGY OF SCISSOR STRUCTURES Journal Article JOURNAL OF THE INTERNATIONAL ASSOCIATION FOR SHELL AND SPATIAL STRUCTURES, 60 (1, SI), pp. 47-64, 2019, ISSN: 1028-365X. @article{ISI:000464014000005, title = {A CRITICAL REVIEW ON CLASSIFICATION AND TERMINOLOGY OF SCISSOR STRUCTURES}, author = {Feray Maden and Yenal Akgun and Gokhan Kiper and Sebnem Gur and Mujde Yar and Koray Korkmaz}, doi = {10.20898/j.iass.2019.199.029}, issn = {1028-365X}, year = {2019}, date = {2019-03-01}, journal = {JOURNAL OF THE INTERNATIONAL ASSOCIATION FOR SHELL AND SPATIAL STRUCTURES}, volume = {60}, number = {1, SI}, pages = {47-64}, abstract = {When the existing literature on the research of scissor structures is thoroughly investigated, it is seen that different researchers use different terminologies and classifications especially for the definition of the primary units and the motion type. Some of the studies define the whole geometry based on the geometric properties of the primary scissor units and the unit lines while some other studies define it according to the loops. All these studies use different names for similar elements. This article aims to review the literature on the classification and terminology of scissor structures and represent the state of art on the studies. Tables are represented showing all approaches in the literature. In addition, the article criticizes the missing points of each terminology and definition, and proposes some new terminology. In order to arrive at this aim, different definitions of the primary scissor units and motion types used in key studies in the literature are investigated thoroughly. With several examples, it is demonstrated that naming the scissor units according to the resulting motion type might be misleading and it is better to specify the motion type for the whole structure. A classification for transformation of planar curves is presented.}, keywords = {}, pubstate = {published}, tppubtype = {article} } When the existing literature on the research of scissor structures is thoroughly investigated, it is seen that different researchers use different terminologies and classifications especially for the definition of the primary units and the motion type. Some of the studies define the whole geometry based on the geometric properties of the primary scissor units and the unit lines while some other studies define it according to the loops. All these studies use different names for similar elements. This article aims to review the literature on the classification and terminology of scissor structures and represent the state of art on the studies. Tables are represented showing all approaches in the literature. In addition, the article criticizes the missing points of each terminology and definition, and proposes some new terminology. In order to arrive at this aim, different definitions of the primary scissor units and motion types used in key studies in the literature are investigated thoroughly. With several examples, it is demonstrated that naming the scissor units according to the resulting motion type might be misleading and it is better to specify the motion type for the whole structure. A classification for transformation of planar curves is presented. |
2017 |
Kiper, Gokhan; Dede, Mehmet Ismet Can; Maaroof, Omar W; Ozkahya, Merve Function generation with two loop mechanisms using decomposition and correction method Journal Article MECHANISM AND MACHINE THEORY, 110 , pp. 16-26, 2017, ISSN: 0094-114X. @article{ISI:000394063500002, title = {Function generation with two loop mechanisms using decomposition and correction method}, author = {Gokhan Kiper and Mehmet Ismet Can Dede and Omar W Maaroof and Merve Ozkahya}, doi = {10.1016/j.mechmachtheory.2016.12.004}, issn = {0094-114X}, year = {2017}, date = {2017-04-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {110}, pages = {16-26}, abstract = {Method of decomposition has been successfully applied to function generation with multi-loop mechanisms. For a two-loop mechanism, a function y = f(x) can be decomposed into two as w = g(x) and y = h(w) = h(g(x)) = f(x). This study makes use of the method of decomposition for two loop mechanisms, where the errors from each loop are forced to match each other. In the first loop, which includes the input of the mechanism, the decomposed function (g) is generated and the resulting structural error is determined. Then, for the second loop, the desired output of the function (f) is considered as an input and the structural error of the decomposed function (g) is determined. By matching the obtained structural errors, the final error in the output of the mechanism is reduced. Three different correction methods are proposed. The first method has three precision points per loop, while the second method has four. In the third method, the extrema of the errors from both loops are matched. The methods are applied to a Watt II type planar six-bar linkage for demonstration. Several numerical examples are worked out and the results are compared with the results in the literature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Method of decomposition has been successfully applied to function generation with multi-loop mechanisms. For a two-loop mechanism, a function y = f(x) can be decomposed into two as w = g(x) and y = h(w) = h(g(x)) = f(x). This study makes use of the method of decomposition for two loop mechanisms, where the errors from each loop are forced to match each other. In the first loop, which includes the input of the mechanism, the decomposed function (g) is generated and the resulting structural error is determined. Then, for the second loop, the desired output of the function (f) is considered as an input and the structural error of the decomposed function (g) is determined. By matching the obtained structural errors, the final error in the output of the mechanism is reduced. Three different correction methods are proposed. The first method has three precision points per loop, while the second method has four. In the third method, the extrema of the errors from both loops are matched. The methods are applied to a Watt II type planar six-bar linkage for demonstration. Several numerical examples are worked out and the results are compared with the results in the literature. |
Atarer, F; Korkmaz, K; Kiper, G Design alternatives of network of Altmann linkages Journal Article International Journal of Computational Methods and Experimental Measurements, 5 (4), pp. 495-503, 2017. @article{Atarer2017495, title = {Design alternatives of network of Altmann linkages}, author = {F Atarer and K Korkmaz and G Kiper}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85032291841&doi=10.2495%2fCMEM-V5-N4-495-503&partnerID=40&md5=21a0c6a12a4aa176556157e4d54db241}, doi = {10.2495/CMEM-V5-N4-495-503}, year = {2017}, date = {2017-01-01}, journal = {International Journal of Computational Methods and Experimental Measurements}, volume = {5}, number = {4}, pages = {495-503}, abstract = {This paper presents a method of building deployable network assemblies derived from the single degree of freedom (DoF) over constrained Altmann linkage as a basic module. The method is based on assembling linkages with common links and joints or overlapping with extra R or 2R joints. New loops are emerged with overlapping method. The networks created have a single DoF, are over-constrained and have both fully deployed and folded configurations. The computer-aided models (CAD) are used to demonstrate these derived novel mechanisms. © 2017 WIT Press.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper presents a method of building deployable network assemblies derived from the single degree of freedom (DoF) over constrained Altmann linkage as a basic module. The method is based on assembling linkages with common links and joints or overlapping with extra R or 2R joints. New loops are emerged with overlapping method. The networks created have a single DoF, are over-constrained and have both fully deployed and folded configurations. The computer-aided models (CAD) are used to demonstrate these derived novel mechanisms. © 2017 WIT Press. |
Yar, M; Korkmaz, K; Kiper, G; Maden, F; Akgün, Y; Aktaş, E A novel planar scissor structure transforming between concave and convex configurations Journal Article International Journal of Computational Methods and Experimental Measurements, 5 (4), pp. 442-450, 2017. @article{Yar2017442, title = {A novel planar scissor structure transforming between concave and convex configurations}, author = {M Yar and K Korkmaz and G Kiper and F Maden and Y Akgün and E Aktaş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85051112573&doi=10.2495%2fCMEM-V5-N4-442-450&partnerID=40&md5=66bb8193b18ce907397210d6eae8b8dc}, doi = {10.2495/CMEM-V5-N4-442-450}, year = {2017}, date = {2017-01-01}, journal = {International Journal of Computational Methods and Experimental Measurements}, volume = {5}, number = {4}, pages = {442-450}, abstract = {In this paper, a novel two-dimensional scissor structure that transforms between concave and convex configurations is presented. The structure is designed by a method of assembling kite or anti-kite loops in the flat configuration. Angulated units are generated from the assembled loops. Finally, a new angulated scissor unit is introduced in order to design the novel scissor structure. © 2017 WIT Press.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, a novel two-dimensional scissor structure that transforms between concave and convex configurations is presented. The structure is designed by a method of assembling kite or anti-kite loops in the flat configuration. Angulated units are generated from the assembled loops. Finally, a new angulated scissor unit is introduced in order to design the novel scissor structure. © 2017 WIT Press. |
2016 |
Uzunoglu, Emre; Dede, Mehmet Ismet Can; Kiper, Gokhan Trajectory planning for a planar macro-micro manipulator of a laser-cutting machine Journal Article INDUSTRIAL ROBOT-THE INTERNATIONAL JOURNAL OF ROBOTICS RESEARCH AND APPLICATION, 43 (5, SI), pp. 513-523, 2016, ISSN: 0143-991X. @article{ISI:000386142100009, title = {Trajectory planning for a planar macro-micro manipulator of a laser-cutting machine}, author = {Emre Uzunoglu and Mehmet Ismet Can Dede and Gokhan Kiper}, doi = {10.1108/IR-02-2016-0057}, issn = {0143-991X}, year = {2016}, date = {2016-01-01}, journal = {INDUSTRIAL ROBOT-THE INTERNATIONAL JOURNAL OF ROBOTICS RESEARCH AND APPLICATION}, volume = {43}, number = {5, SI}, pages = {513-523}, abstract = {Purpose - In the industry, there is always a demand to shorten the task completion durations to maximize the efficiency of the operation. This work focuses on making use of a special type of kinematic redundancy, macro-micro manipulation, to minimize the task completion duration. The purpose of this paper is to develop the most convenient trajectory planner to be integrated with industrial computerized numerical control (CNC) systems to resolve kinematic redundancy for task duration minimization. Design/methodology/approach - A special type of kinematic redundancy is devised by using two kinematically different mechanisms that have different advantages, which are named as macro and micro mechanisms. In this case, the control design including the trajectory planning should be devised taking into account the distinct advantages of both mechanisms. A new trajectory planning algorithm is designed and used for the constructed planar laser-cutting machine, and some benchmark pieces are cut. Findings - Offline method has practical limitations for employment in a real case scenario such as assuming infinite jerk limits for each axis motion. This limitation was removed by using an online trajectory generation technique. Experimental test results indicate that the online trajectory planning technique developed for the macro-micro mechanism to shorten the task duration was successful. Practical implications - Although the new trajectory planning algorithm is implemented for a laser-cutting machine, it can also be used for other manufacturing systems that require higher acceleration and accuracy levels than the conventional machines. The new algorithm is compatible with the commercially available CNC systems. Originality/value - In this work, a new approach to reducing the task duration for planar machining operations was introduced by making use of macro-micro manipulation concept. The core novelty of the work is devising trajectory planning algorithms to get the most efficiency in terms of acceleration limits from a macro-micro manipulation while making these algorithms deployable to most of the CNC systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Purpose - In the industry, there is always a demand to shorten the task completion durations to maximize the efficiency of the operation. This work focuses on making use of a special type of kinematic redundancy, macro-micro manipulation, to minimize the task completion duration. The purpose of this paper is to develop the most convenient trajectory planner to be integrated with industrial computerized numerical control (CNC) systems to resolve kinematic redundancy for task duration minimization. Design/methodology/approach - A special type of kinematic redundancy is devised by using two kinematically different mechanisms that have different advantages, which are named as macro and micro mechanisms. In this case, the control design including the trajectory planning should be devised taking into account the distinct advantages of both mechanisms. A new trajectory planning algorithm is designed and used for the constructed planar laser-cutting machine, and some benchmark pieces are cut. Findings - Offline method has practical limitations for employment in a real case scenario such as assuming infinite jerk limits for each axis motion. This limitation was removed by using an online trajectory generation technique. Experimental test results indicate that the online trajectory planning technique developed for the macro-micro mechanism to shorten the task duration was successful. Practical implications - Although the new trajectory planning algorithm is implemented for a laser-cutting machine, it can also be used for other manufacturing systems that require higher acceleration and accuracy levels than the conventional machines. The new algorithm is compatible with the commercially available CNC systems. Originality/value - In this work, a new approach to reducing the task duration for planar machining operations was introduced by making use of macro-micro manipulation concept. The core novelty of the work is devising trajectory planning algorithms to get the most efficiency in terms of acceleration limits from a macro-micro manipulation while making these algorithms deployable to most of the CNC systems. |
2015 |
Kiper, Gokhan; Bilgincan, Tunc Function generation synthesis of spherical 5R mechanism with regional spacing and Chebyshev approximation Journal Article MECHANISM AND MACHINE THEORY, 90 , pp. 37-46, 2015, ISSN: 0094-114X. @article{ISI:000353985200003, title = {Function generation synthesis of spherical 5R mechanism with regional spacing and Chebyshev approximation}, author = {Gokhan Kiper and Tunc Bilgincan}, doi = {10.1016/j.mechmachtheory.2015.03.001}, issn = {0094-114X}, year = {2015}, date = {2015-08-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {90}, pages = {37-46}, abstract = {The Chebyshev approximation is well known to be applicable for the approximation of single input-single output functions by means of a function generator mechanism. The approximation method may be also applied to multi-input functions, although until recently, it was not used for function generation with multi-degrees-of-freedom mechanisms. In a recent study, the authors applied the approximation method to a two-degrees-of-freedom mechanism for the first time, however the selection and iteration of the design points at which the errors were minimized were not satisfactory. In this study, an alternative method of selection and iteration for these design points is introduced and the corresponding spacing is called the ``regional spacing''. As a case study for the application of the approximation of multi-input functions, a spherical 5R mechanism is used to generate a two input-single-output function. The input joints of the mechanism are selected as one of the fixed joints and the moving mid-joint, whereas the remaining fixed joint represents the output. The synthesis problem is analytically formulated and presented in polynomial form for five and six unknown parameters. The synthesis problem for five unknown parameters is illustrated as a numerical example. Regional spacing is used for the selection and iteration of design points for the synthesis. The Chebyshev approximation along with the Remez algorithm is utilized to find the unknown construction parameters and the error of the function. The design points and the coefficients of the approximation polynomial are determined by numerical iteration using six moving points. At each iteration step, the design points are relocated at the extremum error points in their respective regions. Iterations are repeated until the magnitudes of the extremum point errors are approximately equal. Finally, the construction parameters of the mechanism are determined and the variation of the percentage error between the desired and generated function values is obtained. (C) 2015 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The Chebyshev approximation is well known to be applicable for the approximation of single input-single output functions by means of a function generator mechanism. The approximation method may be also applied to multi-input functions, although until recently, it was not used for function generation with multi-degrees-of-freedom mechanisms. In a recent study, the authors applied the approximation method to a two-degrees-of-freedom mechanism for the first time, however the selection and iteration of the design points at which the errors were minimized were not satisfactory. In this study, an alternative method of selection and iteration for these design points is introduced and the corresponding spacing is called the ``regional spacing''. As a case study for the application of the approximation of multi-input functions, a spherical 5R mechanism is used to generate a two input-single-output function. The input joints of the mechanism are selected as one of the fixed joints and the moving mid-joint, whereas the remaining fixed joint represents the output. The synthesis problem is analytically formulated and presented in polynomial form for five and six unknown parameters. The synthesis problem for five unknown parameters is illustrated as a numerical example. Regional spacing is used for the selection and iteration of design points for the synthesis. The Chebyshev approximation along with the Remez algorithm is utilized to find the unknown construction parameters and the error of the function. The design points and the coefficients of the approximation polynomial are determined by numerical iteration using six moving points. At each iteration step, the design points are relocated at the extremum error points in their respective regions. Iterations are repeated until the magnitudes of the extremum point errors are approximately equal. Finally, the construction parameters of the mechanism are determined and the variation of the percentage error between the desired and generated function values is obtained. (C) 2015 Elsevier Ltd. All rights reserved. |
2014 |
Alizade, Rasim I; Kiper, Gokhan; Bagdadioglu, Baris; Dede, Can M I Function synthesis of Bennett 6R mechanisms using Chebyshev approximation Journal Article MECHANISM AND MACHINE THEORY, 81 , pp. 62-78, 2014, ISSN: 0094-114X. @article{ISI:000341141400006, title = {Function synthesis of Bennett 6R mechanisms using Chebyshev approximation}, author = {Rasim I Alizade and Gokhan Kiper and Baris Bagdadioglu and Can M I Dede}, doi = {10.1016/j.mechmachtheory.2014.06.010}, issn = {0094-114X}, year = {2014}, date = {2014-11-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {81}, pages = {62-78}, abstract = {This study focuses on approximate function synthesis of the three types of overconstrained Bennett 6R mechanisms using Chebyshev approximation. The three mechanisms are the double-planar, double-spherical and the plano-spherical 6R linkages. The single-loop 6R mechanisms are dissected into two imaginary loops and function synthesis is performed for both loops. First, the link lengths are employed as construction parameters of the mechanism. Then extra construction parameters for the input or output joint variables are introduced in order to increase the design points and hence enhance the accuracy of approximation. The synthesis formulations are applied computationally as case studies. The case studies illustrate how a designer can compare the three types of Bennett 6R mechanisms for the same function. Also we present a comparison of the spherical four-bar with the double-spherical 6R mechanism and show that the accuracy is improved when the 6R linkage is used. (C) 2014 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study focuses on approximate function synthesis of the three types of overconstrained Bennett 6R mechanisms using Chebyshev approximation. The three mechanisms are the double-planar, double-spherical and the plano-spherical 6R linkages. The single-loop 6R mechanisms are dissected into two imaginary loops and function synthesis is performed for both loops. First, the link lengths are employed as construction parameters of the mechanism. Then extra construction parameters for the input or output joint variables are introduced in order to increase the design points and hence enhance the accuracy of approximation. The synthesis formulations are applied computationally as case studies. The case studies illustrate how a designer can compare the three types of Bennett 6R mechanisms for the same function. Also we present a comparison of the spherical four-bar with the double-spherical 6R mechanism and show that the accuracy is improved when the 6R linkage is used. (C) 2014 Elsevier Ltd. All rights reserved. |
2013 |
Kiper, G; Söylemez, E Polyhedral linkages obtained as assemblies of planar link groups Journal Article Frontiers of Mechanical Engineering, 8 (1), pp. 3-9, 2013. @article{Kiper20133, title = {Polyhedral linkages obtained as assemblies of planar link groups}, author = {G Kiper and E Söylemez}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84874799475&doi=10.1007%2fs11465-013-0363-6&partnerID=40&md5=f3339513404eac12eb100881e2c6ac47}, doi = {10.1007/s11465-013-0363-6}, year = {2013}, date = {2013-01-01}, journal = {Frontiers of Mechanical Engineering}, volume = {8}, number = {1}, pages = {3-9}, abstract = {The study aims to devise means of obtaining polyhedral linkages for homothetic deployment of polyhedral shapes by embedding planar link groups in faces of the polyhedral shape of interest. The questions of which polyhedral shapes may be suitable for such a purpose and what are the compatibility conditions for spatially assembling planar link groups are addressed. Homohedral and tangential polyhedral shapes are found to be suitable for the task and some examples of linkages are worked out. © 2013 Higher Education Press and Springer-Verlag Berlin Heidelberg.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The study aims to devise means of obtaining polyhedral linkages for homothetic deployment of polyhedral shapes by embedding planar link groups in faces of the polyhedral shape of interest. The questions of which polyhedral shapes may be suitable for such a purpose and what are the compatibility conditions for spatially assembling planar link groups are addressed. Homohedral and tangential polyhedral shapes are found to be suitable for the task and some examples of linkages are worked out. © 2013 Higher Education Press and Springer-Verlag Berlin Heidelberg. |
Kiper, Gökhan; Bilgincan, Tunç; Dede, Mehmet İsmet Can Function generation synthesis of planar 5R mechanism Journal Article 2013. @article{kiper2013function, title = {Function generation synthesis of planar 5R mechanism}, author = {Gökhan Kiper and Tunç Bilgincan and Mehmet İsmet Can Dede}, url = {http://hdl.handle.net/11147/4217}, year = {2013}, date = {2013-01-01}, publisher = {IFToMM}, abstract = {This paper deals with the function generation problem for a planar five-bar mechanism. The inputs to the mechanism are selected as one of the fixed joints and the mid-joint, whereas the remaining fixed joint represents the output. Synthesis problem of the five-bar mechanism is analytically formulated and an objective function is expressed in polynomial form. Function generation synthesis is performed with equal spacing and Chebyshev approximation method. The four unknown construction parameters and the error are evaluated by means of five design points and the coefficients of the objective function are determined by numerical iteration using four stationary and one moving design point. Stationary points are placed at the boundaries of the motion and the moving point is re-selected at each iteration as the point corresponding to the extremum error. Iterations are repeated until the values are stabilized. The stabilization usually occurs at the third iteration. By this method, the maximum error values are approximately equated, hence the total error is bounded at certain limits. Finally the construction parameters of the mechanism are determined.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper deals with the function generation problem for a planar five-bar mechanism. The inputs to the mechanism are selected as one of the fixed joints and the mid-joint, whereas the remaining fixed joint represents the output. Synthesis problem of the five-bar mechanism is analytically formulated and an objective function is expressed in polynomial form. Function generation synthesis is performed with equal spacing and Chebyshev approximation method. The four unknown construction parameters and the error are evaluated by means of five design points and the coefficients of the objective function are determined by numerical iteration using four stationary and one moving design point. Stationary points are placed at the boundaries of the motion and the moving point is re-selected at each iteration as the point corresponding to the extremum error. Iterations are repeated until the values are stabilized. The stabilization usually occurs at the third iteration. By this method, the maximum error values are approximately equated, hence the total error is bounded at certain limits. Finally the construction parameters of the mechanism are determined. |
2012 |
Kiper, Gökhan; Soylemez, Eres Homothetic Jitterbug-like linkages Journal Article MECHANISM AND MACHINE THEORY, 51 , pp. 145-158, 2012, ISSN: 0094-114X. @article{ISI:000300618000010, title = {Homothetic Jitterbug-like linkages}, author = {Gökhan Kiper and Eres Soylemez}, doi = {10.1016/j.mechmachtheory.2011.11.014}, issn = {0094-114X}, year = {2012}, date = {2012-05-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {51}, pages = {145-158}, abstract = {Conformal polyhedral linkages have drawn attention of scientists and engineers since the invention of Buckminster Fuller: a highly overconstrained spatial linkage, the Jitterbug. Many studies aimed to generalize Jitterbug-like linkages have been published, however a complete classification does not yet exist. This study introduces a definition for Jitterbug-like linkages and two major assumptions and then focuses on the properties of homothetic linkages. (C) 2011 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Conformal polyhedral linkages have drawn attention of scientists and engineers since the invention of Buckminster Fuller: a highly overconstrained spatial linkage, the Jitterbug. Many studies aimed to generalize Jitterbug-like linkages have been published, however a complete classification does not yet exist. This study introduces a definition for Jitterbug-like linkages and two major assumptions and then focuses on the properties of homothetic linkages. (C) 2011 Elsevier Ltd. All rights reserved. |
2010 |
Akgun, Yenal; Gantes, Charis J; Kalochairetis, Konstantinos E; Kiper, Gokhan A novel concept of convertible roofs with high transformability consisting of planar scissor-hinge structures Journal Article ENGINEERING STRUCTURES, 32 (9), pp. 2873-2883, 2010, ISSN: 0141-0296. @article{ISI:000281995300032, title = {A novel concept of convertible roofs with high transformability consisting of planar scissor-hinge structures}, author = {Yenal Akgun and Charis J Gantes and Konstantinos E Kalochairetis and Gokhan Kiper}, doi = {10.1016/j.engstruct.2010.05.006}, issn = {0141-0296}, year = {2010}, date = {2010-09-01}, journal = {ENGINEERING STRUCTURES}, volume = {32}, number = {9}, pages = {2873-2883}, abstract = {In this paper, a new adaptive scissor-hinge structure is introduced, which can be converted by means of actuators between a multitude of curvilinear arch-like shapes, where it can be stabilized and carry loads. The key point of this new structure is the proposed Modified Scissor-Like Element (M-SLE). With the development of this element, it becomes possible to change the geometry of the whole system without changing the dimensions of the struts or the span. The proposed scissor-hinge structure discussed here is planar, but it is also possible to combine structures in groups to create spatial systems. After outlining the differences of the proposed structure with existing designs, the dimensional properties of the M-SLE are introduced. Then, geometric principles and shape limitations of the whole structure are explained. Finally, structural analysis of the structure in different geometric configurations is performed, in order to discuss stiffness limitations associated with the advantage of increased mobility. (C) 2010 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, a new adaptive scissor-hinge structure is introduced, which can be converted by means of actuators between a multitude of curvilinear arch-like shapes, where it can be stabilized and carry loads. The key point of this new structure is the proposed Modified Scissor-Like Element (M-SLE). With the development of this element, it becomes possible to change the geometry of the whole system without changing the dimensions of the struts or the span. The proposed scissor-hinge structure discussed here is planar, but it is also possible to combine structures in groups to create spatial systems. After outlining the differences of the proposed structure with existing designs, the dimensional properties of the M-SLE are introduced. Then, geometric principles and shape limitations of the whole structure are explained. Finally, structural analysis of the structure in different geometric configurations is performed, in order to discuss stiffness limitations associated with the advantage of increased mobility. (C) 2010 Elsevier Ltd. All rights reserved. |
2008 |
Kiper, Gökhan; Soylemez, Eres; Kisisel, Özgür A U A family of deployable polygons and polyhedra Journal Article MECHANISM AND MACHINE THEORY, 43 (5), pp. 627-640, 2008, ISSN: 0094-114X. @article{ISI:000255728900007, title = {A family of deployable polygons and polyhedra}, author = {Gökhan Kiper and Eres Soylemez and Özgür A U Kisisel}, doi = {10.1016/j.mechmachtheory.2007.04.011}, issn = {0094-114X}, year = {2008}, date = {2008-05-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {43}, number = {5}, pages = {627-640}, abstract = {A new linkage type for resizing polygonal and polyhedral shapes is proposed. The single degree-of-freedom planar linkages considered mainly consist of links connected by revolute joints. It is shown that the group of mechanisms obtained realize Cardanic Motion. The polyhedral linkages proposed are constructed by implementing the proposed planar linkages on the faces and interconnecting them by links at the vertices to retain the solid angles of the polyhedral shape of interest. (C) 2007 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A new linkage type for resizing polygonal and polyhedral shapes is proposed. The single degree-of-freedom planar linkages considered mainly consist of links connected by revolute joints. It is shown that the group of mechanisms obtained realize Cardanic Motion. The polyhedral linkages proposed are constructed by implementing the proposed planar linkages on the faces and interconnecting them by links at the vertices to retain the solid angles of the polyhedral shape of interest. (C) 2007 Elsevier Ltd. All rights reserved. |
Res. Assist. Dr. Ayşe Korucu
Educational Background
B.Sc. Kocaeli University,Mechanical Engineering, 2007
M.Sc. Clemson University,Mechanical Engineering, 2011
Ph.D. Clemson University,Mechanical Engineering, 2016
Research Interests
- CFD
- Fluid Dynamics
- Turbulent Combustion Modeling
- +90 232 750 6759
- +90 232 750 6701
- Mechanical Engineering Building (Z27)
- aysekorucu@iyte.edu.tr
Publications
2023 |
Benim, Ali Cemal; Korucu, Ayse Computational investigation of non-premixed hydrogen-air laminar flames Journal Article International Journal of Hydrogen Energy, 2023. @article{Benim2023, title = {Computational investigation of non-premixed hydrogen-air laminar flames}, author = {Ali Cemal Benim and Ayse Korucu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85146346018&doi=10.1016%2fj.ijhydene.2022.12.248&partnerID=40&md5=89d0b1a520d385f2e21b07190741c33b}, doi = {10.1016/j.ijhydene.2022.12.248}, year = {2023}, date = {2023-01-01}, journal = {International Journal of Hydrogen Energy}, abstract = {Laminar diffusion hydrogen/air flames are numerically investigated. Detailed and global mechanisms are compared. NO formation is modelled by full nitrogen chemistry and the extended Zeldovich mechanism. A satisfactory agreement between the present predictions and the experiments of other authors is observed. Significance of different ingredients of mathematical modelling is analyzed. Minor roles of thermal diffusion and radiation, but a significant role of buoyancy is observed. It is observed that the full and quasi multi-component diffusion deliver the same results, whereas assuming Le = 1 to a remarkable difference. NO emissions logarithmically increase with increasing residence time. NO is the dominating nitrogen oxide. Its share increases with residence time, whereby NO2 and N2O show a reverse trend. It is observed that the NNH route plays a remarkable role in NO formation, where the share of the Zeldovich mechanism increases with residence time from about 20% to 85%, within the considered range. © 2022 Hydrogen Energy Publications LLC}, keywords = {}, pubstate = {published}, tppubtype = {article} } Laminar diffusion hydrogen/air flames are numerically investigated. Detailed and global mechanisms are compared. NO formation is modelled by full nitrogen chemistry and the extended Zeldovich mechanism. A satisfactory agreement between the present predictions and the experiments of other authors is observed. Significance of different ingredients of mathematical modelling is analyzed. Minor roles of thermal diffusion and radiation, but a significant role of buoyancy is observed. It is observed that the full and quasi multi-component diffusion deliver the same results, whereas assuming Le = 1 to a remarkable difference. NO emissions logarithmically increase with increasing residence time. NO is the dominating nitrogen oxide. Its share increases with residence time, whereby NO2 and N2O show a reverse trend. It is observed that the NNH route plays a remarkable role in NO formation, where the share of the Zeldovich mechanism increases with residence time from about 20% to 85%, within the considered range. © 2022 Hydrogen Energy Publications LLC |
Korucu, Ayşe; Miller, Richard Journal of the Faculty of Engineering and Architecture of Gazi University, 39 (1), pp. 91 – 99, 2023, (All Open Access, Bronze Open Access). @article{Korucu202391, title = {Differential diffusion and pressure effects on heavily sooting 2D Kerosene/Air shear flames; [Yüksek derecede kurum üreten 2B Gazyağı/Hava difüzyon alevleri üzerinde diferansiyel difüzyonun ve basıncın etkileri]}, author = {Ayşe Korucu and Richard Miller}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85174150376&doi=10.17341%2fgazimmfd.1153044&partnerID=40&md5=83c25552abccd22fffbfce453c52ba54}, doi = {10.17341/gazimmfd.1153044}, year = {2023}, date = {2023-01-01}, journal = {Journal of the Faculty of Engineering and Architecture of Gazi University}, volume = {39}, number = {1}, pages = {91 – 99}, abstract = {(Figure Presented). Purpose: The current study aims to test the limits of the Unity Lewis number simplification coupled with both the ideal gas (IGL) and a real gas (RGL) equation of state (EOS) for predicting flame and soot characteristics of heavily sooting Kerosene/Air shear flames at 4 different operating pressures. Theory and Methods: Fully compressible Navier-Stokes equations are adopted in DNS environment. For the computational mesh, equivalently spaced grid points from 0 < x1 < L1 are used, while in the cross-stream direction the mesh has been stretched in the x2 direction. An 8th order central explicit finite difference method and a 4th order Runge-Kutta are employed to solve for the spatial and time derivatives, respectively. The temperature contour plot created using 2D DNS data are provided in Figure A. Boundary conditions of the problem: I - in x2 direction, far from the flame kernel, flow is set to have free stream characteristics and II - in x1 direction, periodic boundary conditions are embedded to solve the turbulent flow. Results: Comparisons to the earlier studies have been revealed that the mean peak flame temperature predictions done by the unity-Le number model are lessened; implying that the soot production/oxidation rates calculations will be debilitated comparably to the low mean flame temperature of the unity-Le number cases regardless of the operating pressure. The unity-Le number model’s under-prediction of the flame temperatures results in intensifying incomplete combustion which not only emanates the soot load but also weaken the soot oxidation rate for the RGL EOS cases, while causes under-prediction of mass fraction of soot for the IGL EOS cases in comparison to the non-unity Le number results. As the operating pressure increases to 35 atm, the mean flame temperature increases hence, the soot load in the flame kernels increases even though the soot oxidation process is enhanced by the increasing flame temperature. An increase in the mean flame temperature has been noted for the IGL EOS model predictions at 35 atm case, which will cause an inevitable increment in soot load throughout the flame kernel. Conclusion: The analyses have revealed the that the unity-Le number simplification estimates the average flame temperature lower than expected for each operating pressure increasing the possibility of an incomplete combustion or even local flame weakening and extinction which stems ‘abnormally’ high soot load throughout the flame kernel essentially for 10 and 35 atm operating pressure cases of the IGL EOS model. © 2023 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.}, note = {All Open Access, Bronze Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } (Figure Presented). Purpose: The current study aims to test the limits of the Unity Lewis number simplification coupled with both the ideal gas (IGL) and a real gas (RGL) equation of state (EOS) for predicting flame and soot characteristics of heavily sooting Kerosene/Air shear flames at 4 different operating pressures. Theory and Methods: Fully compressible Navier-Stokes equations are adopted in DNS environment. For the computational mesh, equivalently spaced grid points from 0 < x1 < L1 are used, while in the cross-stream direction the mesh has been stretched in the x2 direction. An 8th order central explicit finite difference method and a 4th order Runge-Kutta are employed to solve for the spatial and time derivatives, respectively. The temperature contour plot created using 2D DNS data are provided in Figure A. Boundary conditions of the problem: I - in x2 direction, far from the flame kernel, flow is set to have free stream characteristics and II - in x1 direction, periodic boundary conditions are embedded to solve the turbulent flow. Results: Comparisons to the earlier studies have been revealed that the mean peak flame temperature predictions done by the unity-Le number model are lessened; implying that the soot production/oxidation rates calculations will be debilitated comparably to the low mean flame temperature of the unity-Le number cases regardless of the operating pressure. The unity-Le number model’s under-prediction of the flame temperatures results in intensifying incomplete combustion which not only emanates the soot load but also weaken the soot oxidation rate for the RGL EOS cases, while causes under-prediction of mass fraction of soot for the IGL EOS cases in comparison to the non-unity Le number results. As the operating pressure increases to 35 atm, the mean flame temperature increases hence, the soot load in the flame kernels increases even though the soot oxidation process is enhanced by the increasing flame temperature. An increase in the mean flame temperature has been noted for the IGL EOS model predictions at 35 atm case, which will cause an inevitable increment in soot load throughout the flame kernel. Conclusion: The analyses have revealed the that the unity-Le number simplification estimates the average flame temperature lower than expected for each operating pressure increasing the possibility of an incomplete combustion or even local flame weakening and extinction which stems ‘abnormally’ high soot load throughout the flame kernel essentially for 10 and 35 atm operating pressure cases of the IGL EOS model. © 2023 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved. |
2015 |
Ma, Zhiyuan; Korucu, Ayse; Miller, Richard Steven A priori analysis of subgrid scale pressure and heat flux in high pressure mixing and reacting shear layers Journal Article COMBUSTION THEORY AND MODELLING, 19 (6), pp. 807-832, 2015, ISSN: 1364-7830. @article{ISI:000366248600006, title = {A priori analysis of subgrid scale pressure and heat flux in high pressure mixing and reacting shear layers}, author = {Zhiyuan Ma and Ayse Korucu and Richard Steven Miller}, doi = {10.1080/13647830.2015.1100753}, issn = {1364-7830}, year = {2015}, date = {2015-11-01}, journal = {COMBUSTION THEORY AND MODELLING}, volume = {19}, number = {6}, pages = {807-832}, abstract = {Direct Numerical Simulation (DNS) data on high pressure H-2/O-2 and H-2/air flames using the compressible flow formulation, detailed kinetics, a real fluid equation of state, and generalised diffusion are analysed. The DNS is filtered over a range of filter widths to provide exact terms in the Large Eddy Simulation (LES) governing equations, including unclosed terms. The filtered pressure and the filtered heat flux vector are extensively compared with the pressure and the heat flux vector calculated as a function of the filtered primitive variables (i.e. the exact LES term is compared with its form available within an actual LES). The difference between these forms defines the subgrid pressure and the subgrid heat flux vector. The analyses are done both globally across the entire flame, as well as by conditionally averaging over specific regions of the flame; including regions of large subgrid kinetic energy, subgrid scalar dissipation, subgrid temperature variance, flame temperature, etc. In this work, although negligible for purely mixing cases, the gradient of the subgrid pressure is shown to be of the same order as, and larger than, the corresponding divergence of the turbulent subgrid stresses for reacting cases. This is despite the fact that all species behave essentially as ideal gases for this flame and holds true even when the ideal gas law is used to calculate the pressure. The ratio of the subgrid pressure gradient to the subgrid stress tensor divergence is shown to increase with increasing Reynolds number. Both the subgrid heat flux vector and its divergence are found to be substantially larger in reacting flows in comparison with mixing due to the associated larger temperature gradients. However, the divergence of the subgrid heat flux vector tends to be significantly smaller than other unclosed terms in the energy equation with decreasing significance with increasing Reynolds number.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Direct Numerical Simulation (DNS) data on high pressure H-2/O-2 and H-2/air flames using the compressible flow formulation, detailed kinetics, a real fluid equation of state, and generalised diffusion are analysed. The DNS is filtered over a range of filter widths to provide exact terms in the Large Eddy Simulation (LES) governing equations, including unclosed terms. The filtered pressure and the filtered heat flux vector are extensively compared with the pressure and the heat flux vector calculated as a function of the filtered primitive variables (i.e. the exact LES term is compared with its form available within an actual LES). The difference between these forms defines the subgrid pressure and the subgrid heat flux vector. The analyses are done both globally across the entire flame, as well as by conditionally averaging over specific regions of the flame; including regions of large subgrid kinetic energy, subgrid scalar dissipation, subgrid temperature variance, flame temperature, etc. In this work, although negligible for purely mixing cases, the gradient of the subgrid pressure is shown to be of the same order as, and larger than, the corresponding divergence of the turbulent subgrid stresses for reacting cases. This is despite the fact that all species behave essentially as ideal gases for this flame and holds true even when the ideal gas law is used to calculate the pressure. The ratio of the subgrid pressure gradient to the subgrid stress tensor divergence is shown to increase with increasing Reynolds number. Both the subgrid heat flux vector and its divergence are found to be substantially larger in reacting flows in comparison with mixing due to the associated larger temperature gradients. However, the divergence of the subgrid heat flux vector tends to be significantly smaller than other unclosed terms in the energy equation with decreasing significance with increasing Reynolds number. |
Assoc. Prof. Dr. Şenay Mihçin
Educational Background
B.Sc. Middle East Technical University, Mechanical Engineering, 2001
M.Sc. Sabanci University- Leaders for Industry Program Double MSc in Mechatronics and Management Sciences, 2003
Ph.D. Computational Biomechanics, Loughborough University, United Kingdom, 2008
Research Interests
- Biomechancis, Validation, Verification
- Translational Research (Pre-Clinical)
- Motion Analysis, Simulations
- FE Modelling
- ISO 13485 Certifications
- Implant Design
- Crash Simulations
- +90 232 750 6783
- +90 232 750 6701
- Mechanical Engineering Building (K1-13)
Publications
2023 |
Mihcin, Senay; Sahin, Ahmet Mert; Yilmaz, Mehmet; Alpkaya, Alican Tuncay; Tuna, Merve; Akdeniz, Sevinc; Korkmaz, Nuray Can; Tosun, Aliye; Sahin, Serap Database covering the prayer movements which were not available previously Journal Article Scientific Data, 10 (1), 2023, (All Open Access, Gold Open Access, Green Open Access). @article{Mihcin2023, title = {Database covering the prayer movements which were not available previously}, author = {Senay Mihcin and Ahmet Mert Sahin and Mehmet Yilmaz and Alican Tuncay Alpkaya and Merve Tuna and Sevinc Akdeniz and Nuray Can Korkmaz and Aliye Tosun and Serap Sahin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85159738866&doi=10.1038%2fs41597-023-02196-x&partnerID=40&md5=04869d265c2a00af6d7e25dad86d8231}, doi = {10.1038/s41597-023-02196-x}, year = {2023}, date = {2023-01-01}, journal = {Scientific Data}, volume = {10}, number = {1}, abstract = {Lower body implants are designed according to the boundary conditions of gait data and tested against. However, due to diversity in cultural backgrounds, religious rituals might cause different ranges of motion and different loading patterns. Especially in the Eastern part of the world, diverse Activities of Daily Living (ADL) consist of salat, yoga rituals, and different style sitting postures. A database covering these diverse activities of the Eastern world is non-existent. This study focuses on data collection protocol and the creation of an online database of previously excluded ADL activities, targeting 200 healthy subjects via Qualisys and IMU motion capture systems, and force plates, from West and Middle East Asian populations with a special focus on the lower body joints. The current version of the database covers 50 volunteers for 13 different activities. The tasks are defined and listed in a table to create a database to search based on age, gender, BMI, type of activity, and motion capture system. The collected data is to be used for designing implants to allow these sorts of activities to be performed. © 2023, The Author(s).}, note = {All Open Access, Gold Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Lower body implants are designed according to the boundary conditions of gait data and tested against. However, due to diversity in cultural backgrounds, religious rituals might cause different ranges of motion and different loading patterns. Especially in the Eastern part of the world, diverse Activities of Daily Living (ADL) consist of salat, yoga rituals, and different style sitting postures. A database covering these diverse activities of the Eastern world is non-existent. This study focuses on data collection protocol and the creation of an online database of previously excluded ADL activities, targeting 200 healthy subjects via Qualisys and IMU motion capture systems, and force plates, from West and Middle East Asian populations with a special focus on the lower body joints. The current version of the database covers 50 volunteers for 13 different activities. The tasks are defined and listed in a table to create a database to search based on age, gender, BMI, type of activity, and motion capture system. The collected data is to be used for designing implants to allow these sorts of activities to be performed. © 2023, The Author(s). |
Alpkaya, Alican Tuncay; Mihcin, Senay Dynamic computational wear model of PEEK-on-XLPE bearing couple in total hip replacements Journal Article Medical Engineering and Physics, 117 , 2023. @article{Alpkaya2023, title = {Dynamic computational wear model of PEEK-on-XLPE bearing couple in total hip replacements}, author = {Alican Tuncay Alpkaya and Senay Mihcin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85161750490&doi=10.1016%2fj.medengphy.2023.104006&partnerID=40&md5=37b73bc1035463a7dbadce39c74acb55}, doi = {10.1016/j.medengphy.2023.104006}, year = {2023}, date = {2023-01-01}, journal = {Medical Engineering and Physics}, volume = {117}, abstract = {Understanding wear mechanisms is a key factor to prevent primary failures causing revision surgery in total hip replacement (THR) applications. This study introduces a wear prediction model of (Polyetheretherketone) PEEK-on-XLPE (cross-linked polyethylene) bearing couple utilized to investigate the wear mechanism under 3D-gait cycle loading over 5 million cycles (Mc). A 32-mm PEEK femoral head and 4-mm thick XLPE bearing liner with a 3-mm PEEK shell are modeled in a 3D explicit finite element modeling (FEM) program. The volumetric and linear wear rates of XLPE liner per every million cycles were predicted as 1.965 mm3/Mc, and 0.0032 mm/Mc respectively. These results are consistent with the literature. PEEK-on-XLPE bearing couple exhibits a promising wear performance used in THR application. The wear pattern evolution of the model is similar to that of conventional polyethylene liners. Therefore, PEEK could be proposed as an alternative material to the CoCr head, especially used in XLPE-bearing couples. The wear prediction model could be utilized to improve the design parameters with the aim of prolonging the life span of hip implants. © 2023}, keywords = {}, pubstate = {published}, tppubtype = {article} } Understanding wear mechanisms is a key factor to prevent primary failures causing revision surgery in total hip replacement (THR) applications. This study introduces a wear prediction model of (Polyetheretherketone) PEEK-on-XLPE (cross-linked polyethylene) bearing couple utilized to investigate the wear mechanism under 3D-gait cycle loading over 5 million cycles (Mc). A 32-mm PEEK femoral head and 4-mm thick XLPE bearing liner with a 3-mm PEEK shell are modeled in a 3D explicit finite element modeling (FEM) program. The volumetric and linear wear rates of XLPE liner per every million cycles were predicted as 1.965 mm3/Mc, and 0.0032 mm/Mc respectively. These results are consistent with the literature. PEEK-on-XLPE bearing couple exhibits a promising wear performance used in THR application. The wear pattern evolution of the model is similar to that of conventional polyethylene liners. Therefore, PEEK could be proposed as an alternative material to the CoCr head, especially used in XLPE-bearing couples. The wear prediction model could be utilized to improve the design parameters with the aim of prolonging the life span of hip implants. © 2023 |
Torabnia, Shams; Mihcin, Senay; Lazoglu, Ismail Design and manufacturing of a hip joint motion simulator with a novel modular design approach Journal Article International Journal on Interactive Design and Manufacturing, 2023, (All Open Access, Green Open Access). @article{Torabnia2023, title = {Design and manufacturing of a hip joint motion simulator with a novel modular design approach}, author = {Shams Torabnia and Senay Mihcin and Ismail Lazoglu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85171144946&doi=10.1007%2fs12008-023-01506-2&partnerID=40&md5=e978abee3f2263e3283041cbd26677ba}, doi = {10.1007/s12008-023-01506-2}, year = {2023}, date = {2023-01-01}, journal = {International Journal on Interactive Design and Manufacturing}, abstract = {The study is aimed to develop a hip joint wear simulator using a modular design approach to help experimentally monitor and control critical wear parameters to validate in-silico wear models. The proper control and application of wear parameters such as the range of motion, and the applied force values while estimating the lost material due to wear are essential for thorough analysis of wear phenomena for artificial joints. The simulator's dynamics were first modeled, then dynamic loading data was used to calculate the forces, which were further used for topology optimization to reduce the forces acting on each joint. The reduction of the link weights, connected to the actuators, intends to improve the quality of motion transferred to the femoral head. The modular design approach enables topology-optimized geometry, associated gravitational and dynamic forces, resulting in a cost-effective, energy-efficient product. Moreover, this design allows integration of the subject specific data by allowing different boundary conditions following the requirements of industry 5.0. Overall, the in-vitro motion stimulations of the hip-joint prosthesis and the modular design approach used in the study might help improve the accuracy and the effectiveness of wear simulations, which could lead into the development of better and longer-lasting joint prostheses for all. The subject-specific and society-based daily life data implemented as boundary conditions enable inclusion of the personalized effects. Next, with the results of the simulator, CEN Workshop Agreement (CWA) application is intended to cover the personalized effects for previously excluded populations, providing solution to inclusive design for all. © 2023, The Author(s), under exclusive licence to Springer-Verlag France SAS, part of Springer Nature.}, note = {All Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } The study is aimed to develop a hip joint wear simulator using a modular design approach to help experimentally monitor and control critical wear parameters to validate in-silico wear models. The proper control and application of wear parameters such as the range of motion, and the applied force values while estimating the lost material due to wear are essential for thorough analysis of wear phenomena for artificial joints. The simulator's dynamics were first modeled, then dynamic loading data was used to calculate the forces, which were further used for topology optimization to reduce the forces acting on each joint. The reduction of the link weights, connected to the actuators, intends to improve the quality of motion transferred to the femoral head. The modular design approach enables topology-optimized geometry, associated gravitational and dynamic forces, resulting in a cost-effective, energy-efficient product. Moreover, this design allows integration of the subject specific data by allowing different boundary conditions following the requirements of industry 5.0. Overall, the in-vitro motion stimulations of the hip-joint prosthesis and the modular design approach used in the study might help improve the accuracy and the effectiveness of wear simulations, which could lead into the development of better and longer-lasting joint prostheses for all. The subject-specific and society-based daily life data implemented as boundary conditions enable inclusion of the personalized effects. Next, with the results of the simulator, CEN Workshop Agreement (CWA) application is intended to cover the personalized effects for previously excluded populations, providing solution to inclusive design for all. © 2023, The Author(s), under exclusive licence to Springer-Verlag France SAS, part of Springer Nature. |
Alpkaya, Alican Tuncay; Mihçin, Şenay The Computational Approach to Predicting Wear: Comparison of Wear Performance of CFR-PEEK and XLPE Liners in Total Hip Replacement Journal Article Tribology Transactions, 66 (1), pp. 59 – 72, 2023. @article{Alpkaya202359, title = {The Computational Approach to Predicting Wear: Comparison of Wear Performance of CFR-PEEK and XLPE Liners in Total Hip Replacement}, author = {Alican Tuncay Alpkaya and Şenay Mihçin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85144145526&doi=10.1080%2f10402004.2022.2140727&partnerID=40&md5=727b9b4294502f860c17ec5352419b28}, doi = {10.1080/10402004.2022.2140727}, year = {2023}, date = {2023-01-01}, journal = {Tribology Transactions}, volume = {66}, number = {1}, pages = {59 – 72}, abstract = {Wear on articulating bearing surfaces is a key factor causing revision in total hip replacement (THR). Wear debris that releases particles from bearing surfaces might result in adverse soft tissue reactions requiring revision surgeries. In this study, a comprehensive computational wear model based on the Archard wear equation was performed to investigate the wear performance under a three-dimensional (3D) physiological gait cycle, mimicking a normal walking condition (5 million cycles). The study shows that the accuracy of the model is highly dependent on the mesh convergence, the wear fraction, and the scaling factor. The simulations were run to provide a vast amount of detail for the reproducibility of the work. Cobalt chromium (CoCr) on cross-linked polyethylene (XLPE) and CoCr on carbon-fiber-reinforced polyether ether ketone (CFR-PEEK) prototype models were created in silico. The volumetric wear rates for CoCr-on-XLPE were calculated as 0.2989 (Formula presented.) for CoCr head and 21.0271 (Formula presented.) for XLPE liner, while for CoCr-on-CFR-PEEK they were 0.3484 (Formula presented.) for CoCr head and 1.8476 (Formula presented.) for CFR-PEEK liner. When compared to in vivo and in vitro studies, the wear patterns of these two prototypes are consistent with those of the conventional polyethylene liners in the literature. Although the volumetric wear rate of the CFR-PEEK liner is about 11 times lower than the counterpart of XLPE in MoP implants, the wear rate of CoCr was higher when compared to its use with XLPE. Therefore, CFR-PEEK articulating against orthopaedic metals may not be as good an alternative as XLPE, due to higher indicative metallic wear. This detailed computational wear modeling methodology could be utilized in design improvements of implants. © 2022 Society of Tribologists and Lubrication Engineers.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Wear on articulating bearing surfaces is a key factor causing revision in total hip replacement (THR). Wear debris that releases particles from bearing surfaces might result in adverse soft tissue reactions requiring revision surgeries. In this study, a comprehensive computational wear model based on the Archard wear equation was performed to investigate the wear performance under a three-dimensional (3D) physiological gait cycle, mimicking a normal walking condition (5 million cycles). The study shows that the accuracy of the model is highly dependent on the mesh convergence, the wear fraction, and the scaling factor. The simulations were run to provide a vast amount of detail for the reproducibility of the work. Cobalt chromium (CoCr) on cross-linked polyethylene (XLPE) and CoCr on carbon-fiber-reinforced polyether ether ketone (CFR-PEEK) prototype models were created in silico. The volumetric wear rates for CoCr-on-XLPE were calculated as 0.2989 (Formula presented.) for CoCr head and 21.0271 (Formula presented.) for XLPE liner, while for CoCr-on-CFR-PEEK they were 0.3484 (Formula presented.) for CoCr head and 1.8476 (Formula presented.) for CFR-PEEK liner. When compared to in vivo and in vitro studies, the wear patterns of these two prototypes are consistent with those of the conventional polyethylene liners in the literature. Although the volumetric wear rate of the CFR-PEEK liner is about 11 times lower than the counterpart of XLPE in MoP implants, the wear rate of CoCr was higher when compared to its use with XLPE. Therefore, CFR-PEEK articulating against orthopaedic metals may not be as good an alternative as XLPE, due to higher indicative metallic wear. This detailed computational wear modeling methodology could be utilized in design improvements of implants. © 2022 Society of Tribologists and Lubrication Engineers. |
2022 |
