umesh gandhi - Academia.edu (original) (raw)
Papers by umesh gandhi
ASME 2022 Conference on Smart Materials, Adaptive Structures and Intelligent Systems
We develop a finite element methodology to characterize the effects of silicone coating on Shape ... more We develop a finite element methodology to characterize the effects of silicone coating on Shape Memory Alloy (SMA) actuators during continuous actuation cycles. Slow cooling rates of thermally actuated SMA actuators have long been a hurdle for their widespread adoption. The use of a thermally conductive silicone coating provides a potential solution that improves cooling rates without much impact on the actuator thermal performance under single actuation. However, the effects of the coating on the thermal performance under cyclic actuation is unexplored. To verify the finite element model results, various thicknesses between 0.2 mm to 2.5 mm of the coating material were applied to 0.5 mm diameter SMA wires using a specially fabricated coating machine. The results of finite element models were first compared with and calibrated against experimentally measured thermal performance for single actuation cycle. Next, the actuation responses of the numerical models of these coated SMA wir...
IEEE/ASME Transactions on Mechatronics
ASME 2019 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2019
Inflatable structures provide significant volume and weight savings for future space and soft rob... more Inflatable structures provide significant volume and weight savings for future space and soft robotic applications. Structural health monitoring (SHM) of these structures is essential to ensuring safe operation, providing early warnings of damage, and measuring structural changes over time. In this paper, we propose the design of a single flexible strain sensor for distributed monitoring of an inflatable tube, in particular, the detection and localization of a kink should that occur. Several commercially available conductive materials, including 3D-printing filaments, conductive paint, and conductive fabrics are explored for their strain-sensing performance, where the resistance change under uniaxial tension is measured, and the corresponding gauge factor (GF) is characterized. Flexible strain sensors are then fabricated and integrated with an inflatable structure fabric using screen-printing or 3D-printing techniques, depending on the nature of the raw conductive material. Among th...
AIAA SCITECH 2022 Forum, 2022
Electroactive Polymer Actuators and Devices (EAPAD) XXI, 2019
Soft robotics research has been motivated in part by the versatility and functionality of human m... more Soft robotics research has been motivated in part by the versatility and functionality of human muscle. Researchers have tried to mimic the speed and performance of human muscle by using soft fluid actuators; however, these actuators are often slow and bulky. Research conducted in the use of dielectric elastomers has proven to be promising. These dielectric elastomers can produce large strains using high voltage electrical input. However, the development of these dielectric elastomer actuators has been inhibited due to their susceptibility to dielectric breakdown and electrical aging. One recent technology that can solve these issues and advance the field of soft actuators, is that of the hydraulically amplified self-healing electrostatic (HASEL) actuator. Such actuators are comprised of a liquid dielectric enclosed in an elastomer shell with electrodes on either side of the shell. Incorporating a liquid dielectric dramatically reduces the impact of dielectric breakdown on the performance of HASEL actuators and allows for hydraulically-coupled modes of actuation. However, the voltages that are required to operate these actuators are still challenging for commercial applications. Our work uses a simulation-driven approach to determine design parameters for donut HASEL actuators that provide a high actuation strain at a reduced pull-in voltage. We outline a modeling approach that is comprised of calibrating the properties of a multiphysics finite element model using actual HASEL actuator experimental data. The model is validated using a donut-shape HASEL actuator from literature. The model is then applied to determine the optimal electrode size and fluid dielectric permittivity for achieving a low operating voltage. This simulation-driven design assists in the fabrication of soft actuators with potential application to a variety of industries.
AIAA SCITECH 2022 Forum, 2022
Advanced Engineering Materials, 2021
Discontinuous Fiber-Reinforced Composites, 2020
Discontinuous Fiber-Reinforced Composites, 2020
Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation, and Control of Adaptive Systems; Integrated System Design and Implementation, 2018
Stretchable strain sensors with large strain range, high sensitivity, and excellent reliability a... more Stretchable strain sensors with large strain range, high sensitivity, and excellent reliability are of great interest for applications in soft robotics, wearable devices, and structure-monitoring systems. Unlike conventional template lithography-based approaches, 3D-printing can be used to fabricate complex devices in a simple and cost-effective manner. In this paper, we report 3D-printed stretchable strain sensors that embeds a flexible conductive composite material in a hyper-plastic substrate. Three commercially available conductive filaments are explored, among which the conductive thermoplastic polyurethane (ETPU) shows the highest sensitivity (gauge factor of 5), with a working strain range of 0%–20%. The ETPU strain sensor exhibits an interesting behavior where the conductivity increases with the strain. In addition, an experiment for measuring the wind speed is conducted inside a wind tunnel, where the ETPU sensor shows sensitivity to the wind speed beyond 5.6 m/s.