Yu, Hao; Feng, Zhihong; Wang, Ling; Mihcin, Senay; Kang, Jianfeng; Bai, Shizhu; Zhao, Yimin Finite Element Study of PEEK Materials Applied in Post-Retained Restorations Journal Article POLYMERS, 14 (16), 2022. @article{WOS:000846652600001, title = {Finite Element Study of PEEK Materials Applied in Post-Retained Restorations}, author = {Hao Yu and Zhihong Feng and Ling Wang and Senay Mihcin and Jianfeng Kang and Shizhu Bai and Yimin Zhao}, doi = {10.3390/polym14163422}, year = {2022}, date = {2022-08-01}, journal = {POLYMERS}, volume = {14}, number = {16}, abstract = {Background: This study aimed to investigate the biomechanical behaviors of polyether ether ketone (PEEK) and traditional materials (titanium and fiber) when used to restore tooth defects in the form of prefabricated post or customized post via computational modelling. Methods: First, the prototype of natural tooth, and the prototypes of prefabricated post and customized post were established, respectively, whilst the residual root was restored with dentin ferrule using reverse engineering methods. Then, the stress and strain of CFR-PEEK (PEEK reinforced by 30% carbon fiber) and pure PEEK (PEEK without any reprocessing) post were compared with those made in traditional materials using the three-dimensional finite element method. Results: From the stress point of view, compared with metal and fiber posts, CFR-PEEK and pure PEEK prefabricated post both demonstrated reduced post-core interface stress, post stress, post-root cement stress and root cement stress; moreover, CFR-PEEK and pure PEEK customized post demonstrated reduced post stress, post-root cement stress and root cement stress, while the strain of CFR-PEEK post was the closest to that of dentin. Conclusions: Compared with the traditional posts, both the CFR-PEEK and pure PEEK posts could reduce the risk of debonding and vertical root fracture, whether they were used as prefabricated posts or customized posts, but the biomechanical behavior of carbon fiber-reinforced CFR-PEEK restorations was the closest to dentin, no matter if they were used as prefabricated post or customized post. Therefore, the CFR-PEEK post could be more suitable to restore massive tooth defects. Pure PEEK needs filler reinforcement to be used for post-retained restoration.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Background: This study aimed to investigate the biomechanical behaviors of polyether ether ketone (PEEK) and traditional materials (titanium and fiber) when used to restore tooth defects in the form of prefabricated post or customized post via computational modelling. Methods: First, the prototype of natural tooth, and the prototypes of prefabricated post and customized post were established, respectively, whilst the residual root was restored with dentin ferrule using reverse engineering methods. Then, the stress and strain of CFR-PEEK (PEEK reinforced by 30% carbon fiber) and pure PEEK (PEEK without any reprocessing) post were compared with those made in traditional materials using the three-dimensional finite element method. Results: From the stress point of view, compared with metal and fiber posts, CFR-PEEK and pure PEEK prefabricated post both demonstrated reduced post-core interface stress, post stress, post-root cement stress and root cement stress; moreover, CFR-PEEK and pure PEEK customized post demonstrated reduced post stress, post-root cement stress and root cement stress, while the strain of CFR-PEEK post was the closest to that of dentin. Conclusions: Compared with the traditional posts, both the CFR-PEEK and pure PEEK posts could reduce the risk of debonding and vertical root fracture, whether they were used as prefabricated posts or customized posts, but the biomechanical behavior of carbon fiber-reinforced CFR-PEEK restorations was the closest to dentin, no matter if they were used as prefabricated post or customized post. Therefore, the CFR-PEEK post could be more suitable to restore massive tooth defects. Pure PEEK needs filler reinforcement to be used for post-retained restoration. |
Mihcin, Senay BIOMEDICAL ENGINEERING-BIOMEDIZINISCHE TECHNIK, 67 (3), pp. 185-199, 2022. @article{WOS:000796085500001, title = {Simultaneous validation of wearable motion capture system for lower body applications: over single plane range of motion (ROM) and gait activities}, author = {Senay Mihcin}, doi = {10.1515/bmt-2021-0429}, year = {2022}, date = {2022-06-01}, journal = {BIOMEDICAL ENGINEERING-BIOMEDIZINISCHE TECHNIK}, volume = {67}, number = {3}, pages = {185-199}, abstract = {Extracting data from Zhu, 2019 #5 daily life activities is important in biomechanical applications to define exact boundary conditions for the intended use-based applications. Although optoelectronic camera-marker based systems are used as gold standard tools for medical applications, due to line-of-sight problem, there is a need for wearable, affordable motion capture (MOCAP) systems. We investigate the potential use of a wearable inertial measurement unit (IMU) based-wearable MOCAP system for biomechanical applications. The in vitro proof of concept is provided for the full lower body consisting of hip, knee, and ankle joints via controlled single-plane anatomical range of motion (ROM) simulations using an electrical motor, while collecting data simultaneously via opto-electronic markers and IMU sensors. On 15 healthy volunteers the flexion-extension, abduction-adduction, internal-external rotation (ROM) values of hip and, the flexion - extension ROM values of the knee and ankle joints are calculated for both systems. The Bland-Altman graphs showed promising agreement both for in vitro and in vivo experiments. The maximum Root Mean Square Errors (RMSE) between the systems in vitro was 3.4 degrees for hip and 5.9 degrees for knee flexion motion in vivo, respectively. The gait data of the volunteers were assessed between the heel strike and toe off events to investigate the limits of agreement, calculating the population averages and standard deviation for both systems over the gait cycle. The maximum difference was for the ankle joint <6 degrees. The results show that proposed system could be an option as an affordable-democratic solution.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Extracting data from Zhu, 2019 #5 daily life activities is important in biomechanical applications to define exact boundary conditions for the intended use-based applications. Although optoelectronic camera-marker based systems are used as gold standard tools for medical applications, due to line-of-sight problem, there is a need for wearable, affordable motion capture (MOCAP) systems. We investigate the potential use of a wearable inertial measurement unit (IMU) based-wearable MOCAP system for biomechanical applications. The in vitro proof of concept is provided for the full lower body consisting of hip, knee, and ankle joints via controlled single-plane anatomical range of motion (ROM) simulations using an electrical motor, while collecting data simultaneously via opto-electronic markers and IMU sensors. On 15 healthy volunteers the flexion-extension, abduction-adduction, internal-external rotation (ROM) values of hip and, the flexion - extension ROM values of the knee and ankle joints are calculated for both systems. The Bland-Altman graphs showed promising agreement both for in vitro and in vivo experiments. The maximum Root Mean Square Errors (RMSE) between the systems in vitro was 3.4 degrees for hip and 5.9 degrees for knee flexion motion in vivo, respectively. The gait data of the volunteers were assessed between the heel strike and toe off events to investigate the limits of agreement, calculating the population averages and standard deviation for both systems over the gait cycle. The maximum difference was for the ankle joint <6 degrees. The results show that proposed system could be an option as an affordable-democratic solution. |
Mihcin, Senay; Ciklacandir, Samet TOWARDS INTEGRATION OF THE FINITE ELEMENT MODELING TECHNIQUE INTO BIOMEDICAL ENGINEERING EDUCATION Journal Article BIOMEDICAL ENGINEERING-APPLICATIONS BASIS COMMUNICATIONS, 34 (02), 2022. @article{WOS:000786971300005, title = {TOWARDS INTEGRATION OF THE FINITE ELEMENT MODELING TECHNIQUE INTO BIOMEDICAL ENGINEERING EDUCATION}, author = {Senay Mihcin and Samet Ciklacandir}, doi = {10.4015/S101623722150054X}, year = {2022}, date = {2022-04-01}, journal = {BIOMEDICAL ENGINEERING-APPLICATIONS BASIS COMMUNICATIONS}, volume = {34}, number = {02}, abstract = {Biomedical engineering (BME) is a multidisciplinary field, resulting in a heavy course load from different fields. We hypothesize that, the engineering curriculum be tailored according to the requirements of the BME profession. In this study, we focus on the teaching of the finite element modeling (FEM) technique by redesigning the course to address the needs of the BME profession by some custom-made changes to meet the unmet. needs. After the completion of the course, evaluation methods of the students were analyzed and detailed over a survey providing feedback from the students. The surveys were related to the teaching the theory of FEM, the laboratory sessions, and the project sessions. The survey results were evaluated using statistical methods. The Pearson correlation coefficient showed a linear agreement between theoretical and practical sessions indicating efficient blending of skills because of the custom-made changes. The survey analysis showed that the students were in favour of the changes, allowing them to be more resourceful and confident with their skills. The positive results indicate a positive attitude among the students towards their profession. As the course design addresses the needs of the profession allowing students to fit in better, the students might, follow their own profession after graduation. A wider follow-up study might be planned next to compare the results between who received tailor-designed courses and those who did not.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Biomedical engineering (BME) is a multidisciplinary field, resulting in a heavy course load from different fields. We hypothesize that, the engineering curriculum be tailored according to the requirements of the BME profession. In this study, we focus on the teaching of the finite element modeling (FEM) technique by redesigning the course to address the needs of the BME profession by some custom-made changes to meet the unmet. needs. After the completion of the course, evaluation methods of the students were analyzed and detailed over a survey providing feedback from the students. The surveys were related to the teaching the theory of FEM, the laboratory sessions, and the project sessions. The survey results were evaluated using statistical methods. The Pearson correlation coefficient showed a linear agreement between theoretical and practical sessions indicating efficient blending of skills because of the custom-made changes. The survey analysis showed that the students were in favour of the changes, allowing them to be more resourceful and confident with their skills. The positive results indicate a positive attitude among the students towards their profession. As the course design addresses the needs of the profession allowing students to fit in better, the students might, follow their own profession after graduation. A wider follow-up study might be planned next to compare the results between who received tailor-designed courses and those who did not. |
Ciklacandir, S; Mihcin, S; Isler, Y IRBM, 43 (6), pp. 604-613, 2022. @article{Ciklacandir2022604, title = {Detailed Investigation of Three-Dimensional Modeling and Printing Technologies from Medical Images to Analyze Femoral Head Fractures Using Finite Element Analysis}, author = {S Ciklacandir and S Mihcin and Y Isler}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85129883533&doi=10.1016%2fj.irbm.2022.04.005&partnerID=40&md5=31017add921b2693916e42e10bdb9b45}, doi = {10.1016/j.irbm.2022.04.005}, year = {2022}, date = {2022-01-01}, journal = {IRBM}, volume = {43}, number = {6}, pages = {604-613}, abstract = {Objectives: One of the fields, where additive manufacturing has numerous applications, is biomedical engineering. 3D printing is preferred over traditional manufacturing methodologies, mostly while developing subject-specific implants and medical devices. This study aims to provide a process flow detailing all the stages starting from the acquisition of radiological images from different imaging modalities; such as computed tomography (CT) and magnetic resonance imaging (MRI) to the printing of the bone morphology and finite element analysis; including the validation process. Materials & Methods: First, the CT scan of a lower abdomen area of a patient was converted into a 3D image using interactive medical imaging control system software. The segmentation process was applied to isolate the femoral head from the soft tissue and the pelvic bone. After the roughness errors and the gaps in the segments were removed using the 3Matic software, the file was converted to stereolithography (STL) file format to transfer to the 3D printer. The printing process was carried out via commercial powder-based Selective Laser Sintering (SLS) printer. The subject-specific femoral head model was formed in 3D. The Finite Element Analysis (FEA) of the femoral head was performed using a commercial FE software package. Results: The results show that experimental analysis and the CT scan-based FEA were compatible both for the stress distributions and the strain values as predicted by the models (R2=0.99). The deviation was calculated as approximately 12% between the experimental results and the Finite Element (FE) results. In addition, it was observed that the SLS technique produced useful results for modeling biomedical tissues with about 24x faster prototyping time. Conclusion: The prescribed process flow could be utilized in clinical settings for the pre-planning of the surgeries (≈428 minutes for femoral head) and also as an educational tool in the biomedical engineering field. © 2022 AGBM}, keywords = {}, pubstate = {published}, tppubtype = {article} } Objectives: One of the fields, where additive manufacturing has numerous applications, is biomedical engineering. 3D printing is preferred over traditional manufacturing methodologies, mostly while developing subject-specific implants and medical devices. This study aims to provide a process flow detailing all the stages starting from the acquisition of radiological images from different imaging modalities; such as computed tomography (CT) and magnetic resonance imaging (MRI) to the printing of the bone morphology and finite element analysis; including the validation process. Materials & Methods: First, the CT scan of a lower abdomen area of a patient was converted into a 3D image using interactive medical imaging control system software. The segmentation process was applied to isolate the femoral head from the soft tissue and the pelvic bone. After the roughness errors and the gaps in the segments were removed using the 3Matic software, the file was converted to stereolithography (STL) file format to transfer to the 3D printer. The printing process was carried out via commercial powder-based Selective Laser Sintering (SLS) printer. The subject-specific femoral head model was formed in 3D. The Finite Element Analysis (FEA) of the femoral head was performed using a commercial FE software package. Results: The results show that experimental analysis and the CT scan-based FEA were compatible both for the stress distributions and the strain values as predicted by the models (R2=0.99). The deviation was calculated as approximately 12% between the experimental results and the Finite Element (FE) results. In addition, it was observed that the SLS technique produced useful results for modeling biomedical tissues with about 24x faster prototyping time. Conclusion: The prescribed process flow could be utilized in clinical settings for the pre-planning of the surgeries (≈428 minutes for femoral head) and also as an educational tool in the biomedical engineering field. © 2022 AGBM |
2021 |
Mihcin, Senay; Ciklacandir, Samet; Kocak, Mertcan; Tosun, Aliye Wearable Motion Capture System Evaluation for Biomechanical Studies for Hip Joints Journal Article JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, 143 (4), 2021. @article{WOS:000626080400016, title = {Wearable Motion Capture System Evaluation for Biomechanical Studies for Hip Joints}, author = {Senay Mihcin and Samet Ciklacandir and Mertcan Kocak and Aliye Tosun}, doi = {10.1115/1.4049199}, year = {2021}, date = {2021-04-01}, journal = {JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, volume = {143}, number = {4}, abstract = {Human motion capture (MOCAP) systems are vital while determining the loads occurring at the joints. Most of the clinical MOCAP systems are very costly, requiring investment and infrastructure. Therefore, alternative technologies are in demand. In this study, a novel markerless wearable MOCAP system was assessed for its compatibility with a biomechanical modeling software. To collect evidence, experiments were designed in two stages for quantifying the range of motion (ROM) of the hip joint, in vitro and in vivo. Three constrained single-plane motions-abduction/adduction, flexion/extension, and internal/external rotation movements of the active leg-were analyzed. The data were collected from 14 healthy volunteers, using the wearable system and a medical grade optoelectronic MOCAP system simultaneously and compared against. For the in vitro study, the root-mean-square error (RMSE) for the abduction/adduction motion of the hip joint was calculated as 0.11deg/0.30deg and 0.11deg/0.09deg, respectively, for the wearable and the opto-electronic system. The in vivo Bland-Altman plots showed that the two system data are comparable. The simulation software is found compatible to run the simulations in offline mode. The wearable system could be utilized in the field of biomechanics software for running the kinetic simulations. The results demonstrated that the wearable system could be an alternative in the field of biomechanics based on the evidence collected.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Human motion capture (MOCAP) systems are vital while determining the loads occurring at the joints. Most of the clinical MOCAP systems are very costly, requiring investment and infrastructure. Therefore, alternative technologies are in demand. In this study, a novel markerless wearable MOCAP system was assessed for its compatibility with a biomechanical modeling software. To collect evidence, experiments were designed in two stages for quantifying the range of motion (ROM) of the hip joint, in vitro and in vivo. Three constrained single-plane motions-abduction/adduction, flexion/extension, and internal/external rotation movements of the active leg-were analyzed. The data were collected from 14 healthy volunteers, using the wearable system and a medical grade optoelectronic MOCAP system simultaneously and compared against. For the in vitro study, the root-mean-square error (RMSE) for the abduction/adduction motion of the hip joint was calculated as 0.11deg/0.30deg and 0.11deg/0.09deg, respectively, for the wearable and the opto-electronic system. The in vivo Bland-Altman plots showed that the two system data are comparable. The simulation software is found compatible to run the simulations in offline mode. The wearable system could be utilized in the field of biomechanics software for running the kinetic simulations. The results demonstrated that the wearable system could be an alternative in the field of biomechanics based on the evidence collected. |
2017 |
Mihcin, Senay; Karakitsios, Ioannis; Le, Nhan; Strehlow, Jan; Demedts, Daniel; Schwenke, Michael; Haase, Sabrina; Preusser, Tobias; Melzer, Andreas Methodology on quantification of sonication duration for safe application of MR guided focused ultrasound for liver tumour ablation Journal Article COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE, 152 , pp. 125-130, 2017, ISSN: 0169-2607. @article{ISI:000413258300013, title = {Methodology on quantification of sonication duration for safe application of MR guided focused ultrasound for liver tumour ablation}, author = {Senay Mihcin and Ioannis Karakitsios and Nhan Le and Jan Strehlow and Daniel Demedts and Michael Schwenke and Sabrina Haase and Tobias Preusser and Andreas Melzer}, doi = {10.1016/j.cmpb.2017.09.006}, issn = {0169-2607}, year = {2017}, date = {2017-12-01}, journal = {COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE}, volume = {152}, pages = {125-130}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Schwenke, Michael; Strehlow, Jan; Demedts, Daniel; Haase, Sabrina; Romero, Diego Barrios; Rothluebbers, Sven; von Dresky, Caroline; Zidowitz, Stephan; Georgii, Joachim; Mihcin, Senay; Bezzi, Mario; Tanner, Christine; Sat, Giora; Levy, Yoav; Jenne, Juergen; Guenther, Matthias; Melzer, Andreas; Preusser, Tobias A focused ultrasound treatment system for moving targets (part I): generic system design and in-silico first-stage evaluation Journal Article JOURNAL OF THERAPEUTIC ULTRASOUND, 5 , pp. 1-14, 2017, ISSN: 2050-5736. @article{ISI:000406663900001, title = {A focused ultrasound treatment system for moving targets (part I): generic system design and in-silico first-stage evaluation}, author = {Michael Schwenke and Jan Strehlow and Daniel Demedts and Sabrina Haase and Diego Barrios Romero and Sven Rothluebbers and Caroline von Dresky and Stephan Zidowitz and Joachim Georgii and Senay Mihcin and Mario Bezzi and Christine Tanner and Giora Sat and Yoav Levy and Juergen Jenne and Matthias Guenther and Andreas Melzer and Tobias Preusser}, doi = {10.1186/s40349-017-0098-7}, issn = {2050-5736}, year = {2017}, date = {2017-07-01}, journal = {JOURNAL OF THERAPEUTIC ULTRASOUND}, volume = {5}, pages = {1-14}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Karakitsios, Ioannis; Joy, Joyce; Mihcin, Senay; Melzer, Andreas Acoustic characterization of Thiel liver for magnetic resonance-guided focused ultrasound treatment Journal Article MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES, 26 (2), pp. 92-96, 2017, ISSN: 1364-5706. @article{ISI:000398127600005, title = {Acoustic characterization of Thiel liver for magnetic resonance-guided focused ultrasound treatment}, author = {Ioannis Karakitsios and Joyce Joy and Senay Mihcin and Andreas Melzer}, doi = {10.1080/13645706.2016.1253589}, issn = {1364-5706}, year = {2017}, date = {2017-01-01}, journal = {MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES}, volume = {26}, number = {2}, pages = {92-96}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2016 |
Mihcin, Senay Spinal curvature for the assessment of spinal stability Journal Article INTERNATIONAL JOURNAL OF BIOMEDICAL ENGINEERING AND TECHNOLOGY, 20 (3), pp. 226-242, 2016, ISSN: 1752-6418. @article{ISI:000384710300003, title = {Spinal curvature for the assessment of spinal stability}, author = {Senay Mihcin}, doi = {10.1504/IJBET.2016.075425}, issn = {1752-6418}, year = {2016}, date = {2016-01-01}, journal = {INTERNATIONAL JOURNAL OF BIOMEDICAL ENGINEERING AND TECHNOLOGY}, volume = {20}, number = {3}, pages = {226-242}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Karakitsios, Ioannis; Mihcin, Senay; Saliev, Timur; Melzer, Andreas Feasibility study of pre-clinical Thiel embalmed human cadaver for MR-guided focused ultrasound of the spine Journal Article MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES, 25 (3), pp. 154-161, 2016, ISSN: 1364-5706. @article{ISI:000383343900006, title = {Feasibility study of pre-clinical Thiel embalmed human cadaver for MR-guided focused ultrasound of the spine}, author = {Ioannis Karakitsios and Senay Mihcin and Timur Saliev and Andreas Melzer}, doi = {10.3109/13645706.2016.1150297}, issn = {1364-5706}, year = {2016}, date = {2016-01-01}, journal = {MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES}, volume = {25}, number = {3}, pages = {154-161}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
0000 |
Alpkaya, Alican Tuncay; Mihcin, Senay The Computational Approach to Predicting Wear: Comparison of Wear Performance of CFR-PEEK and XLPE Liners in Total Hip Replacement Journal Article TRIBOLOGY TRANSACTIONS, 0000. @article{WOS:000899732300001, title = {The Computational Approach to Predicting Wear: Comparison of Wear Performance of CFR-PEEK and XLPE Liners in Total Hip Replacement}, author = {Alican Tuncay Alpkaya and Senay Mihcin}, doi = {10.1080/10402004.2022.2140727}, journal = {TRIBOLOGY TRANSACTIONS}, abstract = {Wear on articulating bearing surfaces is a key factor causing revision in total hip replacement (THR). Wear debris that releases particles from bearing surfaces might result in adverse soft tissue reactions requiring revision surgeries. In this study, a comprehensive computational wear model based on the Archard wear equation was performed to investigate the wear performance under a three-dimensional (3D) physiological gait cycle, mimicking a normal walking condition (5 million cycles). The study shows that the accuracy of the model is highly dependent on the mesh convergence, the wear fraction, and the scaling factor. The simulations were run to provide a vast amount of detail for the reproducibility of the work. Cobalt chromium (CoCr) on cross-linked polyethylene (XLPE) and CoCr on carbon-fiber-reinforced polyether ether ketone (CFR-PEEK) prototype models were created in silico. The volumetric wear rates for CoCr-on-XLPE were calculated as 0.2989 mm(3)/year for CoCr head and 21.0271 mm(3)/year for XLPE liner, while for CoCr-on-CFR-PEEK they were 0.3484 mm(3)/year for CoCr head and 1.8476 mm(3)/year for CFR-PEEK liner. When compared to in vivo and in vitro studies, the wear patterns of these two prototypes are consistent with those of the conventional polyethylene liners in the literature. Although the volumetric wear rate of the CFR-PEEK liner is about 11 times lower than the counterpart of XLPE in MoP implants, the wear rate of CoCr was higher when compared to its use with XLPE. Therefore, CFR-PEEK articulating against orthopatextbackslashedic metals may not be as good an alternative as XLPE, due to higher indicative metallic wear. This detailed computational wear modeling methodology could be utilized in design improvements of implants.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Wear on articulating bearing surfaces is a key factor causing revision in total hip replacement (THR). Wear debris that releases particles from bearing surfaces might result in adverse soft tissue reactions requiring revision surgeries. In this study, a comprehensive computational wear model based on the Archard wear equation was performed to investigate the wear performance under a three-dimensional (3D) physiological gait cycle, mimicking a normal walking condition (5 million cycles). The study shows that the accuracy of the model is highly dependent on the mesh convergence, the wear fraction, and the scaling factor. The simulations were run to provide a vast amount of detail for the reproducibility of the work. Cobalt chromium (CoCr) on cross-linked polyethylene (XLPE) and CoCr on carbon-fiber-reinforced polyether ether ketone (CFR-PEEK) prototype models were created in silico. The volumetric wear rates for CoCr-on-XLPE were calculated as 0.2989 mm(3)/year for CoCr head and 21.0271 mm(3)/year for XLPE liner, while for CoCr-on-CFR-PEEK they were 0.3484 mm(3)/year for CoCr head and 1.8476 mm(3)/year for CFR-PEEK liner. When compared to in vivo and in vitro studies, the wear patterns of these two prototypes are consistent with those of the conventional polyethylene liners in the literature. Although the volumetric wear rate of the CFR-PEEK liner is about 11 times lower than the counterpart of XLPE in MoP implants, the wear rate of CoCr was higher when compared to its use with XLPE. Therefore, CFR-PEEK articulating against orthopatextbackslashedic metals may not be as good an alternative as XLPE, due to higher indicative metallic wear. This detailed computational wear modeling methodology could be utilized in design improvements of implants. |
Alpkaya, Alican Tuncay; Mihcin, Senay The Computational Approach to Predicting Wear: Comparison of Wear Performance of CFR-PEEK and XLPE Liners in Total Hip Replacement Journal Article TRIBOLOGY TRANSACTIONS, 0000. @article{WOS:000899732300001b, title = {The Computational Approach to Predicting Wear: Comparison of Wear Performance of CFR-PEEK and XLPE Liners in Total Hip Replacement}, author = {Alican Tuncay Alpkaya and Senay Mihcin}, doi = {10.1080/10402004.2022.2140727}, journal = {TRIBOLOGY TRANSACTIONS}, abstract = {Wear on articulating bearing surfaces is a key factor causing revision in total hip replacement (THR). Wear debris that releases particles from bearing surfaces might result in adverse soft tissue reactions requiring revision surgeries. In this study, a comprehensive computational wear model based on the Archard wear equation was performed to investigate the wear performance under a three-dimensional (3D) physiological gait cycle, mimicking a normal walking condition (5 million cycles). The study shows that the accuracy of the model is highly dependent on the mesh convergence, the wear fraction, and the scaling factor. The simulations were run to provide a vast amount of detail for the reproducibility of the work. Cobalt chromium (CoCr) on cross-linked polyethylene (XLPE) and CoCr on carbon-fiber-reinforced polyether ether ketone (CFR-PEEK) prototype models were created in silico. The volumetric wear rates for CoCr-on-XLPE were calculated as 0.2989 mm(3)/year for CoCr head and 21.0271 mm(3)/year for XLPE liner, while for CoCr-on-CFR-PEEK they were 0.3484 mm(3)/year for CoCr head and 1.8476 mm(3)/year for CFR-PEEK liner. When compared to in vivo and in vitro studies, the wear patterns of these two prototypes are consistent with those of the conventional polyethylene liners in the literature. Although the volumetric wear rate of the CFR-PEEK liner is about 11 times lower than the counterpart of XLPE in MoP implants, the wear rate of CoCr was higher when compared to its use with XLPE. Therefore, CFR-PEEK articulating against orthopatextbackslashedic metals may not be as good an alternative as XLPE, due to higher indicative metallic wear. This detailed computational wear modeling methodology could be utilized in design improvements of implants.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Wear on articulating bearing surfaces is a key factor causing revision in total hip replacement (THR). Wear debris that releases particles from bearing surfaces might result in adverse soft tissue reactions requiring revision surgeries. In this study, a comprehensive computational wear model based on the Archard wear equation was performed to investigate the wear performance under a three-dimensional (3D) physiological gait cycle, mimicking a normal walking condition (5 million cycles). The study shows that the accuracy of the model is highly dependent on the mesh convergence, the wear fraction, and the scaling factor. The simulations were run to provide a vast amount of detail for the reproducibility of the work. Cobalt chromium (CoCr) on cross-linked polyethylene (XLPE) and CoCr on carbon-fiber-reinforced polyether ether ketone (CFR-PEEK) prototype models were created in silico. The volumetric wear rates for CoCr-on-XLPE were calculated as 0.2989 mm(3)/year for CoCr head and 21.0271 mm(3)/year for XLPE liner, while for CoCr-on-CFR-PEEK they were 0.3484 mm(3)/year for CoCr head and 1.8476 mm(3)/year for CFR-PEEK liner. When compared to in vivo and in vitro studies, the wear patterns of these two prototypes are consistent with those of the conventional polyethylene liners in the literature. Although the volumetric wear rate of the CFR-PEEK liner is about 11 times lower than the counterpart of XLPE in MoP implants, the wear rate of CoCr was higher when compared to its use with XLPE. Therefore, CFR-PEEK articulating against orthopatextbackslashedic metals may not be as good an alternative as XLPE, due to higher indicative metallic wear. This detailed computational wear modeling methodology could be utilized in design improvements of implants. |
Prof. Dr. Serhan Özdemir
Educational Background
B.Sc. Dokuz Eylül University, Turkey, Mechanical Engineering, 1991
M.Sc. Illinois Institute of Technology, USA, Mechanical and Aerospace Engineering, 1996
Ph.D. University of Florida, USA, Mechanical Engineering, 1999
Research Interests
- Machine Health and Diagnostics
- Intelligent Control
- Intelligent Modelling
- +90 232 750 6773
- +90 232 750 6701
- Mechanical Engineering Building (116)
Publications
2017 |
Kosun, Caglar; Ozdemir, Serhan Determining the complexity of multi-component conformal systems: A platoon-based approach Journal Article PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, 471 , pp. 688-695, 2017, ISSN: 0378-4371. @article{ISI:000393733300064, title = {Determining the complexity of multi-component conformal systems: A platoon-based approach}, author = {Caglar Kosun and Serhan Ozdemir}, doi = {10.1016/j.physa.2016.12.027}, issn = {0378-4371}, year = {2017}, date = {2017-04-01}, journal = {PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS}, volume = {471}, pages = {688-695}, abstract = {Many systems in nature and engineering are composed of subsystems. These subsystems may be formed in a linear, planar or spatial array. A typical example of these formations is a chain of vehicles known as platoon formation in traffic flow. Platoon formation of vehicles is a linear or planar formation of vehicles where a certain and a constant headway, and sideway if applicable, is provided in between every and each one of them. It is argued in this paper that a well-automated platoon formation of vehicles is an extreme case of conformity. During this transformation from a many degrees of freedom formation to a solid object, Tsallis q value is computed to be ranging from one extreme case of q = 3 to the other where q = 1, when classified in terms of inverse temperatures of clearance fluctuations. At one-extreme of q = 3, one observes unbounded fluctuations in clearance fluctuations so that inverse temperature distributions approach a Dirac delta at the origin. At the other extreme of g = 1, fluctuations in clearance tend to zero asymptotically, where a solid structure of agents (vehicles) emerges. The transition from q = 3 to q = 1 is investigated through synthetic and experimental clearance fluctuations between the cars. The results show that during the transition from q = 3 to q = 1, the platoon loses its many degrees of freedom (dof) of motion until a solid single object emerges. Authors assert that the Tsallis q value of a platoon of vehicles is limited to 3 > q > 1. (C) 2016 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Many systems in nature and engineering are composed of subsystems. These subsystems may be formed in a linear, planar or spatial array. A typical example of these formations is a chain of vehicles known as platoon formation in traffic flow. Platoon formation of vehicles is a linear or planar formation of vehicles where a certain and a constant headway, and sideway if applicable, is provided in between every and each one of them. It is argued in this paper that a well-automated platoon formation of vehicles is an extreme case of conformity. During this transformation from a many degrees of freedom formation to a solid object, Tsallis q value is computed to be ranging from one extreme case of q = 3 to the other where q = 1, when classified in terms of inverse temperatures of clearance fluctuations. At one-extreme of q = 3, one observes unbounded fluctuations in clearance fluctuations so that inverse temperature distributions approach a Dirac delta at the origin. At the other extreme of g = 1, fluctuations in clearance tend to zero asymptotically, where a solid structure of agents (vehicles) emerges. The transition from q = 3 to q = 1 is investigated through synthetic and experimental clearance fluctuations between the cars. The results show that during the transition from q = 3 to q = 1, the platoon loses its many degrees of freedom (dof) of motion until a solid single object emerges. Authors assert that the Tsallis q value of a platoon of vehicles is limited to 3 > q > 1. (C) 2016 Elsevier B.V. All rights reserved. |
Kosun, Caglar; Ozdemir, Serhan An entropy-based analysis of lane changing behavior: An interactive approach Journal Article TRAFFIC INJURY PREVENTION, 18 (4), pp. 441-447, 2017, ISSN: 1538-9588. @article{ISI:000399359600018, title = {An entropy-based analysis of lane changing behavior: An interactive approach}, author = {Caglar Kosun and Serhan Ozdemir}, doi = {10.1080/15389588.2016.1204446}, issn = {1538-9588}, year = {2017}, date = {2017-01-01}, journal = {TRAFFIC INJURY PREVENTION}, volume = {18}, number = {4}, pages = {441-447}, abstract = {Objectives: As a novelty, this article proposes the nonadditive entropy framework for the description of driver behaviors during lane changing. The authors also state that this entropy framework governs the lane changing behavior in traffic flow in accordance with the long-range vehicular interactions and traffic safety.Methods: The nonadditive entropy framework is the new generalized theory of thermostatistical mechanics. Vehicular interactions during lane changing are considered within this framework. The interactive approach for the lane changing behavior of the drivers is presented in the traffic flow scenarios presented in the article. According to the traffic flow scenarios, 4 categories of traffic flow and driver behaviors are obtained. Through the scenarios, comparative analyses of nonadditive and additive entropy domains are also provided.Results: Two quadrants of the categories belong to the nonadditive entropy; the rest are involved in the additive entropy domain. Driving behaviors are extracted and the scenarios depict that nonadditivity matches safe driving well, whereas additivity corresponds to unsafe driving. Furthermore, the cooperative traffic system is considered in nonadditivity where the long-range interactions are present. However, the uncooperative traffic system falls into the additivity domain. The analyses also state that there would be possible traffic flow transitions among the quadrants. This article shows that lane changing behavior could be generalized as nonadditive, with additivity as a special case, based on the given traffic conditions.Conclusions: The nearest and close neighbor models are well within the conventional additive entropy framework. In this article, both the long-range vehicular interactions and safe driving behavior in traffic are handled in the nonadditive entropy domain. It is also inferred that the Tsallis entropy region would correspond to mandatory lane changing behavior, whereas additive and either the extensive or nonextensive entropy region would match discretionary lane changing behavior. This article states that driver behaviors would be in the nonadditive entropy domain to provide a safe traffic stream and hence with vehicle accident prevention in mind.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Objectives: As a novelty, this article proposes the nonadditive entropy framework for the description of driver behaviors during lane changing. The authors also state that this entropy framework governs the lane changing behavior in traffic flow in accordance with the long-range vehicular interactions and traffic safety.Methods: The nonadditive entropy framework is the new generalized theory of thermostatistical mechanics. Vehicular interactions during lane changing are considered within this framework. The interactive approach for the lane changing behavior of the drivers is presented in the traffic flow scenarios presented in the article. According to the traffic flow scenarios, 4 categories of traffic flow and driver behaviors are obtained. Through the scenarios, comparative analyses of nonadditive and additive entropy domains are also provided.Results: Two quadrants of the categories belong to the nonadditive entropy; the rest are involved in the additive entropy domain. Driving behaviors are extracted and the scenarios depict that nonadditivity matches safe driving well, whereas additivity corresponds to unsafe driving. Furthermore, the cooperative traffic system is considered in nonadditivity where the long-range interactions are present. However, the uncooperative traffic system falls into the additivity domain. The analyses also state that there would be possible traffic flow transitions among the quadrants. This article shows that lane changing behavior could be generalized as nonadditive, with additivity as a special case, based on the given traffic conditions.Conclusions: The nearest and close neighbor models are well within the conventional additive entropy framework. In this article, both the long-range vehicular interactions and safe driving behavior in traffic are handled in the nonadditive entropy domain. It is also inferred that the Tsallis entropy region would correspond to mandatory lane changing behavior, whereas additive and either the extensive or nonextensive entropy region would match discretionary lane changing behavior. This article states that driver behaviors would be in the nonadditive entropy domain to provide a safe traffic stream and hence with vehicle accident prevention in mind. |
2016 |
Kosun, Caglar; Ozdemir, Serhan A superstatistical model of vehicular traffic flow Journal Article PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, 444 , pp. 466-475, 2016, ISSN: 0378-4371. @article{ISI:000366785900043, title = {A superstatistical model of vehicular traffic flow}, author = {Caglar Kosun and Serhan Ozdemir}, doi = {10.1016/j.physa.2015.10.042}, issn = {0378-4371}, year = {2016}, date = {2016-02-01}, journal = {PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS}, volume = {444}, pages = {466-475}, abstract = {In the analysis of vehicular traffic flow, a myriad of techniques have been implemented. In this study, superstatistics is used in modeling the traffic flow on a highway segment. Traffic variables such as vehicular speeds, volume, and headway were collected for three days. For the superstatistical approach, at least two distinct time scales must exist, so that a superposition of nonequilibrium systems assumption could hold. When the slow dynamics of the vehicle speeds exhibit a Gaussian distribution in between the fluctuations of the system at large, one speaks of a relaxation to a local equilibrium. These Gaussian distributions are found with corresponding standard deviations 1/root beta. This translates into a series of fluctuating beta values, hence the statistics of statistics, superstatistics. The traffic flow model has generated an inverse temperature parameter (beta) distribution as well as the speed distribution. This beta distribution has shown that the fluctuations in beta are distributed with respect to a chi-square distribution. It must be mentioned that two distinct Tsallis q values are specified: one is time-dependent and the other is independent. A ramification of these q values is that the highway segment and the traffic flow generate separate characteristics. This highway segment in question is not only nonadditive in nature, but a nonequilibrium driven system, with frequent relaxations to a Gaussian. (C) 2015 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In the analysis of vehicular traffic flow, a myriad of techniques have been implemented. In this study, superstatistics is used in modeling the traffic flow on a highway segment. Traffic variables such as vehicular speeds, volume, and headway were collected for three days. For the superstatistical approach, at least two distinct time scales must exist, so that a superposition of nonequilibrium systems assumption could hold. When the slow dynamics of the vehicle speeds exhibit a Gaussian distribution in between the fluctuations of the system at large, one speaks of a relaxation to a local equilibrium. These Gaussian distributions are found with corresponding standard deviations 1/root beta. This translates into a series of fluctuating beta values, hence the statistics of statistics, superstatistics. The traffic flow model has generated an inverse temperature parameter (beta) distribution as well as the speed distribution. This beta distribution has shown that the fluctuations in beta are distributed with respect to a chi-square distribution. It must be mentioned that two distinct Tsallis q values are specified: one is time-dependent and the other is independent. A ramification of these q values is that the highway segment and the traffic flow generate separate characteristics. This highway segment in question is not only nonadditive in nature, but a nonequilibrium driven system, with frequent relaxations to a Gaussian. (C) 2015 Elsevier B.V. All rights reserved. |
2015 |
Kosun, Caglar; Celik, Huseyin Murat; Ozdemir, Serhan AN ANALYSIS OF VEHICULAR TRAFFIC FLOW USING LANGEVIN EQUATION Journal Article PROMET-TRAFFIC & TRANSPORTATION, 27 (4), pp. 317-324, 2015, ISSN: 0353-5320. @article{ISI:000361265300005, title = {AN ANALYSIS OF VEHICULAR TRAFFIC FLOW USING LANGEVIN EQUATION}, author = {Caglar Kosun and Huseyin Murat Celik and Serhan Ozdemir}, doi = {10.7307/ptt.v27i4.1613}, issn = {0353-5320}, year = {2015}, date = {2015-01-01}, journal = {PROMET-TRAFFIC & TRANSPORTATION}, volume = {27}, number = {4}, pages = {317-324}, abstract = {Traffic flow data are stochastic in nature, and an abundance of literature exists thereof. One way to express stochastic data is the Langevin equation. Langevin equation consists of two parts. The first part is known as the deterministic drift term, the other as the stochastic diffusion term. Langevin equation does not only help derive the deterministic and random terms of the selected portion of the city of Istanbul traffic empirically, but also sheds light on the underlying dynamics of the flow. Drift diagrams have shown that slow lane tends to get congested faster when vehicle speeds attain a value of 25 km/h, and it is 20 km/h for the fast lane. Three or four distinct regimes may be discriminated again from the drift diagrams; congested, intermediate, and free-flow regimes. At places, even the intermediate regime may be divided in two, often with readiness to congestion. This has revealed the fact that for the selected portion of the highway, there are two main states of flow, namely, congestion and free-flow, with an intermediate state where the noise-driven traffic flow forces the flow into either of the distinct regimes.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Traffic flow data are stochastic in nature, and an abundance of literature exists thereof. One way to express stochastic data is the Langevin equation. Langevin equation consists of two parts. The first part is known as the deterministic drift term, the other as the stochastic diffusion term. Langevin equation does not only help derive the deterministic and random terms of the selected portion of the city of Istanbul traffic empirically, but also sheds light on the underlying dynamics of the flow. Drift diagrams have shown that slow lane tends to get congested faster when vehicle speeds attain a value of 25 km/h, and it is 20 km/h for the fast lane. Three or four distinct regimes may be discriminated again from the drift diagrams; congested, intermediate, and free-flow regimes. At places, even the intermediate regime may be divided in two, often with readiness to congestion. This has revealed the fact that for the selected portion of the highway, there are two main states of flow, namely, congestion and free-flow, with an intermediate state where the noise-driven traffic flow forces the flow into either of the distinct regimes. |
2011 |
Gezgin, Erkin; Ozdemir, Serhan Classification of manipulators of the same origin by virtue of compactness and complexity Journal Article MECHANISM AND MACHINE THEORY, 46 (10), pp. 1425-1433, 2011, ISSN: 0094-114X. @article{ISI:000293062700007, title = {Classification of manipulators of the same origin by virtue of compactness and complexity}, author = {Erkin Gezgin and Serhan Ozdemir}, doi = {10.1016/j.mechmachtheory.2011.05.009}, issn = {0094-114X}, year = {2011}, date = {2011-10-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {46}, number = {10}, pages = {1425-1433}, abstract = {This work deals with a classification method that employs concepts such as complexity and compactness. The idea is to classify manipulators, or any other mechanism for that matter, of the same origin, based on the geometry of the joints, the tasks performed by the joints, the efficiency and the manufacturing cost to generate the specified efficiency. It is known that successive units on a single branch create individual uncertainties that affect the eventual quality of the performed operation [1]. An entropic expression quantifies this uncertainty in terms of the number of links and the unit effectiveness. The concepts of compactness and complexity have been formulated, and these concepts are explained through serial and parallel manipulators with varying parameters. Eventually, a cost function is created which is a function of complexity, uncertainty and the manufacturing cost. A worked example on M = 6 Stewart-Gough platform is given how this cost function could be taken advantage of when deciding an initial manipulator. A genetic algorithm is used for the optimization of the cost function, where the results are tabulated. (C) 2011 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This work deals with a classification method that employs concepts such as complexity and compactness. The idea is to classify manipulators, or any other mechanism for that matter, of the same origin, based on the geometry of the joints, the tasks performed by the joints, the efficiency and the manufacturing cost to generate the specified efficiency. It is known that successive units on a single branch create individual uncertainties that affect the eventual quality of the performed operation [1]. An entropic expression quantifies this uncertainty in terms of the number of links and the unit effectiveness. The concepts of compactness and complexity have been formulated, and these concepts are explained through serial and parallel manipulators with varying parameters. Eventually, a cost function is created which is a function of complexity, uncertainty and the manufacturing cost. A worked example on M = 6 Stewart-Gough platform is given how this cost function could be taken advantage of when deciding an initial manipulator. A genetic algorithm is used for the optimization of the cost function, where the results are tabulated. (C) 2011 Elsevier Ltd. All rights reserved. |
Coskun, Anil; Sevil, Hakki Erhan; Ozdemir, Serhan Cost effective localization in distributed sensory networks Journal Article ENGINEERING APPLICATIONS OF ARTIFICIAL INTELLIGENCE, 24 (2), pp. 232-237, 2011, ISSN: 0952-1976. @article{ISI:000287066800003, title = {Cost effective localization in distributed sensory networks}, author = {Anil Coskun and Hakki Erhan Sevil and Serhan Ozdemir}, doi = {10.1016/j.engappai.2010.10.006}, issn = {0952-1976}, year = {2011}, date = {2011-03-01}, journal = {ENGINEERING APPLICATIONS OF ARTIFICIAL INTELLIGENCE}, volume = {24}, number = {2}, pages = {232-237}, abstract = {The most important mechanism to occur in biological distributed sensory networks (DSNs) is called lateral inhibition, (LI). LI relies on one simple principle. Each sensor strives to suppress its neighbors in proportion to its own excitation. In this study, LI mechanism is exploited to localize the unknown position of a light source that illuminated the photosensitive sensory network containing high and low quality sensors. Each photosensitive sensor was then calibrated to accurately read the distance to the light source. A series of experiments were conducted employing both quality sensors. Low quality array was allowed to take advantage of LI, whereas the high quality one was not. Results showed that the lateral inhibition mechanism increased the sensitivity of inferior quality sensors, giving the ability to make the localization as sensitive as high quality sensors do. This suggests that the networks with multitude of sensors could be made cost-effective, were these sensory networks equipped with LI. (C) 2010 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The most important mechanism to occur in biological distributed sensory networks (DSNs) is called lateral inhibition, (LI). LI relies on one simple principle. Each sensor strives to suppress its neighbors in proportion to its own excitation. In this study, LI mechanism is exploited to localize the unknown position of a light source that illuminated the photosensitive sensory network containing high and low quality sensors. Each photosensitive sensor was then calibrated to accurately read the distance to the light source. A series of experiments were conducted employing both quality sensors. Low quality array was allowed to take advantage of LI, whereas the high quality one was not. Results showed that the lateral inhibition mechanism increased the sensitivity of inferior quality sensors, giving the ability to make the localization as sensitive as high quality sensors do. This suggests that the networks with multitude of sensors could be made cost-effective, were these sensory networks equipped with LI. (C) 2010 Elsevier Ltd. All rights reserved. |
Sevil, Hakki Erhan; Ozdemir, Serhan Prediction of microdrill breakage using rough sets Journal Article AI EDAM-ARTIFICIAL INTELLIGENCE FOR ENGINEERING DESIGN ANALYSIS AND MANUFACTURING, 25 (1), pp. 15-23, 2011, ISSN: 0890-0604. @article{ISI:000287388000002, title = {Prediction of microdrill breakage using rough sets}, author = {Hakki Erhan Sevil and Serhan Ozdemir}, doi = {10.1017/S0890060410000144}, issn = {0890-0604}, year = {2011}, date = {2011-02-01}, journal = {AI EDAM-ARTIFICIAL INTELLIGENCE FOR ENGINEERING DESIGN ANALYSIS AND MANUFACTURING}, volume = {25}, number = {1}, pages = {15-23}, abstract = {This study attempts to correlate the nonlinear invariants' with the changing conditions of a drilling process through a series of condition monitoring experiments on small diameter (1 mm) drill bits. Run-to-failure tests are performed on these drill bits, and vibration data are consecutively gathered at equal time intervals. Nonlinear invariants, such as the Kolmogorov entropy and correlation dimension, and statistical parameters are calculated based on the corresponding conditions of the drill bits. By intervariations of these values between two successive measurements, a drop rise table is created. Any variation that is within a certain threshold (+/-20% of the measurements in this case) is assumed to be constant. Any fluctuation above or below is assumed to be either a rise or a drop. The reduct and conflict tables then help eliminate incongruous and redundant data by the use of rough sets (RSs). Inconsistent data, which by definition is the boundary region, are classified through certainty and coverage factors. By handling inconsistencies and redundancies, 11 rules are extracted from 39 experiments, representing the underlying rules. Then 22 new experiments are used to check the validity of the rule space. The RS decision frame performs best at predicting no failure cases. It is believed that RSs are superior in dealing with real-life data over fuzzy set logic in that actual measured data are never as consistent as here and may dominate the monitoring of the manufacturing processes as it becomes more widespread.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study attempts to correlate the nonlinear invariants' with the changing conditions of a drilling process through a series of condition monitoring experiments on small diameter (1 mm) drill bits. Run-to-failure tests are performed on these drill bits, and vibration data are consecutively gathered at equal time intervals. Nonlinear invariants, such as the Kolmogorov entropy and correlation dimension, and statistical parameters are calculated based on the corresponding conditions of the drill bits. By intervariations of these values between two successive measurements, a drop rise table is created. Any variation that is within a certain threshold (+/-20% of the measurements in this case) is assumed to be constant. Any fluctuation above or below is assumed to be either a rise or a drop. The reduct and conflict tables then help eliminate incongruous and redundant data by the use of rough sets (RSs). Inconsistent data, which by definition is the boundary region, are classified through certainty and coverage factors. By handling inconsistencies and redundancies, 11 rules are extracted from 39 experiments, representing the underlying rules. Then 22 new experiments are used to check the validity of the rule space. The RS decision frame performs best at predicting no failure cases. It is believed that RSs are superior in dealing with real-life data over fuzzy set logic in that actual measured data are never as consistent as here and may dominate the monitoring of the manufacturing processes as it becomes more widespread. |
2008 |
Ozdemir, Serhan Power transmission entropy Journal Article International Journal of Heavy Vehicle Systems, 15 (1), pp. 82–88, 2008. @article{ozdemir2008power, title = {Power transmission entropy}, author = {Serhan Ozdemir}, year = {2008}, date = {2008-01-01}, journal = {International Journal of Heavy Vehicle Systems}, volume = {15}, number = {1}, pages = {82--88}, publisher = {Inderscience Publishers}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2007 |
Ozdemir, Serhan Measures of uncertainty in power split systems Journal Article MECHANISM AND MACHINE THEORY, 42 (2), pp. 159-167, 2007, ISSN: 0094-114X. @article{ISI:000243623800003, title = {Measures of uncertainty in power split systems}, author = {Serhan Ozdemir}, doi = {10.1016/j.mechmachtheory.2006.04.008}, issn = {0094-114X}, year = {2007}, date = {2007-02-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {42}, number = {2}, pages = {159-167}, abstract = {This paper discusses the overlooked uncertainty inherent in every transmission. The uncertainty aspect has been often, for the sake of clarity, ignored. Instead, mechanical transmissions have been characterized traditionally by their transmission efficacies. It is known that transmission localities are sources of power loss, depending on many factors, hence sources of uncertainty. Thus each transmission of power should not only be designated by a constant of efficiency but also by an expression of uncertainty, reflecting the probability of transmission. Furthermore, Shannon's and Renyi's expressions of entropy have been used to quantify this so-called transmission uncertainty. The entropy of a transmitting unit is given in these two forms and then compared. Practical formulations for flow optimization are given. (C) 2006 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper discusses the overlooked uncertainty inherent in every transmission. The uncertainty aspect has been often, for the sake of clarity, ignored. Instead, mechanical transmissions have been characterized traditionally by their transmission efficacies. It is known that transmission localities are sources of power loss, depending on many factors, hence sources of uncertainty. Thus each transmission of power should not only be designated by a constant of efficiency but also by an expression of uncertainty, reflecting the probability of transmission. Furthermore, Shannon's and Renyi's expressions of entropy have been used to quantify this so-called transmission uncertainty. The entropy of a transmitting unit is given in these two forms and then compared. Practical formulations for flow optimization are given. (C) 2006 Elsevier Ltd. All rights reserved. |
2006 |
Alpay, S; Bilir, L; Ozdemir, S; Ozerdem, B Wind speed time series characterization by Hilbert transform Journal Article INTERNATIONAL JOURNAL OF ENERGY RESEARCH, 30 (5), pp. 359-364, 2006, ISSN: 0363-907X. @article{ISI:000236746700006, title = {Wind speed time series characterization by Hilbert transform}, author = {S Alpay and L Bilir and S Ozdemir and B Ozerdem}, doi = {10.1002/er.1156}, issn = {0363-907X}, year = {2006}, date = {2006-04-01}, journal = {INTERNATIONAL JOURNAL OF ENERGY RESEARCH}, volume = {30}, number = {5}, pages = {359-364}, abstract = {Predictions of wind energy potential in a given region are based on on-location observations. The time series of these observations would later be analysed and modelled either by a probability density function (pdf) such as a Weibull curve to represent the data or recently by soft computing techniques, such as neural networks (NNs). In this paper, discrete Hilbert transform has been applied to characterize the wind sample data measured on Izmir Institute of Technology campus area which is located in Urla, Izmir, Turkey, in March 2001 and 2002. By applying discrete Hilbert transform filter, the instantaneous amplitude, phase and frequency are found, and characterization of wind speed is accomplished. Authors have also tried to estimate the hourly wind data using daily sequence by Hilbert transform technique. Results are varying. Copyright (c) 2005 John Wiley & Sons, Ltd.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Predictions of wind energy potential in a given region are based on on-location observations. The time series of these observations would later be analysed and modelled either by a probability density function (pdf) such as a Weibull curve to represent the data or recently by soft computing techniques, such as neural networks (NNs). In this paper, discrete Hilbert transform has been applied to characterize the wind sample data measured on Izmir Institute of Technology campus area which is located in Urla, Izmir, Turkey, in March 2001 and 2002. By applying discrete Hilbert transform filter, the instantaneous amplitude, phase and frequency are found, and characterization of wind speed is accomplished. Authors have also tried to estimate the hourly wind data using daily sequence by Hilbert transform technique. Results are varying. Copyright (c) 2005 John Wiley & Sons, Ltd. |
2005 |
Atan, E; Ozdemir, S Intelligence modeling of the transient asperity temperatures in meshing spur gears Journal Article MECHANISM AND MACHINE THEORY, 40 (1), pp. 119-127, 2005, ISSN: 0094-114X. @article{ISI:000226442400009, title = {Intelligence modeling of the transient asperity temperatures in meshing spur gears}, author = {E Atan and S Ozdemir}, doi = {10.1016/j.mechmachtheory.2004.06.006}, issn = {0094-114X}, year = {2005}, date = {2005-01-01}, journal = {MECHANISM AND MACHINE THEORY}, volume = {40}, number = {1}, pages = {119-127}, abstract = {Temperature rise in the contact zone of meshing gears is a serious problem in gear design. The temperature rise on lubricated surfaces may result in the significant decrease on the material strength and lubricant viscosity which reduces the film thickness, causing solid to solid contact. The equations and the evaluations of the rise in temperature were given in [Proc. VDI Berichte 2 (1665) (2002) 615-626] and reiterated in this paper briefly. The data from [Proc. VDI Berichte 2 (1665) (2002) 615-626] are used to establish an artificial intelligence model where a multi layer feedforward neural network has been employed. The model accepts surface roughness, gear ratio, horsepower and the number of teeth as input variables, and outputs calculated pinion surface asperity temperatures. The aim of the present work is to provide a straightforward and simple way to compute the asperity temperature rise for a given set of variables. R-square value for the computed temperature values proves the method satisfactory. (C) 2004 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Temperature rise in the contact zone of meshing gears is a serious problem in gear design. The temperature rise on lubricated surfaces may result in the significant decrease on the material strength and lubricant viscosity which reduces the film thickness, causing solid to solid contact. The equations and the evaluations of the rise in temperature were given in [Proc. VDI Berichte 2 (1665) (2002) 615-626] and reiterated in this paper briefly. The data from [Proc. VDI Berichte 2 (1665) (2002) 615-626] are used to establish an artificial intelligence model where a multi layer feedforward neural network has been employed. The model accepts surface roughness, gear ratio, horsepower and the number of teeth as input variables, and outputs calculated pinion surface asperity temperatures. The aim of the present work is to provide a straightforward and simple way to compute the asperity temperature rise for a given set of variables. R-square value for the computed temperature values proves the method satisfactory. (C) 2004 Elsevier Ltd. All rights reserved. |
Ozdemir, S Local sparse coding control of CVPSTs Journal Article INTERNATIONAL JOURNAL OF HEAVY VEHICLE SYSTEMS, 12 (2), pp. 104-120, 2005, ISSN: 1744-232X. @article{ISI:000240128000004, title = {Local sparse coding control of CVPSTs}, author = {S Ozdemir}, doi = {10.1504/IJHVS.2005.006378}, issn = {1744-232X}, year = {2005}, date = {2005-01-01}, journal = {INTERNATIONAL JOURNAL OF HEAVY VEHICLE SYSTEMS}, volume = {12}, number = {2}, pages = {104-120}, abstract = {This paper discusses simulations of a control scheme based on locally sparse coded networks (CMACs) for a novel previously proposed continuously variable transmission (CVT), a hybrid continuously variable power split transmission (CVPST) (Osdemir and Schueller, 2002). Automotive transmissions match the speed and the torque of the power source to the speed and torque requirements of the load. Properly designed CVTs have shown potential to improve efficiency and performance. The main advantage of CMACs is fast computation because of their simple operational principles. Simulation results have shown that memory contents either reach a stable limit cycle or an attractor based on the selection of network parameters and the training method. Both online and offline training are possible.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper discusses simulations of a control scheme based on locally sparse coded networks (CMACs) for a novel previously proposed continuously variable transmission (CVT), a hybrid continuously variable power split transmission (CVPST) (Osdemir and Schueller, 2002). Automotive transmissions match the speed and the torque of the power source to the speed and torque requirements of the load. Properly designed CVTs have shown potential to improve efficiency and performance. The main advantage of CMACs is fast computation because of their simple operational principles. Simulation results have shown that memory contents either reach a stable limit cycle or an attractor based on the selection of network parameters and the training method. Both online and offline training are possible. |
2004 |
Boke, H; Akkurt, S; Ozdemir, S; Gokturk, EH; Saltik, ENC Quantification of CaCO3-CaSO3 center dot 0.5H(2)O-CaSO4 center dot 2H(2)O mixtures by FTIR analysis and its ANN model Journal Article MATERIALS LETTERS, 58 (5), pp. 723-726, 2004, ISSN: 0167-577X. @article{ISI:000188216300035, title = {Quantification of CaCO3-CaSO3 center dot 0.5H(2)O-CaSO4 center dot 2H(2)O mixtures by FTIR analysis and its ANN model}, author = {H Boke and S Akkurt and S Ozdemir and EH Gokturk and ENC Saltik}, doi = {10.1016/j.matlet.2003.07.008}, issn = {0167-577X}, year = {2004}, date = {2004-02-01}, journal = {MATERIALS LETTERS}, volume = {58}, number = {5}, pages = {723-726}, abstract = {A new quantitative analysis method for mixtures of calcium carbonate (CaCO3), calcium sulphite hemihydrate (CaSO3.1/2H(2)O) and gypsum (CaSO4.2H(2)O) by FTIR spectroscopy is developed. The method involves the FTIR analysis of powder mixtures of several compositions on KBr disc specimens. Intensities of the resulting absorbance peaks for CaCO3, CaSO3.1/2H(2)O and CaSO4.2H(2)O at 1453, 980, 1146 cm(-1) were used as input data for an artificial neural network (ANN) model, the output being the weight percent compositions of the mixtures. The training and testing data were randomly separated from the complete original data set. Testing of the model was done with successfully low-average error levels. The utility of the model is in the potential ability to use FTIR spectrum to predict the proportions of the three substances in unknown mixtures. (C) 2003 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A new quantitative analysis method for mixtures of calcium carbonate (CaCO3), calcium sulphite hemihydrate (CaSO3.1/2H(2)O) and gypsum (CaSO4.2H(2)O) by FTIR spectroscopy is developed. The method involves the FTIR analysis of powder mixtures of several compositions on KBr disc specimens. Intensities of the resulting absorbance peaks for CaCO3, CaSO3.1/2H(2)O and CaSO4.2H(2)O at 1453, 980, 1146 cm(-1) were used as input data for an artificial neural network (ANN) model, the output being the weight percent compositions of the mixtures. The training and testing data were randomly separated from the complete original data set. Testing of the model was done with successfully low-average error levels. The utility of the model is in the potential ability to use FTIR spectrum to predict the proportions of the three substances in unknown mixtures. (C) 2003 Elsevier B.V. All rights reserved. |
2003 |
Tayfur, G; Ozdemir, S; Singh, VP Fuzzy logic algorithm for runoff-induced sediment transport from bare soil surfaces Journal Article ADVANCES IN WATER RESOURCES, 26 (12), pp. 1249-1256, 2003, ISSN: 0309-1708. @article{ISI:000186662500004, title = {Fuzzy logic algorithm for runoff-induced sediment transport from bare soil surfaces}, author = {G Tayfur and S Ozdemir and VP Singh}, doi = {10.1016/j.advwatres.2003.08.005}, issn = {0309-1708}, year = {2003}, date = {2003-12-01}, journal = {ADVANCES IN WATER RESOURCES}, volume = {26}, number = {12}, pages = {1249-1256}, abstract = {Utilizing the rainfall intensity, and slope data, a fuzzy logic algorithm was developed to estimate sediment loads from bare soil surfaces. Considering slope and rainfall as input variables, the variables were fuzzified into fuzzy subsets. The fuzzy subsets of the variables were considered to have triangular membership functions. The relations among rainfall intensity, slope, and sediment transport were represented by a set of fuzzy rules. The fuzzy rules relating input variables to the output variable of sediment discharge were laid out in the IF-THEN format. The commonly used weighted average method was employed for the defuzzification procedure. The sediment load predicted by the fuzzy model was in satisfactory agreement with the measured sediment load data. Predicting the mean sediment loads from experimental runs, the performance of the fuzzy model was compared with that of the artificial neural networks (ANNs) and the physics-based models. The results of showed revealed that the fuzzy model performed better under very high rainfall intensities over different slopes and over very steep slopes under different rainfall intensities. This is closely related to the selection of the shape and frequency of the fuzzy membership functions in the fuzzy model. (C) 2003 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Utilizing the rainfall intensity, and slope data, a fuzzy logic algorithm was developed to estimate sediment loads from bare soil surfaces. Considering slope and rainfall as input variables, the variables were fuzzified into fuzzy subsets. The fuzzy subsets of the variables were considered to have triangular membership functions. The relations among rainfall intensity, slope, and sediment transport were represented by a set of fuzzy rules. The fuzzy rules relating input variables to the output variable of sediment discharge were laid out in the IF-THEN format. The commonly used weighted average method was employed for the defuzzification procedure. The sediment load predicted by the fuzzy model was in satisfactory agreement with the measured sediment load data. Predicting the mean sediment loads from experimental runs, the performance of the fuzzy model was compared with that of the artificial neural networks (ANNs) and the physics-based models. The results of showed revealed that the fuzzy model performed better under very high rainfall intensities over different slopes and over very steep slopes under different rainfall intensities. This is closely related to the selection of the shape and frequency of the fuzzy membership functions in the fuzzy model. (C) 2003 Elsevier Ltd. All rights reserved. |
Akkurt, S; Ozdemir, S; Tayfur, G; Akyol, B The use of GA-ANNs in the modelling of compressive strength of cement mortar Journal Article CEMENT AND CONCRETE RESEARCH, 33 (7), pp. 973-979, 2003, ISSN: 0008-8846. @article{ISI:000183190600005, title = {The use of GA-ANNs in the modelling of compressive strength of cement mortar}, author = {S Akkurt and S Ozdemir and G Tayfur and B Akyol}, doi = {10.1016/S0008-8846(03)00006-1}, issn = {0008-8846}, year = {2003}, date = {2003-07-01}, journal = {CEMENT AND CONCRETE RESEARCH}, volume = {33}, number = {7}, pages = {973-979}, abstract = {In this paper, results of a project aimed at modelling the compressive strength of cement mortar under standard curing conditions are reported. Plant data were collected for 6 months for the chemical and physical properties of the cement that were used in model construction and testing. The training and testing data were separated from the complete original data set by the use of genetic algorithms (GAs). A GA-artificial neural network (ANN) model based on the training data of the cement strength was created. Testing of the model was also done within low average error levels (2.24%). The model was subjected to sensitivity analysis to predict the response of the system to different values of the factors affecting the strength. The plots obtained after sensitivity analysis indicated that increasing the amount Of C3S, SO3 and surface area led to increased strength within the limits of the model. C2S decreased the strength whereas C(3)A decreased or increased the strength depending on the SO3 level. Because of the limited data range used for training, the prediction results were good only within the same range. The utility of the model is in the potential ability to control processing parameters to yield the desired strength levels and in providing information regarding the most favourable experimental conditions to obtain maximum compressive strength. (C) 2003 Elsevier Science Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, results of a project aimed at modelling the compressive strength of cement mortar under standard curing conditions are reported. Plant data were collected for 6 months for the chemical and physical properties of the cement that were used in model construction and testing. The training and testing data were separated from the complete original data set by the use of genetic algorithms (GAs). A GA-artificial neural network (ANN) model based on the training data of the cement strength was created. Testing of the model was also done within low average error levels (2.24%). The model was subjected to sensitivity analysis to predict the response of the system to different values of the factors affecting the strength. The plots obtained after sensitivity analysis indicated that increasing the amount Of C3S, SO3 and surface area led to increased strength within the limits of the model. C2S decreased the strength whereas C(3)A decreased or increased the strength depending on the SO3 level. Because of the limited data range used for training, the prediction results were good only within the same range. The utility of the model is in the potential ability to control processing parameters to yield the desired strength levels and in providing information regarding the most favourable experimental conditions to obtain maximum compressive strength. (C) 2003 Elsevier Science Ltd. All rights reserved. |
Assoc. Prof. Dr. Ünver Özkol
Educational Background
B.Sc. İstanbul Technical University, Turkey, Mechanical Engineering, 1991
M.Sc. Illinois Institute of Technology, USA, Mechanical and Aerospace Engineering, 1996
Ph.D. Illinois Institute of Technology, USA, Mechanical and Aerospace Engineering, 2002
Research Interests
- Turbulent and Separated Flows in machinery
- Experimental fluid mechanics (Optical techniques, thermal anemometry and flow visualization)
- Heat transfer enhancement, Cooling of Electronic Equipment with single and multiphase heat transfer
- +90 232 750 6770
- +90 232 750 6701
- Mechanical Engineering Building (113)
Publications
2022 |
Ulu, A; Yildiz, G; Rodriguez, A D; Özkol, Ü Spray Analysis of Biodiesels Derived from Various Biomass Resources in a Constant Volume Spray Chamber Journal Article ACS Omega, 7 (23), pp. 19365-19379, 2022. @article{Ulu202219365, title = {Spray Analysis of Biodiesels Derived from Various Biomass Resources in a Constant Volume Spray Chamber}, author = {A Ulu and G Yildiz and A D Rodriguez and Ü Özkol}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85132107803&doi=10.1021%2facsomega.2c00952&partnerID=40&md5=995ab045ec0310695a47b69c61b69c80}, doi = {10.1021/acsomega.2c00952}, year = {2022}, date = {2022-01-01}, journal = {ACS Omega}, volume = {7}, number = {23}, pages = {19365-19379}, abstract = {This research aimed to analyze the spray characteristics of various biodiesels, which have rarely been investigated in terms of spray analysis in the literature compared to fossil diesel. For this purpose, four different methyl ester-type biodiesels were produced from canola, corn, cottonseed, and sunflower oils. These feedstocks were selected due to their wide availability in Turkey and being among the significant resources for biodiesel production. Measured physical properties of biodiesel samples showed that biodiesel fuels had, on average, 1.7 to 1.9 times higher viscosities, 5.3 to 6.6% larger densities, and 37 to 39.1% higher contact angle values than the reference diesel fuel. Spray characteristics of all fuels were experimentally examined in a constant volume spray chamber under chamber pressures of 0, 5, 10, and 15 bar and injection pressures of 600, 800, and 1000 bar. All tested biodiesels performed, on average, 3 to 20% longer spray penetration lengths, 5 to 30% narrower spray cone angles, and 5-18% lesser spray areas than the reference diesel fuel under chamber pressures of 5 and 10 bar. No significant differences occurred at 15 bar ambient pressure between biodiesels and diesel. In addition, analytical and empirical predictions showed that biodiesels had around 21.2-35.1% larger SMD values and approximately 7% lower air entrainment. © 2022 American Chemical Society. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This research aimed to analyze the spray characteristics of various biodiesels, which have rarely been investigated in terms of spray analysis in the literature compared to fossil diesel. For this purpose, four different methyl ester-type biodiesels were produced from canola, corn, cottonseed, and sunflower oils. These feedstocks were selected due to their wide availability in Turkey and being among the significant resources for biodiesel production. Measured physical properties of biodiesel samples showed that biodiesel fuels had, on average, 1.7 to 1.9 times higher viscosities, 5.3 to 6.6% larger densities, and 37 to 39.1% higher contact angle values than the reference diesel fuel. Spray characteristics of all fuels were experimentally examined in a constant volume spray chamber under chamber pressures of 0, 5, 10, and 15 bar and injection pressures of 600, 800, and 1000 bar. All tested biodiesels performed, on average, 3 to 20% longer spray penetration lengths, 5 to 30% narrower spray cone angles, and 5-18% lesser spray areas than the reference diesel fuel under chamber pressures of 5 and 10 bar. No significant differences occurred at 15 bar ambient pressure between biodiesels and diesel. In addition, analytical and empirical predictions showed that biodiesels had around 21.2-35.1% larger SMD values and approximately 7% lower air entrainment. © 2022 American Chemical Society. All rights reserved. |
Ulu, A; Yildiz, G; Özkol, Ü; Rodriguez, A D Experimental investigation of spray characteristics of ethyl esters in a constant volume chamber Journal Article Biomass Conversion and Biorefinery, 2022. @article{Ulu2022b, title = {Experimental investigation of spray characteristics of ethyl esters in a constant volume chamber}, author = {A Ulu and G Yildiz and Ü Özkol and A D Rodriguez}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85125134221&doi=10.1007%2fs13399-022-02476-3&partnerID=40&md5=f56d167f075688de07dc30653fa40c64}, doi = {10.1007/s13399-022-02476-3}, year = {2022}, date = {2022-01-01}, journal = {Biomass Conversion and Biorefinery}, abstract = {Abstract: Biodiesels are mainly produced via the utilization of methanol in transesterification, which is the widespread biodiesel production process. The majority of this methanol is currently obtained from fossil resources, i.e. coal and natural gas. However, in contrast with methanol, biomass-based ethanol can also be used to produce biodiesels; this could allow the production line to become fully renewable. This study aimed to investigate the spray characteristics of various ethyl ester type biodiesels derived from sunflower and corn oils in comparison to methyl esters based on the same feedstocks and reference petroleum-based diesel. Spray penetration length (SPL) and spray cone angle (SCA) were experimentally evaluated in a constant volume chamber allowing optical access, under chamber pressures of 0, 5, 10 and 15 bar and injection pressures of 600 and 800 bar. Sauter mean diameter (SMD) values were estimated by using an analytical correlation. Consequently, ethyl esters performed longer SPL (2.8–20%) and narrower SCA (5.1–19%) than diesel under ambient pressures of 5 and 10 bar. Although the SMD values of ethyl esters were 48% higher than diesel on average, their macroscopic spray characteristics were very similar to those of diesel under 15 bar chamber pressure. Moreover, ethyl esters were found to be very similar to methyl esters in terms of spray characteristics. The differences in SPL, SCA and SMD values for both types of biodiesels were lower than 4%. When considering the uncertainty (± 0.84%) and repeatability (±5%) ratios, the difference between the spray characteristics of methyl and ethyl esters was not major. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Abstract: Biodiesels are mainly produced via the utilization of methanol in transesterification, which is the widespread biodiesel production process. The majority of this methanol is currently obtained from fossil resources, i.e. coal and natural gas. However, in contrast with methanol, biomass-based ethanol can also be used to produce biodiesels; this could allow the production line to become fully renewable. This study aimed to investigate the spray characteristics of various ethyl ester type biodiesels derived from sunflower and corn oils in comparison to methyl esters based on the same feedstocks and reference petroleum-based diesel. Spray penetration length (SPL) and spray cone angle (SCA) were experimentally evaluated in a constant volume chamber allowing optical access, under chamber pressures of 0, 5, 10 and 15 bar and injection pressures of 600 and 800 bar. Sauter mean diameter (SMD) values were estimated by using an analytical correlation. Consequently, ethyl esters performed longer SPL (2.8–20%) and narrower SCA (5.1–19%) than diesel under ambient pressures of 5 and 10 bar. Although the SMD values of ethyl esters were 48% higher than diesel on average, their macroscopic spray characteristics were very similar to those of diesel under 15 bar chamber pressure. Moreover, ethyl esters were found to be very similar to methyl esters in terms of spray characteristics. The differences in SPL, SCA and SMD values for both types of biodiesels were lower than 4%. When considering the uncertainty (± 0.84%) and repeatability (±5%) ratios, the difference between the spray characteristics of methyl and ethyl esters was not major. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature. |
2019 |
Acarer, Sercan; Özkol, Ünver Off-Design Analysis of Transonic Bypass Fan Systems Using Streamline Curvature Through-Flow Method Journal Article International Journal of Turbo and Jet Engines, 36 (2), pp. 137 – 146, 2019, (All Open Access, Green Open Access). @article{Acarer2019137, title = {Off-Design Analysis of Transonic Bypass Fan Systems Using Streamline Curvature Through-Flow Method}, author = {Sercan Acarer and Ünver Özkol}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85046815136&doi=10.1515%2ftjj-2016-0083&partnerID=40&md5=3b24de44dd45ff48c0814f96a18258cc}, doi = {10.1515/tjj-2016-0083}, year = {2019}, date = {2019-01-01}, journal = {International Journal of Turbo and Jet Engines}, volume = {36}, number = {2}, pages = {137 – 146}, abstract = {The two-dimensional streamline curvature through-flow modeling of turbomachinery is still a key element for turbomachinery preliminary analysis. Basically, axisymmetric swirling flow field is solved numerically. The effects of blades are imposed as sources of swirl, work input/output and entropy generation. Although the topic is studied vastly in the literature for compressors and turbines, combined modeling of the transonic fan and the downstream splitter of turbofan engine configuration, to the authors' best knowledge, is limited. In a prior study, the authors presented a new method for bypass fan modeling for inverse design calculations. Moreover, new set of practical empirical correlations are calibrated and validated. This paper is an extension of this study to rapid off-design analysis of transonic by-pass fan systems. The methodology is validated by two test cases: NASA 2-stage fan and GE-NASA bypass fan case. The proposed methodology is a simple extension for streamline curvature method and can be applied to existing compressor methodologies with minimum numerical effort. © 2019 Walter de Gruyter GmbH, Berlin/Boston.}, note = {All Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } The two-dimensional streamline curvature through-flow modeling of turbomachinery is still a key element for turbomachinery preliminary analysis. Basically, axisymmetric swirling flow field is solved numerically. The effects of blades are imposed as sources of swirl, work input/output and entropy generation. Although the topic is studied vastly in the literature for compressors and turbines, combined modeling of the transonic fan and the downstream splitter of turbofan engine configuration, to the authors' best knowledge, is limited. In a prior study, the authors presented a new method for bypass fan modeling for inverse design calculations. Moreover, new set of practical empirical correlations are calibrated and validated. This paper is an extension of this study to rapid off-design analysis of transonic by-pass fan systems. The methodology is validated by two test cases: NASA 2-stage fan and GE-NASA bypass fan case. The proposed methodology is a simple extension for streamline curvature method and can be applied to existing compressor methodologies with minimum numerical effort. © 2019 Walter de Gruyter GmbH, Berlin/Boston. |
Celik, Hasan; Mobedi, Moghtada; Nakayama, Akira; Ozkol, Unver Journal of Porous Media, 22 (5), pp. 511 – 529, 2019, (All Open Access, Green Open Access). @article{Celik2019511, title = {A study on numerical determination of permeability and inertia coefficient of aluminum foam using X-ray microtomography technique: Focus on inspection methods for reliability (permeability and inertia coefficient by tomography)}, author = {Hasan Celik and Moghtada Mobedi and Akira Nakayama and Unver Ozkol}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85065613946&doi=10.1615%2fJPorMedia.2019028887&partnerID=40&md5=cc89991bf14176783bc2c187db3358c8}, doi = {10.1615/JPorMedia.2019028887}, year = {2019}, date = {2019-01-01}, journal = {Journal of Porous Media}, volume = {22}, number = {5}, pages = {511 – 529}, abstract = {The volume-averaged (i.e., macroscopic) transport properties such as permeability and inertia coefficient of two aluminum foams with 10 and 20 pores per inch (PPI) pore density are found using microtomography images. It is shown that a comparison between the numerical values and the experimental results may not be sufficient to prove the correctness of the obtained results. Hence, in addition to traditional validation methods such as grid independency and comparison with reported results in literature, further inspections such as (a) checking the development of flow, (b) inspection of Darcy and non-Darcy regions, (c) conservation of flow rate through the porous media, (d) sufficiency of number of voxels in the narrow throats, and (e) observation of transverse velocity gradients in pores for high and low Reynolds numbers can be performed to further validate the achieved results. These techniques have been discussed and explained in detail for the performed study. Moreover, the obtained permeability and inertia coefficient values are compared with 19 reported theoretical, numerical, and experimental studies. The maximum deviation between the present results and the reported studies for 10 PPI is below 25%, while for 20 PPI it is below 28%. © 2019 by Begell House, Inc.}, note = {All Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } The volume-averaged (i.e., macroscopic) transport properties such as permeability and inertia coefficient of two aluminum foams with 10 and 20 pores per inch (PPI) pore density are found using microtomography images. It is shown that a comparison between the numerical values and the experimental results may not be sufficient to prove the correctness of the obtained results. Hence, in addition to traditional validation methods such as grid independency and comparison with reported results in literature, further inspections such as (a) checking the development of flow, (b) inspection of Darcy and non-Darcy regions, (c) conservation of flow rate through the porous media, (d) sufficiency of number of voxels in the narrow throats, and (e) observation of transverse velocity gradients in pores for high and low Reynolds numbers can be performed to further validate the achieved results. These techniques have been discussed and explained in detail for the performed study. Moreover, the obtained permeability and inertia coefficient values are compared with 19 reported theoretical, numerical, and experimental studies. The maximum deviation between the present results and the reported studies for 10 PPI is below 25%, while for 20 PPI it is below 28%. © 2019 by Begell House, Inc. |
2018 |
Kor, Orcun; Acarer, Sercan; Ozkol, Unver Aerodynamic optimization of through-flow design model of a high by-pass transonic aero-engine fan using genetic algorithm Journal Article PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY, 232 (3), pp. 211-224, 2018, ISSN: 0957-6509. @article{ISI:000435491500001, title = {Aerodynamic optimization of through-flow design model of a high by-pass transonic aero-engine fan using genetic algorithm}, author = {Orcun Kor and Sercan Acarer and Unver Ozkol}, doi = {10.1177/0957650917730466}, issn = {0957-6509}, year = {2018}, date = {2018-05-01}, journal = {PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY}, volume = {232}, number = {3}, pages = {211-224}, abstract = {This study deals with aerodynamic optimization of a high by-pass transonic aero-engine fan module in a through-flow inverse design model at cruise condition. To the authors' best knowledge, although the literature contains through-flow optimization of the simplified cases of compressors and turbines, an optimization study targeting the more elaborate case of combined transonic fan and splitter through-flow model is not considered in the literature. Such a through-flow optimization of a transonic fan, combined with bypass and core streams separated by an aerodynamically shaped flow splitter, possesses significant challenges to any optimizer, due to highly non-linear nature of the problem and the high number of constraints, including the fulfillment of the targeted bypass ratio. It is the aim of this study to consider this previously untouched area in detail and therefore present a more sophisticated and accurate optimization environment for actual bypass fan systems. An in-house optimization code using genetic algorithm is coupled with a previously developed in-house through-flow solver which is using a streamline curvature technique and a set of in-house calibrated empirical models for incidence, deviation, loss and blockage. As the through-flow models are the backbone of turbo-machinery design, and great majority of design decisions are taken in this phase, such a study is assessed to result in significant guidelines to the gas turbine community.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study deals with aerodynamic optimization of a high by-pass transonic aero-engine fan module in a through-flow inverse design model at cruise condition. To the authors' best knowledge, although the literature contains through-flow optimization of the simplified cases of compressors and turbines, an optimization study targeting the more elaborate case of combined transonic fan and splitter through-flow model is not considered in the literature. Such a through-flow optimization of a transonic fan, combined with bypass and core streams separated by an aerodynamically shaped flow splitter, possesses significant challenges to any optimizer, due to highly non-linear nature of the problem and the high number of constraints, including the fulfillment of the targeted bypass ratio. It is the aim of this study to consider this previously untouched area in detail and therefore present a more sophisticated and accurate optimization environment for actual bypass fan systems. An in-house optimization code using genetic algorithm is coupled with a previously developed in-house through-flow solver which is using a streamline curvature technique and a set of in-house calibrated empirical models for incidence, deviation, loss and blockage. As the through-flow models are the backbone of turbo-machinery design, and great majority of design decisions are taken in this phase, such a study is assessed to result in significant guidelines to the gas turbine community. |
Celik, Hasan; Mobedi, Moghtada; Nakayama, Akira; Ozkol, Unver Numerical Heat Transfer; Part A: Applications, 74 (7), pp. 1368 – 1386, 2018, (All Open Access, Green Open Access). @article{Celik20181368, title = {A numerical study on determination of volume averaged thermal transport properties of metal foam structures using X-ray microtomography technique}, author = {Hasan Celik and Moghtada Mobedi and Akira Nakayama and Unver Ozkol}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85057255888&doi=10.1080%2f10407782.2018.1494936&partnerID=40&md5=48bd8293534537dec7583acb2bf5c66f}, doi = {10.1080/10407782.2018.1494936}, year = {2018}, date = {2018-01-01}, journal = {Numerical Heat Transfer; Part A: Applications}, volume = {74}, number = {7}, pages = {1368 – 1386}, abstract = {Volume averaged thermal transport properties of two metal foams with 10 and 20 PPI are obtained by using microtomography technique. The digital 3D structures of samples are generated in computer environment. The governing equations are solved for the entire domain and the volume averaged technique is used to determine interfacial heat transfer coefficient, longitudinal and transverse thermal dispersion conductivity. The study is performed for the pore scale Reynolds number from 100 to 600. The obtained results are within the ranges of the suggested correlations in literature. The present study supports the correlations suggested by Calmidi and Mahajan (2000) and Zhang et al. (2016). © 2018, © 2018 Taylor & Francis Group, LLC.}, note = {All Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Volume averaged thermal transport properties of two metal foams with 10 and 20 PPI are obtained by using microtomography technique. The digital 3D structures of samples are generated in computer environment. The governing equations are solved for the entire domain and the volume averaged technique is used to determine interfacial heat transfer coefficient, longitudinal and transverse thermal dispersion conductivity. The study is performed for the pore scale Reynolds number from 100 to 600. The obtained results are within the ranges of the suggested correlations in literature. The present study supports the correlations suggested by Calmidi and Mahajan (2000) and Zhang et al. (2016). © 2018, © 2018 Taylor & Francis Group, LLC. |
2017 |
Celik, Hasan; Mobedi, Moghtada; Manca, Oronzio; Ozkol, Unver A pore scale analysis for determination of interfacial convective heat transfer coefficient for thin periodic porousmedia undermixed convection Journal Article INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW, 27 (12), pp. 2775-2798, 2017, ISSN: 0961-5539. @article{ISI:000416431600006b, title = {A pore scale analysis for determination of interfacial convective heat transfer coefficient for thin periodic porousmedia undermixed convection}, author = {Hasan Celik and Moghtada Mobedi and Oronzio Manca and Unver Ozkol}, doi = {10.1108/HFF-01-2017-0036}, issn = {0961-5539}, year = {2017}, date = {2017-01-01}, journal = {INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW}, volume = {27}, number = {12}, pages = {2775-2798}, abstract = {Purpose - The purpose of this study is to determine interfacial convective heat transfer coefficient numerically, for a porous media consisting of square blocks in inline arrangement under mixed convection heat transfer. Design/methodology/approach - The continuity, momentum and energy equations are solved in dimensionless form for a representative elementary volume of porous media, numerically. The velocity and temperature fields for different values of porosity, Ri and Re numbers are obtained. The study is performed for the range of Ri number from 0.01 to 10, Re number from 100 to 500 and porosity value from 0.51 to 0.96. Based on the obtained results, the value of the interfacial convective heat transfer coefficient is calculated by using volume average method. Findings - It was found that at low porosities (such as 0.51), the interfacial Nusselt number does not considerably change with Ri and Re numbers. However, for porous media with high Ri number and porosity (such as 10 and 0.51, respectively), secondary flows occur in the middle of the channel between rods improving heat transfer between solid and fluid, considerably. It is shown that the available correlations of interfacial heat transfer coefficient suggested for forced convection can be used for mixed convection for the porous media with low porosity (such as 0.51) or for the flow with low Ri number (such as 0.01). Originality/value - To the best of the authors' knowledge, there is no study on determination of interfacial convective heat transfer coefficient for mixed convection in porous media in literature. The present study might be the first study providing an accurate idea on the range of this important parameter, which will be useful particularly for researchers who study on mixed convection heat transfer in porous media, macroscopically.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Purpose - The purpose of this study is to determine interfacial convective heat transfer coefficient numerically, for a porous media consisting of square blocks in inline arrangement under mixed convection heat transfer. Design/methodology/approach - The continuity, momentum and energy equations are solved in dimensionless form for a representative elementary volume of porous media, numerically. The velocity and temperature fields for different values of porosity, Ri and Re numbers are obtained. The study is performed for the range of Ri number from 0.01 to 10, Re number from 100 to 500 and porosity value from 0.51 to 0.96. Based on the obtained results, the value of the interfacial convective heat transfer coefficient is calculated by using volume average method. Findings - It was found that at low porosities (such as 0.51), the interfacial Nusselt number does not considerably change with Ri and Re numbers. However, for porous media with high Ri number and porosity (such as 10 and 0.51, respectively), secondary flows occur in the middle of the channel between rods improving heat transfer between solid and fluid, considerably. It is shown that the available correlations of interfacial heat transfer coefficient suggested for forced convection can be used for mixed convection for the porous media with low porosity (such as 0.51) or for the flow with low Ri number (such as 0.01). Originality/value - To the best of the authors' knowledge, there is no study on determination of interfacial convective heat transfer coefficient for mixed convection in porous media in literature. The present study might be the first study providing an accurate idea on the range of this important parameter, which will be useful particularly for researchers who study on mixed convection heat transfer in porous media, macroscopically. |
2014 |
Ozgumus, Turkuler; Mobedi, Moghtada; Ozkol, Unver DETERMINATION OF KOZENY CONSTANT BASED ON POROSITY AND PORE TO THROAT SIZE RATIO IN POROUS MEDIUM WITH RECTANGULAR RODS Journal Article ENGINEERING APPLICATIONS OF COMPUTATIONAL FLUID MECHANICS, 8 (2), pp. 308-318, 2014, ISSN: 1994-2060. @article{ISI:000337224100010, title = {DETERMINATION OF KOZENY CONSTANT BASED ON POROSITY AND PORE TO THROAT SIZE RATIO IN POROUS MEDIUM WITH RECTANGULAR RODS}, author = {Turkuler Ozgumus and Moghtada Mobedi and Unver Ozkol}, doi = {10.1080/19942060.2014.11015516}, issn = {1994-2060}, year = {2014}, date = {2014-06-01}, journal = {ENGINEERING APPLICATIONS OF COMPUTATIONAL FLUID MECHANICS}, volume = {8}, number = {2}, pages = {308-318}, abstract = {Kozeny-Carman permeability equation is an important relation for the determination of permeability in porous media. In this study, the permeabilities of porous media that contains rectangular rods are determined, numerically. The applicability of Kozeny-Carman equation for the periodic porous media is investigated and the effects of porosity and pore to throat size ratio on Kozeny constant are studied. The continuity and Navier-Stokes equations are solved to determine the velocity and pressure fields in the voids between the rods. Based on the obtained flow field, the permeability values for different porosities from 0.2 to 0.9 and pore to throat size ratio values from 1.63 to 7.46 are computed. Then Kozeny constants for different porous media with various porosity and pore to throat size ratios are obtained and a relationship between Kozeny constant, porosity and pore to throat size ratio is constructed. The study reveals that the pore to throat size ratio is an important geometrical parameter that should be taken into account for deriving a correlation for permeability. The suggestion of a fixed value for Kozeny constant makes the application of Kozeny-Carman permeability equation too narrow for a very specific porous medium. However, it is possible to apply the Kozeny-Carman permeability equation for wide ranges of porous media with different geometrical parameters (various porosity, hydraulic diameter, particle size and aspect ratio) if Kozeny constant is a function of two parameters as porosity and pore to throat size ratios.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Kozeny-Carman permeability equation is an important relation for the determination of permeability in porous media. In this study, the permeabilities of porous media that contains rectangular rods are determined, numerically. The applicability of Kozeny-Carman equation for the periodic porous media is investigated and the effects of porosity and pore to throat size ratio on Kozeny constant are studied. The continuity and Navier-Stokes equations are solved to determine the velocity and pressure fields in the voids between the rods. Based on the obtained flow field, the permeability values for different porosities from 0.2 to 0.9 and pore to throat size ratio values from 1.63 to 7.46 are computed. Then Kozeny constants for different porous media with various porosity and pore to throat size ratios are obtained and a relationship between Kozeny constant, porosity and pore to throat size ratio is constructed. The study reveals that the pore to throat size ratio is an important geometrical parameter that should be taken into account for deriving a correlation for permeability. The suggestion of a fixed value for Kozeny constant makes the application of Kozeny-Carman permeability equation too narrow for a very specific porous medium. However, it is possible to apply the Kozeny-Carman permeability equation for wide ranges of porous media with different geometrical parameters (various porosity, hydraulic diameter, particle size and aspect ratio) if Kozeny constant is a function of two parameters as porosity and pore to throat size ratios. |
2013 |
Ozgumus, Turkuler; Mobedi, Moghtada; Ozkol, Unver; Nakayama, Akira Thermal Dispersion in Porous Media-A Review on the Experimental Studies for Packed Beds Journal Article APPLIED MECHANICS REVIEWS, 65 (3), 2013, ISSN: 0003-6900. @article{ISI:000329612200001, title = {Thermal Dispersion in Porous Media-A Review on the Experimental Studies for Packed Beds}, author = {Turkuler Ozgumus and Moghtada Mobedi and Unver Ozkol and Akira Nakayama}, doi = {10.1115/1.4024351}, issn = {0003-6900}, year = {2013}, date = {2013-05-01}, journal = {APPLIED MECHANICS REVIEWS}, volume = {65}, number = {3}, abstract = {Thermal dispersion is an important topic in the convective heat transfer in porous media. In order to determine the heat transfer in a packed bed, the effective thermal conductivity including both stagnant and dispersion thermal conductivities should be known. Several theoretical and experimental studies have been performed on the determination of the effective thermal conductivity. The aim of this study is to review the experimental studies done on the determination of the effective thermal conductivity of the packed beds. In this study, firstly brief information on the definition of the thermal dispersion is presented and then the reported experimental studies on the determination of the effective thermal conductivity are summarized and compared. The reported experimental methods are classified into three groups: (1) heat addition/removal at the lateral boundaries, (2) heat addition at the inlet/outlet boundary, (3) heat addition inside the bed. For each performed study, the experimental details, methods, obtained results, and suggested correlations for the determination of the effective thermal conductivity are presented. The similarities and differences between experimental methods and reported studies are shown by tables. Comparison of the correlations for the effective thermal conductivity is made by using figures and the results of the studies are discussed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Thermal dispersion is an important topic in the convective heat transfer in porous media. In order to determine the heat transfer in a packed bed, the effective thermal conductivity including both stagnant and dispersion thermal conductivities should be known. Several theoretical and experimental studies have been performed on the determination of the effective thermal conductivity. The aim of this study is to review the experimental studies done on the determination of the effective thermal conductivity of the packed beds. In this study, firstly brief information on the definition of the thermal dispersion is presented and then the reported experimental studies on the determination of the effective thermal conductivity are summarized and compared. The reported experimental methods are classified into three groups: (1) heat addition/removal at the lateral boundaries, (2) heat addition at the inlet/outlet boundary, (3) heat addition inside the bed. For each performed study, the experimental details, methods, obtained results, and suggested correlations for the determination of the effective thermal conductivity are presented. The similarities and differences between experimental methods and reported studies are shown by tables. Comparison of the correlations for the effective thermal conductivity is made by using figures and the results of the studies are discussed. |
2010 |
Mobedi, Moghtada; Ozkol, Uenver; Sunden, Bengt Visualization of diffusion and convection heat transport in a square cavity with natural convection Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 53 (1-3), pp. 99-109, 2010, ISSN: 0017-9310. @article{ISI:000272877900012, title = {Visualization of diffusion and convection heat transport in a square cavity with natural convection}, author = {Moghtada Mobedi and Uenver Ozkol and Bengt Sunden}, doi = {10.1016/j.ijheatmasstransfer.2009.09.048}, issn = {0017-9310}, year = {2010}, date = {2010-01-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {53}, number = {1-3}, pages = {99-109}, abstract = {In this study, the total heatfunction equation which includes diffusion and convection transport is divided into the corresponding heatfunction equations. The superposition rule is used to obtain the mathematical definitions of diffusion and convection heatfunctions and corresponding boundary conditions. It is observed that the separate visualization of diffusion and convection heatlines provides significant information on understanding of the mechanism of heat transfer in a convective flow. The direction of the diffusion and convection heat transport as well as the strength of convection compared to the conduction in entire or in a portion of a domain can be visualized. The diffusion heatlines demonstrate a potential flow like behavior while convective heat flow rotates due to the source term of the convection heatfunction equation, similar to the rotation of fluid flow generated by fluid flow vorticity. The similarity between the streamfunction and the total heatfunction yields a concept of heat flow vorticity, Omega(t). The obtained results show that the maximum absolute value of the convection heatfunction may be an appropriate parameter for determination of the convection strength. The diffusion and convection heatfunction equations for natural convection in a differentially heated square cavity for four different length of the heated surface on the right vertical wall as s(p) = L/4, L/2, 3L/4 and L and a fixed length of the cooled surface on the right vertical wall as L/4 are obtained and corresponding heatlines are drawn. The values of the conduction heatfunction are positive while the sign of convection heatfunction values is negative for the studied cases. Based on the distribution of total heatlines, two regions are detected in the cavity, an active region with the positive values of heatlines signifying dominant conduction heat transfer and a passive region with the negative heatfunction values in where convection heat flow is dominant and heat only rotates in a closed contour pattern. The variations of average Nusselt number, average of heat flow vorticity. maximum absolute values of convection heatfunction and streamfunction at different Rayleigh numbers and lengths of the heated surface are presented. (C) 2009 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, the total heatfunction equation which includes diffusion and convection transport is divided into the corresponding heatfunction equations. The superposition rule is used to obtain the mathematical definitions of diffusion and convection heatfunctions and corresponding boundary conditions. It is observed that the separate visualization of diffusion and convection heatlines provides significant information on understanding of the mechanism of heat transfer in a convective flow. The direction of the diffusion and convection heat transport as well as the strength of convection compared to the conduction in entire or in a portion of a domain can be visualized. The diffusion heatlines demonstrate a potential flow like behavior while convective heat flow rotates due to the source term of the convection heatfunction equation, similar to the rotation of fluid flow generated by fluid flow vorticity. The similarity between the streamfunction and the total heatfunction yields a concept of heat flow vorticity, Omega(t). The obtained results show that the maximum absolute value of the convection heatfunction may be an appropriate parameter for determination of the convection strength. The diffusion and convection heatfunction equations for natural convection in a differentially heated square cavity for four different length of the heated surface on the right vertical wall as s(p) = L/4, L/2, 3L/4 and L and a fixed length of the cooled surface on the right vertical wall as L/4 are obtained and corresponding heatlines are drawn. The values of the conduction heatfunction are positive while the sign of convection heatfunction values is negative for the studied cases. Based on the distribution of total heatlines, two regions are detected in the cavity, an active region with the positive values of heatlines signifying dominant conduction heat transfer and a passive region with the negative heatfunction values in where convection heat flow is dominant and heat only rotates in a closed contour pattern. The variations of average Nusselt number, average of heat flow vorticity. maximum absolute values of convection heatfunction and streamfunction at different Rayleigh numbers and lengths of the heated surface are presented. (C) 2009 Elsevier Ltd. All rights reserved. |
Res. Assist. Dr. Hüseyin Sarıaltın
Internship Coordinator
Educational Background
B.Sc. Selcuk University, Mechanical Engineering, 2006
M.Sc. University of California – Riverside, Mechanical Engineering, 2010
Ph.D. Ege University, Solar Energy Institute, 2019
Research Interests
- Energy System Modelling
- Organic Photovoltaics Technologies
- +90 232 750 6788
- +90 232 750 6701
- Mechanical Engineering Building, Research Assistant Office-2 (Z46)
Publications
2021 |
Sarialtin, H; Geyer, R; Zafer, C Environmental assessment of transparent conductive oxide-free efficient flexible organo-lead halide perovskite solar cell Journal Article Energy Sources, Part A: Recovery, Utilization and Environmental Effects, 43 (20), pp. 2544-2553, 2021. @article{Sarialtin20212544, title = {Environmental assessment of transparent conductive oxide-free efficient flexible organo-lead halide perovskite solar cell}, author = {H Sarialtin and R Geyer and C Zafer}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85095721962&doi=10.1080%2f15567036.2020.1842560&partnerID=40&md5=fce22be696576207a0d582736c5feda1}, doi = {10.1080/15567036.2020.1842560}, year = {2021}, date = {2021-01-01}, journal = {Energy Sources, Part A: Recovery, Utilization and Environmental Effects}, volume = {43}, number = {20}, pages = {2544-2553}, abstract = {Perovskite solar cells (PSCs), one of the third-generation photovoltaic (PV) technologies, have recently become a very popular topic in photovoltaic research. This technology, which is a candidate for commercialization in the future, needs to be evaluated from an environmental point of view. The amount of electricity consumption is the most important factor that directly determines the environmental impact values of photovoltaic cell manufacturing. Transparent conductive oxide (TCO) coated glass is one of the major contributors to electricity consumption in PSC architecture. It is therefore useful to investigate the environmental profile of TCO coated glass-free PSC architecture with conventional PVs. One of the solutions to this issue is manufacturing PSC on a flexible substrate. Flexible PVs are considered to be one of the most promising candidates for mass production with its advantages of low-temperature manufacturing, higher efficiency with a lower weight, portability, and compatibility with a roll to roll fabrication. In this work, we show that the environmental impacts of a representative PSCs with a flexible substrate. While the energy payback time (EPBT) of the flexible PSC is already competitive with commercial PVs, the device must reach a 25-year cell lifetime for its global warming potential (GWP) to reach a reasonable range. © 2020 Taylor & Francis Group, LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Perovskite solar cells (PSCs), one of the third-generation photovoltaic (PV) technologies, have recently become a very popular topic in photovoltaic research. This technology, which is a candidate for commercialization in the future, needs to be evaluated from an environmental point of view. The amount of electricity consumption is the most important factor that directly determines the environmental impact values of photovoltaic cell manufacturing. Transparent conductive oxide (TCO) coated glass is one of the major contributors to electricity consumption in PSC architecture. It is therefore useful to investigate the environmental profile of TCO coated glass-free PSC architecture with conventional PVs. One of the solutions to this issue is manufacturing PSC on a flexible substrate. Flexible PVs are considered to be one of the most promising candidates for mass production with its advantages of low-temperature manufacturing, higher efficiency with a lower weight, portability, and compatibility with a roll to roll fabrication. In this work, we show that the environmental impacts of a representative PSCs with a flexible substrate. While the energy payback time (EPBT) of the flexible PSC is already competitive with commercial PVs, the device must reach a 25-year cell lifetime for its global warming potential (GWP) to reach a reasonable range. © 2020 Taylor & Francis Group, LLC. |
Prof. Dr. Metin Tanoğlu
Educational Background
B.Sc. İstanbul Technical University, Turkey, Metallurgical and Materials Engineering, 1992
M.Sc. University of Delaware, USA, Materials Science & Engineering, 1996
Ph.D. University of Delaware, USA, Materials Science & Engineering, 2000
Research Interests
- Composite materials
- Mechanical, Physical, Thermal and Microstructural Characterization of Materials
- Impact/Ballistic Behavior of Materials
- Armor Materials
- Porous Materials
- Nanocomposites
- Layered Clays and Carbon Nanotubes (CNTs)
- +90 232 765 90 91
- +90 232 750 6701
- Mechanical Engineering Building (106)
Publications
2023 |
İplikçi, Hande; Barisik, Murat; Türkdoğan, Ceren; Martin, Seçkin; Yeke, Melisa; Nuhoğlu, Kaan; Esenoğlu, Gözde; Tanoğlu, Metin; Aktaş, Engin; Dehneliler, Serkan; İriş, Mehmet Erdem Effects of nanosecond laser ablation parameters on surface modification of carbon fiber reinforced polymer composites Journal Article Journal of Composite Materials, 57 (18), pp. 2843 – 2855, 2023. @article{İplikçi20232843, title = {Effects of nanosecond laser ablation parameters on surface modification of carbon fiber reinforced polymer composites}, author = {Hande İplikçi and Murat Barisik and Ceren Türkdoğan and Seçkin Martin and Melisa Yeke and Kaan Nuhoğlu and Gözde Esenoğlu and Metin Tanoğlu and Engin Aktaş and Serkan Dehneliler and Mehmet Erdem İriş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85162945413&doi=10.1177%2f00219983231178892&partnerID=40&md5=1e698a002a7d62e7f42a2444aafff1d5}, doi = {10.1177/00219983231178892}, year = {2023}, date = {2023-01-01}, journal = {Journal of Composite Materials}, volume = {57}, number = {18}, pages = {2843 – 2855}, abstract = {Removal of contaminants and top polymer layer from the surface of carbon-fiber-reinforced polymer (CFRP) composites is critical for high-quality adhesive-joining with direct bonding to the reinforcing fiber constituents. Surface treatment with a laser beam provides selective removal of the polymer matrix without damaging the fibers and increasing the wettability. However, inhomogeneous thermal properties of CFRP make control of laser ablation difficult as the laser energy absorbed by the carbon fibers is converted into heat and transmitted through the fiber structures during the laser operation. In this study, the effect of scanning speed and laser power on nanosecond laser surface treatment was characterized by scanning electron microscope images and wetting angle measurements. Low scanning speeds allowed laser energy to be conducted as thermal energy through the fibers, which resulted in less epoxy matrix removal and substantial thermal damage. Low laser power partially degraded the epoxy the surface while the high power damaged the carbon fibers. For the studied CFRP specimens consisting of unidirectional [45/0/−45/90]2s stacking of carbon/epoxy prepregs (HexPly®-M91), 100 mJ/mm2 generated by 10 m/s scanning speed and 30 W power appeared as optimum processing parameters for the complete removal of epoxy matrix from the top surface with mostly undamaged carbon fibers and super hydrophilic surface condition. © The Author(s) 2023.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Removal of contaminants and top polymer layer from the surface of carbon-fiber-reinforced polymer (CFRP) composites is critical for high-quality adhesive-joining with direct bonding to the reinforcing fiber constituents. Surface treatment with a laser beam provides selective removal of the polymer matrix without damaging the fibers and increasing the wettability. However, inhomogeneous thermal properties of CFRP make control of laser ablation difficult as the laser energy absorbed by the carbon fibers is converted into heat and transmitted through the fiber structures during the laser operation. In this study, the effect of scanning speed and laser power on nanosecond laser surface treatment was characterized by scanning electron microscope images and wetting angle measurements. Low scanning speeds allowed laser energy to be conducted as thermal energy through the fibers, which resulted in less epoxy matrix removal and substantial thermal damage. Low laser power partially degraded the epoxy the surface while the high power damaged the carbon fibers. For the studied CFRP specimens consisting of unidirectional [45/0/−45/90]2s stacking of carbon/epoxy prepregs (HexPly®-M91), 100 mJ/mm2 generated by 10 m/s scanning speed and 30 W power appeared as optimum processing parameters for the complete removal of epoxy matrix from the top surface with mostly undamaged carbon fibers and super hydrophilic surface condition. © The Author(s) 2023. |
Nuhoğlu, Kaan; Aktaş, Engin; Tanoğlu, Metin; Martin, Seçkin; İplikçi, Hande; Barışık, Murat; Yeke, Melisa; Türkdoğan, Ceren; Esenoğlu, Gözde; Dehneliler, Serkan; İriş, Mehmet Erdem Analysis of adhesively bonded joints of laser surface treated composite primary components of aircraft structures Journal Article International Journal of Adhesion and Adhesives, 126 , 2023. @article{Nuhoğlu2023, title = {Analysis of adhesively bonded joints of laser surface treated composite primary components of aircraft structures}, author = {Kaan Nuhoğlu and Engin Aktaş and Metin Tanoğlu and Seçkin Martin and Hande İplikçi and Murat Barışık and Melisa Yeke and Ceren Türkdoğan and Gözde Esenoğlu and Serkan Dehneliler and Mehmet Erdem İriş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85166291425&doi=10.1016%2fj.ijadhadh.2023.103456&partnerID=40&md5=aa5024e2ac1955cb1a3ff85d46fc3589}, doi = {10.1016/j.ijadhadh.2023.103456}, year = {2023}, date = {2023-01-01}, journal = {International Journal of Adhesion and Adhesives}, volume = {126}, abstract = {The performance of the adhesively bonded aerospace structures highly depends on the adhesion strength between the adhesive and adherents, which is affected by, in particular, the condition of the bonding surface. Among the various surface treatment methods, as state of the art, laser surface treatment is a suitable option for the CFRP composite structures to enhance the adhesion performance, adjusting the roughness and surface free energy with relatively minimizing the damage to the fibers. The aim of this study is the validation and evaluation of the adhesive bonding behavior of the laser surface-treated CFRP composite structures, using the finite element technique to perform a conservative prediction of the failure load and damage growth. Such objectives were achieved by executing both experimental and numerical analyses of the secondary bonded CFRP parts using a structural adhesive. In this regard, to complement physical experiments by means of numerical simulation, macro-scale 3D FEA of adhesively bonded Single Lap Joint and Skin-Spar Joint specimens has been developed employing the Cohesive Zone Model (CZM) technique in order to simulate bonding behavior in composite structures especially skin-spar relation in the aircraft wing-box. © 2023 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The performance of the adhesively bonded aerospace structures highly depends on the adhesion strength between the adhesive and adherents, which is affected by, in particular, the condition of the bonding surface. Among the various surface treatment methods, as state of the art, laser surface treatment is a suitable option for the CFRP composite structures to enhance the adhesion performance, adjusting the roughness and surface free energy with relatively minimizing the damage to the fibers. The aim of this study is the validation and evaluation of the adhesive bonding behavior of the laser surface-treated CFRP composite structures, using the finite element technique to perform a conservative prediction of the failure load and damage growth. Such objectives were achieved by executing both experimental and numerical analyses of the secondary bonded CFRP parts using a structural adhesive. In this regard, to complement physical experiments by means of numerical simulation, macro-scale 3D FEA of adhesively bonded Single Lap Joint and Skin-Spar Joint specimens has been developed employing the Cohesive Zone Model (CZM) technique in order to simulate bonding behavior in composite structures especially skin-spar relation in the aircraft wing-box. © 2023 Elsevier Ltd |
Esenoğlu, Gözde; Tanoğlu, Metin; Barisik, Murat; İplikçi, Hande; Yeke, Melisa; Nuhoğlu, Kaan; Türkdoğan, Ceren; Martin, Seçkin; Aktaş, Engin; Dehneliler, Serkan; Gürbüz, Ahmet Ayberk; İriş, Mehmet Erdem Investigating the Effects of PA66 Electrospun Nanofibers Layered within an Adhesive Composite Joint Fabricated under Autoclave Curing Journal Article ACS Omega, 8 (36), pp. 32656 – 32666, 2023, (All Open Access, Gold Open Access, Green Open Access). @article{Esenoğlu202332656, title = {Investigating the Effects of PA66 Electrospun Nanofibers Layered within an Adhesive Composite Joint Fabricated under Autoclave Curing}, author = {Gözde Esenoğlu and Metin Tanoğlu and Murat Barisik and Hande İplikçi and Melisa Yeke and Kaan Nuhoğlu and Ceren Türkdoğan and Seçkin Martin and Engin Aktaş and Serkan Dehneliler and Ahmet Ayberk Gürbüz and Mehmet Erdem İriş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85172448706&doi=10.1021%2facsomega.3c03419&partnerID=40&md5=7f3ddea2390eb013c802b710a5aaf695}, doi = {10.1021/acsomega.3c03419}, year = {2023}, date = {2023-01-01}, journal = {ACS Omega}, volume = {8}, number = {36}, pages = {32656 – 32666}, abstract = {Enhancing the performance of adhesively joined composite components is crucial for various industrial applications. In this study, polyamide 66 (PA66) nanofibers produced by electrospinning were coated on unidirectional carbon/epoxy prepregs to increase the bond strength of the composites. Carbon/epoxy prepregs with/without PA66 nanofiber coating on the bonding region were fabricated using the autoclave, which is often used in the aerospace industry. The single lap shear Charpy impact energy and Mode-I fracture toughness tests were employed to examine the effects of PA66 nanofibers on the mechanical properties of the joint region. Scanning electron microscopy (SEM) was used to investigate the nanofiber morphology and fracture modes. The thermal characteristics of Polyamide 66 nanofibers were explored by using differential scanning calorimetry (DSC). We observed that the electrospun PA66 nanofiber coating on the prepreg surfaces substantially improves the joint strength. Results revealed that the single lap shear and Charpy impact strength values of the composite joint are increased by about 79 and 24%, respectively, by coating PA66 nanofibers onto the joining region. The results also showed that by coating PA66 nanofibers, the Mode-I fracture toughness value was improved by about 107% while the glass transition temperature remained constant. © 2023 The Authors. Published by American Chemical Society.}, note = {All Open Access, Gold Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Enhancing the performance of adhesively joined composite components is crucial for various industrial applications. In this study, polyamide 66 (PA66) nanofibers produced by electrospinning were coated on unidirectional carbon/epoxy prepregs to increase the bond strength of the composites. Carbon/epoxy prepregs with/without PA66 nanofiber coating on the bonding region were fabricated using the autoclave, which is often used in the aerospace industry. The single lap shear Charpy impact energy and Mode-I fracture toughness tests were employed to examine the effects of PA66 nanofibers on the mechanical properties of the joint region. Scanning electron microscopy (SEM) was used to investigate the nanofiber morphology and fracture modes. The thermal characteristics of Polyamide 66 nanofibers were explored by using differential scanning calorimetry (DSC). We observed that the electrospun PA66 nanofiber coating on the prepreg surfaces substantially improves the joint strength. Results revealed that the single lap shear and Charpy impact strength values of the composite joint are increased by about 79 and 24%, respectively, by coating PA66 nanofibers onto the joining region. The results also showed that by coating PA66 nanofibers, the Mode-I fracture toughness value was improved by about 107% while the glass transition temperature remained constant. © 2023 The Authors. Published by American Chemical Society. |