Discontinuous Fiber-Reinforced Composites, 2020
Preface examples covering compression molding, injection molding, hybrid structures, and joining.... more Preface examples covering compression molding, injection molding, hybrid structures, and joining. The case studies of practical examples take the readers through all the steps necessary to arrive at a full structural model of a component and compare the predictive models to actual measurements. Some of the work presented here started in 2012 when the Toyota Research Institute North America (TRINA) began to develop know-how to design lightweight components for automotive applications using discontinuous fiber-reinforced composites. Realizing many fundamental technical challenges, TRINA approached Professor Tim Osswald from the Polymer Engineering Center (PEC) at the University of Wisconsin-Madison for help. What followed was an outstanding collaboration between industry and academia, resulting in significant improvements in the know-how to design using discontinuous fiber-reinforced composites, which is the essence of this book. The authors would like to acknowledge the invaluable help of many during the preparation of this manuscript. We would like to thank Dr. Huan-Chang Tseng, Dr. Jim Hsu, and Dr. Anthony Yang of CoreTech System for contributing the chapter on process simulation (Chapter 7) and other members of the CoreTech team for their continuous support in many other areas. We are grateful to Tobias Mattner for his outstanding job in not only drawing the figures, but also making excellent suggestions on how to present the information more clearly. We would like to offer special thanks to Prof. Noboru Kikuchi, president of Toyota Central R & D Lab, for the unceasing encouragement to write this book. Takeshi Sekito, Hidetoshi Okada, Masaya Miura, and Yoshinori Suga of Toyota Motor Company for serving as sounding boards and for their technical input. Prof. Uday Vaidya and his group at the University of Tennessee are thanked for their help with the processing technology. We are grateful to Dr. Vlastimil Kunk, from Oakridge National Laboratory, for the help in the characterization of compression molded parts. Dr. Suresh Shah of the Society of Plastics Engineers is thanked for sharing many practical insights and suggestions, and Dr. Danil Prokhorov from TRINA for his continuous cheering and support. Dr. Roger Assaker and his team at e-Xstream Engineering are thanked for their valuable assistance with multiscale modeling. Thanks are due to Dr. Mark Smith and Dr. Julia Diaz Luque of Carl Hanser Verlag for their valuable expertise in editing this book, as well as Jörg Strohbach for his support throughout this project. Above all, the authors would like to thank their families for their continued support of their work and their input throughout the writing of this book.
Chopped fibers reinforced polymer composites are considered for use in many automotive applicatio... more Chopped fibers reinforced polymer composites are considered for use in many automotive applications. Commonly used structural design software have difficulties predicting manufacturing parameters and constituent properties of short or long fiber reinforced polymer composites to meet mandated design requirements. A computational method is introduced for the virtual simulation of performance of chopped fibers in polymer composites. This new approach did lead to the development of a specialized Multi-Scale Material Characterization of composite system comprising of: a) chopped fiber based on Eshelby and Mori Tanaka failure theory, b) micro-macro mechanics, and damage failure theory, c) tensor stiffness averaging technique; and d) optimizer as part of the durability analysis software GENOA. The material model established in MCQ-Chopped is used in FEA interface with GENOA Multi Scale Progressive Failure Analysis (MS-PFA). The crush modeling of composite crushed tube was test validated us...
INTER-NOISE and NOISE-CON Congress and Conference Proceedings, 2021
Cone disc springs exhibit quasi-zero stiffness behavior that is useful in isolating objects from ... more Cone disc springs exhibit quasi-zero stiffness behavior that is useful in isolating objects from low frequency vibrations. However, the stroke of a single disc spring is too low for most applications, and springs are stacked to increase the displacement. A method to contain the isolator stack then becomes critical for practical uses. Many challenges in developing these containment methods have been identified and can be collectively described as how to appropriately contain the stack without affecting isolation performance. In this work, three designs are considered: a retaining ring design, tube and shaft design, and zero poisson ratio sleeve design. Disc spring stacks with containment method are built, and load-deflection curves are measured and compared with standalone stacks. Under quasi-static compression testing, each containment method has minimal effect on the standalone stack load-deflection curve. However, significant differences in isolation performance are observed in vi...