Uz, Yusuf Can; Tanoğlu, Metin Determination of activation energy for carbon/epoxy prepregs containing carbon nanotubes by differential scanning calorimetry Journal Article High Performance Polymers, 35 (2), pp. 166 – 180, 2023. @article{Uz2023166, title = {Determination of activation energy for carbon/epoxy prepregs containing carbon nanotubes by differential scanning calorimetry}, author = {Yusuf Can Uz and Metin Tanoğlu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85135891731&doi=10.1177%2f09540083221115987&partnerID=40&md5=4b3d7c567d57a6b645d854737e03917d}, doi = {10.1177/09540083221115987}, year = {2023}, date = {2023-01-01}, journal = {High Performance Polymers}, volume = {35}, number = {2}, pages = {166 – 180}, abstract = {The aim of the present study is the thermal characterization of laboratory-scale carbon fiber/epoxy-based prepregs by incorporating single-wall carbon nanotubes (SWCNTs). Investigation of the cure behavior of a prepreg system is crucial for the characterization and optimization of the fiber reinforced polymeric (FRP) composite. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with carboxyl (-COOH) group using an acid treatment. The modified resin system contained 0.05, 0.1, and 0.2 wt. % functionalized SWCNTs (F-SWCNTs). Carbon fiber (CF) reinforced prepregs containing various amount of F-SWCNTs were prepared using drum-type winding technique. FTIR was performed to identify new bonding groups formed after the functionalization of SWCNTs. Cure kinetics of prepregs prepared with/without F-SWCNTs were investigated using isoconversional methods. © The Author(s) 2022.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The aim of the present study is the thermal characterization of laboratory-scale carbon fiber/epoxy-based prepregs by incorporating single-wall carbon nanotubes (SWCNTs). Investigation of the cure behavior of a prepreg system is crucial for the characterization and optimization of the fiber reinforced polymeric (FRP) composite. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with carboxyl (-COOH) group using an acid treatment. The modified resin system contained 0.05, 0.1, and 0.2 wt. % functionalized SWCNTs (F-SWCNTs). Carbon fiber (CF) reinforced prepregs containing various amount of F-SWCNTs were prepared using drum-type winding technique. FTIR was performed to identify new bonding groups formed after the functionalization of SWCNTs. Cure kinetics of prepregs prepared with/without F-SWCNTs were investigated using isoconversional methods. © The Author(s) 2022. |
2022 |
Esenoğlu, G; Barisik, M; Tanoğlu, M; Yeke, M; Türkdoğan, C; İplikçi, H; Martin, S; Nuhoğlu, K; Aktaş, E; Dehneliler, S; İriş, M E Improving adhesive behavior of fiber reinforced composites by incorporating electrospun Polyamide-6,6 nanofibers in joining region Journal Article Journal of Composite Materials, 56 (29), pp. 4449-4459, 2022. @article{Esenoğlu20224449, title = {Improving adhesive behavior of fiber reinforced composites by incorporating electrospun Polyamide-6,6 nanofibers in joining region}, author = {G Esenoğlu and M Barisik and M Tanoğlu and M Yeke and C Türkdoğan and H İplikçi and S Martin and K Nuhoğlu and E Aktaş and S Dehneliler and M E İriş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85139985112&doi=10.1177%2f00219983221133478&partnerID=40&md5=699a47f9c6bc7948245cdc6f370c483e}, doi = {10.1177/00219983221133478}, year = {2022}, date = {2022-01-01}, journal = {Journal of Composite Materials}, volume = {56}, number = {29}, pages = {4449-4459}, abstract = {Adhesive joining of fiber reinforced polymer (CFRP) composite components is demanded in various industrial applications. However, the joining locations frequently suffer from adhesive bond failure between adhesive and adherent. The aim of the present study is improving bonding behavior of adhesive joints by electrospun nanofiber coatings on the prepreg surfaces that have been used for composite manufacturing. Secondary bonding of woven and unidirectional CFRP parts was selected since this configuration is preferred commonly in aerospace practices. The optimum nanofiber coating with a low average fiber diameter and areal weight density is succeed by studying various solution concentrations and spinning durations of the polyamide-6.6 (PA 66) electrospinning. We obtained homogeneous and beadles nanofiber productions. As a result, an average diameter of 36.50 ± 12 nm electrospun nanofibers were obtained and coated onto the prepreg surfaces. Prepreg systems with/without PA 66 nanofibers were hot pressed to fabricate the CFRP composite laminates. The single-lap shear test coupons were prepared from the fabricated laminates to examine the effects of PA 66 nanofibers on the mechanical properties of the joint region of the composites. The single-lap shear test results showed that the bonding strength is improved by about 40% with minimal adhesive use due to the presence of the electrospun nanofibers within the joint region. The optical and SEM images of fractured surfaces showed that nanofiber-coated joints exhibited a coherent failure while the bare surfaces underwent adhesive failure. The PA66 nanofibers created better coupling between the adhesive and the composite surface by increasing the surface area and roughness. As a result, electrospun nanofibers turned adhesive failure into cohesive and enhanced the adhesion performance composite joints substantially. © The Author(s) 2022.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Adhesive joining of fiber reinforced polymer (CFRP) composite components is demanded in various industrial applications. However, the joining locations frequently suffer from adhesive bond failure between adhesive and adherent. The aim of the present study is improving bonding behavior of adhesive joints by electrospun nanofiber coatings on the prepreg surfaces that have been used for composite manufacturing. Secondary bonding of woven and unidirectional CFRP parts was selected since this configuration is preferred commonly in aerospace practices. The optimum nanofiber coating with a low average fiber diameter and areal weight density is succeed by studying various solution concentrations and spinning durations of the polyamide-6.6 (PA 66) electrospinning. We obtained homogeneous and beadles nanofiber productions. As a result, an average diameter of 36.50 ± 12 nm electrospun nanofibers were obtained and coated onto the prepreg surfaces. Prepreg systems with/without PA 66 nanofibers were hot pressed to fabricate the CFRP composite laminates. The single-lap shear test coupons were prepared from the fabricated laminates to examine the effects of PA 66 nanofibers on the mechanical properties of the joint region of the composites. The single-lap shear test results showed that the bonding strength is improved by about 40% with minimal adhesive use due to the presence of the electrospun nanofibers within the joint region. The optical and SEM images of fractured surfaces showed that nanofiber-coated joints exhibited a coherent failure while the bare surfaces underwent adhesive failure. The PA66 nanofibers created better coupling between the adhesive and the composite surface by increasing the surface area and roughness. As a result, electrospun nanofibers turned adhesive failure into cohesive and enhanced the adhesion performance composite joints substantially. © The Author(s) 2022. |
Güneş, M D; Karabaş, İmamoğlu N; Deveci, H A; Tanoğlu, G; Tanoğlu, M Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 236 (19), pp. 10290-10303, 2022. @article{Güneş202210290, title = {Fatigue life prediction and optimization of GFRP composites based on Failure Tensor Polynomial in Fatigue model with exponential fitting approach}, author = {M D Güneş and N İmamoğlu Karabaş and H A Deveci and G Tanoğlu and M Tanoğlu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85130983288&doi=10.1177%2f09544062221101462&partnerID=40&md5=144a189eaf81ed03065a753253307cad}, doi = {10.1177/09544062221101462}, year = {2022}, date = {2022-01-01}, journal = {Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science}, volume = {236}, number = {19}, pages = {10290-10303}, abstract = {In this study, a new fatigue life prediction and optimization strategy utilizing the Failure Tensor Polynomial in Fatigue (FTPF) model with exponential fitting and numerical bisection method for fiber reinforced polymer composites has been proposed. Within the experimental stage, glass/epoxy composite laminates with (Formula presented.), (Formula presented.), and (Formula presented.) lay-up configurations were fabricated, quasi-static and fatigue mechanical behavior of GFRP composites was characterized to be used in the FTPF model. The prediction capability of the FTPF model was tested based on the experimental data obtained for multidirectional laminates of various composite materials. Fatigue life prediction results of the glass/epoxy laminates were found to be better as compared to those for the linear fitting predictions. The results also indicated that the approach with exponential fitting provides better fatigue life predictions as compared to those obtained by linear fitting, especially for glass/epoxy laminates. Moreover, an optimization study using the proposed methodology for fatigue life advancement of the glass/epoxy laminates was performed by a powerful hybrid algorithm, PSA/GPSA. So, two optimization scenarios including various loading configurations were considered. The optimization results exhibited that the optimized stacking sequences having maximized fatigue life can be obtained in various loading cases. It was also revealed that the tension-compression loading and the loadings involving shear loads are critical for fatigue, and further improvement in fatigue life may be achieved by designing only symmetric lay-ups instead of symmetric-balanced and diversification of fiber angles to be used in the optimization. © IMechE 2022.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, a new fatigue life prediction and optimization strategy utilizing the Failure Tensor Polynomial in Fatigue (FTPF) model with exponential fitting and numerical bisection method for fiber reinforced polymer composites has been proposed. Within the experimental stage, glass/epoxy composite laminates with (Formula presented.), (Formula presented.), and (Formula presented.) lay-up configurations were fabricated, quasi-static and fatigue mechanical behavior of GFRP composites was characterized to be used in the FTPF model. The prediction capability of the FTPF model was tested based on the experimental data obtained for multidirectional laminates of various composite materials. Fatigue life prediction results of the glass/epoxy laminates were found to be better as compared to those for the linear fitting predictions. The results also indicated that the approach with exponential fitting provides better fatigue life predictions as compared to those obtained by linear fitting, especially for glass/epoxy laminates. Moreover, an optimization study using the proposed methodology for fatigue life advancement of the glass/epoxy laminates was performed by a powerful hybrid algorithm, PSA/GPSA. So, two optimization scenarios including various loading configurations were considered. The optimization results exhibited that the optimized stacking sequences having maximized fatigue life can be obtained in various loading cases. It was also revealed that the tension-compression loading and the loadings involving shear loads are critical for fatigue, and further improvement in fatigue life may be achieved by designing only symmetric lay-ups instead of symmetric-balanced and diversification of fiber angles to be used in the optimization. © IMechE 2022. |
Üstün, Sinan H; Toksoy, Kaan A; Tanoğlu, M Investigation of hybridization effect on ballistic performance of multi-layered fiber reinforced composite structures Journal Article Journal of Composite Materials, 56 (15), pp. 2411-2431, 2022. @article{SinanÜstün20222411, title = {Investigation of hybridization effect on ballistic performance of multi-layered fiber reinforced composite structures}, author = {H Sinan Üstün and A Kaan Toksoy and M Tanoğlu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85130035790&doi=10.1177%2f00219983221090018&partnerID=40&md5=c04588512f22392bf8cac3ef9d118408}, doi = {10.1177/00219983221090018}, year = {2022}, date = {2022-01-01}, journal = {Journal of Composite Materials}, volume = {56}, number = {15}, pages = {2411-2431}, abstract = {The aim of this study is enhancing the ballistic performance of multi-layered fiber reinforced composite structures by hybridization approach against fragment simulating projectile (FSP). For manufacturing of homogeneous and hybrid composite structures, 170 g/m2 twill weave aramid and 280 g/m2 plain weave E-Glass fibers were used with epoxy resin systems and two different thickness values for each composite panel were fabricated and tested to obtain a relationship between areal density and V50 parameters. Tensile, 3-point bending, and short beam strength tests of composite panels were performed, and ballistic performance of composite structures were measured by V50 test method with 1.1 g FSP threat. Ballistic performance of hybrid composite structures was compared with high-performance composite ballistic panel test results reported in literature. As a result, it was found that E-Glass fabric layers together with aramid fabrics increased the energy absorbing capability of hybrid composite panels and ballistic performance was enhanced to be similar or higher than ballistic fiber reinforced composites. Hence, hybridization was found to be an effective way to enhance ballistic performance of fiber reinforced composite structures. © The Author(s) 2022.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The aim of this study is enhancing the ballistic performance of multi-layered fiber reinforced composite structures by hybridization approach against fragment simulating projectile (FSP). For manufacturing of homogeneous and hybrid composite structures, 170 g/m2 twill weave aramid and 280 g/m2 plain weave E-Glass fibers were used with epoxy resin systems and two different thickness values for each composite panel were fabricated and tested to obtain a relationship between areal density and V50 parameters. Tensile, 3-point bending, and short beam strength tests of composite panels were performed, and ballistic performance of composite structures were measured by V50 test method with 1.1 g FSP threat. Ballistic performance of hybrid composite structures was compared with high-performance composite ballistic panel test results reported in literature. As a result, it was found that E-Glass fabric layers together with aramid fabrics increased the energy absorbing capability of hybrid composite panels and ballistic performance was enhanced to be similar or higher than ballistic fiber reinforced composites. Hence, hybridization was found to be an effective way to enhance ballistic performance of fiber reinforced composite structures. © The Author(s) 2022. |
Uz, Y C; Tanoğlu, M Determination of activation energy for carbon/epoxy prepregs containing carbon nanotubes by differential scanning calorimetry Journal Article High Performance Polymers, 2022. @article{Uz2022, title = {Determination of activation energy for carbon/epoxy prepregs containing carbon nanotubes by differential scanning calorimetry}, author = {Y C Uz and M Tanoğlu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85135891731&doi=10.1177%2f09540083221115987&partnerID=40&md5=4b3d7c567d57a6b645d854737e03917d}, doi = {10.1177/09540083221115987}, year = {2022}, date = {2022-01-01}, journal = {High Performance Polymers}, abstract = {The aim of the present study is the thermal characterization of laboratory-scale carbon fiber/epoxy-based prepregs by incorporating single-wall carbon nanotubes (SWCNTs). Investigation of the cure behavior of a prepreg system is crucial for the characterization and optimization of the fiber reinforced polymeric (FRP) composite. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with carboxyl (-COOH) group using an acid treatment. The modified resin system contained 0.05, 0.1, and 0.2 wt. % functionalized SWCNTs (F-SWCNTs). Carbon fiber (CF) reinforced prepregs containing various amount of F-SWCNTs were prepared using drum-type winding technique. FTIR was performed to identify new bonding groups formed after the functionalization of SWCNTs. Cure kinetics of prepregs prepared with/without F-SWCNTs were investigated using isoconversional methods. © The Author(s) 2022.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The aim of the present study is the thermal characterization of laboratory-scale carbon fiber/epoxy-based prepregs by incorporating single-wall carbon nanotubes (SWCNTs). Investigation of the cure behavior of a prepreg system is crucial for the characterization and optimization of the fiber reinforced polymeric (FRP) composite. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with carboxyl (-COOH) group using an acid treatment. The modified resin system contained 0.05, 0.1, and 0.2 wt. % functionalized SWCNTs (F-SWCNTs). Carbon fiber (CF) reinforced prepregs containing various amount of F-SWCNTs were prepared using drum-type winding technique. FTIR was performed to identify new bonding groups formed after the functionalization of SWCNTs. Cure kinetics of prepregs prepared with/without F-SWCNTs were investigated using isoconversional methods. © The Author(s) 2022. |
Solak, Ay Z; Kartav, O; Tanoglu, M Enhancement of filament wound glass fiber/epoxy-based cylindrical composites by toughening with single-walled carbon nanotubes Journal Article Polymers and Polymer Composites, 30 , 2022. @article{AySolak2022, title = {Enhancement of filament wound glass fiber/epoxy-based cylindrical composites by toughening with single-walled carbon nanotubes}, author = {Z Ay Solak and O Kartav and M Tanoglu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85131795670&doi=10.1177%2f09673911221086718&partnerID=40&md5=ee2274734defe29b42d80148622b6359}, doi = {10.1177/09673911221086718}, year = {2022}, date = {2022-01-01}, journal = {Polymers and Polymer Composites}, volume = {30}, abstract = {In this study, the effect of incorporating nano-sized fillers (noncovalently functionalized with ethoxylated alcohol chemical-vapor-deposition-grown SWCNTs) within an epoxy resin on the performance of filament wound glass fiber (GF)-based cylindrical composites (GFCCs) was investigated. For this purpose, SWCNTs were dispersed with the concentration of 0.05 and 0.1 weight percent (wt.%) within an epoxy resin using mechanical stirring and calendaring (3-roll-milling) techniques. The rheological behavior of the SWCNT incorporated epoxy mixture was characterized to determine the suitability of blends for the filament winding process. It was revealed that the viscosity value of the resin was not significantly affected by the addition of SWCNTs in given concentrations. Moreover, contact angle measurements were also performed on the SWCNT/epoxy blends dropped on the GF for the evaluation of the wettability behavior of the GF in the presence of the SWCNTs in relevant concentrations. Eventually, it was observed that the wettability behavior of GF was not reasonably affected by the presence of the SWCNTs. The double cantilever beam (DCB), flexural, and short beam shear (SBS) tests were performed on the reference and SWCNT-modified GFCC specimens to evaluate the effects of the SWCNT presence on the interlaminar fracture toughness and out-of-plane properties of GFCCs. The fractured surfaces after the DCB and SBS tests were analyzed under the scanning electron microscopy to reveal the toughening mechanisms and the filler morphologies. Consequently, although SWCNT incorporation was on the outermost layer of GFCCs, it was found that the interlaminar shear strength (ILSS) values and Mode I interlaminar fracture toughness values of the curved composite samples were improved up to 22 and 216%, respectively, due to the presence of the SWCNTs. © The Author(s) 2022.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, the effect of incorporating nano-sized fillers (noncovalently functionalized with ethoxylated alcohol chemical-vapor-deposition-grown SWCNTs) within an epoxy resin on the performance of filament wound glass fiber (GF)-based cylindrical composites (GFCCs) was investigated. For this purpose, SWCNTs were dispersed with the concentration of 0.05 and 0.1 weight percent (wt.%) within an epoxy resin using mechanical stirring and calendaring (3-roll-milling) techniques. The rheological behavior of the SWCNT incorporated epoxy mixture was characterized to determine the suitability of blends for the filament winding process. It was revealed that the viscosity value of the resin was not significantly affected by the addition of SWCNTs in given concentrations. Moreover, contact angle measurements were also performed on the SWCNT/epoxy blends dropped on the GF for the evaluation of the wettability behavior of the GF in the presence of the SWCNTs in relevant concentrations. Eventually, it was observed that the wettability behavior of GF was not reasonably affected by the presence of the SWCNTs. The double cantilever beam (DCB), flexural, and short beam shear (SBS) tests were performed on the reference and SWCNT-modified GFCC specimens to evaluate the effects of the SWCNT presence on the interlaminar fracture toughness and out-of-plane properties of GFCCs. The fractured surfaces after the DCB and SBS tests were analyzed under the scanning electron microscopy to reveal the toughening mechanisms and the filler morphologies. Consequently, although SWCNT incorporation was on the outermost layer of GFCCs, it was found that the interlaminar shear strength (ILSS) values and Mode I interlaminar fracture toughness values of the curved composite samples were improved up to 22 and 216%, respectively, due to the presence of the SWCNTs. © The Author(s) 2022. |
2021 |
Kangal, Serkan; Say, Harun A; Ayakda, Ozan; Kartav, Osman; Aydin, Levent; Artem, Secil H; Aktas, Engin; Yuceturk, Kutay; Tanoglu, Metin; Kandemir, Sinan; Beylergil, Bertan A Comprehensive Study on Burst Pressure Performance of Aluminum Liner for Hydrogen Storage Vessels Journal Article JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME, 143 (4), 2021. @article{WOS:000669955100012, title = {A Comprehensive Study on Burst Pressure Performance of Aluminum Liner for Hydrogen Storage Vessels}, author = {Serkan Kangal and Harun A Say and Ozan Ayakda and Osman Kartav and Levent Aydin and Secil H Artem and Engin Aktas and Kutay Yuceturk and Metin Tanoglu and Sinan Kandemir and Bertan Beylergil}, doi = {10.1115/1.4049644}, year = {2021}, date = {2021-08-01}, journal = {JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME}, volume = {143}, number = {4}, abstract = {This paper presents a comparative study on the burst pressure performance of aluminum (Al) liner for type-III composite overwrapped pressure vessels (COPVs). In the analysis, the vessels were loaded with increasing internal pressure up to the burst pressure level. In the analytical part of the study, the burst pressure of the cylindrical part was predicted based on the modified von Mises, Tresca, and average shear stress criterion (ASSC). In the numerical analysis, a finite element (FE) model was established in order to predict the behavior of the vessel as a function of increasing internal pressure and determine the final burst. The Al pressure vessels made of Al-6061-T6 alloy with a capacity of 5 L were designed. The manufacturing of the metallic vessels was purchased from a metal forming company. The experimental study was conducted by pressurizing the Al vessels until the burst failure occurred. The radial and axial strain behaviors were monitored at various locations on the vessels during loading. The results obtained through analytical, numerical, and experimental work were compared. The average experimental burst pressure of the vessels was found to be 279 bar. The experimental strain data were compared with the results of the FE analysis. The results indicated that the FE analysis and ASSC-based elastoplastic analytical approaches yielded the best predictions which are within 2.2% of the experimental burst failure values. It was also found that the elastic analysis underestimated the burst failure results; however, it was effective for determining the critical regions over the vessel structure. The strain behavior of the vessels obtained through experimental investigations was well correlated with those predicted through FE analysis.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper presents a comparative study on the burst pressure performance of aluminum (Al) liner for type-III composite overwrapped pressure vessels (COPVs). In the analysis, the vessels were loaded with increasing internal pressure up to the burst pressure level. In the analytical part of the study, the burst pressure of the cylindrical part was predicted based on the modified von Mises, Tresca, and average shear stress criterion (ASSC). In the numerical analysis, a finite element (FE) model was established in order to predict the behavior of the vessel as a function of increasing internal pressure and determine the final burst. The Al pressure vessels made of Al-6061-T6 alloy with a capacity of 5 L were designed. The manufacturing of the metallic vessels was purchased from a metal forming company. The experimental study was conducted by pressurizing the Al vessels until the burst failure occurred. The radial and axial strain behaviors were monitored at various locations on the vessels during loading. The results obtained through analytical, numerical, and experimental work were compared. The average experimental burst pressure of the vessels was found to be 279 bar. The experimental strain data were compared with the results of the FE analysis. The results indicated that the FE analysis and ASSC-based elastoplastic analytical approaches yielded the best predictions which are within 2.2% of the experimental burst failure values. It was also found that the elastic analysis underestimated the burst failure results; however, it was effective for determining the critical regions over the vessel structure. The strain behavior of the vessels obtained through experimental investigations was well correlated with those predicted through FE analysis. |
Kartav, O; Kangal, S; Yücetürk, K; Tanoğlu, M; Aktaş, E; Artem, H S Development and analysis of composite overwrapped pressure vessels for hydrogen storage Journal Article Journal of Composite Materials, 55 (28), pp. 4141-4155, 2021. @article{Kartav20214141, title = {Development and analysis of composite overwrapped pressure vessels for hydrogen storage}, author = {O Kartav and S Kangal and K Yücetürk and M Tanoğlu and E Aktaş and H S Artem}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85110939454&doi=10.1177%2f00219983211033568&partnerID=40&md5=c31db8e0f0de63135bf2da9bf634900d}, doi = {10.1177/00219983211033568}, year = {2021}, date = {2021-01-01}, journal = {Journal of Composite Materials}, volume = {55}, number = {28}, pages = {4141-4155}, abstract = {In this study, composite overwrapped pressure vessels (COPVs) for high-pressure hydrogen storage were designed, modeled by finite element (FE) method, manufactured by filament winding technique and tested for burst pressure. Aluminum 6061-T6 was selected as a metallic liner material. Epoxy impregnated carbon filaments were overwrapped over the liner with a winding angle of ±14° to obtain fully overwrapped composite reinforced vessels with non-identical front and back dome layers. The COPVs were loaded with increasing internal pressure up to the burst pressure level. During loading, deformation of the vessels was measured locally with strain gauges. The mechanical performances of COPVs designed with various number of helical, hoop and doily layers were investigated by both experimental and numerical methods. In numerical method, FE analysis containing a simple progressive damage model available in ANSYS software package for the composite section was performed. The results revealed that the FE model provides a good correlation as compared to experimental strain results for the developed COPVs. The burst pressure test results showed that integration of doily layers to the filament winding process resulted with an improvement of the COPVs performance. © The Author(s) 2021.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, composite overwrapped pressure vessels (COPVs) for high-pressure hydrogen storage were designed, modeled by finite element (FE) method, manufactured by filament winding technique and tested for burst pressure. Aluminum 6061-T6 was selected as a metallic liner material. Epoxy impregnated carbon filaments were overwrapped over the liner with a winding angle of ±14° to obtain fully overwrapped composite reinforced vessels with non-identical front and back dome layers. The COPVs were loaded with increasing internal pressure up to the burst pressure level. During loading, deformation of the vessels was measured locally with strain gauges. The mechanical performances of COPVs designed with various number of helical, hoop and doily layers were investigated by both experimental and numerical methods. In numerical method, FE analysis containing a simple progressive damage model available in ANSYS software package for the composite section was performed. The results revealed that the FE model provides a good correlation as compared to experimental strain results for the developed COPVs. The burst pressure test results showed that integration of doily layers to the filament winding process resulted with an improvement of the COPVs performance. © The Author(s) 2021. |
2020 |
Beylergil, Bertan; Tanoglu, Metin; Aktas, Engin Experimental and statistical analysis of carbon fiber/epoxy composites interleaved with nylon 6,6 nonwoven fabric interlayers Journal Article JOURNAL OF COMPOSITE MATERIALS, 54 (27), pp. 4173-4184, 2020, ISSN: 0021-9983. @article{ISI:000535519800001, title = {Experimental and statistical analysis of carbon fiber/epoxy composites interleaved with nylon 6,6 nonwoven fabric interlayers}, author = {Bertan Beylergil and Metin Tanoglu and Engin Aktas}, doi = {10.1177/0021998320927740, Early Access Date = MAY 2020}, issn = {0021-9983}, year = {2020}, date = {2020-11-01}, journal = {JOURNAL OF COMPOSITE MATERIALS}, volume = {54}, number = {27}, pages = {4173-4184}, abstract = {Thermoplastic interleaving is a promising technique to improve delamination resistance of laminated composites. In this study, plain-weave carbon fiber/epoxy composites were interleaved with nylon 6,6 nonwoven fabrics with an areal weight density of 17 gsm. The carbon fiber/epoxy composite laminates with/without nylon 6,6 nonwoven fabric interlayers were manufactured by VARTM technique. Double cantilever beam fracture toughness tests were carried out on the prepared composite test specimens in accordance with ASTM 5528 standard. The experimental test data were statistically analyzed by two-parameter Weibull distribution. The results showed that the initiation and propagation fracture toughness Mode-I fracture toughness of carbon fiber/epoxy composites could be improved by about 34 and 156% (corresponding to a reliability level of 0.50) with the incorporation of nylon 6,6 interlayers in the interlaminar region, respectively. The results also revealed that the percent increase in the propagation fracture toughness value was 67 and 41% at reliability levels of 0.90 and 0.95, respectively.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Thermoplastic interleaving is a promising technique to improve delamination resistance of laminated composites. In this study, plain-weave carbon fiber/epoxy composites were interleaved with nylon 6,6 nonwoven fabrics with an areal weight density of 17 gsm. The carbon fiber/epoxy composite laminates with/without nylon 6,6 nonwoven fabric interlayers were manufactured by VARTM technique. Double cantilever beam fracture toughness tests were carried out on the prepared composite test specimens in accordance with ASTM 5528 standard. The experimental test data were statistically analyzed by two-parameter Weibull distribution. The results showed that the initiation and propagation fracture toughness Mode-I fracture toughness of carbon fiber/epoxy composites could be improved by about 34 and 156% (corresponding to a reliability level of 0.50) with the incorporation of nylon 6,6 interlayers in the interlaminar region, respectively. The results also revealed that the percent increase in the propagation fracture toughness value was 67 and 41% at reliability levels of 0.90 and 0.95, respectively. |
Ay, Z; Tanoglu, M The Effect of Single-Walled Carbon Nanotube (SWCNT) Concentration on the Mechanical and Rheological Behavior of Epoxy Matrix Journal Article MECHANICS OF COMPOSITE MATERIALS, 56 (4), pp. 523-532, 2020, ISSN: 0191-5665. @article{ISI:000567735300002, title = {The Effect of Single-Walled Carbon Nanotube (SWCNT) Concentration on the Mechanical and Rheological Behavior of Epoxy Matrix}, author = {Z Ay and M Tanoglu}, doi = {10.1007/s11029-020-09900-7, Early Access Date = SEP 2020}, issn = {0191-5665}, year = {2020}, date = {2020-09-01}, journal = {MECHANICS OF COMPOSITE MATERIALS}, volume = {56}, number = {4}, pages = {523-532}, abstract = {The improvement of Mode I fracture toughness of epoxy by the addition of single-walled carbon nanotubes (SWCNTs) is considered. To prepare nanocomposites, chemical-vapor-deposition-grown SWCNTs noncovalently functionalized with an ethoxylated alcohol was used as the additive and a diglycidyl ether of bisphenol-A-based epoxy as the matrix material. The SWCNTs were dispersed in the epoxy matrix via a mechanical stirrer and a 3-roll mill. The effect of their concentration (0.0125, 0.025, 0.05, 0.1, 0.3, and 0.5 wt.%) on the mechanical properties of the nanocomposites was investigated, and the optimum concentration was determined. Mode I fracture toughness (single-edge-notch 3-point bending) and tensile tests were carried out on neat epoxy and SWCNT-reinforced epoxy nanocomposites. The fractured surfaces of fracture toughness and tensile test specimens were examined by the SEM to reveal the effect of SWCNTs on their failure modes.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The improvement of Mode I fracture toughness of epoxy by the addition of single-walled carbon nanotubes (SWCNTs) is considered. To prepare nanocomposites, chemical-vapor-deposition-grown SWCNTs noncovalently functionalized with an ethoxylated alcohol was used as the additive and a diglycidyl ether of bisphenol-A-based epoxy as the matrix material. The SWCNTs were dispersed in the epoxy matrix via a mechanical stirrer and a 3-roll mill. The effect of their concentration (0.0125, 0.025, 0.05, 0.1, 0.3, and 0.5 wt.%) on the mechanical properties of the nanocomposites was investigated, and the optimum concentration was determined. Mode I fracture toughness (single-edge-notch 3-point bending) and tensile tests were carried out on neat epoxy and SWCNT-reinforced epoxy nanocomposites. The fractured surfaces of fracture toughness and tensile test specimens were examined by the SEM to reveal the effect of SWCNTs on their failure modes. |
Kangal, S; Kartav, O; Tanoğlu, M; Aktaş, E; Artem, H S Journal of Composite Materials, 54 (7), pp. 961-980, 2020. @article{Kangal2020961, title = {Investigation of interlayer hybridization effect on burst pressure performance of composite overwrapped pressure vessels with load-sharing metallic liner}, author = {S Kangal and O Kartav and M Tanoğlu and E Aktaş and H S Artem}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85071956589&doi=10.1177%2f0021998319870588&partnerID=40&md5=90d8ba513531b1cd09c963d447aebf4a}, doi = {10.1177/0021998319870588}, year = {2020}, date = {2020-01-01}, journal = {Journal of Composite Materials}, volume = {54}, number = {7}, pages = {961-980}, abstract = {In this study, multi-layered composite overwrapped pressure vessels for high-pressure gaseous storage were designed, modeled by finite element method and manufactured by filament winding technique. 34CrMo4 steel was selected as a load-sharing metallic liner. Glass and carbon filaments were overwrapped on the liner with a winding angle of [±11°/90°2]3 to obtain fully overwrapped composite reinforced vessel with non-identical front and back dome endings. The vessels were loaded with increasing internal pressure up to the burst pressure level. The mechanical performances of pressure vessels, (i) fully overwrapped with glass fibers and (ii) with additional two carbon hoop layers on the cylindrical section, were investigated by both experimental and numerical approaches. In numerical approaches, finite element analysis was performed featuring a simple progressive damage model available in ANSYS software package for the composite section. The metal liner was modeled as elastic–plastic material. The results reveal that the finite element model provides a good correlation between experimental and numerical strain results for the vessels, together with the indication of the positive effect on radial deformation of the COPVs due to the composite interlayer hybridization. The constructed model was also able to predict experimental burst pressures within a range of 8%. However, the experimental and finite element analysis results showed that hybridization of hoop layers did not have any significant impact on the burst pressure performance of the vessels. This finding was attributed to the change of load-sharing capacity of composite layers due to the stiffness difference of carbon and glass fibers. © The Author(s) 2019.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, multi-layered composite overwrapped pressure vessels for high-pressure gaseous storage were designed, modeled by finite element method and manufactured by filament winding technique. 34CrMo4 steel was selected as a load-sharing metallic liner. Glass and carbon filaments were overwrapped on the liner with a winding angle of [±11°/90°2]3 to obtain fully overwrapped composite reinforced vessel with non-identical front and back dome endings. The vessels were loaded with increasing internal pressure up to the burst pressure level. The mechanical performances of pressure vessels, (i) fully overwrapped with glass fibers and (ii) with additional two carbon hoop layers on the cylindrical section, were investigated by both experimental and numerical approaches. In numerical approaches, finite element analysis was performed featuring a simple progressive damage model available in ANSYS software package for the composite section. The metal liner was modeled as elastic–plastic material. The results reveal that the finite element model provides a good correlation between experimental and numerical strain results for the vessels, together with the indication of the positive effect on radial deformation of the COPVs due to the composite interlayer hybridization. The constructed model was also able to predict experimental burst pressures within a range of 8%. However, the experimental and finite element analysis results showed that hybridization of hoop layers did not have any significant impact on the burst pressure performance of the vessels. This finding was attributed to the change of load-sharing capacity of composite layers due to the stiffness difference of carbon and glass fibers. © The Author(s) 2019. |
Yardimci, Atike Ince; Tanoglu, Metin; Yilmaz, Selahattin; Selamet, Yusuf Effect of CNT incorporation on PAN/PPy nanofibers synthesized by electrospinning method Journal Article TURKISH JOURNAL OF CHEMISTRY, 44 (4), pp. 1002-1015, 2020, ISSN: 1300-0527. @article{ISI:000560919000010, title = {Effect of CNT incorporation on PAN/PPy nanofibers synthesized by electrospinning method}, author = {Atike Ince Yardimci and Metin Tanoglu and Selahattin Yilmaz and Yusuf Selamet}, doi = {10.3906/kim-1911-49}, issn = {1300-0527}, year = {2020}, date = {2020-01-01}, journal = {TURKISH JOURNAL OF CHEMISTRY}, volume = {44}, number = {4}, pages = {1002-1015}, abstract = {In this study, carbon nanotubes (CNTs) added polyacrylonitrile/polypyrrole (PAN/PPy) electrospun nanofibers were produced. Average diameters of the nanofibers were measured as 268 and 153 nm for 10 and 25 wt% of PPy contents, respectively. A relatively higher strain to failure values (23.3%) were observed for the low PPy content. When as-grown CNTs (1 and 4 wt%) were added into the PAN/PPy blends, disordered nanofibers were observed to form within the microstructure. To improve the interfacial properties of CNTs/PAN/PPy composites, CNTs were functionalized with H2SO4/HNO3/HCl solution. The functionalized CNTs were well dispersed within the nanofibers and aligned along the direction of nanofibers. Therefore, beads formation on nanofibers decreased. The impedance of the nanofibers was found to decrease with the PPy content and CNT addition. These nanofibers had a great potential to be used as an electrochemical actuator or a tissue engineering scaffold.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, carbon nanotubes (CNTs) added polyacrylonitrile/polypyrrole (PAN/PPy) electrospun nanofibers were produced. Average diameters of the nanofibers were measured as 268 and 153 nm for 10 and 25 wt% of PPy contents, respectively. A relatively higher strain to failure values (23.3%) were observed for the low PPy content. When as-grown CNTs (1 and 4 wt%) were added into the PAN/PPy blends, disordered nanofibers were observed to form within the microstructure. To improve the interfacial properties of CNTs/PAN/PPy composites, CNTs were functionalized with H2SO4/HNO3/HCl solution. The functionalized CNTs were well dispersed within the nanofibers and aligned along the direction of nanofibers. Therefore, beads formation on nanofibers decreased. The impedance of the nanofibers was found to decrease with the PPy content and CNT addition. These nanofibers had a great potential to be used as an electrochemical actuator or a tissue engineering scaffold. |
2019 |
Beylergil, B; Tanoǧlu, M; Aktaş, E Mode-I fracture toughness of carbon fiber/epoxy composites interleaved by aramid nonwoven veils Journal Article Steel and Composite Structures, 31 (2), pp. 113-123, 2019. @article{Beylergil2019113, title = {Mode-I fracture toughness of carbon fiber/epoxy composites interleaved by aramid nonwoven veils}, author = {B Beylergil and M Tanoǧlu and E Aktaş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85065238224&doi=10.12989%2fscs.2019.31.2.113&partnerID=40&md5=c8783b96f972924d7754bb7820373a14}, doi = {10.12989/scs.2019.31.2.113}, year = {2019}, date = {2019-01-01}, journal = {Steel and Composite Structures}, volume = {31}, number = {2}, pages = {113-123}, abstract = {In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of 8.5 g/m 2 to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites. Copyright © 2019 Techno-Press, Ltd.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of 8.5 g/m 2 to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites. Copyright © 2019 Techno-Press, Ltd. |
2018 |
Oztoprak, N; Gunes, M D; Tanoglu, M; Aktas, E; Egilmez, O O; Senocak, C; Kulac, G Developing polymer composite-based leaf spring systems for automotive industry Journal Article Science and Engineering of Composite Materials, 25 (6), pp. 1167-1176, 2018. @article{Oztoprak20181167, title = {Developing polymer composite-based leaf spring systems for automotive industry}, author = {N Oztoprak and M D Gunes and M Tanoglu and E Aktas and O O Egilmez and C Senocak and G Kulac}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85056594508&doi=10.1515%2fsecm-2016-0335&partnerID=40&md5=f8692f0ca38d12eec3006c474b120b21}, doi = {10.1515/secm-2016-0335}, year = {2018}, date = {2018-01-01}, journal = {Science and Engineering of Composite Materials}, volume = {25}, number = {6}, pages = {1167-1176}, abstract = {Composite-based mono-leaf spring systems were designed and manufactured to replace existing mono-leaf metal leaf spring in a light commercial vehicle. In this study, experimentally obtained mechanical properties of different fiber-reinforced polymer materials are presented first, followed by the description of the finite element analytical model created in Abaqus 6.12-1 (Dassault Systemes Simulia Corp., RI, US) using the obtained properties. The results from the finite element analysis are presented next and compared with actual size experimental tests conducted on manufactured prototypes. The results demonstrated that the reinforcement type and orientation dramatically influenced the spring rate. The prototypes showed significant weight reduction of about 80% with improved mechanical properties. The hybrid composite systems can be utilized for composite-based leaf springs with considerable mechanical performance. © 2018 Walter de Gruyter GmbH, Berlin/Boston.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Composite-based mono-leaf spring systems were designed and manufactured to replace existing mono-leaf metal leaf spring in a light commercial vehicle. In this study, experimentally obtained mechanical properties of different fiber-reinforced polymer materials are presented first, followed by the description of the finite element analytical model created in Abaqus 6.12-1 (Dassault Systemes Simulia Corp., RI, US) using the obtained properties. The results from the finite element analysis are presented next and compared with actual size experimental tests conducted on manufactured prototypes. The results demonstrated that the reinforcement type and orientation dramatically influenced the spring rate. The prototypes showed significant weight reduction of about 80% with improved mechanical properties. The hybrid composite systems can be utilized for composite-based leaf springs with considerable mechanical performance. © 2018 Walter de Gruyter GmbH, Berlin/Boston. |
Beylergil, B; Tanoğlu, M; Aktaş, E Effect of polyamide-6,6 (PA 66) nonwoven veils on the mechanical performance of carbon fiber/epoxy composites Journal Article Composite Structures, 194 , pp. 21-35, 2018. @article{Beylergil201821, title = {Effect of polyamide-6,6 (PA 66) nonwoven veils on the mechanical performance of carbon fiber/epoxy composites}, author = {B Beylergil and M Tanoğlu and E Aktaş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85044992271&doi=10.1016%2fj.compstruct.2018.03.097&partnerID=40&md5=5a48cd887d9aa73061331019a3e6b047}, doi = {10.1016/j.compstruct.2018.03.097}, year = {2018}, date = {2018-01-01}, journal = {Composite Structures}, volume = {194}, pages = {21-35}, abstract = {In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with polyamide-6,6 (PA 66) nonwoven veils at two different areal weight densities (17 and 50 gsm) to improve their delamination resistance against Mode-I loading. Mode-I fracture toughness (DCB), tensile, open hole tensile (OHT), flexural, compression, short beam shear (ILSS) and Charpy-impact tests were performed on the reference and PA 66 interleaved composite specimens. The DCB test results showed that the initiation and propagation Mode-I fracture toughness values of the composites were significantly improved by 84 and 171% using PA 66-17 gsm veils respectively, as compared to reference laminates. The use of denser PA 66-50 gsm veils in the interlaminar region led to higher improvement in fracture toughness values (349% for initiation and 718% for propagation) due to the higher amount of veil fibers involved in fiber bridging toughening mechanism. The incorporation of PA 66-50 gsm nonwoven veils also increased the ILSS and Charpy impact strength of the composites by 25 and 15%, respectively. On the other hand, the PA 66 veils reduced in-plane mechanical properties of CF/EP composites due to lower carbon fiber volume fraction and increased thickness. © 2018}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with polyamide-6,6 (PA 66) nonwoven veils at two different areal weight densities (17 and 50 gsm) to improve their delamination resistance against Mode-I loading. Mode-I fracture toughness (DCB), tensile, open hole tensile (OHT), flexural, compression, short beam shear (ILSS) and Charpy-impact tests were performed on the reference and PA 66 interleaved composite specimens. The DCB test results showed that the initiation and propagation Mode-I fracture toughness values of the composites were significantly improved by 84 and 171% using PA 66-17 gsm veils respectively, as compared to reference laminates. The use of denser PA 66-50 gsm veils in the interlaminar region led to higher improvement in fracture toughness values (349% for initiation and 718% for propagation) due to the higher amount of veil fibers involved in fiber bridging toughening mechanism. The incorporation of PA 66-50 gsm nonwoven veils also increased the ILSS and Charpy impact strength of the composites by 25 and 15%, respectively. On the other hand, the PA 66 veils reduced in-plane mechanical properties of CF/EP composites due to lower carbon fiber volume fraction and increased thickness. © 2018 |
2017 |
Beylergil, Bertan; Tanoglu, Metin; Aktas, Engin Enhancement of interlaminar fracture toughness of carbon fiber-epoxy composites using polyamide-6,6 electrospun nanofibers Journal Article JOURNAL OF APPLIED POLYMER SCIENCE, 134 (35), 2017, ISSN: 0021-8995. @article{ISI:000403346000012, title = {Enhancement of interlaminar fracture toughness of carbon fiber-epoxy composites using polyamide-6,6 electrospun nanofibers}, author = {Bertan Beylergil and Metin Tanoglu and Engin Aktas}, doi = {10.1002/app.45244}, issn = {0021-8995}, year = {2017}, date = {2017-09-01}, journal = {JOURNAL OF APPLIED POLYMER SCIENCE}, volume = {134}, number = {35}, abstract = {In this study, carbon fiber-epoxy composites are interleaved with electrospun polyamide-6,6 (PA 66) nanofibers to improve their Mode-I fracture toughness. These nanofibers are directly deposited onto carbon fabrics before composite manufacturing via vacuum infusion. Three-point bending, tensile, compression, interlaminar shear strength, Charpy impact, and double cantilever beam tests are performed on the reference and PA 66 interleaved specimens to evaluate the effects of PA 66 nanofibers on the mechanical properties of composites. To investigate the effect of nanofiber areal weight density (AWD), nanointerlayers with various AWD are prepared by changing the electrospinning duration. It is found that the electrospun PA 66 nanofibers are very effective in improving Mode-I toughness and impact resistance, compressive strength, flexural modulus, and strength of the composites. However, these nanofibers cause a decrease in the tensile strength of the composites. The glass-transition temperature of the composites is not affected by the addition of PA 66 nanofibers. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45244.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, carbon fiber-epoxy composites are interleaved with electrospun polyamide-6,6 (PA 66) nanofibers to improve their Mode-I fracture toughness. These nanofibers are directly deposited onto carbon fabrics before composite manufacturing via vacuum infusion. Three-point bending, tensile, compression, interlaminar shear strength, Charpy impact, and double cantilever beam tests are performed on the reference and PA 66 interleaved specimens to evaluate the effects of PA 66 nanofibers on the mechanical properties of composites. To investigate the effect of nanofiber areal weight density (AWD), nanointerlayers with various AWD are prepared by changing the electrospinning duration. It is found that the electrospun PA 66 nanofibers are very effective in improving Mode-I toughness and impact resistance, compressive strength, flexural modulus, and strength of the composites. However, these nanofibers cause a decrease in the tensile strength of the composites. The glass-transition temperature of the composites is not affected by the addition of PA 66 nanofibers. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45244. |
Beylergil, B; Tanoğlu, M; Aktaş, E Enhancement of interlaminar fracture toughness of carbon fiber–epoxy composites using polyamide-6,6 electrospun nanofibers Journal Article Journal of Applied Polymer Science, 134 (35), 2017. @article{Beylergil2017, title = {Enhancement of interlaminar fracture toughness of carbon fiber–epoxy composites using polyamide-6,6 electrospun nanofibers}, author = {B Beylergil and M Tanoğlu and E Aktaş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85019089440&doi=10.1002%2fapp.45244&partnerID=40&md5=ef8bdba44c46b9b1bc9aaedfbbbde061}, doi = {10.1002/app.45244}, year = {2017}, date = {2017-01-01}, journal = {Journal of Applied Polymer Science}, volume = {134}, number = {35}, abstract = {In this study, carbon fiber–epoxy composites are interleaved with electrospun polyamide-6,6 (PA 66) nanofibers to improve their Mode-I fracture toughness. These nanofibers are directly deposited onto carbon fabrics before composite manufacturing via vacuum infusion. Three-point bending, tensile, compression, interlaminar shear strength, Charpy impact, and double cantilever beam tests are performed on the reference and PA 66 interleaved specimens to evaluate the effects of PA 66 nanofibers on the mechanical properties of composites. To investigate the effect of nanofiber areal weight density (AWD), nanointerlayers with various AWD are prepared by changing the electrospinning duration. It is found that the electrospun PA 66 nanofibers are very effective in improving Mode-I toughness and impact resistance, compressive strength, flexural modulus, and strength of the composites. However, these nanofibers cause a decrease in the tensile strength of the composites. The glass-transition temperature of the composites is not affected by the addition of PA 66 nanofibers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45244. © 2017 Wiley Periodicals, Inc.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, carbon fiber–epoxy composites are interleaved with electrospun polyamide-6,6 (PA 66) nanofibers to improve their Mode-I fracture toughness. These nanofibers are directly deposited onto carbon fabrics before composite manufacturing via vacuum infusion. Three-point bending, tensile, compression, interlaminar shear strength, Charpy impact, and double cantilever beam tests are performed on the reference and PA 66 interleaved specimens to evaluate the effects of PA 66 nanofibers on the mechanical properties of composites. To investigate the effect of nanofiber areal weight density (AWD), nanointerlayers with various AWD are prepared by changing the electrospinning duration. It is found that the electrospun PA 66 nanofibers are very effective in improving Mode-I toughness and impact resistance, compressive strength, flexural modulus, and strength of the composites. However, these nanofibers cause a decrease in the tensile strength of the composites. The glass-transition temperature of the composites is not affected by the addition of PA 66 nanofibers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45244. © 2017 Wiley Periodicals, Inc. |
2016 |
Merter, Emrah N; Baser, Gulnur; Tanoglu, Metin JOURNAL OF COMPOSITE MATERIALS, 50 (12, SI), pp. 1697-1706, 2016, ISSN: 0021-9983. @article{ISI:000374328300014, title = {Effects of hybrid yarn preparation technique and fiber sizing on the mechanical properties of continuous glass fiber-reinforced polypropylene composites}, author = {Emrah N Merter and Gulnur Baser and Metin Tanoglu}, doi = {10.1177/0021998315595710}, issn = {0021-9983}, year = {2016}, date = {2016-05-01}, journal = {JOURNAL OF COMPOSITE MATERIALS}, volume = {50}, number = {12, SI}, pages = {1697-1706}, abstract = {In this study, hybrid yarns were developed by commingling the continuous polypropylene and glass fibers using air jet and direct twist preparation techniques. The non-crimp fabrics were obtained with +/- 45 degrees fiber orientation from these hybrid yarns. The fabrics were prepared with fiber sizings that are compatible and incompatible with polypropylene matrix to investigate the effect of interfacial adhesion on the properties of the thermoplastic composites. Composite panels were produced from the developed fabrics by hot press compression method and microstructural and mechanical properties of the composites were investigated. It was found that type of the hybrid yarn preparation technique and glass fiber sizing applied on the glass fibers have some important role on the properties of the composites. Composites made of fabrics produced by air jet hybrid yarn preparation technique exhibited better results than those produced by direct twist covering (single or double) hybrid yarn preparation techniques. The highest flexural properties (99.1MPa flexural strength and 9.55 GPa flexural modulus) were obtained from the composites manufactured from fabric containing compatible sizing, due to better adhesion at the interface of glass fibers and polypropylene matrix. The composite fabricated from fabric with polypropylene compatible sizing also exhibited the highest peel resistance (interlaminar peel strength value of 5.87N/mm). On the other hand, it was found that hybrid yarn preparation technique and type of the glass fiber sizing have insignificant effect on the impact properties of the glass fiber/polypropylene composites.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, hybrid yarns were developed by commingling the continuous polypropylene and glass fibers using air jet and direct twist preparation techniques. The non-crimp fabrics were obtained with +/- 45 degrees fiber orientation from these hybrid yarns. The fabrics were prepared with fiber sizings that are compatible and incompatible with polypropylene matrix to investigate the effect of interfacial adhesion on the properties of the thermoplastic composites. Composite panels were produced from the developed fabrics by hot press compression method and microstructural and mechanical properties of the composites were investigated. It was found that type of the hybrid yarn preparation technique and glass fiber sizing applied on the glass fibers have some important role on the properties of the composites. Composites made of fabrics produced by air jet hybrid yarn preparation technique exhibited better results than those produced by direct twist covering (single or double) hybrid yarn preparation techniques. The highest flexural properties (99.1MPa flexural strength and 9.55 GPa flexural modulus) were obtained from the composites manufactured from fabric containing compatible sizing, due to better adhesion at the interface of glass fibers and polypropylene matrix. The composite fabricated from fabric with polypropylene compatible sizing also exhibited the highest peel resistance (interlaminar peel strength value of 5.87N/mm). On the other hand, it was found that hybrid yarn preparation technique and type of the glass fiber sizing have insignificant effect on the impact properties of the glass fiber/polypropylene composites. |
Basturk, S B; Tanoglu, M; Cankaya, M A; Egilmez, O O Dynamic behavior predictions of fiber-metal laminate/aluminum foam sandwiches under various explosive weights Journal Article JOURNAL OF SANDWICH STRUCTURES & MATERIALS, 18 (3), pp. 321-342, 2016, ISSN: 1099-6362. @article{ISI:000375128600003b, title = {Dynamic behavior predictions of fiber-metal laminate/aluminum foam sandwiches under various explosive weights}, author = {S B Basturk and M Tanoglu and M A Cankaya and O O Egilmez}, doi = {10.1177/1099636215603036}, issn = {1099-6362}, year = {2016}, date = {2016-05-01}, journal = {JOURNAL OF SANDWICH STRUCTURES & MATERIALS}, volume = {18}, number = {3}, pages = {321-342}, abstract = {Application of blast tests causes some problems to characterize the performance of panels due to the drastic conditions of explosive medium. Real test has high safety concerns and is not easily accessible because of its extra budget. Some approaches are needed for the preliminary predictions of dynamic characteristics of panels under blast loading conditions. In this study, the response of sandwiches under blast effect was evaluated by combining quasi-static experiments and computational blast test data. The primary aim is to relate the quasi-static panel analysis to dynamic blast load. Based on this idea, lightweight sandwich composites were subjected to quasi-static compression loading with a special test apparatus and the samples were assumed as single degree-of-freedom mass-spring systems to include dynamic effect. This approach provides a simpler way to simulate the blast loading over the surface of the panels and reveals the possible failure mechanisms without applying any explosives. Therefore the design of the panels can be revised by considering quasi-static test results. In this work, the peak deflections and survivabilities of sandwiches for various explosive weights were predicted based on the formulations reported in the literature. Major failure types were also identified and evaluated with respect to their thicknesses.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Application of blast tests causes some problems to characterize the performance of panels due to the drastic conditions of explosive medium. Real test has high safety concerns and is not easily accessible because of its extra budget. Some approaches are needed for the preliminary predictions of dynamic characteristics of panels under blast loading conditions. In this study, the response of sandwiches under blast effect was evaluated by combining quasi-static experiments and computational blast test data. The primary aim is to relate the quasi-static panel analysis to dynamic blast load. Based on this idea, lightweight sandwich composites were subjected to quasi-static compression loading with a special test apparatus and the samples were assumed as single degree-of-freedom mass-spring systems to include dynamic effect. This approach provides a simpler way to simulate the blast loading over the surface of the panels and reveals the possible failure mechanisms without applying any explosives. Therefore the design of the panels can be revised by considering quasi-static test results. In this work, the peak deflections and survivabilities of sandwiches for various explosive weights were predicted based on the formulations reported in the literature. Major failure types were also identified and evaluated with respect to their thicknesses. |
Beylergil, B; Tanoǧlu, M; Aktaş, E Modification of carbon fibre/epoxy composites by polyvinyl alcohol (PVA) based electrospun nanofibres Journal Article Advanced Composites Letters, 25 (3), pp. 69-76, 2016. @article{Beylergil201669, title = {Modification of carbon fibre/epoxy composites by polyvinyl alcohol (PVA) based electrospun nanofibres}, author = {B Beylergil and M Tanoǧlu and E Aktaş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84977637333&partnerID=40&md5=eeaf6e446994c4a0238e3299047cf132}, year = {2016}, date = {2016-01-01}, journal = {Advanced Composites Letters}, volume = {25}, number = {3}, pages = {69-76}, abstract = {In this study, the effects of modifying interlaminar region of unidirectional carbon fibre/epoxy composites by the incorporation of electrospun polyvinyl alcohol (PVA) nanofibres were investigated. PVA nanofibres were directly deposited onto the carbon fabrics by electrospinning method to improve mechanical performance of those composites. The features of the electrospun nanofibres were characterized by microscopy techniques. The unidirectional carbon fibre/epoxy composite laminates with/without PVA nanofibre interlayers were manufactured by vacuum-infusion technique in a [0]4 configuration. Tensile, three-point bending, compression, Charpy-impact and Mode-I fracture toughness tests (Double Cantilever Beam (DCB)) were carried out in accordance with ASTM standards to evaluate mechanical performance of the composites. Scanning electron microscopy (SEM) observations were made on the specimens to evaluate microstructural features. It was observed that the carbon fabrics were successfully coated with a thin layer of PVA nanofibres by electrospinning technique. The results showed that P VA nanofibres improve the mechanical properties of unidirectional carbon/epoxy composite laminates when subjected to in-plane loading. On the other hand, PVA nanofibres slightly reduced the mode-I fracture toughness values although they led to more stable crack propagation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, the effects of modifying interlaminar region of unidirectional carbon fibre/epoxy composites by the incorporation of electrospun polyvinyl alcohol (PVA) nanofibres were investigated. PVA nanofibres were directly deposited onto the carbon fabrics by electrospinning method to improve mechanical performance of those composites. The features of the electrospun nanofibres were characterized by microscopy techniques. The unidirectional carbon fibre/epoxy composite laminates with/without PVA nanofibre interlayers were manufactured by vacuum-infusion technique in a [0]4 configuration. Tensile, three-point bending, compression, Charpy-impact and Mode-I fracture toughness tests (Double Cantilever Beam (DCB)) were carried out in accordance with ASTM standards to evaluate mechanical performance of the composites. Scanning electron microscopy (SEM) observations were made on the specimens to evaluate microstructural features. It was observed that the carbon fabrics were successfully coated with a thin layer of PVA nanofibres by electrospinning technique. The results showed that P VA nanofibres improve the mechanical properties of unidirectional carbon/epoxy composite laminates when subjected to in-plane loading. On the other hand, PVA nanofibres slightly reduced the mode-I fracture toughness values although they led to more stable crack propagation. |
Merter, Emrah N; Başer, Gülnur; Tanoğlu, Metin Journal of Composite Materials, 50 (12), pp. 1697-1706, 2016. @article{doi:10.1177/0021998315595710, title = {Effects of hybrid yarn preparation technique and fiber sizing on the mechanical properties of continuous glass fiber-reinforced polypropylene composites}, author = {Emrah N Merter and Gülnur Başer and Metin Tanoğlu}, url = {https://doi.org/10.1177/0021998315595710}, doi = {10.1177/0021998315595710}, year = {2016}, date = {2016-01-01}, journal = {Journal of Composite Materials}, volume = {50}, number = {12}, pages = {1697-1706}, abstract = {In this study, hybrid yarns were developed by commingling the continuous polypropylene and glass fibers using air jet and direct twist preparation techniques. The non-crimp fabrics were obtained with ± 45 ° fiber orientation from these hybrid yarns. The fabrics were prepared with fiber sizings that are compatible and incompatible with polypropylene matrix to investigate the effect of interfacial adhesion on the properties of the thermoplastic composites. Composite panels were produced from the developed fabrics by hot press compression method and microstructural and mechanical properties of the composites were investigated. It was found that type of the hybrid yarn preparation technique and glass fiber sizing applied on the glass fibers have some important role on the properties of the composites. Composites made of fabrics produced by air jet hybrid yarn preparation technique exhibited better results than those produced by direct twist covering (single or double) hybrid yarn preparation techniques. The highest flexural properties (99.1 MPa flexural strength and 9.55 GPa flexural modulus) were obtained from the composites manufactured from fabric containing compatible sizing, due to better adhesion at the interface of glass fibers and polypropylene matrix. The composite fabricated from fabric with polypropylene compatible sizing also exhibited the highest peel resistance (interlaminar peel strength value of 5.87 N/mm). On the other hand, it was found that hybrid yarn preparation technique and type of the glass fiber sizing have insignificant effect on the impact properties of the glass fiber/polypropylene composites.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, hybrid yarns were developed by commingling the continuous polypropylene and glass fibers using air jet and direct twist preparation techniques. The non-crimp fabrics were obtained with ± 45 ° fiber orientation from these hybrid yarns. The fabrics were prepared with fiber sizings that are compatible and incompatible with polypropylene matrix to investigate the effect of interfacial adhesion on the properties of the thermoplastic composites. Composite panels were produced from the developed fabrics by hot press compression method and microstructural and mechanical properties of the composites were investigated. It was found that type of the hybrid yarn preparation technique and glass fiber sizing applied on the glass fibers have some important role on the properties of the composites. Composites made of fabrics produced by air jet hybrid yarn preparation technique exhibited better results than those produced by direct twist covering (single or double) hybrid yarn preparation techniques. The highest flexural properties (99.1 MPa flexural strength and 9.55 GPa flexural modulus) were obtained from the composites manufactured from fabric containing compatible sizing, due to better adhesion at the interface of glass fibers and polypropylene matrix. The composite fabricated from fabric with polypropylene compatible sizing also exhibited the highest peel resistance (interlaminar peel strength value of 5.87 N/mm). On the other hand, it was found that hybrid yarn preparation technique and type of the glass fiber sizing have insignificant effect on the impact properties of the glass fiber/polypropylene composites. |
Baştürk, SB; Tanoğlu, M; Çankaya, MA; Eğilmez, OÖ Dynamic behavior predictions of fiber-metal laminate/aluminum foam sandwiches under various explosive weights Journal Article Journal of Sandwich Structures & Materials, 18 (3), pp. 321-342, 2016. @article{doi:10.1177/1099636215603036, title = {Dynamic behavior predictions of fiber-metal laminate/aluminum foam sandwiches under various explosive weights}, author = {SB Baştürk and M Tanoğlu and MA Çankaya and OÖ Eğilmez}, url = {https://doi.org/10.1177/1099636215603036}, doi = {10.1177/1099636215603036}, year = {2016}, date = {2016-01-01}, journal = {Journal of Sandwich Structures & Materials}, volume = {18}, number = {3}, pages = {321-342}, abstract = {Application of blast tests causes some problems to characterize the performance of panels due to the drastic conditions of explosive medium. Real test has high safety concerns and is not easily accessible because of its extra budget. Some approaches are needed for the preliminary predictions of dynamic characteristics of panels under blast loading conditions. In this study, the response of sandwiches under blast effect was evaluated by combining quasi-static experiments and computational blast test data. The primary aim is to relate the quasi-static panel analysis to dynamic blast load. Based on this idea, lightweight sandwich composites were subjected to quasi-static compression loading with a special test apparatus and the samples were assumed as single degree-of-freedom mass-spring systems to include dynamic effect. This approach provides a simpler way to simulate the blast loading over the surface of the panels and reveals the possible failure mechanisms without applying any explosives. Therefore the design of the panels can be revised by considering quasi-static test results. In this work, the peak deflections and survivabilities of sandwiches for various explosive weights were predicted based on the formulations reported in the literature. Major failure types were also identified and evaluated with respect to their thicknesses.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Application of blast tests causes some problems to characterize the performance of panels due to the drastic conditions of explosive medium. Real test has high safety concerns and is not easily accessible because of its extra budget. Some approaches are needed for the preliminary predictions of dynamic characteristics of panels under blast loading conditions. In this study, the response of sandwiches under blast effect was evaluated by combining quasi-static experiments and computational blast test data. The primary aim is to relate the quasi-static panel analysis to dynamic blast load. Based on this idea, lightweight sandwich composites were subjected to quasi-static compression loading with a special test apparatus and the samples were assumed as single degree-of-freedom mass-spring systems to include dynamic effect. This approach provides a simpler way to simulate the blast loading over the surface of the panels and reveals the possible failure mechanisms without applying any explosives. Therefore the design of the panels can be revised by considering quasi-static test results. In this work, the peak deflections and survivabilities of sandwiches for various explosive weights were predicted based on the formulations reported in the literature. Major failure types were also identified and evaluated with respect to their thicknesses. |
2011 |
Basturk, Bahar S; Tanoglu, Metin Mechanical and energy absorption behaviors of metal/polymer layered sandwich structures Journal Article JOURNAL OF REINFORCED PLASTICS AND COMPOSITES, 30 (18), pp. 1539-1547, 2011, ISSN: 0731-6844. @article{ISI:000297764900003, title = {Mechanical and energy absorption behaviors of metal/polymer layered sandwich structures}, author = {Bahar S Basturk and Metin Tanoglu}, doi = {10.1177/0731684411421844}, issn = {0731-6844}, year = {2011}, date = {2011-09-01}, journal = {JOURNAL OF REINFORCED PLASTICS AND COMPOSITES}, volume = {30}, number = {18}, pages = {1539-1547}, abstract = {This article considers the sandwich structures with aluminium (Al) foams of various thicknesses in conjunction with skins composed of fibre-metal laminates (FML). The FMLs with Al sheet and glass fiber reinforced polypropylene (GFPP) composites were integrated with Al foam for composing the sandwich panels. The FML-foam sandwich systems were manufactured by hot pressing in a mold at 200 degrees C under 1.5 MPa pressure. The bonding between the components of the sandwich was achieved by various surface modification techniques, i.e., silane surface treatment, PP adhesive film additition, and their combination. The Al sheet/Al foam sandwiches were also prepared by bonding the components with an epoxy adhesive for comparing the effect of GFPP on the mechanical performance of the sandwich structures. The energy absorption capacities together with compressive mechanical behavior of both Al foams and FML-foam sandwich systems were evaluated by flatwise compression tests. Experiments were performed on samples of varying foam thicknesses.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This article considers the sandwich structures with aluminium (Al) foams of various thicknesses in conjunction with skins composed of fibre-metal laminates (FML). The FMLs with Al sheet and glass fiber reinforced polypropylene (GFPP) composites were integrated with Al foam for composing the sandwich panels. The FML-foam sandwich systems were manufactured by hot pressing in a mold at 200 degrees C under 1.5 MPa pressure. The bonding between the components of the sandwich was achieved by various surface modification techniques, i.e., silane surface treatment, PP adhesive film additition, and their combination. The Al sheet/Al foam sandwiches were also prepared by bonding the components with an epoxy adhesive for comparing the effect of GFPP on the mechanical performance of the sandwich structures. The energy absorption capacities together with compressive mechanical behavior of both Al foams and FML-foam sandwich systems were evaluated by flatwise compression tests. Experiments were performed on samples of varying foam thicknesses. |
2010 |
Yurdakul, Hilmi; Seyhan, Tugrul A; Turan, Servet; Tanoglu, Metin; Bauhofer, Wolfgang; Schulte, Karl Electric field effects on CNTs/vinyl ester suspensions and the resulting electrical and thermal composite properties Journal Article COMPOSITES SCIENCE AND TECHNOLOGY, 70 (14), pp. 2102-2110, 2010, ISSN: 0266-3538. @article{ISI:000283759400010, title = {Electric field effects on CNTs/vinyl ester suspensions and the resulting electrical and thermal composite properties}, author = {Hilmi Yurdakul and Tugrul A Seyhan and Servet Turan and Metin Tanoglu and Wolfgang Bauhofer and Karl Schulte}, doi = {10.1016/j.compscitech.2010.08.007}, issn = {0266-3538}, year = {2010}, date = {2010-11-01}, journal = {COMPOSITES SCIENCE AND TECHNOLOGY}, volume = {70}, number = {14}, pages = {2102-2110}, abstract = {In this study, electrical conductivity of a vinyl ester based composite containing low content (0.05, 0.1 and 0.3 wt.%) of double and multi-walled carbon nanotubes with and without amine functional groups (DWCNTs, MWCNTs, DWCNT-NH2 and MWCNT-NH2) was investigated. The composite with pristine MWCNTs was found to exhibit the highest electrical conductivity. Experiments aimed to induce an aligned conductive network with application of an alternating current (AC) electric field during cure were carried out on the resin suspensions with MWCNTs. Formation of electric anisotropy within the composite was verified. Light microscopy (LM), scanning electron (SEM) and transmission electron microscopy (TEM) were conducted to visualize dispersion state and the extent of alignment of MWCNTs within the polymer cured with and without application of the electric field. To gain a better understanding of electric field induced effects, glass transition temperature (T-g) of the composites was measured via Differential Scanning Calorimetry (DSC). It was determined that at 0.05 wt.% loading rate of MWCNTs, the composites, cured with application of the AC electric field, possessed a higher T-g than the composites cured without application of the AC electric field. (C) 2010 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, electrical conductivity of a vinyl ester based composite containing low content (0.05, 0.1 and 0.3 wt.%) of double and multi-walled carbon nanotubes with and without amine functional groups (DWCNTs, MWCNTs, DWCNT-NH2 and MWCNT-NH2) was investigated. The composite with pristine MWCNTs was found to exhibit the highest electrical conductivity. Experiments aimed to induce an aligned conductive network with application of an alternating current (AC) electric field during cure were carried out on the resin suspensions with MWCNTs. Formation of electric anisotropy within the composite was verified. Light microscopy (LM), scanning electron (SEM) and transmission electron microscopy (TEM) were conducted to visualize dispersion state and the extent of alignment of MWCNTs within the polymer cured with and without application of the electric field. To gain a better understanding of electric field induced effects, glass transition temperature (T-g) of the composites was measured via Differential Scanning Calorimetry (DSC). It was determined that at 0.05 wt.% loading rate of MWCNTs, the composites, cured with application of the AC electric field, possessed a higher T-g than the composites cured without application of the AC electric field. (C) 2010 Elsevier Ltd. All rights reserved. |
Sezgin, F E; Tanoglu, M; Egilmez, O O; Donmez, C Mechanical Behavior of Polypropylene-based Honeycomb-Core Composite Sandwich Structures Journal Article JOURNAL OF REINFORCED PLASTICS AND COMPOSITES, 29 (10), pp. 1569-1579, 2010, ISSN: 0731-6844. @article{ISI:000278117500013, title = {Mechanical Behavior of Polypropylene-based Honeycomb-Core Composite Sandwich Structures}, author = {F E Sezgin and M Tanoglu and O O Egilmez and C Donmez}, doi = {10.1177/0731684409341674}, issn = {0731-6844}, year = {2010}, date = {2010-05-01}, journal = {JOURNAL OF REINFORCED PLASTICS AND COMPOSITES}, volume = {29}, number = {10}, pages = {1569-1579}, abstract = {This article presents results from an experimental study, investigating the effects of core thickness on the mechanical properties of composite sandwich structures with polypropylene( PP)-based honeycomb core and glass fiber-reinforced polymer (GFRP) face-sheets fabricated by hand lay-up technique. Epoxy matrix and non-crimp glass fibers were used for the production of GFRP laminates. Flatwise compression (FC), edgewise compression (EC), three-point bending (3PB) and double cantilever beam (DCB) tests were performed to evaluate the mechanical behavior of the composite sandwich structures (CSSs). Based on the FC tests, an increase in the compressive modulus and strength was observed with an increase in the core thickness. For EC tests, peak loads up to crush of the sandwich panel is discussed using core thickness. According to the 3PB tests, a decrease in core shear stress and facesheet bending stress was observed as the core thickness increases.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This article presents results from an experimental study, investigating the effects of core thickness on the mechanical properties of composite sandwich structures with polypropylene( PP)-based honeycomb core and glass fiber-reinforced polymer (GFRP) face-sheets fabricated by hand lay-up technique. Epoxy matrix and non-crimp glass fibers were used for the production of GFRP laminates. Flatwise compression (FC), edgewise compression (EC), three-point bending (3PB) and double cantilever beam (DCB) tests were performed to evaluate the mechanical behavior of the composite sandwich structures (CSSs). Based on the FC tests, an increase in the compressive modulus and strength was observed with an increase in the core thickness. For EC tests, peak loads up to crush of the sandwich panel is discussed using core thickness. According to the 3PB tests, a decrease in core shear stress and facesheet bending stress was observed as the core thickness increases. |
Coskun, Selim; Ovecoglu, Lutfi M; Ozkal, Burak; Tanoglu, Metin Characterization investigations during mechanical alloying and sintering of W-20 vol% SiC composites Journal Article JOURNAL OF ALLOYS AND COMPOUNDS, 492 (1-2), pp. 576-584, 2010, ISSN: 0925-8388. @article{ISI:000276018900125, title = {Characterization investigations during mechanical alloying and sintering of W-20 vol% SiC composites}, author = {Selim Coskun and Lutfi M Ovecoglu and Burak Ozkal and Metin Tanoglu}, doi = {10.1016/j.jallcom.2009.11.185}, issn = {0925-8388}, year = {2010}, date = {2010-03-01}, journal = {JOURNAL OF ALLOYS AND COMPOUNDS}, volume = {492}, number = {1-2}, pages = {576-584}, abstract = {The effect of mechanical alloying and the sintering regime on the microstructural and the physical properties of W-SiC composites were investigated. Powder mixtures of W-20 vol.% SiC were mechanically alloyed (MA'd) using a Spex mill for 3 h, 6 h and 24 h. MA'd powders were characterized by Laser Diffraction Particle Size Analyzer, SEM and XRD investigations. MA'd W-20 vol.% SiC powder composites were sintered under inert Ar and reducing H(2) gas conditions at 1680 degrees C and 1770 degrees C for 1 h. The microstructural and mechanical characterizations of the sintered samples were carried out by scanning electron microscope (SEM) and X-ray diffraction (XRD) and Vickers Hardness analyses. The addition of SiC remarkably increases the hardness of the composites. Hardness is also increased with decreasing grain size and increasing amount of MA. (C) 2009 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of mechanical alloying and the sintering regime on the microstructural and the physical properties of W-SiC composites were investigated. Powder mixtures of W-20 vol.% SiC were mechanically alloyed (MA'd) using a Spex mill for 3 h, 6 h and 24 h. MA'd powders were characterized by Laser Diffraction Particle Size Analyzer, SEM and XRD investigations. MA'd W-20 vol.% SiC powder composites were sintered under inert Ar and reducing H(2) gas conditions at 1680 degrees C and 1770 degrees C for 1 h. The microstructural and mechanical characterizations of the sintered samples were carried out by scanning electron microscope (SEM) and X-ray diffraction (XRD) and Vickers Hardness analyses. The addition of SiC remarkably increases the hardness of the composites. Hardness is also increased with decreasing grain size and increasing amount of MA. (C) 2009 Elsevier B.V. All rights reserved. |
2009 |
Seyhan, A T; Sun, Z; Deitzel, J; Tanoglu, M; Heider, D Cure kinetics of vapor grown carbon nanofiber (VGCNF) modified epoxy resin suspensions and fracture toughness of their resulting nanocomposites Journal Article MATERIALS CHEMISTRY AND PHYSICS, 118 (1), pp. 234-242, 2009, ISSN: 0254-0584. @article{ISI:000271556000042, title = {Cure kinetics of vapor grown carbon nanofiber (VGCNF) modified epoxy resin suspensions and fracture toughness of their resulting nanocomposites}, author = {A T Seyhan and Z Sun and J Deitzel and M Tanoglu and D Heider}, doi = {10.1016/j.matchemphys.2009.07.045}, issn = {0254-0584}, year = {2009}, date = {2009-11-01}, journal = {MATERIALS CHEMISTRY AND PHYSICS}, volume = {118}, number = {1}, pages = {234-242}, abstract = {In this study, the cure kinetics of Cycom 977-20. an aerospace grade toughened epoxy resin, and its suspensions containing various amounts (1, 3 and 5 wt.%) of vapor grown carbon nanofibers (VGCNFs) with and without chemical treatment were monitored via dynamic and isothermal dynamic scanning calorimetry (DSC) measurements. For this purpose, VGCNFs were first oxidized in nitric acid and then functionalized with 3-glycidoxypropyltrimethoxy silane (GPTMS) coupling agent. Fourier transform infrared (FTIR) spectroscopy was subsequently used to verify the chemical functional groups grafted onto the surfaces of VGCNFs. Sonication technique was conducted to facilitate proper dispersion of as-received, acid treated and silanized VGCNFs within epoxy resin. Dynamic DSC measurements showed that silanized VGCNF modified resin suspensions exhibited higher heat of cure compared to those with as-received VGCNFs. Experimentally obtained isothermal DSC data was then con elated with Kamal phenomenological model. Based on the model predictions, it was found that silanized VGCNFs; maximized the cure reaction rates at the very initial stage of the reaction. Accordingly, an optimized curing cycle was applied to harden resin suspensions. Fracture testing was then carried out on the cured samples in order to relate the curing behavior of VGCNF modified resin suspensions to mechanical response of their resulting nanocomposites With addition of 1 wt % of silanized VGCNFs, the fracture toughness value of neat epoxy was found to be improved by 12%. SEM was further employed to examine the fracture surfaces of the samples. (C) 2009 Elsevier B V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, the cure kinetics of Cycom 977-20. an aerospace grade toughened epoxy resin, and its suspensions containing various amounts (1, 3 and 5 wt.%) of vapor grown carbon nanofibers (VGCNFs) with and without chemical treatment were monitored via dynamic and isothermal dynamic scanning calorimetry (DSC) measurements. For this purpose, VGCNFs were first oxidized in nitric acid and then functionalized with 3-glycidoxypropyltrimethoxy silane (GPTMS) coupling agent. Fourier transform infrared (FTIR) spectroscopy was subsequently used to verify the chemical functional groups grafted onto the surfaces of VGCNFs. Sonication technique was conducted to facilitate proper dispersion of as-received, acid treated and silanized VGCNFs within epoxy resin. Dynamic DSC measurements showed that silanized VGCNF modified resin suspensions exhibited higher heat of cure compared to those with as-received VGCNFs. Experimentally obtained isothermal DSC data was then con elated with Kamal phenomenological model. Based on the model predictions, it was found that silanized VGCNFs; maximized the cure reaction rates at the very initial stage of the reaction. Accordingly, an optimized curing cycle was applied to harden resin suspensions. Fracture testing was then carried out on the cured samples in order to relate the curing behavior of VGCNF modified resin suspensions to mechanical response of their resulting nanocomposites With addition of 1 wt % of silanized VGCNFs, the fracture toughness value of neat epoxy was found to be improved by 12%. SEM was further employed to examine the fracture surfaces of the samples. (C) 2009 Elsevier B V. All rights reserved. |
Seyhan, Tugrul A; Tanoglu, Metin; Schulte, Karl MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 523 (1-2), pp. 85-92, 2009, ISSN: 0921-5093. @article{ISI:000270632900014, title = {Tensile mechanical behavior and fracture toughness of MWCNT and DWCNT modified vinyl-ester/polyester hybrid nanocomposites produced by 3-roll milling}, author = {Tugrul A Seyhan and Metin Tanoglu and Karl Schulte}, doi = {10.1016/j.msea.2009.05.035}, issn = {0921-5093}, year = {2009}, date = {2009-10-01}, journal = {MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, volume = {523}, number = {1-2}, pages = {85-92}, abstract = {This study aims to investigate the tensile mechanical behavior and fracture toughness of vinyl-ester/polyester hybrid nanocomposites containing various types of nanofillers, including multi- and double-walled carbon nanotubes with and without amine functional groups (MWCNTs, DWCNTs, MWCNT-NH2 and DWCNT-NH2). To prepare the resin suspensions, very low contents (0.05, 0.1 and 0.3 wt.%) of carbon nanotubes (CNTs) were dispersed within a specially synthesized styrene-free polyester resin, conducting 3-roll milling technique. The collected resin stuff was subsequently blended with vinyl-ester via mechanical stirring to achieve final suspensions prior to polymerization. Nanocomposites containing MWCNTs and MWCNT-NH2 were found to exhibit higher tensile strength and modulus as well as larger fracture toughness and fracture energy compared to neat hybrid polymer. However, incorporation of similar contents of DWCNTs and DWCNT-NH2 into the hybrid resin did not reflect the same improvement in the corresponding mechanical properties. Furthermore, experimentally measured elastic moduli of the nanocomposites containing DWCNTs, DWCNT-NH2, MWCNTs and MWCNT-NH2 were fitted to Halphin-Tsai model. Regardless of amine functional groups or content of carbon nanotubes, MWCNT modified nanocomposites exhibited better agreement between the predicted and the measured elastic moduli values compared to nanocomposites with DWCNTs. Furthermore, Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to reveal dispersion state of the carbon nanotubes within the hybrid polymer and to examine the CNT induced failure modes that occurred under mechanical loading, respectively. Based on the experimental findings obtained, it was emphasized that the types of CNTs and presence of amine functional groups on the surface of CNTs affects substantially the chemical interactions at the interface, thus tuning the ultimate mechanical performance of the resulting nanocomposites. (C) 2009 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study aims to investigate the tensile mechanical behavior and fracture toughness of vinyl-ester/polyester hybrid nanocomposites containing various types of nanofillers, including multi- and double-walled carbon nanotubes with and without amine functional groups (MWCNTs, DWCNTs, MWCNT-NH2 and DWCNT-NH2). To prepare the resin suspensions, very low contents (0.05, 0.1 and 0.3 wt.%) of carbon nanotubes (CNTs) were dispersed within a specially synthesized styrene-free polyester resin, conducting 3-roll milling technique. The collected resin stuff was subsequently blended with vinyl-ester via mechanical stirring to achieve final suspensions prior to polymerization. Nanocomposites containing MWCNTs and MWCNT-NH2 were found to exhibit higher tensile strength and modulus as well as larger fracture toughness and fracture energy compared to neat hybrid polymer. However, incorporation of similar contents of DWCNTs and DWCNT-NH2 into the hybrid resin did not reflect the same improvement in the corresponding mechanical properties. Furthermore, experimentally measured elastic moduli of the nanocomposites containing DWCNTs, DWCNT-NH2, MWCNTs and MWCNT-NH2 were fitted to Halphin-Tsai model. Regardless of amine functional groups or content of carbon nanotubes, MWCNT modified nanocomposites exhibited better agreement between the predicted and the measured elastic moduli values compared to nanocomposites with DWCNTs. Furthermore, Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to reveal dispersion state of the carbon nanotubes within the hybrid polymer and to examine the CNT induced failure modes that occurred under mechanical loading, respectively. Based on the experimental findings obtained, it was emphasized that the types of CNTs and presence of amine functional groups on the surface of CNTs affects substantially the chemical interactions at the interface, thus tuning the ultimate mechanical performance of the resulting nanocomposites. (C) 2009 Elsevier B.V. All rights reserved. |
2008 |
Erdogan, B C; Seyhan, A T; Ocak, Y; Tanoglu, M; Balkose, D; Ulku, S Cure kinetics of epoxy resin-natural zeolite composites Journal Article JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 94 (3), pp. 743-747, 2008, ISSN: 1388-6150, (31st International Conference on Vacuum Microbalance Techniques, Izmir Inst Technol, Izmir, TURKEY, SEP 12-14, 2007). @article{ISI:000261832000025, title = {Cure kinetics of epoxy resin-natural zeolite composites}, author = {B C Erdogan and A T Seyhan and Y Ocak and M Tanoglu and D Balkose and S Ulku}, doi = {10.1007/s10973-008-9366-7}, issn = {1388-6150}, year = {2008}, date = {2008-12-01}, journal = {JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY}, volume = {94}, number = {3}, pages = {743-747}, organization = {Izmir Inst Technol, Engn Fac, Dept Chem Engn; Turkish Sci & Technol Res Council; Ege Branch Chamber Chem Engineers; Ege Reg Chamber Ind; Bausparkasse Mainz; Rubothem; Pigment A; Terra Lab; Terra A; IItek Ltd}, abstract = {The cure kinetics of epoxy resin and epoxy resin containing 10 mass% of natural zeolite were investigated using differential scanning calorimetry (DSC). The conformity of the cure kinetic data of epoxy and epoxy-zeolite system was checked with the auto-catalytic cure rate model. The results indicated that the hydroxyl group on the zeolite surface played a significant role in the autocatalytic reaction mechanism. This group was able to form a new transition state between anhydride hardener and epoxide group. The natural zeolite particles acted as catalyst for the epoxy system by promoting its curing rate.}, note = {31st International Conference on Vacuum Microbalance Techniques, Izmir Inst Technol, Izmir, TURKEY, SEP 12-14, 2007}, keywords = {}, pubstate = {published}, tppubtype = {article} } The cure kinetics of epoxy resin and epoxy resin containing 10 mass% of natural zeolite were investigated using differential scanning calorimetry (DSC). The conformity of the cure kinetic data of epoxy and epoxy-zeolite system was checked with the auto-catalytic cure rate model. The results indicated that the hydroxyl group on the zeolite surface played a significant role in the autocatalytic reaction mechanism. This group was able to form a new transition state between anhydride hardener and epoxide group. The natural zeolite particles acted as catalyst for the epoxy system by promoting its curing rate. |
Seyhan, Tugrul A; Tanoglu, Metin; Schulte, Karl Mode I and mode II fracture toughness of E-glass non-crimp fabric/carbon nanotube (CNT) modified polymer based composites Journal Article ENGINEERING FRACTURE MECHANICS, 75 (18), pp. 5151-5162, 2008, ISSN: 0013-7944. @article{ISI:000261562000013, title = {Mode I and mode II fracture toughness of E-glass non-crimp fabric/carbon nanotube (CNT) modified polymer based composites}, author = {Tugrul A Seyhan and Metin Tanoglu and Karl Schulte}, doi = {10.1016/j.engfracmech.2008.08.003}, issn = {0013-7944}, year = {2008}, date = {2008-12-01}, journal = {ENGINEERING FRACTURE MECHANICS}, volume = {75}, number = {18}, pages = {5151-5162}, abstract = {In this study, mode I and mode II interlaminar fracture toughness, and interlaminar shear strength of E-glass non-crimp fabric/carbon nanotube modified polymer matrix composites were investigated. The matrix resin containing 0.1 wt.% of amino functionalized multi walled carbon nanotubes were prepared, utilizing the 3-roll milling technique. Composite laminates were manufactured via vacuum assisted resin transfer molding process. Carbon nanotube modified laminates were found to exhibit 8% and 11% higher mode 11 interlaminar fracture toughness and interlaminar shear strength values, respectively, as compared to the base laminates. However, no significant improvement was observed for mode I interlaminar fracture toughness values. Furthermore, Optical microscopy and scanning electron microscopy were utilized to monitor the distribution of carbon nanotubes within the composite microstructure and to examine the fracture surfaces of the failed specimens, respectively. (c) 2008 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, mode I and mode II interlaminar fracture toughness, and interlaminar shear strength of E-glass non-crimp fabric/carbon nanotube modified polymer matrix composites were investigated. The matrix resin containing 0.1 wt.% of amino functionalized multi walled carbon nanotubes were prepared, utilizing the 3-roll milling technique. Composite laminates were manufactured via vacuum assisted resin transfer molding process. Carbon nanotube modified laminates were found to exhibit 8% and 11% higher mode 11 interlaminar fracture toughness and interlaminar shear strength values, respectively, as compared to the base laminates. However, no significant improvement was observed for mode I interlaminar fracture toughness values. Furthermore, Optical microscopy and scanning electron microscopy were utilized to monitor the distribution of carbon nanotubes within the composite microstructure and to examine the fracture surfaces of the failed specimens, respectively. (c) 2008 Elsevier Ltd. All rights reserved. |
Rahimov, R N; Khalilova, A A; Arasly, D H; Aliyev, M I; Tanoglu, M; Ozyuzer, L Thermostable tensoresistors of Co doped GaSb-FeGa1.3 eutectic composites Journal Article SENSORS AND ACTUATORS A-PHYSICAL, 147 (2), pp. 436-440, 2008, ISSN: 0924-4247. @article{ISI:000259685600013, title = {Thermostable tensoresistors of Co doped GaSb-FeGa1.3 eutectic composites}, author = {R N Rahimov and A A Khalilova and D H Arasly and M I Aliyev and M Tanoglu and L Ozyuzer}, doi = {10.1016/j.sna.2008.05.032}, issn = {0924-4247}, year = {2008}, date = {2008-10-01}, journal = {SENSORS AND ACTUATORS A-PHYSICAL}, volume = {147}, number = {2}, pages = {436-440}, abstract = {The microstructure and tensoresistive properties of GaSb-FeCa1.3 eutectic composites doped with 0.1% Co have been investigated. It was found that the Co impurity atoms mainly accumulate in the metallic inclusions. The length of the inclusions in GaSb-FeGa1.3(Co) was measured to be about half of those in uncloped GaSb-FeGa1.3 eutectics. The tensometric characteristics of gauges based on GaSb-FeGa1.3(Co) have been found to be more thermostable than uncloped samples. (C) 2008 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The microstructure and tensoresistive properties of GaSb-FeCa1.3 eutectic composites doped with 0.1% Co have been investigated. It was found that the Co impurity atoms mainly accumulate in the metallic inclusions. The length of the inclusions in GaSb-FeGa1.3(Co) was measured to be about half of those in uncloped GaSb-FeGa1.3 eutectics. The tensometric characteristics of gauges based on GaSb-FeGa1.3(Co) have been found to be more thermostable than uncloped samples. (C) 2008 Elsevier B.V. All rights reserved. |
Kaya, Elcin; Tanoglu, Metin; Okur, Salih Layered clay/epoxy nanocomposites: Thermomechanical, flame retardancy, and optical properties Journal Article JOURNAL OF APPLIED POLYMER SCIENCE, 109 (2), pp. 834-840, 2008, ISSN: 0021-8995. @article{ISI:000256267200020, title = {Layered clay/epoxy nanocomposites: Thermomechanical, flame retardancy, and optical properties}, author = {Elcin Kaya and Metin Tanoglu and Salih Okur}, doi = {10.1002/app.28168}, issn = {0021-8995}, year = {2008}, date = {2008-07-01}, journal = {JOURNAL OF APPLIED POLYMER SCIENCE}, volume = {109}, number = {2}, pages = {834-840}, abstract = {In this study, layered clay/polymer nanocomposites were developed based on epoxy resins and montmorillonite as the nanoplatelet reinforcement. Clay particles were treated with hexadecyltrimethylammonium chloride (HTCA) through an ion exchange reaction. In this way, Na+ interlayer cations of the clay is exchanged with onium cation of the surfactant that turns the hydrophilic clays (MMT) to organophilic (OMMT) characteristics. Thermal analysis results revealed that the glass transition temperature (T-g) and the dynamic mechanical properties including the storage and loss modulus of the neat epoxy resin increases by the incorporation of clay particles. It was also found that flame resistance of the polymer is improved by the addition of the clay particles. (C) 2008 Wiley Periodicals, Inc.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, layered clay/polymer nanocomposites were developed based on epoxy resins and montmorillonite as the nanoplatelet reinforcement. Clay particles were treated with hexadecyltrimethylammonium chloride (HTCA) through an ion exchange reaction. In this way, Na+ interlayer cations of the clay is exchanged with onium cation of the surfactant that turns the hydrophilic clays (MMT) to organophilic (OMMT) characteristics. Thermal analysis results revealed that the glass transition temperature (T-g) and the dynamic mechanical properties including the storage and loss modulus of the neat epoxy resin increases by the incorporation of clay particles. It was also found that flame resistance of the polymer is improved by the addition of the clay particles. (C) 2008 Wiley Periodicals, Inc. |
Alpöz, Riza A; Ertuḡrul, Fahinur; Cogulu, Dilsah; Ak, Asli Topaloḡlu; Tanoḡlu, Metin; ç, El Effects of light curing method and exposure time on mechanical properties of resin based dental materials Journal Article European journal of dentistry, 2 , pp. 37, 2008. @article{alpoz2008effects, title = {Effects of light curing method and exposure time on mechanical properties of resin based dental materials}, author = {Riza A Alpöz and Fahinur Ertuḡrul and Dilsah Cogulu and Asli Topaloḡlu Ak and Metin Tanoḡlu and El{ç}in Kaya}, year = {2008}, date = {2008-01-01}, journal = {European journal of dentistry}, volume = {2}, pages = {37}, publisher = {Dental Investigations Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2007 |
Guden, M; Yueksel, S; Tasdemirci, A; Tanoglu, M COMPOSITE STRUCTURES, 81 (4), pp. 480-490, 2007, ISSN: 0263-8223. @article{ISI:000249256200002, title = {Effect of aluminum closed-cell foam filling on the quasi-static axial crush performance of glass fiber reinforced polyester composite and aluminum/composite hybrid tubes}, author = {M Guden and S Yueksel and A Tasdemirci and M Tanoglu}, doi = {10.1016/j.compstruct.2006.09.005}, issn = {0263-8223}, year = {2007}, date = {2007-12-01}, journal = {COMPOSITE STRUCTURES}, volume = {81}, number = {4}, pages = {480-490}, abstract = {The effect of Al closed-cell foam filling on the quasi-static crushing behavior of an E-glass woven fabric polyester composite tube and thin-walled Al/polyester composite hybrid tube was experimentally investigated. For comparison, empty Al, empty composite and empty hybrid tubes were also tested. Empty composite and empty hybrid tubes crushed predominantly in progressive crushing mode, without applying any triggering mechanism. Foam filling was found to be ineffective in increasing the crushing loads of the composite tubes over the sum of the crushing loads of empty composite tube and foam. However, foam filling stabilized the composite progressive crushing mode. In empty hybrid tubes, the deformation mode of the inner Al tube was found to be a more complex form of the diamond mode of deformation of empty Al tube, leading to higher crushing load values than the sum of the crushing load values of empty composite tube and empty metal tube. The foam filling of hybrid tubes however resulted in axial splitting of the outer composite tube due to the resistance imposed by the foam filler to Al tube inward folding and hence it was ineffective in increasing crushing load and SAE values over those of empty hybrid tubes. (C) 2006 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of Al closed-cell foam filling on the quasi-static crushing behavior of an E-glass woven fabric polyester composite tube and thin-walled Al/polyester composite hybrid tube was experimentally investigated. For comparison, empty Al, empty composite and empty hybrid tubes were also tested. Empty composite and empty hybrid tubes crushed predominantly in progressive crushing mode, without applying any triggering mechanism. Foam filling was found to be ineffective in increasing the crushing loads of the composite tubes over the sum of the crushing loads of empty composite tube and foam. However, foam filling stabilized the composite progressive crushing mode. In empty hybrid tubes, the deformation mode of the inner Al tube was found to be a more complex form of the diamond mode of deformation of empty Al tube, leading to higher crushing load values than the sum of the crushing load values of empty composite tube and empty metal tube. The foam filling of hybrid tubes however resulted in axial splitting of the outer composite tube due to the resistance imposed by the foam filler to Al tube inward folding and hence it was ineffective in increasing crushing load and SAE values over those of empty hybrid tubes. (C) 2006 Elsevier Ltd. All rights reserved. |
Bozkurt, Emrah; Kaya, Elcin; Tanoglu, Metin Mechanical and thermal behavior of non-crimp glass fiber reinforced layered clay/epoxy nanocomposites Journal Article COMPOSITES SCIENCE AND TECHNOLOGY, 67 (15-16), pp. 3394-3403, 2007, ISSN: 0266-3538. @article{ISI:000250910600040, title = {Mechanical and thermal behavior of non-crimp glass fiber reinforced layered clay/epoxy nanocomposites}, author = {Emrah Bozkurt and Elcin Kaya and Metin Tanoglu}, doi = {10.1016/j.compscitech.2007.03.021}, issn = {0266-3538}, year = {2007}, date = {2007-12-01}, journal = {COMPOSITES SCIENCE AND TECHNOLOGY}, volume = {67}, number = {15-16}, pages = {3394-3403}, abstract = {Mechanical and thermal properties of non-crimp glass fiber reinforced clay/epoxy nanocomposites were investigated. Clay/epoxy natiocomposite systems were prepared to use as the matrix material for composite laminates. X-ray diffraction results obtained from natural and modified clays indicated that intergallery spacing of the layered clay increases with surface treatment. Tensile tests indicated that clay loading has minor effect on the tensile properties. Flexural properties of laminates were improved by clay addition due to the improved interface between glass fibers and epoxy. Differential scanning calorimetry (DSC) results showed that the modified clay particles affected the glass transition temperatures (T-g) of the nanocomposites. Incorporation of surface treated clay particles increased the dynamic mechanical properties of nanocomposite laminates. It was found that the flame resistance of composites was improved significantly by clay addition into the epoxy matrix. (C) 2007 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Mechanical and thermal properties of non-crimp glass fiber reinforced clay/epoxy nanocomposites were investigated. Clay/epoxy natiocomposite systems were prepared to use as the matrix material for composite laminates. X-ray diffraction results obtained from natural and modified clays indicated that intergallery spacing of the layered clay increases with surface treatment. Tensile tests indicated that clay loading has minor effect on the tensile properties. Flexural properties of laminates were improved by clay addition due to the improved interface between glass fibers and epoxy. Differential scanning calorimetry (DSC) results showed that the modified clay particles affected the glass transition temperatures (T-g) of the nanocomposites. Incorporation of surface treated clay particles increased the dynamic mechanical properties of nanocomposite laminates. It was found that the flame resistance of composites was improved significantly by clay addition into the epoxy matrix. (C) 2007 Elsevier Ltd. All rights reserved. |
Simsek, Yilmaz; Ozyuzer, Lutfi; Seyhan, Tugrul A; Tanoglu, Metin; Schulte, Karl Temperature dependence of electrical conductivity in double-wall and multi-wall carbon nanotube/polyester nanocomposites Journal Article JOURNAL OF MATERIALS SCIENCE, 42 (23), pp. 9689-9695, 2007, ISSN: 0022-2461. @article{ISI:000249657500026, title = {Temperature dependence of electrical conductivity in double-wall and multi-wall carbon nanotube/polyester nanocomposites}, author = {Yilmaz Simsek and Lutfi Ozyuzer and Tugrul A Seyhan and Metin Tanoglu and Karl Schulte}, doi = {10.1007/s10853-007-1943-9}, issn = {0022-2461}, year = {2007}, date = {2007-12-01}, journal = {JOURNAL OF MATERIALS SCIENCE}, volume = {42}, number = {23}, pages = {9689-9695}, abstract = {The aim of this study is to investigate temperature dependence of electrical conductivity of carbon nanotube (CNT)/polyester nanocomposites from room temperature to 77 K using four-point probe test method. To produce nanocomposites, various types and amounts of CNTs (0.1, 0.3 and 0.5 wt.%) were dispersed via 3-roll mill technique within a specially formulized resin blend of thermoset polyesters. CNTs used in the study include multi walled carbon nanotubes (MWCNT) and double-walled carbon nanotubes (DWCNT) with and without amine functional groups (-NH2). It was observed that the incorporation of carbon nanotubes into resin blend yields electrically percolating networks and electrical conductivity of the resulting nanocomposites increases with increasing amount of nanotubes. However, nanocomposites containing amino functionalized carbon nanotubes exhibit relatively lower electrical conductivity compared to those with non-functionalized carbon nanotubes. To get better interpretation of the mechanism leading to conductive network via CNTs with and without amine functional groups, the experimental results were fitted to fluctuation-induced tunneling through the barriers between the metallic regions model. It was found that the results are in good agreement with prediction of proposed model.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The aim of this study is to investigate temperature dependence of electrical conductivity of carbon nanotube (CNT)/polyester nanocomposites from room temperature to 77 K using four-point probe test method. To produce nanocomposites, various types and amounts of CNTs (0.1, 0.3 and 0.5 wt.%) were dispersed via 3-roll mill technique within a specially formulized resin blend of thermoset polyesters. CNTs used in the study include multi walled carbon nanotubes (MWCNT) and double-walled carbon nanotubes (DWCNT) with and without amine functional groups (-NH2). It was observed that the incorporation of carbon nanotubes into resin blend yields electrically percolating networks and electrical conductivity of the resulting nanocomposites increases with increasing amount of nanotubes. However, nanocomposites containing amino functionalized carbon nanotubes exhibit relatively lower electrical conductivity compared to those with non-functionalized carbon nanotubes. To get better interpretation of the mechanism leading to conductive network via CNTs with and without amine functional groups, the experimental results were fitted to fluctuation-induced tunneling through the barriers between the metallic regions model. It was found that the results are in good agreement with prediction of proposed model. |
Altay, E; Shahwan, T; Tanoglu, M POWDER TECHNOLOGY, 178 (3), pp. 194-202, 2007, ISSN: 0032-5910. @article{ISI:000249773000007, title = {Morphosynthesis of CaCO3 at different reaction temperatures and the effects of PDDA, CTAB, and EDTA on the particle morphology and polymorph stability}, author = {E Altay and T Shahwan and M Tanoglu}, doi = {10.1016/j.powtec.2007.05.004}, issn = {0032-5910}, year = {2007}, date = {2007-09-01}, journal = {POWDER TECHNOLOGY}, volume = {178}, number = {3}, pages = {194-202}, abstract = {Facile precipitation of CaCO3 was performed using aqueous solutions of CaCl2 with Na2CO3 over a wide range of mixing and aging temperatures. The precipitation process was then repeated in the presence of PDDA, CTAB, and EDTA at the mixing temperatures of 30 degrees C, 50 degrees C, 70 degrees C, and 90 degrees C. The presence of these additives was seen to greatly suppress the formation of aragonite. Among these additives, EDTA was the one that showed the most prominent effects on particle morphology of CaCO3. The sequence of pH adjustment appeared to be a critical factor for the additive functionality. (C) 2007 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Facile precipitation of CaCO3 was performed using aqueous solutions of CaCl2 with Na2CO3 over a wide range of mixing and aging temperatures. The precipitation process was then repeated in the presence of PDDA, CTAB, and EDTA at the mixing temperatures of 30 degrees C, 50 degrees C, 70 degrees C, and 90 degrees C. The presence of these additives was seen to greatly suppress the formation of aragonite. Among these additives, EDTA was the one that showed the most prominent effects on particle morphology of CaCO3. The sequence of pH adjustment appeared to be a critical factor for the additive functionality. (C) 2007 Elsevier B.V. All rights reserved. |
Seyhan, A T; Gojny, F H; Tanoglu, M; Schulte, K Rheological and dynamic-mechanical behavior of carbon nanotube/vinyl ester-polyester suspensions and their nanocomposites Journal Article EUROPEAN POLYMER JOURNAL, 43 (7), pp. 2836-2847, 2007, ISSN: 0014-3057. @article{ISI:000248641400009, title = {Rheological and dynamic-mechanical behavior of carbon nanotube/vinyl ester-polyester suspensions and their nanocomposites}, author = {A T Seyhan and F H Gojny and M Tanoglu and K Schulte}, doi = {10.1016/j.eurpolymj.2007.04.022}, issn = {0014-3057}, year = {2007}, date = {2007-07-01}, journal = {EUROPEAN POLYMER JOURNAL}, volume = {43}, number = {7}, pages = {2836-2847}, abstract = {Rheological properties of vinyl ester polyester resin suspensions containing various amounts (0.05, 0.1 and 0.3 wt.%) of multi walled carbon nanotubes (MWCNT) with and without amine functional groups (-NH2) were investigated by utilization of oscillatory rheometer with parallel plate geometry. Dispersion of corresponding carbon nanotubes within the resin blend was accomplished employing high shear mixing technique (3-roll milling). Based on the dynamic viscoelastic measurements, it was observed that at 0.3 wt.% of CNT loadings, storage modulus (G') values of suspensions containing MWCNTs and MWCNT-NH2 exhibited frequency-independent pseudo solid like behavior especially at lower frequencies. Moreover, the loss modulus (G `') values of the resin suspensions with respect to frequency were observed to increase with an increase in contents of CNTs within the resin blend. In addition, steady shear viscosity measurements implied that at each given loading rate, the resin suspensions demonstrated shear thinning behavior regardless of amine functional groups, while the neat resin blend was almost the Newtonian fluid. Furthermore, dynamic mechanical behavior of the nanocomposites achieved by polymerizing the resin blend suspensions with MWCNTs and MWCNT-NH2 was investigated through dynamic mechanical thermal analyzer (DMTA). It was revealed that storage modulus (E') and the loss modulus (E `') values of the resulting nanocomposites increased with regard to carbon nanotubes incorporated into the resin blend. In addition, at each given loading rate, nanocomposites containing MWCNT-NH2 possessed larger loss and storage modulus values as well as higher glass transition temperatures (T-g) as compared to those with MWCNTs. These findings were attributed to evidences for contribution of amine functional groups to chemical interactions at the interface between CNTs and the resin blend matrix. Transmission electron microscopy (TEM) studies performed on the cured resin samples approved that the dispersion state of carbon nanotubes with and without amine functional groups within the matrix resin blend was adequate. This implies that 3-roll milling process described herein is very appropriate technique for blending of carbon nanotubes with a liquid thermoset resin to manufacture nanocomposites with enhanced final properties. (c) 2007 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Rheological properties of vinyl ester polyester resin suspensions containing various amounts (0.05, 0.1 and 0.3 wt.%) of multi walled carbon nanotubes (MWCNT) with and without amine functional groups (-NH2) were investigated by utilization of oscillatory rheometer with parallel plate geometry. Dispersion of corresponding carbon nanotubes within the resin blend was accomplished employing high shear mixing technique (3-roll milling). Based on the dynamic viscoelastic measurements, it was observed that at 0.3 wt.% of CNT loadings, storage modulus (G') values of suspensions containing MWCNTs and MWCNT-NH2 exhibited frequency-independent pseudo solid like behavior especially at lower frequencies. Moreover, the loss modulus (G `') values of the resin suspensions with respect to frequency were observed to increase with an increase in contents of CNTs within the resin blend. In addition, steady shear viscosity measurements implied that at each given loading rate, the resin suspensions demonstrated shear thinning behavior regardless of amine functional groups, while the neat resin blend was almost the Newtonian fluid. Furthermore, dynamic mechanical behavior of the nanocomposites achieved by polymerizing the resin blend suspensions with MWCNTs and MWCNT-NH2 was investigated through dynamic mechanical thermal analyzer (DMTA). It was revealed that storage modulus (E') and the loss modulus (E `') values of the resulting nanocomposites increased with regard to carbon nanotubes incorporated into the resin blend. In addition, at each given loading rate, nanocomposites containing MWCNT-NH2 possessed larger loss and storage modulus values as well as higher glass transition temperatures (T-g) as compared to those with MWCNTs. These findings were attributed to evidences for contribution of amine functional groups to chemical interactions at the interface between CNTs and the resin blend matrix. Transmission electron microscopy (TEM) studies performed on the cured resin samples approved that the dispersion state of carbon nanotubes with and without amine functional groups within the matrix resin blend was adequate. This implies that 3-roll milling process described herein is very appropriate technique for blending of carbon nanotubes with a liquid thermoset resin to manufacture nanocomposites with enhanced final properties. (c) 2007 Elsevier Ltd. All rights reserved. |
Seyhan, Tugrul A; Gojny, Florian H; Tanoglu, Metin; Schulte, Karl Critical aspects related to processing of carbon nano tube/unsaturated thermoset polyester nanocomposites Journal Article EUROPEAN POLYMER JOURNAL, 43 (2), pp. 374-379, 2007, ISSN: 0014-3057. @article{ISI:000244379900010, title = {Critical aspects related to processing of carbon nano tube/unsaturated thermoset polyester nanocomposites}, author = {Tugrul A Seyhan and Florian H Gojny and Metin Tanoglu and Karl Schulte}, doi = {10.1016/j.eurpolymj.2006.11.018}, issn = {0014-3057}, year = {2007}, date = {2007-02-01}, journal = {EUROPEAN POLYMER JOURNAL}, volume = {43}, number = {2}, pages = {374-379}, abstract = {Carbon nanotubes (CNTs) have outstanding mechanical, thermal and electrical properties. As a result, particular interest has been recently given in exploiting these properties by incorporating carbon nanotubes into some form of matrix. Although unsaturated polyesters with styrene have widespread use in the industrial applications, surprisingly there is no study in the literature about CNT/thermoset polyester nanocomposite systems. In the present paper, we underline some important issues and limitations during the processing of unsaturated polyester resins with different types of carbon nanotubes. In that manner, 3-roll mill and sonication techniques were comparatively evaluated to process nanocomposites made of CNTs with and without amine (NH2) functional groups and polyesters. It was found that styrene evaporation from the polyester resin system was a critical issue for nanocomposite processing. Rheological behaviour of the suspensions containing CNTs and tensile strengths of their resulting nanocomposites were characterized. CNT/polyester suspensions exhibited a shear thinning behaviour, while polyester resin blends act as a Newtonian fluid. It was also found that nanotubes with amine functional groups have better tensile strength, as compared to those with untreated CNTs. Transmission electron microscopy (TEM) was also employed to reveal the degree of dispersion of CNTs in the matrix. (c) 2006 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Carbon nanotubes (CNTs) have outstanding mechanical, thermal and electrical properties. As a result, particular interest has been recently given in exploiting these properties by incorporating carbon nanotubes into some form of matrix. Although unsaturated polyesters with styrene have widespread use in the industrial applications, surprisingly there is no study in the literature about CNT/thermoset polyester nanocomposite systems. In the present paper, we underline some important issues and limitations during the processing of unsaturated polyester resins with different types of carbon nanotubes. In that manner, 3-roll mill and sonication techniques were comparatively evaluated to process nanocomposites made of CNTs with and without amine (NH2) functional groups and polyesters. It was found that styrene evaporation from the polyester resin system was a critical issue for nanocomposite processing. Rheological behaviour of the suspensions containing CNTs and tensile strengths of their resulting nanocomposites were characterized. CNT/polyester suspensions exhibited a shear thinning behaviour, while polyester resin blends act as a Newtonian fluid. It was also found that nanotubes with amine functional groups have better tensile strength, as compared to those with untreated CNTs. Transmission electron microscopy (TEM) was also employed to reveal the degree of dispersion of CNTs in the matrix. (c) 2006 Elsevier Ltd. All rights reserved. |
Tanoglu, Metin; Ergun, Yelda Porous nanocomposites prepared from layered clay and PMMA [poly(methyl methacrylate)] Journal Article COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING, 38 (2), pp. 318-322, 2007, ISSN: 1359-835X. @article{ISI:000244008900011, title = {Porous nanocomposites prepared from layered clay and PMMA [poly(methyl methacrylate)]}, author = {Metin Tanoglu and Yelda Ergun}, doi = {10.1016/j.compositesa.2006.04.002}, issn = {1359-835X}, year = {2007}, date = {2007-01-01}, journal = {COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING}, volume = {38}, number = {2}, pages = {318-322}, abstract = {The aim of the present work is the preparation of PMMA based porous nanocomposites that contain clay (montmorillonite, MMT) platelets as reinforcements within the cell walls of the porous structure. To render the clay layers organophilic, MMT was surface treated by an ion exchange reaction between interlayer cations of the clay and ammonium ions of a surfactant. Clay/PMMA based porous nanocomposites were prepared by polymerization of water-in-oil emulsions with and without clay addition. The microstructure and compressive mechanical behavior of the nanocomposites were investigated. The results of mechanical tests showed that the porous systems with the addition of 1 wt.% of organoclay (OMNIT) exhibited a 90% and 50% increase of collapse stress and elastic modulus values, respectively, as compared to neat porous PMMA. (c) 2006 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The aim of the present work is the preparation of PMMA based porous nanocomposites that contain clay (montmorillonite, MMT) platelets as reinforcements within the cell walls of the porous structure. To render the clay layers organophilic, MMT was surface treated by an ion exchange reaction between interlayer cations of the clay and ammonium ions of a surfactant. Clay/PMMA based porous nanocomposites were prepared by polymerization of water-in-oil emulsions with and without clay addition. The microstructure and compressive mechanical behavior of the nanocomposites were investigated. The results of mechanical tests showed that the porous systems with the addition of 1 wt.% of organoclay (OMNIT) exhibited a 90% and 50% increase of collapse stress and elastic modulus values, respectively, as compared to neat porous PMMA. (c) 2006 Elsevier Ltd. All rights reserved. |
2006 |
Celik, E; Gokcen, Z; Azem, Ak N F; Tanoglu, M; Emrullahoglu, O F Processing, characterization and photocatalytic properties of Cu doped TiO2 thin films on glass substrate by sol-gel technique Journal Article MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 132 (3), pp. 258-265, 2006, ISSN: 0921-5107. @article{ISI:000240149800005, title = {Processing, characterization and photocatalytic properties of Cu doped TiO2 thin films on glass substrate by sol-gel technique}, author = {E Celik and Z Gokcen and Ak N F Azem and M Tanoglu and O F Emrullahoglu}, doi = {10.1016/j.mseb.2006.03.038}, issn = {0921-5107}, year = {2006}, date = {2006-08-01}, journal = {MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, volume = {132}, number = {3}, pages = {258-265}, abstract = {The present paper describes processing, properties and photocatalytic application of Cu doped TiO2 thin films on glass substrate. Cu doped TiO2 coatings were successfully prepared on glass slide substrates using sol-gel method. The obtained solutions exhibit acidic characteristics. The phase structure, thermal, microstructure and surface properties of the coatings were characterized by using XRD, DTA/TG, SEM and AFM. Their adhesion properties and spectroscopic analysis were investigated by a scratch tester and UV-vis spectroscopy. Four different solutions were prepared by changing Cu/Ti ratios. Glass substrates were coated by solutions of Ti-alkoxide, Cu-chloride, glacial acetic acid and isopropanol. The obtained gel films were dried at 300 degrees C for 10 min and subsequently heat-treated at 500 degrees C for 5 min in air. The oxide thin films were annealed at 600 degrees C for 60min in air. TiO2, CuO, Cu4Ti, Ti3O5 and Cu3TiO4 phases were found in the coating. The organic matters were burned at temperatures between 200 and 350 degrees C and TiO2 crystallization was formed at 450 degrees C. The weight loss of the powder during process up to 600 degrees C is approximately 70%. The microstructural observations demonstrated that CuO content was led an improved surface morphology while thickness of the film and surface defects were increased in accordance with number of dipping. According to AFM results, it was found that as the Cu/Ti content increases the surface roughness of the films increases. In addition structural, thermal and microstructural results, it was found that the films of 0.73 ratio have better adhesion strength to the glass substrate among other coatings. The oxide films were found to be active for photocatalytic decomposition of metylene blue. (c) 2006 Published by Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The present paper describes processing, properties and photocatalytic application of Cu doped TiO2 thin films on glass substrate. Cu doped TiO2 coatings were successfully prepared on glass slide substrates using sol-gel method. The obtained solutions exhibit acidic characteristics. The phase structure, thermal, microstructure and surface properties of the coatings were characterized by using XRD, DTA/TG, SEM and AFM. Their adhesion properties and spectroscopic analysis were investigated by a scratch tester and UV-vis spectroscopy. Four different solutions were prepared by changing Cu/Ti ratios. Glass substrates were coated by solutions of Ti-alkoxide, Cu-chloride, glacial acetic acid and isopropanol. The obtained gel films were dried at 300 degrees C for 10 min and subsequently heat-treated at 500 degrees C for 5 min in air. The oxide thin films were annealed at 600 degrees C for 60min in air. TiO2, CuO, Cu4Ti, Ti3O5 and Cu3TiO4 phases were found in the coating. The organic matters were burned at temperatures between 200 and 350 degrees C and TiO2 crystallization was formed at 450 degrees C. The weight loss of the powder during process up to 600 degrees C is approximately 70%. The microstructural observations demonstrated that CuO content was led an improved surface morphology while thickness of the film and surface defects were increased in accordance with number of dipping. According to AFM results, it was found that as the Cu/Ti content increases the surface roughness of the films increases. In addition structural, thermal and microstructural results, it was found that the films of 0.73 ratio have better adhesion strength to the glass substrate among other coatings. The oxide films were found to be active for photocatalytic decomposition of metylene blue. (c) 2006 Published by Elsevier B.V. |
Celik, E; Yildiz, AY; Azem, NFA; Tanoglu, M; Toparli, M; Emrullahoglu, OF; Ozdemir, I Preparation and characterization of Fe2O3-TiO2 thin films on glass substrate for photocatalytic applications Journal Article MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 129 (1-3), pp. 193-199, 2006, ISSN: 0921-5107. @article{ISI:000236952200035, title = {Preparation and characterization of Fe2O3-TiO2 thin films on glass substrate for photocatalytic applications}, author = {E Celik and AY Yildiz and NFA Azem and M Tanoglu and M Toparli and OF Emrullahoglu and I Ozdemir}, doi = {10.1016/j.mseb.2006.01.013}, issn = {0921-5107}, year = {2006}, date = {2006-04-01}, journal = {MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, volume = {129}, number = {1-3}, pages = {193-199}, abstract = {Fe2O3-TiO2 coatings were successfully prepared on glass slide substrates using sol-gel method for photocatalytic applications. The phase structure, thermal, microstructure and surface properties of the coatings were extensively characterized by using X-ray diffractometry (XRD), differential thermal analysis/thermograviometry (DTA/TG), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Their adhesion and absorbance properties were investigated by a scratch tester and UV-vis spectroscopy. Four different solutions were prepared by changing Fe/Ti molar ratios. Glass substrates were coated by solutions of Ti-alkoxide, Fe-chloride, glaciel acetic acid and isopropanol. The obtained gel films were dried at 300 degrees C for 10 min and subsequently heat-treated at 500 degrees C for 5 min in air. The oxide thin films were annealed at 600 degrees C for 60 min in air. The influence of Fe3+ concentration and number of layers on structure of the films was established. In addition, XRD results revealed that Fe2O3-TiO2 films composed of TiO2, Fe2Ti3O9, Ti3O5 and Fe3O4 phases. According to DTA/TG result, it was determined that endothermic and exothermic reactions were formed at temperatures between 80 and 650 degrees C due to solvent removal, combustion of carbon based materials and oxidation of Fe and Ti. SEM observations exhibited that the coating structure becomes more homogeneous depending on an increase of Fe/Ti molar ratios and thus a regular surface morphology forms with increasing Fe/Ti ratio. It was also seen that as the Fe/Ti ratio increases the surface roughness of the films increases. Critical adhesion force of thin films with Fe/Ti ratio of 0, 0.07, 0.18 and 0.73 were found to be 9, 25, 28 and 21 mN, respectively. The methylene blue solutions photocatalyzed by TiO2 based thin films shows characteristic absorption bands at 420 nm. (c) 2006 Elsevier B.V. All fights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Fe2O3-TiO2 coatings were successfully prepared on glass slide substrates using sol-gel method for photocatalytic applications. The phase structure, thermal, microstructure and surface properties of the coatings were extensively characterized by using X-ray diffractometry (XRD), differential thermal analysis/thermograviometry (DTA/TG), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Their adhesion and absorbance properties were investigated by a scratch tester and UV-vis spectroscopy. Four different solutions were prepared by changing Fe/Ti molar ratios. Glass substrates were coated by solutions of Ti-alkoxide, Fe-chloride, glaciel acetic acid and isopropanol. The obtained gel films were dried at 300 degrees C for 10 min and subsequently heat-treated at 500 degrees C for 5 min in air. The oxide thin films were annealed at 600 degrees C for 60 min in air. The influence of Fe3+ concentration and number of layers on structure of the films was established. In addition, XRD results revealed that Fe2O3-TiO2 films composed of TiO2, Fe2Ti3O9, Ti3O5 and Fe3O4 phases. According to DTA/TG result, it was determined that endothermic and exothermic reactions were formed at temperatures between 80 and 650 degrees C due to solvent removal, combustion of carbon based materials and oxidation of Fe and Ti. SEM observations exhibited that the coating structure becomes more homogeneous depending on an increase of Fe/Ti molar ratios and thus a regular surface morphology forms with increasing Fe/Ti ratio. It was also seen that as the Fe/Ti ratio increases the surface roughness of the films increases. Critical adhesion force of thin films with Fe/Ti ratio of 0, 0.07, 0.18 and 0.73 were found to be 9, 25, 28 and 21 mN, respectively. The methylene blue solutions photocatalyzed by TiO2 based thin films shows characteristic absorption bands at 420 nm. (c) 2006 Elsevier B.V. All fights reserved. |
Akkas, Deniz H; Ovecoglu, Lutfi M; Tanoglu, Metin Silicon oxycarbide-based composites produced from pyrolysis of polysiloxanes with active Ti filler Journal Article JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 26 (15), pp. 3441-3449, 2006, ISSN: 0955-2219. @article{ISI:000241086000049, title = {Silicon oxycarbide-based composites produced from pyrolysis of polysiloxanes with active Ti filler}, author = {Deniz H Akkas and Lutfi M Ovecoglu and Metin Tanoglu}, doi = {10.1016/j.jeurceramsoc.2005.08.017}, issn = {0955-2219}, year = {2006}, date = {2006-01-01}, journal = {JOURNAL OF THE EUROPEAN CERAMIC SOCIETY}, volume = {26}, number = {15}, pages = {3441-3449}, abstract = {Phenyl (PPS) and methyl (PMS) containing polysiloxanes were pyrolyzed at elevated temperatures (900-1500 degrees C) under argon atmosphere to investigate the phase developments within the polymers. It was found that pyrolysis of the polymers under inert atmosphere up to 1300 degrees C leads to amorphous silicon oxycarbide (SiOxCy) ceramics. Conversions at higher temperatures results in the transformations into the crystalline beta-SiC phases. Ceramic matrix composites (CMCs) were developed based on the active filler controlled pyrolysis (AFCOP) of polysiloxanes with active Ti filler additions. CMC monoliths were prepared with 60-80 wt.% of active Ti particulates blended into polymer precursors. Green bodies of the composites were made by warm pressing under 15 MPa pressure and ceramics were obtained by pyrolysis at elevated temperatures between 900 and 1500 degrees C under argon atmosphere. The results showed that due to the incorporation of active Ti fillers, formation of crystalline phases such as TiC, TiSi, and TiO occured within the amorphous matrix due to the reactions between the Ti and the polymer decomposition products. The microstructural and mechanical characterization results of the composites are presented within the paper. (c) 2005 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Phenyl (PPS) and methyl (PMS) containing polysiloxanes were pyrolyzed at elevated temperatures (900-1500 degrees C) under argon atmosphere to investigate the phase developments within the polymers. It was found that pyrolysis of the polymers under inert atmosphere up to 1300 degrees C leads to amorphous silicon oxycarbide (SiOxCy) ceramics. Conversions at higher temperatures results in the transformations into the crystalline beta-SiC phases. Ceramic matrix composites (CMCs) were developed based on the active filler controlled pyrolysis (AFCOP) of polysiloxanes with active Ti filler additions. CMC monoliths were prepared with 60-80 wt.% of active Ti particulates blended into polymer precursors. Green bodies of the composites were made by warm pressing under 15 MPa pressure and ceramics were obtained by pyrolysis at elevated temperatures between 900 and 1500 degrees C under argon atmosphere. The results showed that due to the incorporation of active Ti fillers, formation of crystalline phases such as TiC, TiSi, and TiO occured within the amorphous matrix due to the reactions between the Ti and the polymer decomposition products. The microstructural and mechanical characterization results of the composites are presented within the paper. (c) 2005 Elsevier Ltd. All rights reserved. |
2005 |
Seyhan, AT; Tayfur, G; Karakurt, M; Tanoglu, M Artificial neural network (ANN) prediction of compressive strength of VARTM processed polymer composites Journal Article COMPUTATIONAL MATERIALS SCIENCE, 34 (1), pp. 99-105, 2005, ISSN: 0927-0256. @article{ISI:000228943700009, title = {Artificial neural network (ANN) prediction of compressive strength of VARTM processed polymer composites}, author = {AT Seyhan and G Tayfur and M Karakurt and M Tanoglu}, doi = {10.1016/j.commatsci.2004.11.001}, issn = {0927-0256}, year = {2005}, date = {2005-08-01}, journal = {COMPUTATIONAL MATERIALS SCIENCE}, volume = {34}, number = {1}, pages = {99-105}, abstract = {A three layer feed forward artificial neural network (ANN) model having three input neurons, one output neuron and two hidden neurons was developed to predict the ply-lay up compressive strength of VARTM processed E-glass/ polyester composites. The composites were manufactured using fabric preforms consolidated with 0, 3 and 6 wt.% of thermoplastic binder. The learning of ANN was accomplished by a backpropagation algorithm. A good agreement between the measured and the predicted values was obtained. Testing of the model was done within low average error levels of 3.28%. Furthermore, the predictions of ANN model were compared with those obtained from a multi-linear regression (MLR) model. It was found that ANN model has better predictions than MLR model for the experimental data. Also, the ANN model was subjected to a sensitivity analysis to obtain its response. As a result, the ANN model was found to have an ability to yield a desired level of ply-lay up compressive strength values for the composites processed with the addition of the thermoplastic binder. (c) 2004 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A three layer feed forward artificial neural network (ANN) model having three input neurons, one output neuron and two hidden neurons was developed to predict the ply-lay up compressive strength of VARTM processed E-glass/ polyester composites. The composites were manufactured using fabric preforms consolidated with 0, 3 and 6 wt.% of thermoplastic binder. The learning of ANN was accomplished by a backpropagation algorithm. A good agreement between the measured and the predicted values was obtained. Testing of the model was done within low average error levels of 3.28%. Furthermore, the predictions of ANN model were compared with those obtained from a multi-linear regression (MLR) model. It was found that ANN model has better predictions than MLR model for the experimental data. Also, the ANN model was subjected to a sensitivity analysis to obtain its response. As a result, the ANN model was found to have an ability to yield a desired level of ply-lay up compressive strength values for the composites processed with the addition of the thermoplastic binder. (c) 2004 Elsevier B.V. All rights reserved. |
2004 |
Aliyev, MI; Khalilova, AA; Arasly, DH; Rahimov, RN; Tanoglu, M; Ozyuzer, L Strain gauges of GaSb-FeGa1.3 eutectic composites Journal Article APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 79 (8), pp. 2075-2078, 2004, ISSN: 0947-8396. @article{ISI:000224387200044, title = {Strain gauges of GaSb-FeGa1.3 eutectic composites}, author = {MI Aliyev and AA Khalilova and DH Arasly and RN Rahimov and M Tanoglu and L Ozyuzer}, doi = {10.1007/s00339-004-2870-0}, issn = {0947-8396}, year = {2004}, date = {2004-12-01}, journal = {APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING}, volume = {79}, number = {8}, pages = {2075-2078}, abstract = {A needle-shaped metallic FeGa1.3 phase oriented in a specific direction and uniformly distributed within a GaSb matrix was grown by a vertical Bridgman method. Strain-gauge characteristics, such as strain-sensitivity coefficient (S), temperature coefficient of strain sensitivity (TCS) and temperature coefficient of resistance, of GaSb and GaSb-FeGa1.3 eutectic alloy have been investigated in the range of 200 to 400 K under deformation up to strains of 1.3x10(-3). The value of S of the GaSb-FeGa1.3 composition is measured to be 40+/-5 and its TCS is about 0.2% deg(-1) when the current is perpendicular to the needles and the needles are parallel to the plane of the gauge substrate. The strain-sensitivity characteristics are linear and hysteresis free in the investigated temperature range in the aforementioned direction. It was found that GaSb-FeGa1.3-based strain gauges possess better deformation characteristics than GaSb-based gauges.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A needle-shaped metallic FeGa1.3 phase oriented in a specific direction and uniformly distributed within a GaSb matrix was grown by a vertical Bridgman method. Strain-gauge characteristics, such as strain-sensitivity coefficient (S), temperature coefficient of strain sensitivity (TCS) and temperature coefficient of resistance, of GaSb and GaSb-FeGa1.3 eutectic alloy have been investigated in the range of 200 to 400 K under deformation up to strains of 1.3x10(-3). The value of S of the GaSb-FeGa1.3 composition is measured to be 40+/-5 and its TCS is about 0.2% deg(-1) when the current is perpendicular to the needles and the needles are parallel to the plane of the gauge substrate. The strain-sensitivity characteristics are linear and hysteresis free in the investigated temperature range in the aforementioned direction. It was found that GaSb-FeGa1.3-based strain gauges possess better deformation characteristics than GaSb-based gauges. |
Ergun, Y; Dirier, C; Tanoglu, M Polymethyl methacrylate based open-cell porous plastics for high-pressure ceramic casting Journal Article MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 385 (1-2), pp. 279-285, 2004, ISSN: 0921-5093. @article{ISI:000224822000035, title = {Polymethyl methacrylate based open-cell porous plastics for high-pressure ceramic casting}, author = {Y Ergun and C Dirier and M Tanoglu}, doi = {10.1016/j.msea.2004.07.014}, issn = {0921-5093}, year = {2004}, date = {2004-11-01}, journal = {MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, volume = {385}, number = {1-2}, pages = {279-285}, abstract = {The aim of the present study is to investigate the microstructure-property relation in polymethyl methacrylate (PMMA)-based porous mould materials used for high-pressure casting of ceramic articles. For this purpose, porous plastic materials were produced by the polymerization of water-in-oil emulsions with various compositions of emulsion constituents and particle sizes of the filler PMMA beads. Pore morphology, porosity and water permeability of the materials were measured. The compressive stress-strain behavior, collapse stress and elastic modulus values of the macroporous materials were determined by performing compressive mechanical testing. Fracture toughness values of the materials were also measured using the single-edge notched bending method. The results showed that the concentration of emulsion constituents and PMMA bead sizes has significant effects on the pore morphology, porosity, water permeability and mechanical properties of the porous plastics. (C) 2004 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The aim of the present study is to investigate the microstructure-property relation in polymethyl methacrylate (PMMA)-based porous mould materials used for high-pressure casting of ceramic articles. For this purpose, porous plastic materials were produced by the polymerization of water-in-oil emulsions with various compositions of emulsion constituents and particle sizes of the filler PMMA beads. Pore morphology, porosity and water permeability of the materials were measured. The compressive stress-strain behavior, collapse stress and elastic modulus values of the macroporous materials were determined by performing compressive mechanical testing. Fracture toughness values of the materials were also measured using the single-edge notched bending method. The results showed that the concentration of emulsion constituents and PMMA bead sizes has significant effects on the pore morphology, porosity, water permeability and mechanical properties of the porous plastics. (C) 2004 Elsevier B.V. All rights reserved. |
2003 |
Tanoglu, M; Seyhan, AT Compressive mechanical behaviour of E-glass/polyester composite laminates tailored with a thermoplastic preforming binder Journal Article MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 363 (1-2), pp. 335-344, 2003, ISSN: 0921-5093. @article{ISI:000186851000042, title = {Compressive mechanical behaviour of E-glass/polyester composite laminates tailored with a thermoplastic preforming binder}, author = {M Tanoglu and AT Seyhan}, doi = {10.1016/j.msea.2003.08.005}, issn = {0921-5093}, year = {2003}, date = {2003-12-01}, journal = {MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, volume = {363}, number = {1-2}, pages = {335-344}, abstract = {Compressive mechanical behaviour and failure modes of E (electrical)-glass/polyester composite laminates tailored with a thermoplastic preforming polyester binder were investigated under ply-lay up and in-plane loading directions. Fiber preforms with various amount of the binder were consolidated under heat and pressure. The preform compaction experiments were performed by applying compressive pressure to the preforms, and the average thickness as a function of pressure was measured. It was found that the highest compaction of the preforms and therefore the highest fiber volume fraction can be obtained with 3 wt.% of the binder. Further increase of the amount of binder decreases the degree of compaction. Composite panels were fabricated by vacuum-assisted resin transfer molding using fabric preforms with various binder concentrations. The present investigation reveals that there are considerable effects of the binder on the compressive mechanical behaviour of the composites. Compression testing of the composites showed that the average strength values are in the range of 400-600 and 150-300 MPa for ply-lay up and in-plane directions, respectively. Also, both the strength and modulus values increase up to 3 wt.% of the binder, and these values decrease with further addition of the binder. Scanning electron microscopy showed that failure modes of the composites are altered significantly by the presence of the binder. Furthermore, the interaction between the binder and the reacting resin was followed to determine the extent of the binder dissolution and its effects on the viscosity of the resin and the mechanical behaviour of the matrix polymer. The results indicate that there is a partial dissolution of the binder within the matrix resin. (C) 2003 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Compressive mechanical behaviour and failure modes of E (electrical)-glass/polyester composite laminates tailored with a thermoplastic preforming polyester binder were investigated under ply-lay up and in-plane loading directions. Fiber preforms with various amount of the binder were consolidated under heat and pressure. The preform compaction experiments were performed by applying compressive pressure to the preforms, and the average thickness as a function of pressure was measured. It was found that the highest compaction of the preforms and therefore the highest fiber volume fraction can be obtained with 3 wt.% of the binder. Further increase of the amount of binder decreases the degree of compaction. Composite panels were fabricated by vacuum-assisted resin transfer molding using fabric preforms with various binder concentrations. The present investigation reveals that there are considerable effects of the binder on the compressive mechanical behaviour of the composites. Compression testing of the composites showed that the average strength values are in the range of 400-600 and 150-300 MPa for ply-lay up and in-plane directions, respectively. Also, both the strength and modulus values increase up to 3 wt.% of the binder, and these values decrease with further addition of the binder. Scanning electron microscopy showed that failure modes of the composites are altered significantly by the presence of the binder. Furthermore, the interaction between the binder and the reacting resin was followed to determine the extent of the binder dissolution and its effects on the viscosity of the resin and the mechanical behaviour of the matrix polymer. The results indicate that there is a partial dissolution of the binder within the matrix resin. (C) 2003 Elsevier B.V. All rights reserved. |
Prof. Dr. Alper Taşdemirci
Educational Background
B.Sc. Erciyes University, Turkey, Mechanical Engineering, 1998
M.Sc. Erciyes University, Turkey, Mechanical Engineering, 2000
Ph.D. University of Delaware, USA, Mechanical Engineering, 2005
Research Interests
- Static and Dynamic Mechanical Behaviors of materials
- High Strain Rate Testing Methods: Split Hopkinson Pressure Bar
- Drop Weight Test, Dynamic Response and Constitutive Modelling of Materials
- Experimental and Computational Mechanics, Composite Armor Mechanics
- +90 232 750 6780
- +90 232 750 6701
- Mechanical Engineering Building (Z11)
Publications
2023 |
Enser, Samed; Guden, Mustafa; Tasdemirci, Alper; Davut, Kemal The strain rate history effect in a selective-laser-melt 316L stainless steel Journal Article MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 862 , 2023. @article{WOS:000905147200003, title = {The strain rate history effect in a selective-laser-melt 316L stainless steel}, author = {Samed Enser and Mustafa Guden and Alper Tasdemirci and Kemal Davut}, doi = {10.1016/j.msea.2022.144439}, year = {2023}, date = {2023-01-01}, journal = {MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, volume = {862}, abstract = {The strain rate history effect in a selective laser melt 316L (SLM-316L) alloy was investigated through quasi -static (10-3 s- 1) and high strain rate (1600-3200 s-1) interrupted and reloading compression tests. The speci-mens pre-tested until about prescribed strains at quasi-static and high strain rates were reloaded dynamically and quasi-statically, respectively. The results revealed that the flow stress depended on strain and strain rate as well as strain-rate history. Quasi-static reloading the dynamically pre-tested specimens until about prescribed strains induced a higher flow stress than the specimens tested quasi-statically. The strengthening was-70 MPa at 0.11 pre-strain and decreased as the dynamic test pre-strain was increased due to adiabatic heating. On the other side, reloading the quasi-statically pre-tested specimens dynamically at 0.11 pre-strain resulted in-60 MPa lower flow stress than the specimens tested dynamically. The grains of the quasi-statically tested specimens until 0.11 strain were shown to have a lower Taylor factor for twinning and geometrically necessary dislocation density, indicating more potential for twinning than dynamically tested specimen. Although, quasi-statically and dynamically tested specimens were deformed predominantly by the twinning induced plasticity, a higher frac-tion of twin boundaries was shown microscopically in the dynamically pre-tested specimens until 0.11 pre-strain. This phenomenon of boundary strengthening could be used as a tool of strengthening of SLM-316L alloy at low strains.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The strain rate history effect in a selective laser melt 316L (SLM-316L) alloy was investigated through quasi -static (10-3 s- 1) and high strain rate (1600-3200 s-1) interrupted and reloading compression tests. The speci-mens pre-tested until about prescribed strains at quasi-static and high strain rates were reloaded dynamically and quasi-statically, respectively. The results revealed that the flow stress depended on strain and strain rate as well as strain-rate history. Quasi-static reloading the dynamically pre-tested specimens until about prescribed strains induced a higher flow stress than the specimens tested quasi-statically. The strengthening was-70 MPa at 0.11 pre-strain and decreased as the dynamic test pre-strain was increased due to adiabatic heating. On the other side, reloading the quasi-statically pre-tested specimens dynamically at 0.11 pre-strain resulted in-60 MPa lower flow stress than the specimens tested dynamically. The grains of the quasi-statically tested specimens until 0.11 strain were shown to have a lower Taylor factor for twinning and geometrically necessary dislocation density, indicating more potential for twinning than dynamically tested specimen. Although, quasi-statically and dynamically tested specimens were deformed predominantly by the twinning induced plasticity, a higher frac-tion of twin boundaries was shown microscopically in the dynamically pre-tested specimens until 0.11 pre-strain. This phenomenon of boundary strengthening could be used as a tool of strengthening of SLM-316L alloy at low strains. |
Tuncer, C; Güden, M; Orhan, M; Sarıkaya, M K; Taşdemirci, A Quasi-static and dynamic Brazilian testing and failure analysis of a deer antler in the transverse to the osteon growth direction Journal Article Journal of the Mechanical Behavior of Biomedical Materials, 138 , 2023. @article{Tuncer2023, title = {Quasi-static and dynamic Brazilian testing and failure analysis of a deer antler in the transverse to the osteon growth direction}, author = {C Tuncer and M Güden and M Orhan and M K Sarıkaya and A Taşdemirci}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85145658319&doi=10.1016%2fj.jmbbm.2023.105648&partnerID=40&md5=f2b3c0121aa41d2857249a24554f05da}, doi = {10.1016/j.jmbbm.2023.105648}, year = {2023}, date = {2023-01-01}, journal = {Journal of the Mechanical Behavior of Biomedical Materials}, volume = {138}, abstract = {The transverse tensile strength of a naturally fallen red deer antler (Cervus Elaphus) was determined through indirect Brazilian tests using dry disc-shape specimens at quasi-static and high strain rates. Dynamic Brazilian tests were performed in a compression Split-Hopkinson Pressure Bar. Quasi-static tensile and indirect Brazilian tests were also performed along the osteon growth direction for comparison. The quasi-static transverse tensile strength ranged 31.5–44.5 MPa. The strength increased to 83 MPa on the average in the dynamic Brazilian tests, proving a rate sensitive transverse strength. The quasi-static tensile strength in the osteon growth direction was however found comparably higher, 192 MPa. A Weibull analysis indicated a higher tensile ductility in the osteon growth direction than in the transverse to the osteon growth direction. The microscopic analysis of the quasi-static Brazilian test specimens (tensile strain along the osteon growth direction) revealed a micro-cracking mechanism operating by the crack deflection/twisting at the lacunae in the concentric lamellae region and at the interface between concentric lamellae and interstitial lamellae. On the other side, the specimens in the transverse direction fractured in a more brittle manner by the separation/delamination of the concentric lamellae and pulling of the interstitial lamellae. The detected increase in the transverse strength in the high strain rate tests was further ascribed to the pull and fracture of the visco-plastic collagen fibers in the interstitial lamellae. This was also confirmed microscopically; the dynamically tested specimens exhibited flatter fracture surfaces. © 2023 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The transverse tensile strength of a naturally fallen red deer antler (Cervus Elaphus) was determined through indirect Brazilian tests using dry disc-shape specimens at quasi-static and high strain rates. Dynamic Brazilian tests were performed in a compression Split-Hopkinson Pressure Bar. Quasi-static tensile and indirect Brazilian tests were also performed along the osteon growth direction for comparison. The quasi-static transverse tensile strength ranged 31.5–44.5 MPa. The strength increased to 83 MPa on the average in the dynamic Brazilian tests, proving a rate sensitive transverse strength. The quasi-static tensile strength in the osteon growth direction was however found comparably higher, 192 MPa. A Weibull analysis indicated a higher tensile ductility in the osteon growth direction than in the transverse to the osteon growth direction. The microscopic analysis of the quasi-static Brazilian test specimens (tensile strain along the osteon growth direction) revealed a micro-cracking mechanism operating by the crack deflection/twisting at the lacunae in the concentric lamellae region and at the interface between concentric lamellae and interstitial lamellae. On the other side, the specimens in the transverse direction fractured in a more brittle manner by the separation/delamination of the concentric lamellae and pulling of the interstitial lamellae. The detected increase in the transverse strength in the high strain rate tests was further ascribed to the pull and fracture of the visco-plastic collagen fibers in the interstitial lamellae. This was also confirmed microscopically; the dynamically tested specimens exhibited flatter fracture surfaces. © 2023 Elsevier Ltd |
Enser, S; Güden, M; Taşdemirci, A; Davut, K The strain rate history effect in a selective-laser-melt 316L stainless steel Journal Article Materials Science and Engineering A, 862 , 2023. @article{Enser2023, title = {The strain rate history effect in a selective-laser-melt 316L stainless steel}, author = {S Enser and M Güden and A Taşdemirci and K Davut}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85143677799&doi=10.1016%2fj.msea.2022.144439&partnerID=40&md5=d3e4693f86b0e95c1ee6eb89a46551aa}, doi = {10.1016/j.msea.2022.144439}, year = {2023}, date = {2023-01-01}, journal = {Materials Science and Engineering A}, volume = {862}, abstract = {The strain rate history effect in a selective laser melt 316L (SLM-316L) alloy was investigated through quasi-static (10−3 s−1) and high strain rate (1600-3200 s−1) interrupted and reloading compression tests. The specimens pre-tested until about prescribed strains at quasi-static and high strain rates were reloaded dynamically and quasi-statically, respectively. The results revealed that the flow stress depended on strain and strain rate as well as strain-rate history. Quasi-static reloading the dynamically pre-tested specimens until about prescribed strains induced a higher flow stress than the specimens tested quasi-statically. The strengthening was ∼70 MPa at 0.11 pre-strain and decreased as the dynamic test pre-strain was increased due to adiabatic heating. On the other side, reloading the quasi-statically pre-tested specimens dynamically at 0.11 pre-strain resulted in ∼60 MPa lower flow stress than the specimens tested dynamically. The grains of the quasi-statically tested specimens until 0.11 strain were shown to have a lower Taylor factor for twinning and geometrically necessary dislocation density, indicating more potential for twinning than dynamically tested specimen. Although, quasi-statically and dynamically tested specimens were deformed predominantly by the twinning induced plasticity, a higher fraction of twin boundaries was shown microscopically in the dynamically pre-tested specimens until 0.11 pre-strain. This phenomenon of boundary strengthening could be used as a tool of strengthening of SLM-316L alloy at low strains. © 2022 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The strain rate history effect in a selective laser melt 316L (SLM-316L) alloy was investigated through quasi-static (10−3 s−1) and high strain rate (1600-3200 s−1) interrupted and reloading compression tests. The specimens pre-tested until about prescribed strains at quasi-static and high strain rates were reloaded dynamically and quasi-statically, respectively. The results revealed that the flow stress depended on strain and strain rate as well as strain-rate history. Quasi-static reloading the dynamically pre-tested specimens until about prescribed strains induced a higher flow stress than the specimens tested quasi-statically. The strengthening was ∼70 MPa at 0.11 pre-strain and decreased as the dynamic test pre-strain was increased due to adiabatic heating. On the other side, reloading the quasi-statically pre-tested specimens dynamically at 0.11 pre-strain resulted in ∼60 MPa lower flow stress than the specimens tested dynamically. The grains of the quasi-statically tested specimens until 0.11 strain were shown to have a lower Taylor factor for twinning and geometrically necessary dislocation density, indicating more potential for twinning than dynamically tested specimen. Although, quasi-statically and dynamically tested specimens were deformed predominantly by the twinning induced plasticity, a higher fraction of twin boundaries was shown microscopically in the dynamically pre-tested specimens until 0.11 pre-strain. This phenomenon of boundary strengthening could be used as a tool of strengthening of SLM-316L alloy at low strains. © 2022 Elsevier B.V. |
Zeybek, M K; Güden, M; Taşdemirci, A Journal of Materials Engineering and Performance, 2023. @article{Zeybek2023, title = {The Effect of Strain Rate on the Compression Behavior of Additively Manufactured Short Carbon Fiber-Reinforced Polyamide Composites with Different Layer Heights, Infill Patterns, and Built Angles}, author = {M K Zeybek and M Güden and A Taşdemirci}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85147762551&doi=10.1007%2fs11665-023-07918-1&partnerID=40&md5=e7bbc8949f442fcf22b8812d43a6fa1e}, doi = {10.1007/s11665-023-07918-1}, year = {2023}, date = {2023-01-01}, journal = {Journal of Materials Engineering and Performance}, abstract = {Previous studies on the fused deposition modelling (FDM) processed short carbon fiber/Polyamide 6 (PA6) matrix composites and neat PA6 have mostly concentrated on the quasi-static mechanical properties. Present study focused on the strain rate-dependent deformation behavior of a short carbon fiber-reinforced PA6 (Onyx) and neat PA6, produced in different layer heights, infill patterns and built angles. As compared with PA6, Onyx showed a higher compression stress at all strain rates investigated. A layer height of 0.2 mm in PA6 specimens promoted a better bonding between [0/90°] infill layers; hence, a higher flow stress than 0.2 mm layer height specimens, while 0.2 mm layer height induced a higher porosity in Onyx specimens, leading to a lower flow stress. The porosities in Onyx [0/90°] infill specimens were due to the constraining effect of 0/90° fiber layers. Changing infill pattern from a [0/90°] to a concentric one decreased porosity at the same layer height and hence increased the compressive flow stress. The highest compressive strength was found in the specimens with the loading axis 90 and 0° to [0/90°] infill plane. The lowest strength was, however, determined in the specimens with the loading axis 30 and 60o to [0/90°] infill plane in quasi-static loading. However, the specimens with the loading axis of 60, 45, 30 and 0° exhibited a brittle behavior in high strain rate loading (1500 s−1). The specimens with the loading axis of 45° had the lowest fracture stress and strain in the high strain rate loading. This signified the importance of loading angle at high strain rates. Finally, the rate sensitivities of PA6 and Onyx specimens were shown to be similar, showing a matrix dominated deformation. However, the strain rate jump tests indicated a slightly higher rate sensitivity of Onyx specimens at quasi-static strain rates (10−3-10−1 s−1). © 2023, ASM International.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Previous studies on the fused deposition modelling (FDM) processed short carbon fiber/Polyamide 6 (PA6) matrix composites and neat PA6 have mostly concentrated on the quasi-static mechanical properties. Present study focused on the strain rate-dependent deformation behavior of a short carbon fiber-reinforced PA6 (Onyx) and neat PA6, produced in different layer heights, infill patterns and built angles. As compared with PA6, Onyx showed a higher compression stress at all strain rates investigated. A layer height of 0.2 mm in PA6 specimens promoted a better bonding between [0/90°] infill layers; hence, a higher flow stress than 0.2 mm layer height specimens, while 0.2 mm layer height induced a higher porosity in Onyx specimens, leading to a lower flow stress. The porosities in Onyx [0/90°] infill specimens were due to the constraining effect of 0/90° fiber layers. Changing infill pattern from a [0/90°] to a concentric one decreased porosity at the same layer height and hence increased the compressive flow stress. The highest compressive strength was found in the specimens with the loading axis 90 and 0° to [0/90°] infill plane. The lowest strength was, however, determined in the specimens with the loading axis 30 and 60o to [0/90°] infill plane in quasi-static loading. However, the specimens with the loading axis of 60, 45, 30 and 0° exhibited a brittle behavior in high strain rate loading (1500 s−1). The specimens with the loading axis of 45° had the lowest fracture stress and strain in the high strain rate loading. This signified the importance of loading angle at high strain rates. Finally, the rate sensitivities of PA6 and Onyx specimens were shown to be similar, showing a matrix dominated deformation. However, the strain rate jump tests indicated a slightly higher rate sensitivity of Onyx specimens at quasi-static strain rates (10−3-10−1 s−1). © 2023, ASM International. |
Turan, A K; Tasdemirci, A; Kara, A; Sahin, S; Guden, M Thin-Walled Structures, 182 , 2023. @article{Turan2023, title = {Investigation of penetration behavior of combined geometry shells at quasi-static and intermediate strain rates: An experimental and numerical study}, author = {A K Turan and A Tasdemirci and A Kara and S Sahin and M Guden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85140804922&doi=10.1016%2fj.tws.2022.110261&partnerID=40&md5=a68187ac67baf30b83898f98789e157e}, doi = {10.1016/j.tws.2022.110261}, year = {2023}, date = {2023-01-01}, journal = {Thin-Walled Structures}, volume = {182}, abstract = {In this study, the penetration/perforation behavior of a core material with previously determined static and dynamic crushing characteristics was investigated both experimentally and numerically. Penetration/perforation problems occur due to shrapnel effect when sandwich structures containing energy-absorbing core materials by crushing are exposed to blast loads. The penetration behavior of combined geometry shells consisting of a hemispherical cap and a cylindrical segment was investigated experimentally using blunt, conical and hemispherical penetrator tips. The quasi-static penetration tests were performed in a universal test machine, and the intermediate strain rate penetration tests were performed in a drop weight test device. The numerical models of penetration tests were implemented in LS-DYNA at the test strain rates as well as at the higher strain rates. Results showed that different penetrator geometries induced damage forms of symmetrical tearing, petaling, plugging and inversely formed hemispherical domed cone. The increase in the thickness of core geometry resulted in a decent increase in force–displacement curves, as average of force levels increased around 140%, 200% and 220% for blunt, conical and hemispherical tip penetrators, respectively. Numerical results indicated very good correlation with experimental work and enabled to investigate effect of strain rate and micro-inertia over numerical models at elevated penetrator velocities. Penetration behavior was found to be affected from micro-inertia effects up to a threshold displacement of 4 mm for thicker and 5 mm for thinner core units and strain rate effects were found to be dominant beyond that point. © 2022 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, the penetration/perforation behavior of a core material with previously determined static and dynamic crushing characteristics was investigated both experimentally and numerically. Penetration/perforation problems occur due to shrapnel effect when sandwich structures containing energy-absorbing core materials by crushing are exposed to blast loads. The penetration behavior of combined geometry shells consisting of a hemispherical cap and a cylindrical segment was investigated experimentally using blunt, conical and hemispherical penetrator tips. The quasi-static penetration tests were performed in a universal test machine, and the intermediate strain rate penetration tests were performed in a drop weight test device. The numerical models of penetration tests were implemented in LS-DYNA at the test strain rates as well as at the higher strain rates. Results showed that different penetrator geometries induced damage forms of symmetrical tearing, petaling, plugging and inversely formed hemispherical domed cone. The increase in the thickness of core geometry resulted in a decent increase in force–displacement curves, as average of force levels increased around 140%, 200% and 220% for blunt, conical and hemispherical tip penetrators, respectively. Numerical results indicated very good correlation with experimental work and enabled to investigate effect of strain rate and micro-inertia over numerical models at elevated penetrator velocities. Penetration behavior was found to be affected from micro-inertia effects up to a threshold displacement of 4 mm for thicker and 5 mm for thinner core units and strain rate effects were found to be dominant beyond that point. © 2022 Elsevier Ltd |
Güden, Mustafa; Riaz, Arslan Bin; Toksoy, Ahmet Kaan; Yıldıztekin, Murat; Erten, Hacer İrem; Çimen, Gülden; Hızlı, Burak; Çellek, Burçin Seven; Güleç, Efe; Taşdemirci, Alper; Yavaş, Hakan; Altınok, Sertaç Materials Science and Engineering: A, 885 , 2023. @article{Güden2023b, title = {Investigation and validation of the flow stress equation and damage model parameters of an electron beam melted Ti6Al4V alloy with a martensitic phase}, author = {Mustafa Güden and Arslan Bin Riaz and Ahmet Kaan Toksoy and Murat Yıldıztekin and Hacer İrem Erten and Gülden Çimen and Burak Hızlı and Burçin Seven Çellek and Efe Güleç and Alper Taşdemirci and Hakan Yavaş and Sertaç Altınok}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85171624739&doi=10.1016%2fj.msea.2023.145590&partnerID=40&md5=206e908384653029d335d5611a983306}, doi = {10.1016/j.msea.2023.145590}, year = {2023}, date = {2023-01-01}, journal = {Materials Science and Engineering: A}, volume = {885}, abstract = {The Johnson and Cook flow stress and damage model parameters of an electron beam melt (EBM)-Ti64 alloy composed of α' (martensite) and α+β and an extruded-annealed conventional Ti64 alloy were determined experimentally. The validities of the determined flow stress equations and damage model parameters were then verified by the numerical simulations of the compression tests on the Body Centered Cubic lattices produced using the same EBM parameters with the solid EBM samples. In addition, a compression flow stress equation was extracted from the small-size test specimens (1 and 2 mm diameter) taken directly from the struts of the as-built lattices. The microscopic observations, XRD analyses and hardness tests confirmed the presence of α′ phase in the EBM solid samples and in the struts of the BCC lattices, which reduced the ductility of the EBM solid specimens and struts compared to the conventional Ti64. Furthermore, the partially melt particles on the surfaces of the struts acted as the stress concentration sides for micro-cracking; hence, the compression flow stresses of the struts were found to be significantly lower than those of the as-built EBM solid specimens. The flow stress equation derived from the struts predicted more accurately the compression behavior of the lattices. The compression tests and models showed that early damage formation in the lattices was noted to decrease the initial peak and post-peak stresses. As with the experiments, the initial damage occurred in the models with the separation of the nodes at the lattice cell surface edges. This resulted in an abrupt reduction in the stresses after the peak stress. The numerical lattices without damage showed a localized lattice deformation at the mid-sections and the stress increased continuously as a function of normal strain. © 2023 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The Johnson and Cook flow stress and damage model parameters of an electron beam melt (EBM)-Ti64 alloy composed of α' (martensite) and α+β and an extruded-annealed conventional Ti64 alloy were determined experimentally. The validities of the determined flow stress equations and damage model parameters were then verified by the numerical simulations of the compression tests on the Body Centered Cubic lattices produced using the same EBM parameters with the solid EBM samples. In addition, a compression flow stress equation was extracted from the small-size test specimens (1 and 2 mm diameter) taken directly from the struts of the as-built lattices. The microscopic observations, XRD analyses and hardness tests confirmed the presence of α′ phase in the EBM solid samples and in the struts of the BCC lattices, which reduced the ductility of the EBM solid specimens and struts compared to the conventional Ti64. Furthermore, the partially melt particles on the surfaces of the struts acted as the stress concentration sides for micro-cracking; hence, the compression flow stresses of the struts were found to be significantly lower than those of the as-built EBM solid specimens. The flow stress equation derived from the struts predicted more accurately the compression behavior of the lattices. The compression tests and models showed that early damage formation in the lattices was noted to decrease the initial peak and post-peak stresses. As with the experiments, the initial damage occurred in the models with the separation of the nodes at the lattice cell surface edges. This resulted in an abrupt reduction in the stresses after the peak stress. The numerical lattices without damage showed a localized lattice deformation at the mid-sections and the stress increased continuously as a function of normal strain. © 2023 Elsevier B.V. |
Çelik, Muhammet; Güden, Mustafa; Sarıkaya, Mustafa; Taşdemirci, Alper; Genç, Cem; Ersoy, Kurtuluş; Serin, Özgür Composite Structures, 320 , 2023. @article{Çelik2023, title = {The impact response of a Nomex® honeycomb core/E-glass/epoxy composite sandwich structure to increasing velocities: Experimental and numerical analysis}, author = {Muhammet Çelik and Mustafa Güden and Mustafa Sarıkaya and Alper Taşdemirci and Cem Genç and Kurtuluş Ersoy and Özgür Serin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85162005169&doi=10.1016%2fj.compstruct.2023.117205&partnerID=40&md5=fb47471b22e7653bc2d670c7a45b347b}, doi = {10.1016/j.compstruct.2023.117205}, year = {2023}, date = {2023-01-01}, journal = {Composite Structures}, volume = {320}, abstract = {The impact response of an E-glass fiber reinforced epoxy/Nomex® honeycomb core sandwich was investigated both experimentally and numerically at increasing velocities through concentrated quasi-static indentation force (CQIF), low velocity impact (LVI) and high velocity impact (HVI) tests. The composite face sheets and core were modelled using MAT_162 and MAT_026 homogenized material model in LS-DYNA, respectively. The experimental and numerical LVI test forces corresponding to core crushing and face sheet penetration were shown to be higher than those of the CQIF tests and increased as the impactor velocity increased. The increase of the impact forces at increasing velocities was largely ascribed to the inertia and the strain rate sensitive fracture strength of the composite sheets. The core shearing was detected in the CQIF and LVI tests both experimentally and numerically. It was also detected in the HVI tests at the velocities less than 20 m s−1. The deformation in the HVI tests at and above ∼ 29.4 m s−1 was highly localized in the impact area with no core shearing and a large delamination damage area at the front face sheet. The force enhancement due to the micro-inertia of the core deformation was shown to be not significant at the studied velocities. © 2023 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The impact response of an E-glass fiber reinforced epoxy/Nomex® honeycomb core sandwich was investigated both experimentally and numerically at increasing velocities through concentrated quasi-static indentation force (CQIF), low velocity impact (LVI) and high velocity impact (HVI) tests. The composite face sheets and core were modelled using MAT_162 and MAT_026 homogenized material model in LS-DYNA, respectively. The experimental and numerical LVI test forces corresponding to core crushing and face sheet penetration were shown to be higher than those of the CQIF tests and increased as the impactor velocity increased. The increase of the impact forces at increasing velocities was largely ascribed to the inertia and the strain rate sensitive fracture strength of the composite sheets. The core shearing was detected in the CQIF and LVI tests both experimentally and numerically. It was also detected in the HVI tests at the velocities less than 20 m s−1. The deformation in the HVI tests at and above ∼ 29.4 m s−1 was highly localized in the impact area with no core shearing and a large delamination damage area at the front face sheet. The force enhancement due to the micro-inertia of the core deformation was shown to be not significant at the studied velocities. © 2023 Elsevier Ltd |
Sarıkaya, Mustafa; Güden, Mustafa; Kambur, Çağdaş; Özbek, Sevim Çankaya; Taşdemirci, Alper Development of the Johnson-Cook flow stress and damage parameters for the impact response of polycarbonate: Experimental and numerical approach Journal Article International Journal of Impact Engineering, 179 , 2023. @article{Sarıkaya2023, title = {Development of the Johnson-Cook flow stress and damage parameters for the impact response of polycarbonate: Experimental and numerical approach}, author = {Mustafa Sarıkaya and Mustafa Güden and Çağdaş Kambur and Sevim Çankaya Özbek and Alper Taşdemirci}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85160689008&doi=10.1016%2fj.ijimpeng.2023.104674&partnerID=40&md5=26109d206458c5db0dfc878ae314e9b4}, doi = {10.1016/j.ijimpeng.2023.104674}, year = {2023}, date = {2023-01-01}, journal = {International Journal of Impact Engineering}, volume = {179}, abstract = {The Johnson and Cook (JC) flow stress and damage model parameters of a polycarbonate (PC) plate were determined by the mechanical tests and numerical simulations of the tests. The experimental tests included quasi-static and high strain rate tension and compression, quasi-static notched-specimen tension, quasi-static indentation (QSI), low velocity impact (LVI) and projectile impact (PI). Initially, five different quasi-static flow stress-strain equations were extracted from the experimental and numerical tests. The flow stress equation determined from the experimental average true stress-true strain curve well agreed with the effective stress-strain obtained from the quasi-static numerical tension test. The numerical QSI force-displacement curve based on the experimental average true stress-true strain equation was further shown to be very similar to that of the experiment. The LVI and PI test simulations were then continued with the experimental average true stress-true strain equation using five different flow stress-strain rate relations: JC, Huh and Kang (HK), Allen-Rule and Jones (ARJ), Cowper-Symonds (CS) and the nonlinear rate approach (NLA). The rate sensitivity parameters of these relations were extracted from the quasi-static and high strain rate tests. The LVI test simulations using the stress-strain rate relations exhibited force-displacement curves higher than those of the experiments. The detected almost no strain rate sensitivity in the LVI tests was ascribed to low strain rate dependency of the flow stress at these intermediate strain rates and large strains involved. On the other side, all the stress-strain rate relations investigated nearly predicted the experimental damage types: dishing at 100 and 140 m s−1 and petalling at 160 m s−1, except the CS relation which predicted the fracture of the plate at 140 m s−1. The experimental average projectile exit velocity at 160 m s−1 was further well predicted by the used stress-strain rate relations while the experimental average petal thicknesses were under estimated by the models. The absorbed energy at 160 m s−1 PI test was determined 1.6 times that of the QSI test, which proved an increased energy absorption capability of the tested PC at the investigated impact velocities. © 2023 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The Johnson and Cook (JC) flow stress and damage model parameters of a polycarbonate (PC) plate were determined by the mechanical tests and numerical simulations of the tests. The experimental tests included quasi-static and high strain rate tension and compression, quasi-static notched-specimen tension, quasi-static indentation (QSI), low velocity impact (LVI) and projectile impact (PI). Initially, five different quasi-static flow stress-strain equations were extracted from the experimental and numerical tests. The flow stress equation determined from the experimental average true stress-true strain curve well agreed with the effective stress-strain obtained from the quasi-static numerical tension test. The numerical QSI force-displacement curve based on the experimental average true stress-true strain equation was further shown to be very similar to that of the experiment. The LVI and PI test simulations were then continued with the experimental average true stress-true strain equation using five different flow stress-strain rate relations: JC, Huh and Kang (HK), Allen-Rule and Jones (ARJ), Cowper-Symonds (CS) and the nonlinear rate approach (NLA). The rate sensitivity parameters of these relations were extracted from the quasi-static and high strain rate tests. The LVI test simulations using the stress-strain rate relations exhibited force-displacement curves higher than those of the experiments. The detected almost no strain rate sensitivity in the LVI tests was ascribed to low strain rate dependency of the flow stress at these intermediate strain rates and large strains involved. On the other side, all the stress-strain rate relations investigated nearly predicted the experimental damage types: dishing at 100 and 140 m s−1 and petalling at 160 m s−1, except the CS relation which predicted the fracture of the plate at 140 m s−1. The experimental average projectile exit velocity at 160 m s−1 was further well predicted by the used stress-strain rate relations while the experimental average petal thicknesses were under estimated by the models. The absorbed energy at 160 m s−1 PI test was determined 1.6 times that of the QSI test, which proved an increased energy absorption capability of the tested PC at the investigated impact velocities. © 2023 Elsevier Ltd |
2022 |
Tuzgel, F; Akbulut, E F; Guzel, E; Yucesoy, A; Sahin, S; Tasdemirci, A; Guden, M Testing and modeling blast loading of a sandwich structure cored with a bio-inspired (balanus) core Journal Article Thin-Walled Structures, 175 , 2022. @article{Tuzgel2022, title = {Testing and modeling blast loading of a sandwich structure cored with a bio-inspired (balanus) core}, author = {F Tuzgel and E F Akbulut and E Guzel and A Yucesoy and S Sahin and A Tasdemirci and M Guden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85127099692&doi=10.1016%2fj.tws.2022.109185&partnerID=40&md5=598aa9ba4baa82852c1ddd0b8676727c}, doi = {10.1016/j.tws.2022.109185}, year = {2022}, date = {2022-01-01}, journal = {Thin-Walled Structures}, volume = {175}, abstract = {The blast loading response of a sandwich structure consisted of bio-inspired (balanus) cores/units was investigated experimentally and numerically. A Direct Pressure Pulse (DPP) set-up was used to impose a blast-like loading. The equivalent blast conditions corresponding to the used impact velocities were implemented in the models. A benchmark study was performed by using three different methods namely pure Lagrangian, Arbitrary Lagrangian Eulerian, and hybrid. Dynamic crushing behavior was analyzed and exhibited a higher specific energy absorption capacity than its constituents (core and shell). Among the core configurations, all-front configuration was found the most efficient configuration regarding the specific energy absorption. © 2022 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The blast loading response of a sandwich structure consisted of bio-inspired (balanus) cores/units was investigated experimentally and numerically. A Direct Pressure Pulse (DPP) set-up was used to impose a blast-like loading. The equivalent blast conditions corresponding to the used impact velocities were implemented in the models. A benchmark study was performed by using three different methods namely pure Lagrangian, Arbitrary Lagrangian Eulerian, and hybrid. Dynamic crushing behavior was analyzed and exhibited a higher specific energy absorption capacity than its constituents (core and shell). Among the core configurations, all-front configuration was found the most efficient configuration regarding the specific energy absorption. © 2022 Elsevier Ltd |
Güden, M; Alpkaya, A T; Hamat, B A; Hızlı, B; Taşdemirci, A; Tanrıkulu, A A; Yavaş, H Strain, 58 (3), 2022. @article{Güden2022, title = {The quasi-static crush response of electron-beam-melt Ti6Al4V body-centred-cubic lattices: The effect of the number of cells, strut diameter and face sheet}, author = {M Güden and A T Alpkaya and B A Hamat and B Hızlı and A Taşdemirci and A A Tanrıkulu and H Yavaş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85125105289&doi=10.1111%2fstr.12411&partnerID=40&md5=e6515c23c4247096157d4bec2da4a9f3}, doi = {10.1111/str.12411}, year = {2022}, date = {2022-01-01}, journal = {Strain}, volume = {58}, number = {3}, abstract = {The effect of the number of cells, strut diameter and face sheet on the compression of electron-beam-melt (EBM) Ti6Al4V (Ti64) body-centred-cubic (BCC) lattices was investigated experimentally and numerically. The lattices with the same relative density (~0.182) were fabricated with and without 2-mm-thick face sheets in 10 and 5 mm cell size, 8–125 unit cell (two to five cells/edge) and 2 and 1 mm strut diameter. The experimental compression tests were further numerically simulated in the LS-DYNA. Experimentally two bending-dominated crushing modes, namely, lateral and diagonal layer crushing, were determined. The numerical models however exhibited merely a bending-dominated lateral layer crushing mode when the erosion strain was 0.4 and without face-sheet models showed a diagonal layer crushing mode when the erosion strain was 0.3. Lower erosion strains promoted a diagonal layer crushing mode by introducing geometrical inhomogeneity to the lattice, leading to strain localisation as similar to the face sheets which introduced extensive strut bending in the layers adjacent to the face sheets. The face-sheet model showed a higher but decreasing collapse strength at an increasing number of cells, just as opposite to the without face-sheet model, and the collapse strength of both models converged when the number of cells was higher than five-cell/edge. The decrease/increase of the collapse strengths of lattices before the critical number of cells was claimed mainly due to the size-imposed lattice boundary condition, rather than the specimen volume. The difference in the experimental collapse strengths between the 5- and the 10-mm cell-size lattices was ascribed to the variations in the microstructures—hence the material model parameters between the small-diameter and the large-diameter EBM-Ti64 strut lattices. © 2022 John Wiley & Sons Ltd.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of the number of cells, strut diameter and face sheet on the compression of electron-beam-melt (EBM) Ti6Al4V (Ti64) body-centred-cubic (BCC) lattices was investigated experimentally and numerically. The lattices with the same relative density (~0.182) were fabricated with and without 2-mm-thick face sheets in 10 and 5 mm cell size, 8–125 unit cell (two to five cells/edge) and 2 and 1 mm strut diameter. The experimental compression tests were further numerically simulated in the LS-DYNA. Experimentally two bending-dominated crushing modes, namely, lateral and diagonal layer crushing, were determined. The numerical models however exhibited merely a bending-dominated lateral layer crushing mode when the erosion strain was 0.4 and without face-sheet models showed a diagonal layer crushing mode when the erosion strain was 0.3. Lower erosion strains promoted a diagonal layer crushing mode by introducing geometrical inhomogeneity to the lattice, leading to strain localisation as similar to the face sheets which introduced extensive strut bending in the layers adjacent to the face sheets. The face-sheet model showed a higher but decreasing collapse strength at an increasing number of cells, just as opposite to the without face-sheet model, and the collapse strength of both models converged when the number of cells was higher than five-cell/edge. The decrease/increase of the collapse strengths of lattices before the critical number of cells was claimed mainly due to the size-imposed lattice boundary condition, rather than the specimen volume. The difference in the experimental collapse strengths between the 5- and the 10-mm cell-size lattices was ascribed to the variations in the microstructures—hence the material model parameters between the small-diameter and the large-diameter EBM-Ti64 strut lattices. © 2022 John Wiley & Sons Ltd. |
Movahedi, N; Fiedler, T; Taşdemirci, A; Murch, G E; Belova, I V; Güden, M Impact loading of functionally graded metal syntactic foams Journal Article Materials Science and Engineering A, 839 , 2022. @article{Movahedi2022, title = {Impact loading of functionally graded metal syntactic foams}, author = {N Movahedi and T Fiedler and A Taşdemirci and G E Murch and I V Belova and M Güden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85124878036&doi=10.1016%2fj.msea.2022.142831&partnerID=40&md5=7c2f5ff50091f5c640df480605838c8c}, doi = {10.1016/j.msea.2022.142831}, year = {2022}, date = {2022-01-01}, journal = {Materials Science and Engineering A}, volume = {839}, abstract = {The present study addresses the impact loading of functionally graded metal syntactic foams (FG-MSF). For comparison, samples of the same material were also compression loaded at quasi-static velocities. Samples of A356 aluminium FG-MSF were produced using counter-gravity infiltration casting with combination of equal-sized layers of expanded perlite (EP) and activated carbon (AC) particles. A modified Split Hopkinson Pressure Bar test set-up was used to impact the FG-MSFs from their EP or AC layers at 55 m/s or 175 m/s impact velocities. A high-speed camera captured the deformation of the samples during testing. It was shown that increasing the loading velocity enhanced both the compressive proof strength and energy absorption of the impacted FG-MSF from both layers, confirming a dynamic strengthening effect of the foam. The samples impacted from both layers at 55 and 175 m/s showed a transition and a shock mode of deformation, respectively. The impacted samples at 55 m/s experienced lower final average strain values compared to 175 m/s. © 2022 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The present study addresses the impact loading of functionally graded metal syntactic foams (FG-MSF). For comparison, samples of the same material were also compression loaded at quasi-static velocities. Samples of A356 aluminium FG-MSF were produced using counter-gravity infiltration casting with combination of equal-sized layers of expanded perlite (EP) and activated carbon (AC) particles. A modified Split Hopkinson Pressure Bar test set-up was used to impact the FG-MSFs from their EP or AC layers at 55 m/s or 175 m/s impact velocities. A high-speed camera captured the deformation of the samples during testing. It was shown that increasing the loading velocity enhanced both the compressive proof strength and energy absorption of the impacted FG-MSF from both layers, confirming a dynamic strengthening effect of the foam. The samples impacted from both layers at 55 and 175 m/s showed a transition and a shock mode of deformation, respectively. The impacted samples at 55 m/s experienced lower final average strain values compared to 175 m/s. © 2022 Elsevier B.V. |
Güden, M; Enser, S; Bayhan, M; Taşdemirci, A; Yavaş, H Materials Science and Engineering A, 838 , 2022. @article{Güden2022b, title = {The strain rate sensitive flow stresses and constitutive equations of a selective-laser-melt and an annealed-rolled 316L stainless steel: A comparative study}, author = {M Güden and S Enser and M Bayhan and A Taşdemirci and H Yavaş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85124262590&doi=10.1016%2fj.msea.2022.142743&partnerID=40&md5=c9a9ea5a5d2240e3b1fb245fdb7f8e27}, doi = {10.1016/j.msea.2022.142743}, year = {2022}, date = {2022-01-01}, journal = {Materials Science and Engineering A}, volume = {838}, abstract = {The strain rate dependent compressive flow stresses of a Selective-Laser-Melt 316L (SLM-316L) alloy and a commercial (annealed-extruded) 316L (C-316L) alloy were determined, for comparison, between 1x10-4 and ∼2500 s-1 and between 1x10-4 and ∼2800 s-1, respectively. The Johnson and Cook flow stress material model parameters of both alloys were also determined. The microstructural examinations of the deformed cross-sections of tested specimens (interrupted tests) showed a twinning-induced-plasticity in SLM-316L alloy and a martensitic transformation-induced-plasticity in C-316L alloy. Twin and martensite formations were detected microscopically higher in the dynamically tested specimens until about 0.22 strain, while the twin and martensite formations decreased at increasing strains due to adiabatic heating. The rate sensitivity of SLM-316L was determined slightly higher than that of C-316L within the quasi-static strain rate range (1x10-4 and 1x10-2 s-1), while the rate sensitivities of both alloys were similar in the quasi-static-high strain rate range (1x10-4 and ∼2500-2800 s-1) at low strains. A more rapid decrease in the rate sensitivity of C-316L at increasing strains was found in the quasi-static-high strain rate range. The similar activation volumes of both alloys, corresponding to the dislocation intersections, indicated a similar thermally activated deformation process involvement in both alloys. © 2022 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The strain rate dependent compressive flow stresses of a Selective-Laser-Melt 316L (SLM-316L) alloy and a commercial (annealed-extruded) 316L (C-316L) alloy were determined, for comparison, between 1x10-4 and ∼2500 s-1 and between 1x10-4 and ∼2800 s-1, respectively. The Johnson and Cook flow stress material model parameters of both alloys were also determined. The microstructural examinations of the deformed cross-sections of tested specimens (interrupted tests) showed a twinning-induced-plasticity in SLM-316L alloy and a martensitic transformation-induced-plasticity in C-316L alloy. Twin and martensite formations were detected microscopically higher in the dynamically tested specimens until about 0.22 strain, while the twin and martensite formations decreased at increasing strains due to adiabatic heating. The rate sensitivity of SLM-316L was determined slightly higher than that of C-316L within the quasi-static strain rate range (1x10-4 and 1x10-2 s-1), while the rate sensitivities of both alloys were similar in the quasi-static-high strain rate range (1x10-4 and ∼2500-2800 s-1) at low strains. A more rapid decrease in the rate sensitivity of C-316L at increasing strains was found in the quasi-static-high strain rate range. The similar activation volumes of both alloys, corresponding to the dislocation intersections, indicated a similar thermally activated deformation process involvement in both alloys. © 2022 Elsevier B.V. |
2021 |
Güden, M; Yavaş, H; Tanrıkulu, A A; Taşdemirci, A; Akın, B; Enser, S; Karakuş, A; Hamat, B A Orientation dependent tensile properties of a selective-laser-melt 316L stainless steel Journal Article Materials Science and Engineering A, 824 , 2021. @article{Güden2021b, title = {Orientation dependent tensile properties of a selective-laser-melt 316L stainless steel}, author = {M Güden and H Yavaş and A A Tanrıkulu and A Taşdemirci and B Akın and S Enser and A Karakuş and B A Hamat}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85111194339&doi=10.1016%2fj.msea.2021.141808&partnerID=40&md5=d838bade5a0604998ddd4cb8ecce7457}, doi = {10.1016/j.msea.2021.141808}, year = {2021}, date = {2021-01-01}, journal = {Materials Science and Engineering A}, volume = {824}, abstract = {The effect of specimen inclination angle with respect to building direction on the tensile properties of a selective laser melt 316L alloy was investigated. Tensile test specimens were fabricated with the angles between 0° to 90° at 15° intervals using a rotation scanning. In addition, 316L alloy test specimens were generated in the ANSYS 2020R1 additive module and tensile tested in LS-DYNA in order to determine the effect of residual stresses on the tensile strengths. The microscopic analysis revealed a strong ⟨110⟩ fiber texture orientation along the building direction (the loading axis of 0° inclined specimens) and a weak <111> texture or nearly random distribution of directions in the normal to the building direction (tensile loading axis of 90° inclined specimens). The yield and tensile strength increased and ductility decreased with increasing inclination angle. The strength variation with the inclination angle was shown well-fitted with the Tsai-Hill failure criterion. Although, the used numerical models indicated an inclination-dependent residual stress, the difference in the residual stresses was much lower than the difference in the strengths between 0° and 90° inclined specimens. Predictions showed a lower twinning stress in 0° inclined specimens due to ⟨110⟩ fiber texture orientation in the tensile axis. The fiber texture resulted in extensive twinning; hence, higher ductility and tension-compression asymmetry in 0° inclined specimens. Based on these results, the variations in the strength and ductility of tested SLM-316L specimens with the inclination angle was ascribed to the variations in the angle between the fiber texture orientation and loading axis. © 2021 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of specimen inclination angle with respect to building direction on the tensile properties of a selective laser melt 316L alloy was investigated. Tensile test specimens were fabricated with the angles between 0° to 90° at 15° intervals using a rotation scanning. In addition, 316L alloy test specimens were generated in the ANSYS 2020R1 additive module and tensile tested in LS-DYNA in order to determine the effect of residual stresses on the tensile strengths. The microscopic analysis revealed a strong ⟨110⟩ fiber texture orientation along the building direction (the loading axis of 0° inclined specimens) and a weak <111> texture or nearly random distribution of directions in the normal to the building direction (tensile loading axis of 90° inclined specimens). The yield and tensile strength increased and ductility decreased with increasing inclination angle. The strength variation with the inclination angle was shown well-fitted with the Tsai-Hill failure criterion. Although, the used numerical models indicated an inclination-dependent residual stress, the difference in the residual stresses was much lower than the difference in the strengths between 0° and 90° inclined specimens. Predictions showed a lower twinning stress in 0° inclined specimens due to ⟨110⟩ fiber texture orientation in the tensile axis. The fiber texture resulted in extensive twinning; hence, higher ductility and tension-compression asymmetry in 0° inclined specimens. Based on these results, the variations in the strength and ductility of tested SLM-316L specimens with the inclination angle was ascribed to the variations in the angle between the fiber texture orientation and loading axis. © 2021 Elsevier B.V. |
Seven, S B; Çankaya, M A; Uysal, Ç; Tasdemirci, A; Saatçi, S; Güden, M Constitutive equation determination and dynamic numerical modelling of the compression deformation of concrete Journal Article Strain, 57 (2), 2021. @article{Seven2021, title = {Constitutive equation determination and dynamic numerical modelling of the compression deformation of concrete}, author = {S B Seven and M A Çankaya and Ç Uysal and A Tasdemirci and S Saatçi and M Güden}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85099175099&doi=10.1111%2fstr.12377&partnerID=40&md5=4651c623ee9ea5323e2e6b03771b2c5f}, doi = {10.1111/str.12377}, year = {2021}, date = {2021-01-01}, journal = {Strain}, volume = {57}, number = {2}, abstract = {The dynamic compression deformation of an in-house cast concrete (average aggregate size of 2–2.5 mm) was modelled using the finite element (FE), element-free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values. © 2021 John Wiley & Sons Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } The dynamic compression deformation of an in-house cast concrete (average aggregate size of 2–2.5 mm) was modelled using the finite element (FE), element-free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values. © 2021 John Wiley & Sons Ltd |
2020 |
Seven, Semih Berk; Cankaya, Alper M; Uysal, Cetin; Tasdemirci, Alper; Saatci, Selcuk; Guden, Mustafa Constitutive equation determination and dynamic numerical modelling of the compression deformation of concrete Journal Article STRAIN, 2020, ISSN: 0039-2103. @article{ISI:000605351700001, title = {Constitutive equation determination and dynamic numerical modelling of the compression deformation of concrete}, author = {Semih Berk Seven and Alper M Cankaya and Cetin Uysal and Alper Tasdemirci and Selcuk Saatci and Mustafa Guden}, doi = {10.1111/str.12377, Early Access Date = JAN 2021}, issn = {0039-2103}, year = {2020}, date = {2020-00-00}, journal = {STRAIN}, abstract = {The dynamic compression deformation of an in-house cast concrete (average aggregate size of 2-2.5 mm) was modelled using the finite element (FE), element-free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The dynamic compression deformation of an in-house cast concrete (average aggregate size of 2-2.5 mm) was modelled using the finite element (FE), element-free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values. |
2017 |
Odac, Ismet Kutlay; Guden, Mustafa; Klcaslan, Cenk; Tasdemirci, Alper The varying densification strain in a multi-layer aluminum corrugate structure: Direct impact testing and layer-wise numerical modelling Journal Article INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, 103 , pp. 64-75, 2017, ISSN: 0734-743X. @article{ISI:000395844400006, title = {The varying densification strain in a multi-layer aluminum corrugate structure: Direct impact testing and layer-wise numerical modelling}, author = {Ismet Kutlay Odac and Mustafa Guden and Cenk Klcaslan and Alper Tasdemirci}, doi = {10.1016/j.ijimpeng.2016.10.014}, issn = {0734-743X}, year = {2017}, date = {2017-05-01}, journal = {INTERNATIONAL JOURNAL OF IMPACT ENGINEERING}, volume = {103}, pages = {64-75}, abstract = {An aluminum (1050 H14) multi-layer corrugated structure composed of brazed 16 trapezoidal zig-zig fin layers was direct impact tested above the critical velocities for shock formation using a modified Split Hopkinson Pressure Bar. The experimentally measured stress-time histories of the cylindrical test samples in the direct impact tests were verified with the simulations implemented in the explicit finite element code of LS-DYNA. The quasi-static experimental and simulation deformation of the corrugated samples proceeded with the discrete, non-contiguous bands of crushed fin layers, while the dynamic crushing started from the proximal impact end and proceeded with a sequential and in-planar manner, showing shock type deformation characteristic. The experimental and numerical crushing stresses and the numerically determined densification strains of the fin layers increased with increasing impact velocity above the critical velocities. When the numerically determined densification strain at a specific velocity above the critical velocities was incorporated, the rigid-perfectly-plastic-locking idealized model resulted in peak stresses similar to the experimental and simulation mean crushing stresses. However, the model underestimated the experimental and simulation peak stresses below 200 m s(-1). It was proposed, while the micro inertial effects were responsible for the increase of the crushing stresses at and below subcritical velocities, the shock deformation became dominant above the critical velocities. (C) 2016 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } An aluminum (1050 H14) multi-layer corrugated structure composed of brazed 16 trapezoidal zig-zig fin layers was direct impact tested above the critical velocities for shock formation using a modified Split Hopkinson Pressure Bar. The experimentally measured stress-time histories of the cylindrical test samples in the direct impact tests were verified with the simulations implemented in the explicit finite element code of LS-DYNA. The quasi-static experimental and simulation deformation of the corrugated samples proceeded with the discrete, non-contiguous bands of crushed fin layers, while the dynamic crushing started from the proximal impact end and proceeded with a sequential and in-planar manner, showing shock type deformation characteristic. The experimental and numerical crushing stresses and the numerically determined densification strains of the fin layers increased with increasing impact velocity above the critical velocities. When the numerically determined densification strain at a specific velocity above the critical velocities was incorporated, the rigid-perfectly-plastic-locking idealized model resulted in peak stresses similar to the experimental and simulation mean crushing stresses. However, the model underestimated the experimental and simulation peak stresses below 200 m s(-1). It was proposed, while the micro inertial effects were responsible for the increase of the crushing stresses at and below subcritical velocities, the shock deformation became dominant above the critical velocities. (C) 2016 Elsevier Ltd. All rights reserved. |
Tasdemirci, A; Tunusoglu, G JOURNAL OF THERMOPLASTIC COMPOSITE MATERIALS, 30 (1), pp. 88-106, 2017, ISSN: 0892-7057. @article{ISI:000397204900005, title = {Experimental and numerical investigation of the effect of interlayer on the damage formation in a ceramic/composite armor at a low projectile velocity}, author = {A Tasdemirci and G Tunusoglu}, doi = {10.1177/0892705715584410}, issn = {0892-7057}, year = {2017}, date = {2017-01-01}, journal = {JOURNAL OF THERMOPLASTIC COMPOSITE MATERIALS}, volume = {30}, number = {1}, pages = {88-106}, abstract = {The damage formation in a multilayered armor system without and with an interlayer (rubber, Teflon, and aluminum foam) between the front face ceramic layer and the composite backing plate were investigated experimentally and numerically. The projectile impact tests were performed in a low-velocity projectile impact test system and the numerical studies were implemented using the nonlinear finite element code LS-DYNA. The results of numerical simulations showed that the stress wave transmission to the composite backing plate decreased significantly in Teflon and foam interlayer armor configurations. Similar to without interlayer configuration, the rubber interlayer configuration led to the passage of relatively high stress waves to the composite backing plate. This was mainly attributed to the increased rubber interlayer impedance during the impact event. The numerical results of reduced stress wave transmission to the backing plate and the increased damage formation in the ceramic front face layer with the use of Teflon and foam interlayer was further confirmed experimentally.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The damage formation in a multilayered armor system without and with an interlayer (rubber, Teflon, and aluminum foam) between the front face ceramic layer and the composite backing plate were investigated experimentally and numerically. The projectile impact tests were performed in a low-velocity projectile impact test system and the numerical studies were implemented using the nonlinear finite element code LS-DYNA. The results of numerical simulations showed that the stress wave transmission to the composite backing plate decreased significantly in Teflon and foam interlayer armor configurations. Similar to without interlayer configuration, the rubber interlayer configuration led to the passage of relatively high stress waves to the composite backing plate. This was mainly attributed to the increased rubber interlayer impedance during the impact event. The numerical results of reduced stress wave transmission to the backing plate and the increased damage formation in the ceramic front face layer with the use of Teflon and foam interlayer was further confirmed experimentally. |
2016 |
Tasdemirci, Alper; Kara, Ali The effect of perforations on the stress wave propagation characteristics of multilayered materials Journal Article JOURNAL OF THERMOPLASTIC COMPOSITE MATERIALS, 29 (12), pp. 1680-1695, 2016, ISSN: 0892-7057. @article{ISI:000390559000007, title = {The effect of perforations on the stress wave propagation characteristics of multilayered materials}, author = {Alper Tasdemirci and Ali Kara}, doi = {10.1177/0892705715584409}, issn = {0892-7057}, year = {2016}, date = {2016-12-01}, journal = {JOURNAL OF THERMOPLASTIC COMPOSITE MATERIALS}, volume = {29}, number = {12}, pages = {1680-1695}, abstract = {The effect of perforated interlayers on the stress wave transmission of multilayered materials was investigated both experimentally and numerically using the Split Hopkinson pressure bar (SHPB) testing. The multilayer combinations consisted of a ceramic face plate and a glass/epoxy backing plate with a laterally constrained low modulus solid or perforated rubber and Teflon interlayer. The perforations on rubber interlayer delayed the stress rise time and reduced the magnitude of the transmitted stress wave at low strains, while the perforations allowed the passage of relatively high transmitted stresses at large strains similar to the solid rubber interlayer. It was concluded that the effect of perforations were somewhat less pronounced in Teflon interlayer configuration, arising from its relatively low Poisson's ratio. It was finally shown that SHPB testing accompanied with the numerical simulations can be used to analyze the effect of compliant interlayer insertion in the multilayered structures.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of perforated interlayers on the stress wave transmission of multilayered materials was investigated both experimentally and numerically using the Split Hopkinson pressure bar (SHPB) testing. The multilayer combinations consisted of a ceramic face plate and a glass/epoxy backing plate with a laterally constrained low modulus solid or perforated rubber and Teflon interlayer. The perforations on rubber interlayer delayed the stress rise time and reduced the magnitude of the transmitted stress wave at low strains, while the perforations allowed the passage of relatively high transmitted stresses at large strains similar to the solid rubber interlayer. It was concluded that the effect of perforations were somewhat less pronounced in Teflon interlayer configuration, arising from its relatively low Poisson's ratio. It was finally shown that SHPB testing accompanied with the numerical simulations can be used to analyze the effect of compliant interlayer insertion in the multilayered structures. |
Tasdemirci, Alper; Kara, Ali; Turan, Kivanc; Sahin, Selim; Guden, Mustafa Effect of heat treatment on the blast loading response of combined geometry shell core sandwich structures Journal Article THIN-WALLED STRUCTURES, 100 , pp. 180-191, 2016, ISSN: 0263-8231. @article{ISI:000369463600016, title = {Effect of heat treatment on the blast loading response of combined geometry shell core sandwich structures}, author = {Alper Tasdemirci and Ali Kara and Kivanc Turan and Selim Sahin and Mustafa Guden}, doi = {10.1016/j.tws.2015.12.012}, issn = {0263-8231}, year = {2016}, date = {2016-03-01}, journal = {THIN-WALLED STRUCTURES}, volume = {100}, pages = {180-191}, abstract = {The effect of heat treatment on the dynamic crushing and energy absorption behavior of combined geometry shell cores (hemisphere and cylinder) of sandwich structures were investigated both experimentally and numerically. The applied heat treatment on the combined geometry shell cores relieved the stress caused by deep drawing, diminishing the peak transmitted forces. The verified numerical models of the as-received and heat-treated combined geometry shells were used to model blast loading of various sandwich configurations and the additional sandwich configurations of reversing the cylindrical side of the cores to the impacted side. Both the applied heat-treatment and the reversing process decreased the magnitude of the force transmitted to the protected structure. The applied heat treatment increased the arrival time of blast force wave to the protected structure, while the reversing resulted in opposite. (C) 2015 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of heat treatment on the dynamic crushing and energy absorption behavior of combined geometry shell cores (hemisphere and cylinder) of sandwich structures were investigated both experimentally and numerically. The applied heat treatment on the combined geometry shell cores relieved the stress caused by deep drawing, diminishing the peak transmitted forces. The verified numerical models of the as-received and heat-treated combined geometry shells were used to model blast loading of various sandwich configurations and the additional sandwich configurations of reversing the cylindrical side of the cores to the impacted side. Both the applied heat-treatment and the reversing process decreased the magnitude of the force transmitted to the protected structure. The applied heat treatment increased the arrival time of blast force wave to the protected structure, while the reversing resulted in opposite. (C) 2015 Elsevier Ltd. All rights reserved. |
2015 |
Tasdemirci, Alper; Kara, Ali; Turan, Kivanc; Sahin, Selim Dynamic crushing and energy absorption of sandwich structures with combined geometry shell cores Journal Article THIN-WALLED STRUCTURES, 91 , pp. 116-128, 2015, ISSN: 0263-8231. @article{ISI:000352174200011, title = {Dynamic crushing and energy absorption of sandwich structures with combined geometry shell cores}, author = {Alper Tasdemirci and Ali Kara and Kivanc Turan and Selim Sahin}, doi = {10.1016/j.tws.2015.02.015}, issn = {0263-8231}, year = {2015}, date = {2015-06-01}, journal = {THIN-WALLED STRUCTURES}, volume = {91}, pages = {116-128}, abstract = {Dynamic crushing and energy absorption characteristics of sandwich structures with combined geometry shell cores were investigated experimentally and numerically. The effect of strain rate on the crushing behavior was presented by the crushing tests at quasi-static, intermediate and high strain rate regimes. It was shown that absorbed energy increased with increasing impact velocity. The effect of confinement on crushing behavior was shown by conducting confined experiments at quasi-static and dynamic rates. Higher buckling loads at lower deformation were observed in confined quasi-static crushing due to additional lateral support and friction provided by confinement wall. By using fictitious numerical models with strain rate insensitive material models, the effect of inertia and strain rate on crushing were shown. It was observed that, increase in impact velocity caused increase in inertial effects and strain rate effects were nearly independent from the impact velocity. The effects of multilayering were also investigated numerically. (C) 2015 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Dynamic crushing and energy absorption characteristics of sandwich structures with combined geometry shell cores were investigated experimentally and numerically. The effect of strain rate on the crushing behavior was presented by the crushing tests at quasi-static, intermediate and high strain rate regimes. It was shown that absorbed energy increased with increasing impact velocity. The effect of confinement on crushing behavior was shown by conducting confined experiments at quasi-static and dynamic rates. Higher buckling loads at lower deformation were observed in confined quasi-static crushing due to additional lateral support and friction provided by confinement wall. By using fictitious numerical models with strain rate insensitive material models, the effect of inertia and strain rate on crushing were shown. It was observed that, increase in impact velocity caused increase in inertial effects and strain rate effects were nearly independent from the impact velocity. The effects of multilayering were also investigated numerically. (C) 2015 Elsevier Ltd. All rights reserved. |
Tasdemirci, Alper; Sahin, Selim; Kara, Ali; Turan, Kivanc THIN-WALLED STRUCTURES, 86 , pp. 83-93, 2015, ISSN: 0263-8231. @article{ISI:000347130100010, title = {Crushing and energy absorption characteristics of combined geometry shells at quasi-static and dynamic strain rates: Experimental and numerical study}, author = {Alper Tasdemirci and Selim Sahin and Ali Kara and Kivanc Turan}, doi = {10.1016/j.tws.2014.09.020}, issn = {0263-8231}, year = {2015}, date = {2015-01-01}, journal = {THIN-WALLED STRUCTURES}, volume = {86}, pages = {83-93}, abstract = {The quasi-static and dynamic crushing response and the energy absorption characteristics of combined geometry shells composed of a hemispherical cap and a cylindrical segment were investigated both experimentally and numerically. The inelastic deformation of the shells initiated with the inversion of the hemisphere cap and followed by the axisymmetric or diamond folding of the cylindrical segment depending on the loading rate and dimensions. The fracture of the thinner specimens in dynamic tests was ascribed to the rise of the flow stress to the fracture stress with increasing strain rate. The hemisphere cap absorbed more energy at dynamic rates than at quasi-static rates, while it exhibited lower strain rate and inertia sensitivities than the cylinder segment. For both the hemisphere cap and the cylinder segment, the inertial effect was shown to be more pronounced than strain rate effect at increasing impact velocities. (C) 2014 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The quasi-static and dynamic crushing response and the energy absorption characteristics of combined geometry shells composed of a hemispherical cap and a cylindrical segment were investigated both experimentally and numerically. The inelastic deformation of the shells initiated with the inversion of the hemisphere cap and followed by the axisymmetric or diamond folding of the cylindrical segment depending on the loading rate and dimensions. The fracture of the thinner specimens in dynamic tests was ascribed to the rise of the flow stress to the fracture stress with increasing strain rate. The hemisphere cap absorbed more energy at dynamic rates than at quasi-static rates, while it exhibited lower strain rate and inertia sensitivities than the cylinder segment. For both the hemisphere cap and the cylinder segment, the inertial effect was shown to be more pronounced than strain rate effect at increasing impact velocities. (C) 2014 Elsevier Ltd. All rights reserved. |
2014 |
Demir, Mustafa M; Horzum, Nesrin; Tasdemirci, Alper; Turan, Kivanc; Guden, Mustafa Mechanical Interlocking between Porous Electrospun Polystyrene Fibers and an Epoxy Matrix Journal Article ACS APPLIED MATERIALS & INTERFACES, 6 (24), pp. 21901-21905, 2014, ISSN: 1944-8244. @article{ISI:000347139400018, title = {Mechanical Interlocking between Porous Electrospun Polystyrene Fibers and an Epoxy Matrix}, author = {Mustafa M Demir and Nesrin Horzum and Alper Tasdemirci and Kivanc Turan and Mustafa Guden}, doi = {10.1021/am507029c}, issn = {1944-8244}, year = {2014}, date = {2014-12-01}, journal = {ACS APPLIED MATERIALS & INTERFACES}, volume = {6}, number = {24}, pages = {21901-21905}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Kilicaslan, C; Odaci, I K; Tasdemirci, A; Guden, M STRAIN, 50 (3), pp. 236-249, 2014, ISSN: 1475-1305. @article{ISI:000336487800004, title = {Experimental Testing and Full and Homogenized Numerical Models of the Low Velocity and Dynamic Deformation of the Trapezoidal Aluminium Corrugated Core Sandwich}, author = {C Kilicaslan and I K Odaci and A Tasdemirci and M Guden}, doi = {10.1111/str.12085}, issn = {1475-1305}, year = {2014}, date = {2014-06-01}, journal = {STRAIN}, volume = {50}, number = {3}, pages = {236-249}, abstract = {The simulations of the low velocity and dynamic deformation of a multi-layer 1050-H14 Al trapezoidal zig-zag corrugated core sandwich were investigated using the homogenized models (solid models) of a single core layer (without face sheets). In the first part of the study, the LS-DYNA MAT-26 material model parameters of a single core layer were developed through experimental and numerical compression tests on the single core layer. In the second part, the fidelities of the developed numerical models were checked by the split-Hopkinson pressure bar direct impact, low velocity compression and indentation and projectile impact tests. The results indicated that the element size had a significant effect on the initial peak and post-peak stresses of the homogenized models of the direct impact testing of the single-layer corrugated sandwich. This was attributed to the lack of the inertial effects in the homogenized models, which resulted in reduced initial peak stresses as compared with the full model and experiment. However, the homogenized models based on the experimental stress-strain curve of the single core layer predicted the low velocity compression and indentation and projectile impact tests of the multi-layer corrugated sandwich with an acceptable accuracy and reduced the computational time of the models significantly.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The simulations of the low velocity and dynamic deformation of a multi-layer 1050-H14 Al trapezoidal zig-zag corrugated core sandwich were investigated using the homogenized models (solid models) of a single core layer (without face sheets). In the first part of the study, the LS-DYNA MAT-26 material model parameters of a single core layer were developed through experimental and numerical compression tests on the single core layer. In the second part, the fidelities of the developed numerical models were checked by the split-Hopkinson pressure bar direct impact, low velocity compression and indentation and projectile impact tests. The results indicated that the element size had a significant effect on the initial peak and post-peak stresses of the homogenized models of the direct impact testing of the single-layer corrugated sandwich. This was attributed to the lack of the inertial effects in the homogenized models, which resulted in reduced initial peak stresses as compared with the full model and experiment. However, the homogenized models based on the experimental stress-strain curve of the single core layer predicted the low velocity compression and indentation and projectile impact tests of the multi-layer corrugated sandwich with an acceptable accuracy and reduced the computational time of the models significantly. |
Kilicaslan, Cenk; Gueden, Mustafa; Odaci, Ismet Kutlay; Tasdemirci, Alper Experimental and numerical studies on the quasi-static and dynamic crushing responses of multi-layer trapezoidal aluminum corrugated sandwiches Journal Article THIN-WALLED STRUCTURES, 78 , pp. 70-78, 2014, ISSN: 0263-8231. @article{ISI:000335543900007, title = {Experimental and numerical studies on the quasi-static and dynamic crushing responses of multi-layer trapezoidal aluminum corrugated sandwiches}, author = {Cenk Kilicaslan and Mustafa Gueden and Ismet Kutlay Odaci and Alper Tasdemirci}, doi = {10.1016/j.tws.2014.01.017}, issn = {0263-8231}, year = {2014}, date = {2014-05-01}, journal = {THIN-WALLED STRUCTURES}, volume = {78}, pages = {70-78}, abstract = {The axial crushing responses of bonded and brazed multi-layer 1050 H14 trapezoidal aluminum corrugated core (fin) sandwich structures, with and without aluminum interlayer sheets in 0 degrees/0 degrees and 0 degrees/90 degrees core orientations, were both experimentally and numerically investigated at quasi-static and dynamic strain rates. Multi-layering the core layers decreased the buckling stress and increased the densification strain. The experimental and simulation compression stress-strain curves showed reasonable agreements with each other. Two main crushing modes were observed experimentally and numerically: the progressive fin folding and the shearing interlayer aluminum sheets. Both, the simulation and experimental buckling and post-buckling stresses increased when the interlayer sheets were constraint laterally. The multi-layer samples without interlayer sheets in 0 degrees/90 degrees core orientation exhibited higher buckling stresses than the samples in 0 degrees/0 degrees core orientation. The increased buckling stress of 0 degrees/0 degrees oriented core samples without interlayer sheets at high strain rate was attributed to the micro-inertial effects which led to increased bending forces at higher impact velocities. (C) 2014 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The axial crushing responses of bonded and brazed multi-layer 1050 H14 trapezoidal aluminum corrugated core (fin) sandwich structures, with and without aluminum interlayer sheets in 0 degrees/0 degrees and 0 degrees/90 degrees core orientations, were both experimentally and numerically investigated at quasi-static and dynamic strain rates. Multi-layering the core layers decreased the buckling stress and increased the densification strain. The experimental and simulation compression stress-strain curves showed reasonable agreements with each other. Two main crushing modes were observed experimentally and numerically: the progressive fin folding and the shearing interlayer aluminum sheets. Both, the simulation and experimental buckling and post-buckling stresses increased when the interlayer sheets were constraint laterally. The multi-layer samples without interlayer sheets in 0 degrees/90 degrees core orientation exhibited higher buckling stresses than the samples in 0 degrees/0 degrees core orientation. The increased buckling stress of 0 degrees/0 degrees oriented core samples without interlayer sheets at high strain rate was attributed to the micro-inertial effects which led to increased bending forces at higher impact velocities. (C) 2014 Elsevier Ltd. All rights reserved. |
2013 |
Attila, Yigit; Guden, Mustafa; Tasdemirci, Alper Foam glass processing using a polishing glass powder residue Journal Article CERAMICS INTERNATIONAL, 39 (5), pp. 5869-5877, 2013, ISSN: 0272-8842. @article{ISI:000318577600141, title = {Foam glass processing using a polishing glass powder residue}, author = {Yigit Attila and Mustafa Guden and Alper Tasdemirci}, doi = {10.1016/j.ceramint.2012.12.104}, issn = {0272-8842}, year = {2013}, date = {2013-07-01}, journal = {CERAMICS INTERNATIONAL}, volume = {39}, number = {5}, pages = {5869-5877}, abstract = {The foaming behavior of a powder residue/waste of a soda-lime window glass polishing facility was investigated at the temperatures between 700 and 950 degrees C. The results showed that the foaming of the glass powder started at a characteristic temperature between 670 and 680 degrees C. The maximum volume expansions of the glass powder and the density of the foams varied between 600% and 750% and 0.206 and 0.378 g cm(-3), respectively. The expansion of the studied glass powder residue resulted from the decomposition of the organic compounds on the surfaces of the glass powder particles, derived from an oil-based coolant used in the polishing. The collapse stress of the foams ranged between similar to 1 and 4 MPa and the thermal conductivity between 0.048 and 0.079 W K-1 m(-1). Both the collapse stress and thermal conductivity increased with increasing the foam density. The foams showed the characteristics of the compression deformation of the open cell brittle foams, which was attributed to the relatively thick cell edges. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The foaming behavior of a powder residue/waste of a soda-lime window glass polishing facility was investigated at the temperatures between 700 and 950 degrees C. The results showed that the foaming of the glass powder started at a characteristic temperature between 670 and 680 degrees C. The maximum volume expansions of the glass powder and the density of the foams varied between 600% and 750% and 0.206 and 0.378 g cm(-3), respectively. The expansion of the studied glass powder residue resulted from the decomposition of the organic compounds on the surfaces of the glass powder particles, derived from an oil-based coolant used in the polishing. The collapse stress of the foams ranged between similar to 1 and 4 MPa and the thermal conductivity between 0.048 and 0.079 W K-1 m(-1). Both the collapse stress and thermal conductivity increased with increasing the foam density. The foams showed the characteristics of the compression deformation of the open cell brittle foams, which was attributed to the relatively thick cell edges. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. |
Gulturk, E A; Guden, M; Tasdemirci, A Calcined and natural frustules filled epoxy matrices: The effect of volume fraction on the tensile and compression behavior Journal Article COMPOSITES PART B-ENGINEERING, 44 (1), pp. 491-500, 2013, ISSN: 1359-8368. @article{ISI:000313854200059, title = {Calcined and natural frustules filled epoxy matrices: The effect of volume fraction on the tensile and compression behavior}, author = {E A Gulturk and M Guden and A Tasdemirci}, doi = {10.1016/j.compositesb.2012.03.022}, issn = {1359-8368}, year = {2013}, date = {2013-01-01}, journal = {COMPOSITES PART B-ENGINEERING}, volume = {44}, number = {1}, pages = {491-500}, abstract = {The effects of calcined diatom (CD) and natural diatom (ND) frustules filling (0-12 vol.%) on the quasi-static tensile and quasi-static and high strain rate compression behavior of an epoxy matrix were investigated experimentally. The high strain rate testing of frustules-filled and neat epoxy samples was performed in a compression Split Hopkinson Pressure Bar set-up. The frustules filling increased the stress values at a constant strain and decreased the tensile failure strains of the epoxy matrix. Compression tests results showed that frustules filling of epoxy increased both elastic modulus and yield strength values at quasi-static and high strain rates. While, a higher strengthening effect and strain rate sensitivity were found with ND frustules filling. Microscopic observations revealed two main compression deformation modes at quasi-static strain rates: the debonding of the frustules from the epoxy and/or crushing of the frustules. However, the failure of the filled composites at high strain rates was dominated by the fracture of epoxy matrix. (C) 2012 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effects of calcined diatom (CD) and natural diatom (ND) frustules filling (0-12 vol.%) on the quasi-static tensile and quasi-static and high strain rate compression behavior of an epoxy matrix were investigated experimentally. The high strain rate testing of frustules-filled and neat epoxy samples was performed in a compression Split Hopkinson Pressure Bar set-up. The frustules filling increased the stress values at a constant strain and decreased the tensile failure strains of the epoxy matrix. Compression tests results showed that frustules filling of epoxy increased both elastic modulus and yield strength values at quasi-static and high strain rates. While, a higher strengthening effect and strain rate sensitivity were found with ND frustules filling. Microscopic observations revealed two main compression deformation modes at quasi-static strain rates: the debonding of the frustules from the epoxy and/or crushing of the frustules. However, the failure of the filled composites at high strain rates was dominated by the fracture of epoxy matrix. (C) 2012 Elsevier Ltd. All rights reserved. |
2012 |
Tasdemirci, A; Turan, A K; Guden, M The effect of strain rate on the mechanical behavior of Teflon foam Journal Article POLYMER TESTING, 31 (6), pp. 723-727, 2012, ISSN: 0142-9418. @article{ISI:000307614000002, title = {The effect of strain rate on the mechanical behavior of Teflon foam}, author = {A Tasdemirci and A K Turan and M Guden}, doi = {10.1016/j.polymertesting.2012.05.004}, issn = {0142-9418}, year = {2012}, date = {2012-09-01}, journal = {POLYMER TESTING}, volume = {31}, number = {6}, pages = {723-727}, abstract = {The quasi-static (1 x 10(-3), 1 x 10(-2) and 1 x 10(-1) s(-1)) and high strain rate (7200 and 9500 s(-1)) experimental and high strain rate numerical compression deformation of a Gore Polarchip (TM) CP7003 heat insulating Teflon foam was investigated. High strain rate tests were conducted with the insertion of quartz crystal piezoelectric transducers at the end of the transmitter bar of a compression Split Hopkinson Pressure Bar (SHPB) set-up in order to measure the force at the back face of the specimen. A fully developed numerical model of the SHPB test on Teflon was also implemented using LS-DYNA. The simulation stresses showed close correlations with the experimentally measured stresses on the bars. The developed model successfully simulated the high strain rate loading. The damage initiation and progression of experimental high strain rate tests were further recorded using a high speed camera and found to be very similar to those of the simulation high strain rate tests. (C) 2012 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The quasi-static (1 x 10(-3), 1 x 10(-2) and 1 x 10(-1) s(-1)) and high strain rate (7200 and 9500 s(-1)) experimental and high strain rate numerical compression deformation of a Gore Polarchip (TM) CP7003 heat insulating Teflon foam was investigated. High strain rate tests were conducted with the insertion of quartz crystal piezoelectric transducers at the end of the transmitter bar of a compression Split Hopkinson Pressure Bar (SHPB) set-up in order to measure the force at the back face of the specimen. A fully developed numerical model of the SHPB test on Teflon was also implemented using LS-DYNA. The simulation stresses showed close correlations with the experimentally measured stresses on the bars. The developed model successfully simulated the high strain rate loading. The damage initiation and progression of experimental high strain rate tests were further recorded using a high speed camera and found to be very similar to those of the simulation high strain rate tests. (C) 2012 Elsevier Ltd. All rights reserved. |
Tasdemirci, A; Tunusoglu, G; Guden, M The effect of the interlayer on the ballistic performance of ceramic/composite armors: Experimental and numerical study Journal Article INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, 44 , pp. 1-9, 2012, ISSN: 0734-743X. @article{ISI:000301473600001, title = {The effect of the interlayer on the ballistic performance of ceramic/composite armors: Experimental and numerical study}, author = {A Tasdemirci and G Tunusoglu and M Guden}, doi = {10.1016/j.ijimpeng.2011.12.005}, issn = {0734-743X}, year = {2012}, date = {2012-06-01}, journal = {INTERNATIONAL JOURNAL OF IMPACT ENGINEERING}, volume = {44}, pages = {1-9}, abstract = {The effect of rubber, Teflon and aluminum foam interlayer material on the ballistic performance of composite armor was investigated both experimentally and numerically. Although, rubber interlayer did not cause any significant delay in the initial stress build-up in the composite layer, Teflon and aluminum foam interlayer caused a significant delay and reduction in the magnitude of the stress transmitted to the composite backing plate. Damage in the ceramic layer was found to be highly localized around the projectile impact zone for the configuration without interlayer and rubber interlayer while aluminum foam and Teflon interlayer spread the damage zone in the radial direction. Relatively large pieces of the ceramic around the impact axis in the rubber interlayer configuration were observed while the ceramic layer was efficiently fragmented in aluminum foam and Teflon interlayer configuration. (C) 2011 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of rubber, Teflon and aluminum foam interlayer material on the ballistic performance of composite armor was investigated both experimentally and numerically. Although, rubber interlayer did not cause any significant delay in the initial stress build-up in the composite layer, Teflon and aluminum foam interlayer caused a significant delay and reduction in the magnitude of the stress transmitted to the composite backing plate. Damage in the ceramic layer was found to be highly localized around the projectile impact zone for the configuration without interlayer and rubber interlayer while aluminum foam and Teflon interlayer spread the damage zone in the radial direction. Relatively large pieces of the ceramic around the impact axis in the rubber interlayer configuration were observed while the ceramic layer was efficiently fragmented in aluminum foam and Teflon interlayer configuration. (C) 2011 Elsevier Ltd. All rights reserved. |
Odaci, Ismet Kutlay; Kilicaslan, Cenk; Tasdemirci, Alper; Guden, Mustafa INTERNATIONAL JOURNAL OF CRASHWORTHINESS, 17 (5), pp. 508-518, 2012, ISSN: 1358-8265. @article{ISI:000308991800004, title = {Projectile impact testing of glass fiber-reinforced composite and layered corrugated aluminium and aluminium foam core sandwich panels: a comparative study}, author = {Ismet Kutlay Odaci and Cenk Kilicaslan and Alper Tasdemirci and Mustafa Guden}, doi = {10.1080/13588265.2012.690215}, issn = {1358-8265}, year = {2012}, date = {2012-01-01}, journal = {INTERNATIONAL JOURNAL OF CRASHWORTHINESS}, volume = {17}, number = {5}, pages = {508-518}, abstract = {E-glass/polyester composite and layered corrugated aluminium and aluminium foam core sandwich panels were projectile impact tested between 127 m/s and 190 m/s using a hardened steel sphere projectile. The corrugated aluminium cores, constructed from aluminium fin layers and aluminium interlayers and face sheets, exhibited relatively lower-plateau stresses and higher stress oscillations in the plateau region than aluminium foam cores. The applied brazing process resulted in reductions in the plateau stresses of the corrugated aluminium cores. The sandwich panels with 2- and 3-mm-thick composite face sheets and the epoxy-bonded corrugated aluminium sheet cores were perforated, while the sandwich panels with 5-mm-thick composite face sheets were penetrated in the projectile impact tests. On the other hand, the sandwich panels with aluminium foam cores were only penetrated. A simple comparison between the ballistic limits of the sandwich panels as a function of total weight revealed significant increases in the ballistic limits of the cores with the inclusion of composite face sheets. The determined higher impact resistance of the foam core sandwich panels was attributed to the relatively higher strength of the foam cores investigated and the ability to distribute the incident impulse to a relatively large area of the backing composite plate.}, keywords = {}, pubstate = {published}, tppubtype = {article} } E-glass/polyester composite and layered corrugated aluminium and aluminium foam core sandwich panels were projectile impact tested between 127 m/s and 190 m/s using a hardened steel sphere projectile. The corrugated aluminium cores, constructed from aluminium fin layers and aluminium interlayers and face sheets, exhibited relatively lower-plateau stresses and higher stress oscillations in the plateau region than aluminium foam cores. The applied brazing process resulted in reductions in the plateau stresses of the corrugated aluminium cores. The sandwich panels with 2- and 3-mm-thick composite face sheets and the epoxy-bonded corrugated aluminium sheet cores were perforated, while the sandwich panels with 5-mm-thick composite face sheets were penetrated in the projectile impact tests. On the other hand, the sandwich panels with aluminium foam cores were only penetrated. A simple comparison between the ballistic limits of the sandwich panels as a function of total weight revealed significant increases in the ballistic limits of the cores with the inclusion of composite face sheets. The determined higher impact resistance of the foam core sandwich panels was attributed to the relatively higher strength of the foam cores investigated and the ability to distribute the incident impulse to a relatively large area of the backing composite plate. |
2010 |
Tasdemirci, A; Ergonenc, C; Guden, M Split Hopkinson pressure bar multiple reloading and modeling of a 316 L stainless steel metallic hollow sphere structure Journal Article INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, 37 (3), pp. 250-259, 2010, ISSN: 0734-743X. @article{ISI:000273106000003, title = {Split Hopkinson pressure bar multiple reloading and modeling of a 316 L stainless steel metallic hollow sphere structure}, author = {A Tasdemirci and C Ergonenc and M Guden}, doi = {10.1016/j.ijimpeng.2009.06.010}, issn = {0734-743X}, year = {2010}, date = {2010-03-01}, journal = {INTERNATIONAL JOURNAL OF IMPACT ENGINEERING}, volume = {37}, number = {3}, pages = {250-259}, abstract = {The high strain rate (600 s(-1)) compression deformation of a 316 L metallic hollow sphere (MHS) structure (density: 500 kg m(-3): average outer hollow sphere diameter: 2 mm and wall thickness: 45 mu m) was determined both numerically and experimentally. The experimental compressive stress-strain behavior at high strain rates until about large strains was obtained with multiple reloading tests using a large-diameter compression type aluminum Split Hopkinson Pressure Bar (SHPB) test apparatus. The multiple reloading of MHS samples in SHPB was analyzed with a 3D finite element model using the commercial explicit finite element code LS-DYNA. The tested MHS samples showed increased crushing stress values, when the strain rate increased from quasi-static (0.8 x 10(-4) s(-1)) to high strain rate (600 s(-1)). Experimentally and numerically deformed sections of MHS samples tested showed very similar crushing characteristics; plastic hinge formation, the indentation of the spheres at the contact regions and sphere wall buckling at intermediate strains. The extent of micro-inertial effects was further predicted with the strain rate insensitive cell wall material model and with the strain rate sensitive behavior of MHS structure similar to that of the cell wall material. Based on the predictions, the strain rate sensitivity of the studied 316 L MHS sample was attributed to the strain rate sensitivity of the cell wall material and the micro-inertia. (C) 2009 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The high strain rate (600 s(-1)) compression deformation of a 316 L metallic hollow sphere (MHS) structure (density: 500 kg m(-3): average outer hollow sphere diameter: 2 mm and wall thickness: 45 mu m) was determined both numerically and experimentally. The experimental compressive stress-strain behavior at high strain rates until about large strains was obtained with multiple reloading tests using a large-diameter compression type aluminum Split Hopkinson Pressure Bar (SHPB) test apparatus. The multiple reloading of MHS samples in SHPB was analyzed with a 3D finite element model using the commercial explicit finite element code LS-DYNA. The tested MHS samples showed increased crushing stress values, when the strain rate increased from quasi-static (0.8 x 10(-4) s(-1)) to high strain rate (600 s(-1)). Experimentally and numerically deformed sections of MHS samples tested showed very similar crushing characteristics; plastic hinge formation, the indentation of the spheres at the contact regions and sphere wall buckling at intermediate strains. The extent of micro-inertial effects was further predicted with the strain rate insensitive cell wall material model and with the strain rate sensitive behavior of MHS structure similar to that of the cell wall material. Based on the predictions, the strain rate sensitivity of the studied 316 L MHS sample was attributed to the strain rate sensitivity of the cell wall material and the micro-inertia. (C) 2009 Elsevier Ltd. All rights reserved. |
2008 |
Tasdemirci, Alper The effect of tube end constraining on the axial crushing behavior of an aluminum tube Journal Article MATERIALS & DESIGN, 29 (10), pp. 1992-2001, 2008, ISSN: 0261-3069. @article{ISI:000258564800014, title = {The effect of tube end constraining on the axial crushing behavior of an aluminum tube}, author = {Alper Tasdemirci}, doi = {10.1016/j.matdes.2008.04.011}, issn = {0261-3069}, year = {2008}, date = {2008-12-01}, journal = {MATERIALS & DESIGN}, volume = {29}, number = {10}, pages = {1992-2001}, abstract = {The effect of various types of end constraining on the deformation and load-displacement behavior of a 3003-H 14 Al tube were experimentally and numerically studied. No effect of single-end constraining of tubes was found. Few conditions of double-end constraining tended to revert the deformation mode to mixed and/or diamond mode of deformation. Double-end constraining of tube ends further resulted in an increase in initial drop-load values, widening the initial overshot region in average load-displacement curves. The agreement between numerical and experimental results showed the capabilities of the used numerical model in order to predict end-condition effects in tubular structures. (C) 2008 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of various types of end constraining on the deformation and load-displacement behavior of a 3003-H 14 Al tube were experimentally and numerically studied. No effect of single-end constraining of tubes was found. Few conditions of double-end constraining tended to revert the deformation mode to mixed and/or diamond mode of deformation. Double-end constraining of tube ends further resulted in an increase in initial drop-load values, widening the initial overshot region in average load-displacement curves. The agreement between numerical and experimental results showed the capabilities of the used numerical model in order to predict end-condition effects in tubular structures. (C) 2008 Elsevier Ltd. All rights reserved. |
Tasdemirci, A; Yuksel, S; Karsu, D; Gulturk, E; Hall, I W; Guden, M Diatom frustule-filled epoxy: Experimental and numerical study of the quasi-static and high strain rate compression behavior Journal Article MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 480 (1-2), pp. 373-382, 2008, ISSN: 0921-5093. @article{ISI:000255881300049, title = {Diatom frustule-filled epoxy: Experimental and numerical study of the quasi-static and high strain rate compression behavior}, author = {A Tasdemirci and S Yuksel and D Karsu and E Gulturk and I W Hall and M Guden}, doi = {10.1016/j.msea.2007.07.037}, issn = {0921-5093}, year = {2008}, date = {2008-05-01}, journal = {MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, volume = {480}, number = {1-2}, pages = {373-382}, abstract = {In this study, centric type diatom frustules obtained from a diatomaceous earth filter material were used as filler in an epoxy resin with a weight percentage of 15% in order to assess the possible effects on the compressive behavior at quasi-static and high strain rates. The high strain rate testing of frustule-filled and neat epoxy samples was performed in a split-Hopkinson pressure bar (SHPB) set-up and modeled using the commercial explicit finite element code LS-DYNA 970. Result has shown that 15% frustule filling of epoxy increased both modulus and yield strength values at quasi-static and high strain rates without significantly reducing the failure strain. Microscopic observations revealed two main deformation modes: the debonding of the frustules from the epoxy and crushing/fracture of the frustules. The modeling results have further confirmed the attainment of stress equilibrium in the samples in SHPB testing following the initial elastic region and showed good agreement with the experimental stress-time response and deformation sequence of the samples in high strain rate testing. (C) 2007 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, centric type diatom frustules obtained from a diatomaceous earth filter material were used as filler in an epoxy resin with a weight percentage of 15% in order to assess the possible effects on the compressive behavior at quasi-static and high strain rates. The high strain rate testing of frustule-filled and neat epoxy samples was performed in a split-Hopkinson pressure bar (SHPB) set-up and modeled using the commercial explicit finite element code LS-DYNA 970. Result has shown that 15% frustule filling of epoxy increased both modulus and yield strength values at quasi-static and high strain rates without significantly reducing the failure strain. Microscopic observations revealed two main deformation modes: the debonding of the frustules from the epoxy and crushing/fracture of the frustules. The modeling results have further confirmed the attainment of stress equilibrium in the samples in SHPB testing following the initial elastic region and showed good agreement with the experimental stress-time response and deformation sequence of the samples in high strain rate testing. (C) 2007 Elsevier B.V. All rights reserved. |
Tasdemirci, A; Hizal, A; Altindis, M; Hall, I W; Gueden, M The effect of strain rate on the compressive deformation behavior of a sintered Ti6Al4V powder compact Journal Article MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 474 (1-2), pp. 335-341, 2008, ISSN: 0921-5093. @article{ISI:000253030500044, title = {The effect of strain rate on the compressive deformation behavior of a sintered Ti6Al4V powder compact}, author = {A Tasdemirci and A Hizal and M Altindis and I W Hall and M Gueden}, doi = {10.1016/j.msea.2007.05.023}, issn = {0921-5093}, year = {2008}, date = {2008-02-01}, journal = {MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, volume = {474}, number = {1-2}, pages = {335-341}, abstract = {The high strain rate (220-550 s(-1)) and quasi-static (0.0016 s(-1)) compression deformation behavior of a sintered Ti6Al4V powder compact was investigated. The compact was prepared using atomized spherical particles (100-200 mu m) and contained 38 +/- 1% porosity. The deformation sequences of the tested samples were further recorded by high speed camera and analyzed as a function of strain. The failure of the compact, which was found to be similar in the studied high strain rate and quasi-static strain rate testing regimes, occurs through particle decohesion along the surface of the two cones in a ductile (dimpled) mode consisting of void initiation and growth and by void coalescence in the interparticle bond region. The effect of strain rate was to increase the flow stress and compressive strength of the compact while the critical strain corresponding to the maximum stress was shown to be strain rate independent. (C) 2007 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The high strain rate (220-550 s(-1)) and quasi-static (0.0016 s(-1)) compression deformation behavior of a sintered Ti6Al4V powder compact was investigated. The compact was prepared using atomized spherical particles (100-200 mu m) and contained 38 +/- 1% porosity. The deformation sequences of the tested samples were further recorded by high speed camera and analyzed as a function of strain. The failure of the compact, which was found to be similar in the studied high strain rate and quasi-static strain rate testing regimes, occurs through particle decohesion along the surface of the two cones in a ductile (dimpled) mode consisting of void initiation and growth and by void coalescence in the interparticle bond region. The effect of strain rate was to increase the flow stress and compressive strength of the compact while the critical strain corresponding to the maximum stress was shown to be strain rate independent. (C) 2007 Elsevier B.V. All rights reserved. |
2007 |
Guden, M; Yueksel, S; Tasdemirci, A; Tanoglu, M COMPOSITE STRUCTURES, 81 (4), pp. 480-490, 2007, ISSN: 0263-8223. @article{ISI:000249256200002, title = {Effect of aluminum closed-cell foam filling on the quasi-static axial crush performance of glass fiber reinforced polyester composite and aluminum/composite hybrid tubes}, author = {M Guden and S Yueksel and A Tasdemirci and M Tanoglu}, doi = {10.1016/j.compstruct.2006.09.005}, issn = {0263-8223}, year = {2007}, date = {2007-12-01}, journal = {COMPOSITE STRUCTURES}, volume = {81}, number = {4}, pages = {480-490}, abstract = {The effect of Al closed-cell foam filling on the quasi-static crushing behavior of an E-glass woven fabric polyester composite tube and thin-walled Al/polyester composite hybrid tube was experimentally investigated. For comparison, empty Al, empty composite and empty hybrid tubes were also tested. Empty composite and empty hybrid tubes crushed predominantly in progressive crushing mode, without applying any triggering mechanism. Foam filling was found to be ineffective in increasing the crushing loads of the composite tubes over the sum of the crushing loads of empty composite tube and foam. However, foam filling stabilized the composite progressive crushing mode. In empty hybrid tubes, the deformation mode of the inner Al tube was found to be a more complex form of the diamond mode of deformation of empty Al tube, leading to higher crushing load values than the sum of the crushing load values of empty composite tube and empty metal tube. The foam filling of hybrid tubes however resulted in axial splitting of the outer composite tube due to the resistance imposed by the foam filler to Al tube inward folding and hence it was ineffective in increasing crushing load and SAE values over those of empty hybrid tubes. (C) 2006 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of Al closed-cell foam filling on the quasi-static crushing behavior of an E-glass woven fabric polyester composite tube and thin-walled Al/polyester composite hybrid tube was experimentally investigated. For comparison, empty Al, empty composite and empty hybrid tubes were also tested. Empty composite and empty hybrid tubes crushed predominantly in progressive crushing mode, without applying any triggering mechanism. Foam filling was found to be ineffective in increasing the crushing loads of the composite tubes over the sum of the crushing loads of empty composite tube and foam. However, foam filling stabilized the composite progressive crushing mode. In empty hybrid tubes, the deformation mode of the inner Al tube was found to be a more complex form of the diamond mode of deformation of empty Al tube, leading to higher crushing load values than the sum of the crushing load values of empty composite tube and empty metal tube. The foam filling of hybrid tubes however resulted in axial splitting of the outer composite tube due to the resistance imposed by the foam filler to Al tube inward folding and hence it was ineffective in increasing crushing load and SAE values over those of empty hybrid tubes. (C) 2006 Elsevier Ltd. All rights reserved. |
Tasdemirci, A; Hall, I W The effects of plastic deformation on stress wave propagation in multi-layer materials Journal Article INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, 34 (11), pp. 1797-1813, 2007, ISSN: 0734-743X. @article{ISI:000248761400006, title = {The effects of plastic deformation on stress wave propagation in multi-layer materials}, author = {A Tasdemirci and I W Hall}, doi = {10.1016/j.ijimpeng.2006.10.005}, issn = {0734-743X}, year = {2007}, date = {2007-11-01}, journal = {INTERNATIONAL JOURNAL OF IMPACT ENGINEERING}, volume = {34}, number = {11}, pages = {1797-1813}, abstract = {The behavior of a multi-layer material at high strain rate and the effect of plastic deformation on stress wave propagation were investigated by a combination of experimental and numerical techniques. Plastic deformation effects were studied in multi-layer materials consisting of ceramic, copper and aluminum subjected to large strains under high strain rate loading. First, stress wave propagation behavior for the monolithic metals was studied, and then extended to multilayer combinations of these metals with each other and with a ceramic layer. The axial stress distributions were found to be non-uniform in the elastic deformation range of the specimen. The degree of non-uniformity was much more pronounced in the multi-layer samples consisting of different materials. The presence of a ceramic layer increased the magnitudes of stress gradients at the interfaces. It was also found that a major effect of plastic deformation is a tendency to produce a more homogeneous stress distribution within the components. The implications of these observations for practical systems are discussed. (c) 2006 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The behavior of a multi-layer material at high strain rate and the effect of plastic deformation on stress wave propagation were investigated by a combination of experimental and numerical techniques. Plastic deformation effects were studied in multi-layer materials consisting of ceramic, copper and aluminum subjected to large strains under high strain rate loading. First, stress wave propagation behavior for the monolithic metals was studied, and then extended to multilayer combinations of these metals with each other and with a ceramic layer. The axial stress distributions were found to be non-uniform in the elastic deformation range of the specimen. The degree of non-uniformity was much more pronounced in the multi-layer samples consisting of different materials. The presence of a ceramic layer increased the magnitudes of stress gradients at the interfaces. It was also found that a major effect of plastic deformation is a tendency to produce a more homogeneous stress distribution within the components. The implications of these observations for practical systems are discussed. (c) 2006 Elsevier Ltd. All rights reserved. |
2006 |
Guden, M; Akil, O; Tasdemirci, A; Ciftcioglu, M; Hall, I W Effect of strain rate on the compressive mechanical behavior of a continuous alumina fiber reinforced ZE41A magnesium alloy based composite Journal Article MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 425 (1-2), pp. 145-155, 2006, ISSN: 0921-5093. @article{ISI:000241151500019, title = {Effect of strain rate on the compressive mechanical behavior of a continuous alumina fiber reinforced ZE41A magnesium alloy based composite}, author = {M Guden and O Akil and A Tasdemirci and M Ciftcioglu and I W Hall}, doi = {10.1016/j.msea.2006.03.028}, issn = {0921-5093}, year = {2006}, date = {2006-06-01}, journal = {MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, volume = {425}, number = {1-2}, pages = {145-155}, abstract = {The compressive mechanical response of an FP (TM) continuous fiber (35 vol.%) Mg composite has been determined in the transverse and longitudinal directions at quasi-static and high strain rates. It was found that the composite in the transverse direction exhibited strain rate sensitivity of the flow stress and maximum stress within the studied strain-rate range of 1.3 x 10(-4) to 1550 s(-1). The failure strain in this direction, however, decreased with increasing strain rate. Microscopic observations on the failed samples have shown that the composite failed by shear banding along the diagonal axis, 45 degrees to the loading axis. Twinning was observed in the deformed cross-sections of the samples particularly in and near the shear band region. The strain rate sensitivity of the fracture stress of the composite in transverse direction is attributed to the matrix strain rate sensitivity. In the longitudinal direction, the composite failed by kink formation at quasi-static strain rates, while kinking and splitting were observed at the high strain rates. The maximum stress in the longitudinal direction was, however, found to be strain rate insensitive within the strain rate regime of 1.3 x 10(-4) to 500 s(-1). In this direction, similar to transverse direction, twinning was observed in the highly deformed kink region. Several different reasons are proposed for the strain rate insensitive compressive strength in this direction. (c) 2006 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The compressive mechanical response of an FP (TM) continuous fiber (35 vol.%) Mg composite has been determined in the transverse and longitudinal directions at quasi-static and high strain rates. It was found that the composite in the transverse direction exhibited strain rate sensitivity of the flow stress and maximum stress within the studied strain-rate range of 1.3 x 10(-4) to 1550 s(-1). The failure strain in this direction, however, decreased with increasing strain rate. Microscopic observations on the failed samples have shown that the composite failed by shear banding along the diagonal axis, 45 degrees to the loading axis. Twinning was observed in the deformed cross-sections of the samples particularly in and near the shear band region. The strain rate sensitivity of the fracture stress of the composite in transverse direction is attributed to the matrix strain rate sensitivity. In the longitudinal direction, the composite failed by kink formation at quasi-static strain rates, while kinking and splitting were observed at the high strain rates. The maximum stress in the longitudinal direction was, however, found to be strain rate insensitive within the strain rate regime of 1.3 x 10(-4) to 500 s(-1). In this direction, similar to transverse direction, twinning was observed in the highly deformed kink region. Several different reasons are proposed for the strain rate insensitive compressive strength in this direction. (c) 2006 Elsevier B.V. All rights reserved. |
2004 |
Karamis, MB; Nair, F; Tasdemirci, A Analyses of metallurgical behavior of Al-SiCp composites after ballistic impacts Journal Article COMPOSITE STRUCTURES, 64 (2), pp. 219-226, 2004, ISSN: 0263-8223. @article{ISI:000223157500009, title = {Analyses of metallurgical behavior of Al-SiCp composites after ballistic impacts}, author = {MB Karamis and F Nair and A Tasdemirci}, doi = {10.1016/j.compstruct.2003.08.005}, issn = {0263-8223}, year = {2004}, date = {2004-05-01}, journal = {COMPOSITE STRUCTURES}, volume = {64}, number = {2}, pages = {219-226}, abstract = {The dynamic failure of SiC particle reinforced aluminum alloy composite; AA5083 is studied under ballistic impact loading. Tests were done with two different projectile types, AP (Army Piercing) 7.62 and 9 mm, and the hole surfaces created by the projectiles were investigated using both optical and scanning electron microscopy. Examination of the hole surface of the composite after dynamic failure showed microscopically ductile failure in the matrix following brittle cracking of the particles. The dynamic failure process involved both matrix and particle cracking. The high velocity of the projectile led to the melting of some surface layers because of the excess heat resulting from high velocity friction. Because of high friction, some melted regions had a porous structure due to shrinkage during rapid solidification caused by the high-speed projectile at the hole surface. The type of projectile strongly influenced the damage formation and the deformation type was also affected by the backing condition. (C) 2003 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The dynamic failure of SiC particle reinforced aluminum alloy composite; AA5083 is studied under ballistic impact loading. Tests were done with two different projectile types, AP (Army Piercing) 7.62 and 9 mm, and the hole surfaces created by the projectiles were investigated using both optical and scanning electron microscopy. Examination of the hole surface of the composite after dynamic failure showed microscopically ductile failure in the matrix following brittle cracking of the particles. The dynamic failure process involved both matrix and particle cracking. The high velocity of the projectile led to the melting of some surface layers because of the excess heat resulting from high velocity friction. Because of high friction, some melted regions had a porous structure due to shrinkage during rapid solidification caused by the high-speed projectile at the hole surface. The type of projectile strongly influenced the damage formation and the deformation type was also affected by the backing condition. (C) 2003 Elsevier Ltd. All rights reserved. |
Tasdemirci, A; Hall, IW; Gama, BA; Guiden, M Stress wave propagation effects in two- and three-layered composite materials Journal Article JOURNAL OF COMPOSITE MATERIALS, 38 (12), pp. 995-1009, 2004, ISSN: 0021-9983. @article{ISI:000222365200002, title = {Stress wave propagation effects in two- and three-layered composite materials}, author = {A Tasdemirci and IW Hall and BA Gama and M Guiden}, doi = {10.1177/0021998304040564}, issn = {0021-9983}, year = {2004}, date = {2004-01-01}, journal = {JOURNAL OF COMPOSITE MATERIALS}, volume = {38}, number = {12}, pages = {995-1009}, abstract = {Multilayer materials consisting of ceramic and glass/epoxy composites have been subjected to high strain rate compression testing using the Split Hopkinson Pressure Bar. The samples were extensively strain gaged so that dynamic data were generated directly from the samples during testing. Output data from the experiments were compared with numerical simulations of the same experiments and good agreement was noted. It was found that the stress distribution within samples was quite inhomogeneous and that stresses were highest in the region of the bar-sample interface. The presence of a rubber interlayer between the ceramic and glass/epoxy decreased the stress in both components but dramatically increased the degree of stress inhomogeneity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Multilayer materials consisting of ceramic and glass/epoxy composites have been subjected to high strain rate compression testing using the Split Hopkinson Pressure Bar. The samples were extensively strain gaged so that dynamic data were generated directly from the samples during testing. Output data from the experiments were compared with numerical simulations of the same experiments and good agreement was noted. It was found that the stress distribution within samples was quite inhomogeneous and that stresses were highest in the region of the bar-sample interface. The presence of a rubber interlayer between the ceramic and glass/epoxy decreased the stress in both components but dramatically increased the degree of stress inhomogeneity. |
Assist. Prof. Dr. Halil Tetik
Educational Background
B.Sc. İzmir Institute of Technology, Turkiye, Mechanical Engineering, 2013
M.Sc. İzmir Institute of Technology, Turkiye, Mechanical Engineering, 2016
Ph.D. Kansas State University, USA, Industrial Engineering, 2022
Research Interests
- Additive Manufacturing
- Advanced Manufacturing Techniques
- Functional Aerogels and Their Applications
- +90 232 750 6781
- +90 232 750 6701
- Mechanical Engineering Building (Z12)
Publications
Assist. Prof. Dr. Fatih Toksoy
Educational Background
B.Sc. Sakarya University, Turkey, Metallurgical and Materials Engineering, 2006
M.Sc. Rutgers, The State University of New Jersey, USA, Materials Science & Engineering, 2010
Ph.D. Rutgers, The State University of New Jersey, USA, Materials Science & Engineering, 2014
Research Interests
- Boride and Carbide Materials
- Powder Synthesis & Processing
- Materials Characterization
- Sintering
- Hard Ceramics
- +90 232 750 6794
- +90 232 750 6701
- Mechanical Engineering Building (Z09)
Publications
2017 |
Ma, Luoning; Xie, Kelvin Y; Toksoy, Muhammet F; Kuwelkar, Kanak; Haber, Richard A; Hemker, Kevin J The effect of Si on the microstructure and mechanical properties of spark plasma sintered boron carbide Journal Article MATERIALS CHARACTERIZATION, 134 , pp. 274-278, 2017, ISSN: 1044-5803. @article{ISI:000419416400031, title = {The effect of Si on the microstructure and mechanical properties of spark plasma sintered boron carbide}, author = {Luoning Ma and Kelvin Y Xie and Muhammet F Toksoy and Kanak Kuwelkar and Richard A Haber and Kevin J Hemker}, doi = {10.1016/j.matchar.2017.11.010}, issn = {1044-5803}, year = {2017}, date = {2017-12-01}, journal = {MATERIALS CHARACTERIZATION}, volume = {134}, pages = {274-278}, abstract = {Fully dense boron carbide discs were achieved by spark plasma sintering boron carbide powders with 10 wt% silicon. The silicon did not diffuse into boron carbide grains to produce a solid solution of Si-doped boron carbide; instead the silicon reacted with impurities in the starting powder to form beta-SiC and borosilicate glass. The resultant new phases facilitated densification of the multiphase ceramic through liquid phase-assisted sintering. The resultant material exhibits improved hardness (34.3 GPa Vikers hardness under 1 kg load) with toughness comparable to both Si-free and commercially available boron carbide.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Fully dense boron carbide discs were achieved by spark plasma sintering boron carbide powders with 10 wt% silicon. The silicon did not diffuse into boron carbide grains to produce a solid solution of Si-doped boron carbide; instead the silicon reacted with impurities in the starting powder to form beta-SiC and borosilicate glass. The resultant new phases facilitated densification of the multiphase ceramic through liquid phase-assisted sintering. The resultant material exhibits improved hardness (34.3 GPa Vikers hardness under 1 kg load) with toughness comparable to both Si-free and commercially available boron carbide. |
Toksoy, Muhammet Fatih; Rafaniello, William; Xie, Kelvin Yu; Ma, Luoning; Hemker, Kevin Jude; Haber, Richard Alan Densification and characterization of rapid carbothermal synthesized boron carbide Journal Article INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, 14 (3), pp. 443-453, 2017, ISSN: 1546-542X. @article{ISI:000404259000018, title = {Densification and characterization of rapid carbothermal synthesized boron carbide}, author = {Muhammet Fatih Toksoy and William Rafaniello and Kelvin Yu Xie and Luoning Ma and Kevin Jude Hemker and Richard Alan Haber}, doi = {10.1111/ijac.12654}, issn = {1546-542X}, year = {2017}, date = {2017-05-01}, journal = {INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY}, volume = {14}, number = {3}, pages = {443-453}, abstract = {Submicrometer boron carbide powders were synthesized using rapid carbothermal reduction (RCR) method. Synthesized boron carbide powders had smaller particle size, lower free carbon, and high density of twins compared to commercial samples. Powders were sintered using spark plasma sintering at different temperatures and dwell times to compare sintering behavior. Synthesized boron carbide powders reached >99% TD at lower temperature and shorter dwell times compared to commercial powders. Improved microhardness observed in the densified RCR samples was likely caused by the combination of higher purity, better stoichiometry control, finer grain size, and a higher density of twin boundaries.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Submicrometer boron carbide powders were synthesized using rapid carbothermal reduction (RCR) method. Synthesized boron carbide powders had smaller particle size, lower free carbon, and high density of twins compared to commercial samples. Powders were sintered using spark plasma sintering at different temperatures and dwell times to compare sintering behavior. Synthesized boron carbide powders reached >99% TD at lower temperature and shorter dwell times compared to commercial powders. Improved microhardness observed in the densified RCR samples was likely caused by the combination of higher purity, better stoichiometry control, finer grain size, and a higher density of twin boundaries. |
2016 |
An, Qi; III, William Goddard A; Xie, Kelvin Y; Sim, Gi-dong; Hemker, Kevin J; Munhollon, Tyler; Toksoy, Fatih M; Haber, Richard A Superstrength through Nanotwinning Journal Article NANO LETTERS, 16 (12), pp. 7573-7579, 2016, ISSN: 1530-6984. @article{ISI:000389963200038, title = {Superstrength through Nanotwinning}, author = {Qi An and William A Goddard III and Kelvin Y Xie and Gi-dong Sim and Kevin J Hemker and Tyler Munhollon and Fatih M Toksoy and Richard A Haber}, doi = {10.1021/acs.nanolett.6b03414}, issn = {1530-6984}, year = {2016}, date = {2016-12-01}, journal = {NANO LETTERS}, volume = {16}, number = {12}, pages = {7573-7579}, abstract = {The theoretical strength of a material is the minimum stress to deform or fracture the perfect single crystal material that has no defects. This theoretical strength is considered as an upper bound on the attainable strength for a real crystal. In contradiction to this expectation, we use quantum mechanics (QM) simulations to show that for the boron carbide (B4C) hard ceramic, this theoretical shear strength can be exceeded by 11% by imposing nanoscale twins. We also predict from QM that the indentation strength of nanotwinned B4C is 12% higher than that of the perfect crystal. Further, we validate this effect experimentally, showing that nanotwinned samples are harder by 2.3% than the twin-free counterpart of B4C. The origin of this strengthening mechanism is suppression of twin boundary (TB) slip within the nanotwins due to the directional nature of covalent bonds at the TB.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The theoretical strength of a material is the minimum stress to deform or fracture the perfect single crystal material that has no defects. This theoretical strength is considered as an upper bound on the attainable strength for a real crystal. In contradiction to this expectation, we use quantum mechanics (QM) simulations to show that for the boron carbide (B4C) hard ceramic, this theoretical shear strength can be exceeded by 11% by imposing nanoscale twins. We also predict from QM that the indentation strength of nanotwinned B4C is 12% higher than that of the perfect crystal. Further, we validate this effect experimentally, showing that nanotwinned samples are harder by 2.3% than the twin-free counterpart of B4C. The origin of this strengthening mechanism is suppression of twin boundary (TB) slip within the nanotwins due to the directional nature of covalent bonds at the TB. |
Assist. Prof. Dr. Kasım Toprak
Erasmus Co-Coordinator
Educational Background
B.Sc. Zonguldak Karaelmas University, Turkey, Mechanical Engineering, 2006
M.Sc. Rice University, USA, Mechanical Engineering, 2010
Ph.D. Rice University, USA, Mechanical Engineering, 2014
Research Interests
- Energy Efficiency
- Thermal Energy Storage Systems
- Heat Recovery
- HVAC Systems
- Renewable Energy
- Thermal Analysis of Nanomaterials
- Molecular Dynamics
- Thermophysical Properties
- Heat Transfer Enhancement
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Publications
2023 |
Toprak, Kasim; Bayazitoglu, Yildiz LONGITUDINAL THERMAL CONDUCTIVITY OF Cu-SWCNT CORE-SHELL NANOWIRE: MOLECULAR DYNAMICS SIMULATIONS Journal Article Heat Transfer Research, 54 (4), pp. 77 – 89, 2023. @article{Toprak202377, title = {LONGITUDINAL THERMAL CONDUCTIVITY OF Cu-SWCNT CORE-SHELL NANOWIRE: MOLECULAR DYNAMICS SIMULATIONS}, author = {Kasim Toprak and Yildiz Bayazitoglu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85159154476&doi=10.1615%2fHeatTransRes.2022044425&partnerID=40&md5=f5dc57c56947ec56a143fb7cf8346175}, doi = {10.1615/HeatTransRes.2022044425}, year = {2023}, date = {2023-01-01}, journal = {Heat Transfer Research}, volume = {54}, number = {4}, pages = {77 – 89}, abstract = {The phonon thermal conductivity of copper core and armchair single-walled carbon nanotube shell (Cu-SWCNT) coaxial nanostructure is presented using the non-equilibrium molecular dynamics (NEMD) simulations method. The study aims to investigate how the ultrathin Cu nanowire affects the thermal conductivity of Cu-SWCNT. The results have revealed that the thermal conductivity of Cu-SWCNT is more than two orders of magnitude higher than that of the Cu core with the contribution of the SWCNT shell. The influences of length, chirality, defect, and core filling on the thermal conductivity of Cu-SWCNT are studied using the two most used C-C potentials, the AIREBO and Tersoff potentials. The bare SWCNT and Cu-SWCNT simulation results revealed that the thermal conductivity using the AIREBO potential is lower than that of Tersoff. Although the thermal conductivity increases with the length of the coaxial tube, it decreases with the chirality and the filling ratio. Increasing the chirality of SWCNT and the Cu core-filling ratio can boost the core copper's contributions to the thermal conductivity, reducing the overall thermal conductivity. The lengths of the thermostat and buffer regions do not significantly affect the thermal conductivity. In addition, the vacancy concentration in heat flow regions effectively reduces thermal conductivity, whereas the vacancy in the thermostat regions does not have a significant effect. The thermal rectification factor defined as changing the imposed heat flux direction is up to 1.73%for the Cu-SWCNT and 2.63% for the SWCNT. © 2023 by Begell House, Inc.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The phonon thermal conductivity of copper core and armchair single-walled carbon nanotube shell (Cu-SWCNT) coaxial nanostructure is presented using the non-equilibrium molecular dynamics (NEMD) simulations method. The study aims to investigate how the ultrathin Cu nanowire affects the thermal conductivity of Cu-SWCNT. The results have revealed that the thermal conductivity of Cu-SWCNT is more than two orders of magnitude higher than that of the Cu core with the contribution of the SWCNT shell. The influences of length, chirality, defect, and core filling on the thermal conductivity of Cu-SWCNT are studied using the two most used C-C potentials, the AIREBO and Tersoff potentials. The bare SWCNT and Cu-SWCNT simulation results revealed that the thermal conductivity using the AIREBO potential is lower than that of Tersoff. Although the thermal conductivity increases with the length of the coaxial tube, it decreases with the chirality and the filling ratio. Increasing the chirality of SWCNT and the Cu core-filling ratio can boost the core copper's contributions to the thermal conductivity, reducing the overall thermal conductivity. The lengths of the thermostat and buffer regions do not significantly affect the thermal conductivity. In addition, the vacancy concentration in heat flow regions effectively reduces thermal conductivity, whereas the vacancy in the thermostat regions does not have a significant effect. The thermal rectification factor defined as changing the imposed heat flux direction is up to 1.73%for the Cu-SWCNT and 2.63% for the SWCNT. © 2023 by Begell House, Inc. |
2020 |
Toprak, Kasim; Ouedraogo, Kiswendsida Elias Performance Analysis of Thermal Storage Assisted Cooling Tower with Night Cooling Journal Article JOURNAL OF POLYTECHNIC-POLITEKNIK DERGISI, 23 (4), pp. 1027-1035, 2020, ISSN: 1302-0900. @article{ISI:000581901200009, title = {Performance Analysis of Thermal Storage Assisted Cooling Tower with Night Cooling}, author = {Kasim Toprak and Kiswendsida Elias Ouedraogo}, issn = {1302-0900}, year = {2020}, date = {2020-12-01}, journal = {JOURNAL OF POLYTECHNIC-POLITEKNIK DERGISI}, volume = {23}, number = {4}, pages = {1027-1035}, abstract = {As global warming and water scarcity issues continue to grow, it is essential to increase resources efficiency for air conditioners and power plants. In order to increase the efficiency, the systems need to be modified to take the advantages of the low night temperature and thermal storage tanks. In this study, the low night temperature and thermal storage tanks effects on the cooling tower is studied using TRNSYS. Using a chiller operating from 8:00 to 16:00 as a case study, hot water from the condenser is partially stored on daytime and cooled slowly during the night. The storage tank volume is optimized by considering two big tanks and five small tanks. The results show that night cooling reduces cooling water temperature by 5.8 degrees C or 21.8% while the cooling efficiency is increased by 36%. The thermal storage tanks enable to have the low continuous flow rate and help to reduce the fan power by 67.1%. On the storage side, compared to two tanks system, the tanks volume is reduced by 16.5% when 5 tanks are used. In theory this reduction can go up to 50% by increasing the number of tanks and reducing their individual size.}, keywords = {}, pubstate = {published}, tppubtype = {article} } As global warming and water scarcity issues continue to grow, it is essential to increase resources efficiency for air conditioners and power plants. In order to increase the efficiency, the systems need to be modified to take the advantages of the low night temperature and thermal storage tanks. In this study, the low night temperature and thermal storage tanks effects on the cooling tower is studied using TRNSYS. Using a chiller operating from 8:00 to 16:00 as a case study, hot water from the condenser is partially stored on daytime and cooled slowly during the night. The storage tank volume is optimized by considering two big tanks and five small tanks. The results show that night cooling reduces cooling water temperature by 5.8 degrees C or 21.8% while the cooling efficiency is increased by 36%. The thermal storage tanks enable to have the low continuous flow rate and help to reduce the fan power by 67.1%. On the storage side, compared to two tanks system, the tanks volume is reduced by 16.5% when 5 tanks are used. In theory this reduction can go up to 50% by increasing the number of tanks and reducing their individual size. |
Toprak, K; Ouedraogo, K E Effect of storage tanks on solar-powered absorption chiller cooling system performance Journal Article International Journal of Energy Research, 44 (6), pp. 4366-4375, 2020. @article{Toprak20204366, title = {Effect of storage tanks on solar-powered absorption chiller cooling system performance}, author = {K Toprak and K E Ouedraogo}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85079718680&doi=10.1002%2fer.5210&partnerID=40&md5=aa6c4b8eb29c64ec8849ffdd43934cc6}, doi = {10.1002/er.5210}, year = {2020}, date = {2020-01-01}, journal = {International Journal of Energy Research}, volume = {44}, number = {6}, pages = {4366-4375}, abstract = {Thermal storage, low power tariff at night, and low nocturnal temperature can be used in synergy to reduce the cooling costs of the solar-powered absorption chiller cooling systems. This study aims to reduce the required cooling capacity of an absorption chiller (ACH) powered by a solar parabolic trough collector (PTC) and a backup fuel boiler by integrating thermal storage tanks. The thermal performance of the system is simulated for a building that is cooled for 14 h/day. The system uses 1000 m2 PTC with 1020 kW ACH. Chilled water storage (CHWS) and cooling water storage (CWS) effects on the system performance for different operation hours per day of the ACH under Izmir (Turkey) and Phoenix (USA) weather conditions are analyzed. When the ACH operates 14 h/day as the load for both systems and both locations, the variations of the solar collector efficiency and the cooling load to heat input ratio remain less than 4% after the modifications. From the addition of CHWS to the reference system, a parametric study consisting of changing the ACH operation hours per day shows that the required cooling capacity of the ACH can be reduced to 34%. The capacity factor of the ACH is improved from its reference value of 41% up to 96%. © 2020 John Wiley & Sons Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } Thermal storage, low power tariff at night, and low nocturnal temperature can be used in synergy to reduce the cooling costs of the solar-powered absorption chiller cooling systems. This study aims to reduce the required cooling capacity of an absorption chiller (ACH) powered by a solar parabolic trough collector (PTC) and a backup fuel boiler by integrating thermal storage tanks. The thermal performance of the system is simulated for a building that is cooled for 14 h/day. The system uses 1000 m2 PTC with 1020 kW ACH. Chilled water storage (CHWS) and cooling water storage (CWS) effects on the system performance for different operation hours per day of the ACH under Izmir (Turkey) and Phoenix (USA) weather conditions are analyzed. When the ACH operates 14 h/day as the load for both systems and both locations, the variations of the solar collector efficiency and the cooling load to heat input ratio remain less than 4% after the modifications. From the addition of CHWS to the reference system, a parametric study consisting of changing the ACH operation hours per day shows that the required cooling capacity of the ACH can be reduced to 34%. The capacity factor of the ACH is improved from its reference value of 41% up to 96%. © 2020 John Wiley & Sons Ltd |
2014 |
Toprak, Kasim; Bayazitoglu, Yildiz Interfacial thermal resistance of Cu-SWCNT nanowire in water Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 79 , pp. 584-588, 2014, ISSN: 0017-9310. @article{ISI:000343781900056, title = {Interfacial thermal resistance of Cu-SWCNT nanowire in water}, author = {Kasim Toprak and Yildiz Bayazitoglu}, doi = {10.1016/j.ijheatmasstransfer.2014.08.024}, issn = {0017-9310}, year = {2014}, date = {2014-12-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {79}, pages = {584-588}, abstract = {The conduction along the radial direction of CuNW-SWCNT nanocomposite surrounded with water is examined. Due to its simplicity and adaptability, a simple point-charge water model is implemented. Using the Nose-Hoover thermostat, the copper core is kept at a uniform temperature as a heat source, and a circular edge layer of water is kept at a lower temperature as a heat sink in order to impose a radial temperature distribution. The thermal boundary resistance was predicted as 0.1732 x 10(8) m(2) K/W at the interface of CuNW-water, 3.16 x 10(-8) m(2) K/W at the interface of SWCNT-water, and 0.743 x 10(-8) m(2) K/W at the interface of (CuNW-SWCNT)-water. (C) 2014 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The conduction along the radial direction of CuNW-SWCNT nanocomposite surrounded with water is examined. Due to its simplicity and adaptability, a simple point-charge water model is implemented. Using the Nose-Hoover thermostat, the copper core is kept at a uniform temperature as a heat source, and a circular edge layer of water is kept at a lower temperature as a heat sink in order to impose a radial temperature distribution. The thermal boundary resistance was predicted as 0.1732 x 10(8) m(2) K/W at the interface of CuNW-water, 3.16 x 10(-8) m(2) K/W at the interface of SWCNT-water, and 0.743 x 10(-8) m(2) K/W at the interface of (CuNW-SWCNT)-water. (C) 2014 Elsevier Ltd. All rights reserved. |
2013 |
Toprak, K; Bayazitoglu, Y Numerical modeling of a CNT-Cu coaxial nanowire in a vacuum to determine the thermal conductivity Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 61 , pp. 172-175, 2013, ISSN: 0017-9310. @article{ISI:000318260200018, title = {Numerical modeling of a CNT-Cu coaxial nanowire in a vacuum to determine the thermal conductivity}, author = {K Toprak and Y Bayazitoglu}, doi = {10.1016/j.ijheatmasstransfer.2013.01.082}, issn = {0017-9310}, year = {2013}, date = {2013-06-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {61}, pages = {172-175}, abstract = {A molecular dynamics simulation is created to predict the thermal conductivity of a (7,7) single wall carbon nanotube filled with a copper nanowire for lengths ranging from 9.957 nm to 63.091 nm. In the simulations, a temperature difference is created using Nose-Hoover thermostats at the two ends with 320 K and 280 K. The thermal conductivity of the carbon nanotube-copper nanowire nanostructure is calculated to be 24% higher than that of a corresponding pure single wall carbon nanotube and estimated to be 40% lower than that of a pure copper nanowire. (C) 2013 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A molecular dynamics simulation is created to predict the thermal conductivity of a (7,7) single wall carbon nanotube filled with a copper nanowire for lengths ranging from 9.957 nm to 63.091 nm. In the simulations, a temperature difference is created using Nose-Hoover thermostats at the two ends with 320 K and 280 K. The thermal conductivity of the carbon nanotube-copper nanowire nanostructure is calculated to be 24% higher than that of a corresponding pure single wall carbon nanotube and estimated to be 40% lower than that of a pure copper nanowire. (C) 2013 Elsevier Ltd. All rights reserved. |
Assist. Prof. Dr. Benay Uzer Yılmaz
Vice Chair
Educational Background
B.Sc. Koç University, Turkey, Mechanical Engineering, 2013
Ph.D. Koç University, Turkey, Mechanical Engineering, 2017
Research Interests
- Mechanical and Microstructural Design of Metallic Implants
- Additive Manufacturing of Metallic Materials
- Biomimetic Architectures for Functional Biomaterials
- Designing Cell-implant Interface
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- Mechanical Engineering Building (110)
- GCRIS Profile
Publications
2021 |
Uzer-Yilmaz, B In vitro contact guidance of glioblastoma cells on metallic biomaterials Journal Article Journal of Materials Science: Materials in Medicine, 32 (4), 2021. @article{Uzer-Yilmaz2021, title = {In vitro contact guidance of glioblastoma cells on metallic biomaterials}, author = {B Uzer-Yilmaz}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85103594796&doi=10.1007%2fs10856-021-06503-z&partnerID=40&md5=3df5859593f38e768004318b90d166df}, doi = {10.1007/s10856-021-06503-z}, year = {2021}, date = {2021-01-01}, journal = {Journal of Materials Science: Materials in Medicine}, volume = {32}, number = {4}, abstract = {Cancer cells’ ability to sense their microenvironment and interpret these signals for the regulation of directional adhesion plays crucial role in cancer invasion. Furthermore, given the established influence of mechanical properties of the substrate on cell behavior, the present study aims to elucidate the relationship between the contact guidance of glioblastoma cell (GBM) and evolution of microstructural and mechanical properties of the implants. SEM analyses of the specimens subjected to 5 and 25% of plastic strains revealed directional groove-like structures in micro and submicro-sizes, respectively. Microscale cytoplasmic protrusions of GBMs showed elongation favored along the grooves created via deformation markings on 5% deformed sample. Whereas filopodia, submicro-sized protrusions facilitating cancer invasion, elongated in the direction perpendicular to the deformation markings on the 25% deformed sample, which might lead to easy and rapid retraction. Furthermore, number of cell attachment was 1.7-fold greater on 25% deformed sample, where these cells showed the greatest cellular aspect ratio. The directional attachment and contact guidance of GBMs was reported for the first time on metallic implants and these findings propose the idea that GBM response could be regulated by controlling the spacing of the deformation markings, namely the degree of plastic deformation. These findings can be applied in the design of cell-instructive implants for therapeutic purposes to suppress cancer dissemination. [Figure not available: see fulltext.] © 2021, The Author(s).}, keywords = {}, pubstate = {published}, tppubtype = {article} } Cancer cells’ ability to sense their microenvironment and interpret these signals for the regulation of directional adhesion plays crucial role in cancer invasion. Furthermore, given the established influence of mechanical properties of the substrate on cell behavior, the present study aims to elucidate the relationship between the contact guidance of glioblastoma cell (GBM) and evolution of microstructural and mechanical properties of the implants. SEM analyses of the specimens subjected to 5 and 25% of plastic strains revealed directional groove-like structures in micro and submicro-sizes, respectively. Microscale cytoplasmic protrusions of GBMs showed elongation favored along the grooves created via deformation markings on 5% deformed sample. Whereas filopodia, submicro-sized protrusions facilitating cancer invasion, elongated in the direction perpendicular to the deformation markings on the 25% deformed sample, which might lead to easy and rapid retraction. Furthermore, number of cell attachment was 1.7-fold greater on 25% deformed sample, where these cells showed the greatest cellular aspect ratio. The directional attachment and contact guidance of GBMs was reported for the first time on metallic implants and these findings propose the idea that GBM response could be regulated by controlling the spacing of the deformation markings, namely the degree of plastic deformation. These findings can be applied in the design of cell-instructive implants for therapeutic purposes to suppress cancer dissemination. [Figure not available: see fulltext.] © 2021, The Author(s). |
2020 |
Uzer, B Frontiers in Materials, 7 , 2020. @article{Uzer2020, title = {Modulating the Surface Properties of Metallic Implants and the Response of Breast Cancer Cells by Surface Relief Induced via Bulk Plastic Deformation}, author = {B Uzer}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85085159761&doi=10.3389%2ffmats.2020.00099&partnerID=40&md5=74ced050c4b670609a1e8bf00f28b1b7}, doi = {10.3389/fmats.2020.00099}, year = {2020}, date = {2020-01-01}, journal = {Frontiers in Materials}, volume = {7}, abstract = {Micro/nanoscale textured surfaces have presented promising tissue–implant integration via increasing surface roughness, energy, and wettability. Recent studies indicate that surface texture imparted on the metallic implants via surface relief induced with simple bulk plastic deformation methods (e.g., tension or compression tests) does result in enhanced cell response. Considering these recent findings, this study presents a thorough investigation of the effects of surface relief on surface properties of implants and cell adhesion. Experiments are conducted on the samples subjected to interrupted tensile tests up to the plastic strains of 5, 15, 25, and 35%. Main findings from these experiments suggest that, as the plastic deformation level increases up to 35% from the undeformed (control) level, (1) average surface roughness (Ra) increases from 17.58 to 595.29 nm; (2) water contact angle decreases from 84.28 to 58.07°; (3) surface free energy (SFE) increases from 36.06 to 48.89 mJ/m2; and (4) breast cancer cells show 2.4-fold increased number of attachment. Increased surface roughness indicates the distorted topography via surface relief and leads to increased wettability, consistent with Wenzel’s theory. The higher levels of SFE observed were related to high-energy regions provided via activation of strengthening mechanisms, which increased in volume fraction concomitant with plastic deformation. Eventually, the displayed improvements in surface properties have increased the number of breast cancer cell attachments. These findings indicate that surface relief induced upon plastic deformation processes could be utilized in the design of implants for therapeutic or diagnostic purposes through capturing breast cancer cells on the material surface. © Copyright © 2020 Uzer.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Micro/nanoscale textured surfaces have presented promising tissue–implant integration via increasing surface roughness, energy, and wettability. Recent studies indicate that surface texture imparted on the metallic implants via surface relief induced with simple bulk plastic deformation methods (e.g., tension or compression tests) does result in enhanced cell response. Considering these recent findings, this study presents a thorough investigation of the effects of surface relief on surface properties of implants and cell adhesion. Experiments are conducted on the samples subjected to interrupted tensile tests up to the plastic strains of 5, 15, 25, and 35%. Main findings from these experiments suggest that, as the plastic deformation level increases up to 35% from the undeformed (control) level, (1) average surface roughness (Ra) increases from 17.58 to 595.29 nm; (2) water contact angle decreases from 84.28 to 58.07°; (3) surface free energy (SFE) increases from 36.06 to 48.89 mJ/m2; and (4) breast cancer cells show 2.4-fold increased number of attachment. Increased surface roughness indicates the distorted topography via surface relief and leads to increased wettability, consistent with Wenzel’s theory. The higher levels of SFE observed were related to high-energy regions provided via activation of strengthening mechanisms, which increased in volume fraction concomitant with plastic deformation. Eventually, the displayed improvements in surface properties have increased the number of breast cancer cell attachments. These findings indicate that surface relief induced upon plastic deformation processes could be utilized in the design of implants for therapeutic or diagnostic purposes through capturing breast cancer cells on the material surface. © Copyright © 2020 Uzer. |
2018 |
Uzer, B; Picak, S; Liu, J; Jozaghi, T; Canadinc, D; Karaman, I; Chumlyakov, Y I; Kireeva, I On the mechanical response and microstructure evolution of NiCoCr single crystalline medium entropy alloys Journal Article Materials Research Letters, 6 (8), pp. 442-449, 2018. @article{Uzer2018442, title = {On the mechanical response and microstructure evolution of NiCoCr single crystalline medium entropy alloys}, author = {B Uzer and S Picak and J Liu and T Jozaghi and D Canadinc and I Karaman and Y I Chumlyakov and I Kireeva}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85048308085&doi=10.1080%2f21663831.2018.1478331&partnerID=40&md5=fdf9a8d03d121110bc0c015c525b5373}, doi = {10.1080/21663831.2018.1478331}, year = {2018}, date = {2018-01-01}, journal = {Materials Research Letters}, volume = {6}, number = {8}, pages = {442-449}, abstract = {Unusual strain hardening response and ductility of NiCoCr equiatomic alloy were investigated through microstructural analysis of [111], [110] and [123] single crystals deformed under tension. Nano-twinning prevailed at, as early as, 4% strain along the [110] orientation, providing a steady work hardening, and thereby a significant ductility. While single slip dominated in the [123] orientation at the early stages of deformation, multiple slip and nanotwinning was prominent in the [111] orientation. Significant dislocation storage capability and resistance to necking due to nanotwinning provided unprecedented ductility to NiCoCr medium entropy alloys, making it superior than quinary variants, and conventional low and medium stacking fault energy steels. IMPACT STATEMENT: A comparison of the current results on the ternary medium entropy alloy single crystals and those previously reported on the quinary and quaternary fcc equiatomic alloys demonstrates that a higher configurational entropy does not necessarily warrant improved mechanical properties. © 2018, © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Unusual strain hardening response and ductility of NiCoCr equiatomic alloy were investigated through microstructural analysis of [111], [110] and [123] single crystals deformed under tension. Nano-twinning prevailed at, as early as, 4% strain along the [110] orientation, providing a steady work hardening, and thereby a significant ductility. While single slip dominated in the [123] orientation at the early stages of deformation, multiple slip and nanotwinning was prominent in the [111] orientation. Significant dislocation storage capability and resistance to necking due to nanotwinning provided unprecedented ductility to NiCoCr medium entropy alloys, making it superior than quinary variants, and conventional low and medium stacking fault energy steels. IMPACT STATEMENT: A comparison of the current results on the ternary medium entropy alloy single crystals and those previously reported on the quinary and quaternary fcc equiatomic alloys demonstrates that a higher configurational entropy does not necessarily warrant improved mechanical properties. © 2018, © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. |
Canadinc, D; Uzer, B; Elmadagli, M; Guner, F Nanotwin Formation in High-Manganese Austenitic Steels Under Explosive Shock Loading Journal Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 49 (4), pp. 1026-1030, 2018. @article{Canadinc20181026, title = {Nanotwin Formation in High-Manganese Austenitic Steels Under Explosive Shock Loading}, author = {D Canadinc and B Uzer and M Elmadagli and F Guner}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85041919869&doi=10.1007%2fs11661-018-4510-x&partnerID=40&md5=a874b8da4c563aa0e96e5e788ad81251}, doi = {10.1007/s11661-018-4510-x}, year = {2018}, date = {2018-01-01}, journal = {Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science}, volume = {49}, number = {4}, pages = {1026-1030}, abstract = {The micro-deformation mechanisms active in a high-manganese austenitic steel were investigated upon explosive shock loading. Single system of nanotwins forming within primary twins were shown to govern the deformation despite the elevated temperatures attained during testing. The benefits of nanotwin formation for potential armor materials were demonstrated. © 2018, The Minerals, Metals & Materials Society and ASM International.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The micro-deformation mechanisms active in a high-manganese austenitic steel were investigated upon explosive shock loading. Single system of nanotwins forming within primary twins were shown to govern the deformation despite the elevated temperatures attained during testing. The benefits of nanotwin formation for potential armor materials were demonstrated. © 2018, The Minerals, Metals & Materials Society and ASM International. |
Uzer, B; Canadinc, D The effect of plastic deformation on the cell viability and adhesion behavior in metallic implant materials Journal Article Ceramic Transactions, 261 , pp. 187-196, 2018. @article{Uzer2018187, title = {The effect of plastic deformation on the cell viability and adhesion behavior in metallic implant materials}, author = {B Uzer and D Canadinc}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85055448117&doi=10.1002%2f9781119423829.ch16&partnerID=40&md5=3e385fa138796826206feff61faaf2f2}, doi = {10.1002/9781119423829.ch16}, year = {2018}, date = {2018-01-01}, journal = {Ceramic Transactions}, volume = {261}, pages = {187-196}, abstract = {The adhesion and spreading behavior, and viability of the brain tumor and fibroblast cells were analyzed on the austenitic 316L stainless steel samples, which were deformed to different strains, promoting varying degrees of plastic deformation activities. Surface characterization and microscopy analyses showed that increasing plastic deformation significantly altered surface topography by the formation of surface extrusions and grooves, which increased the surface roughness. In addition, twinning and slip mechanisms created regions with high surface energy which catalyzed the adhesion of tCM proteins and formation of focal contacts. Specifically, tumor cells exhibited a greater viability and adhesion behavior on the samples deformed to the largest plastic strains concomitant with the filopodial extensions, which showed the higher affinity of these cells on the deformed samples. Conversely, fibroblast cells did not exhibit enhanced cell response on the deformed samples, which can stem from the surface roughness, size of the cells or the failure of the adhesion of tCM molecules expressed by the fibroblast cells. The current results show that surface and microstructural properties of the implants can be tailored by the activation of plastic deformation mechanisms to obtain ideal materials specific to body location and treatment. © 2017 The American Ceramic Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The adhesion and spreading behavior, and viability of the brain tumor and fibroblast cells were analyzed on the austenitic 316L stainless steel samples, which were deformed to different strains, promoting varying degrees of plastic deformation activities. Surface characterization and microscopy analyses showed that increasing plastic deformation significantly altered surface topography by the formation of surface extrusions and grooves, which increased the surface roughness. In addition, twinning and slip mechanisms created regions with high surface energy which catalyzed the adhesion of tCM proteins and formation of focal contacts. Specifically, tumor cells exhibited a greater viability and adhesion behavior on the samples deformed to the largest plastic strains concomitant with the filopodial extensions, which showed the higher affinity of these cells on the deformed samples. Conversely, fibroblast cells did not exhibit enhanced cell response on the deformed samples, which can stem from the surface roughness, size of the cells or the failure of the adhesion of tCM molecules expressed by the fibroblast cells. The current results show that surface and microstructural properties of the implants can be tailored by the activation of plastic deformation mechanisms to obtain ideal materials specific to body location and treatment. © 2017 The American Ceramic Society. |
2017 |
Uzer, B; Birer, O; Canadinc, D Investigation of the Dissolution–Reformation Cycle of the Passive Oxide Layer on NiTi Orthodontic Archwires Journal Article Shape Memory and Superelasticity, 3 (3), pp. 264-273, 2017. @article{Uzer2017264, title = {Investigation of the Dissolution–Reformation Cycle of the Passive Oxide Layer on NiTi Orthodontic Archwires}, author = {B Uzer and O Birer and D Canadinc}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85070886170&doi=10.1007%2fs40830-017-0114-3&partnerID=40&md5=c157896a2009c27ea7f0b8b4c8b5c33c}, doi = {10.1007/s40830-017-0114-3}, year = {2017}, date = {2017-01-01}, journal = {Shape Memory and Superelasticity}, volume = {3}, number = {3}, pages = {264-273}, abstract = {Dissolution–reformation cycle of the passive oxide layer on the nickel–titanium (NiTi) orthodontic archwires was investigated, which has recently been recognized as one of the key parameters dictating the biocompatibility of archwires. Specifically, commercially available NiTi orthodontic archwires were immersed in artificial saliva solutions of different pH values (2.3, 3.3, and 4.3) for four different immersion periods: 1, 7, 14, and 30 days. Characterization of the virgin and tested samples revealed that the titanium oxide layer on the NiTi archwire surfaces exhibit a dissolution–reformation cycle within the first 14 days of the immersion period: the largest amount of Ni ion release occurred within the first week of immersion, while it significantly decreased during the reformation period from day 7 to day 14. Furthermore, the oxide layer reformation was catalyzed on the grooves within the peaks and valleys due to relatively larger surface energy of these regions, which eventually decreased the surface roughness significantly within the reformation period. Overall, the current results clearly demonstrate that the analyses of dissolution–reformation cycle of the oxide layer in orthodontic archwires, surface roughness, and ion release behavior constitute utmost importance in order to ensure both the highest degree of biocompatibility and an efficient medical treatment. © 2017, ASM International.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Dissolution–reformation cycle of the passive oxide layer on the nickel–titanium (NiTi) orthodontic archwires was investigated, which has recently been recognized as one of the key parameters dictating the biocompatibility of archwires. Specifically, commercially available NiTi orthodontic archwires were immersed in artificial saliva solutions of different pH values (2.3, 3.3, and 4.3) for four different immersion periods: 1, 7, 14, and 30 days. Characterization of the virgin and tested samples revealed that the titanium oxide layer on the NiTi archwire surfaces exhibit a dissolution–reformation cycle within the first 14 days of the immersion period: the largest amount of Ni ion release occurred within the first week of immersion, while it significantly decreased during the reformation period from day 7 to day 14. Furthermore, the oxide layer reformation was catalyzed on the grooves within the peaks and valleys due to relatively larger surface energy of these regions, which eventually decreased the surface roughness significantly within the reformation period. Overall, the current results clearly demonstrate that the analyses of dissolution–reformation cycle of the oxide layer in orthodontic archwires, surface roughness, and ion release behavior constitute utmost importance in order to ensure both the highest degree of biocompatibility and an efficient medical treatment. © 2017, ASM International. |
2016 |
Uzer, B; Toker, S M; Cingoz, A; Bagci-Onder, T; Gerstein, G; Maier, H J; Canadinc, D An exploration of plastic deformation dependence of cell viability and adhesion in metallic implant materials Journal Article Journal of the Mechanical Behavior of Biomedical Materials, 60 , pp. 177-186, 2016. @article{Uzer2016177, title = {An exploration of plastic deformation dependence of cell viability and adhesion in metallic implant materials}, author = {B Uzer and S M Toker and A Cingoz and T Bagci-Onder and G Gerstein and H J Maier and D Canadinc}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84955118639&doi=10.1016%2fj.jmbbm.2016.01.001&partnerID=40&md5=93dcdcf6f5350d917e906984b75d9693}, doi = {10.1016/j.jmbbm.2016.01.001}, year = {2016}, date = {2016-01-01}, journal = {Journal of the Mechanical Behavior of Biomedical Materials}, volume = {60}, pages = {177-186}, abstract = {The relationship between cell viability and adhesion behavior, and micro-deformation mechanisms was investigated on austenitic 316L stainless steel samples, which were subjected to different amounts of plastic strains (5%, 15%, 25%, 35% and 60%) to promote a variety in the slip and twin activities in the microstructure. Confocal laser scanning microscopy (CLSM) and field emission scanning electron microscopy (FESEM) revealed that cells most favored the samples with the largest plastic deformation, such that they spread more and formed significant filopodial extensions. Specifically, brain tumor cells seeded on the 35% deformed samples exhibited the best adhesion performance, where a significant slip activity was prevalent, accompanied by considerable slip-twin interactions. Furthermore, maximum viability was exhibited by the cells seeded on the 60% deformed samples, which were particularly designed in a specific geometry that could endure greater strain values. Overall, the current findings open a new venue for the production of metallic implants with enhanced biocompatibility, such that the adhesion and viability of the cells surrounding an implant can be optimized by tailoring the surface relief of the material, which is dictated by the micro-deformation mechanism activities facilitated by plastic deformation imposed by machining. © 2016 Elsevier Ltd.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The relationship between cell viability and adhesion behavior, and micro-deformation mechanisms was investigated on austenitic 316L stainless steel samples, which were subjected to different amounts of plastic strains (5%, 15%, 25%, 35% and 60%) to promote a variety in the slip and twin activities in the microstructure. Confocal laser scanning microscopy (CLSM) and field emission scanning electron microscopy (FESEM) revealed that cells most favored the samples with the largest plastic deformation, such that they spread more and formed significant filopodial extensions. Specifically, brain tumor cells seeded on the 35% deformed samples exhibited the best adhesion performance, where a significant slip activity was prevalent, accompanied by considerable slip-twin interactions. Furthermore, maximum viability was exhibited by the cells seeded on the 60% deformed samples, which were particularly designed in a specific geometry that could endure greater strain values. Overall, the current findings open a new venue for the production of metallic implants with enhanced biocompatibility, such that the adhesion and viability of the cells surrounding an implant can be optimized by tailoring the surface relief of the material, which is dictated by the micro-deformation mechanism activities facilitated by plastic deformation imposed by machining. © 2016 Elsevier Ltd. |
Retired Faculty Members
Prof. Dr. Gürbüz Atagündüz
Founder Chair
M.Sc. Technology University Braunschweig, Germany, 1961
Ph.D. Technology University Stuttgart, Germany, 1965
Prof. Dr. Rasim Alizade
B.Sc. Kharkov Railway Transport Engineers Institute, Russia, Mechanical Engineering, 1960
M.Sc. Kharkov Railway Transport Engineers Institute, Russia, Mechanical Engineering, 1965
Ph.D. Institue Mashino vedenie AN USSR, Moskow, Mechanical Engineering, 1968
Prof. Dr. Zafer İlken
B.Sc. Middle East Technical University, Turkey, Mechanical Engineering, 1982
M.Sc. Dokuz Eylül University, Turkey, Mechanical Engineering, 1987
Ph.D. Middle East Technical University, Turkey, Mechanical Engineering, 1982
Prof. Dr. M. Barış Özerdem
B.Sc. Dokuz Eylül University, Turkey, Mechanical Engineering, 1982
M.Sc. Dokuz Eylül University, Turkey, Mechanical Engineering, 1985
Ph.D. Dokuz Eylül University, Turkey, Mechanical Engineering, 1991
Prof. Dr. Macit Toksoy
B.Sc. İstanbul Technical University, Turkey, Mechanical Engineering, 1972
M.Sc. İstanbul Technical University, Turkey, Mechanical Engineerging, 1972
Ph.D. Ege University, Turkey, Mechcanical Engineering, 1976
Prof. Dr. Bülent Yardımoğlu
B.Sc. Dokuz Eylül University, Turkey, Mechanical Engineering, 1985
M.Sc. Dokuz Eylül University, Turkey, Mechanical Engineering, 1987
Ph.D. Dokuz Eylül University, Turkey, Mechanical Engineering, 1992