Journal of Composites Science, 2018
Its high-specific strength and stiffness with lower cost make discontinuous fiber-reinforced ther... more Its high-specific strength and stiffness with lower cost make discontinuous fiber-reinforced thermoplastic (FRT) materials an ideal choice for lightweight applications in the automotive industry. Compression molding is one of the preferred manufacturing processes for such materials as it offers the opportunity to maintain a longer fiber length and higher volume production. In the past, we have demonstrated that compression molding of FRT in bulk form can be simulated by treating melt flow as a continuum using the conservation of mass and momentum equations. However, the compression molding of such materials in sheet form using a similar approach does not work well. The assumption of melt flow as a continuum does not hold for such deformation processes. To address this challenge, we have developed a novel simulation approach. First, the draping of the sheet was simulated as a structural deformation using the explicit finite element approach. Next, the draped shape was compressed using fluid mechanics equations. The proposed method was verified by building a physical part and comparing the predicted fiber orientation and warpage measurements performed on the physical parts. The developed method and tools are expected to help in expediting the development of FRT parts, which will help achieve lightweight targets in the automotive industry.
Composites Part A: Applied Science and Manufacturing, 2018
There has been great interest in using fiber-reinforced polymer composites to develop lightweight... more There has been great interest in using fiber-reinforced polymer composites to develop lightweight components for automotive applications. Compression molding of carbon fiber (CF) reinforced thermoplastic is one of the preferred processes, as it offers the opportunity to maintain a longer fiber length and higher volume production. We have developed a unique computer aided engineering (CAE) method by utilizing viscoelastic structural analysis to accurately predict the warpage behavior of fiber-reinforced thermoplastic material under the compression molding process from a bulk charge format. A prototype structure with complex geometry was designed and manufactured for validation purposes. The fiber orientation and warpage results from both the CAE and actual part were compared to verify the accuracy of the CAE method. Additional studies related to the charge footprint effect were also conducted for the compression molding process on the same materials. The developed method and tools are expected to help in expediting the development of lightweight carbon fiber-reinforced thermoplastic parts.
ASME 2022 Conference on Smart Materials, Adaptive Structures and Intelligent Systems
We develop a finite element methodology to characterize the effects of silicone coating on Shape ... more We develop a finite element methodology to characterize the effects of silicone coating on Shape Memory Alloy (SMA) actuators during continuous actuation cycles. Slow cooling rates of thermally actuated SMA actuators have long been a hurdle for their widespread adoption. The use of a thermally conductive silicone coating provides a potential solution that improves cooling rates without much impact on the actuator thermal performance under single actuation. However, the effects of the coating on the thermal performance under cyclic actuation is unexplored. To verify the finite element model results, various thicknesses between 0.2 mm to 2.5 mm of the coating material were applied to 0.5 mm diameter SMA wires using a specially fabricated coating machine. The results of finite element models were first compared with and calibrated against experimentally measured thermal performance for single actuation cycle. Next, the actuation responses of the numerical models of these coated SMA wir...
IEEE/ASME Transactions on Mechatronics
ASME 2019 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2019
Inflatable structures provide significant volume and weight savings for future space and soft rob... more Inflatable structures provide significant volume and weight savings for future space and soft robotic applications. Structural health monitoring (SHM) of these structures is essential to ensuring safe operation, providing early warnings of damage, and measuring structural changes over time. In this paper, we propose the design of a single flexible strain sensor for distributed monitoring of an inflatable tube, in particular, the detection and localization of a kink should that occur. Several commercially available conductive materials, including 3D-printing filaments, conductive paint, and conductive fabrics are explored for their strain-sensing performance, where the resistance change under uniaxial tension is measured, and the corresponding gauge factor (GF) is characterized. Flexible strain sensors are then fabricated and integrated with an inflatable structure fabric using screen-printing or 3D-printing techniques, depending on the nature of the raw conductive material. Among th...
AIAA SCITECH 2022 Forum, 2022
Electroactive Polymer Actuators and Devices (EAPAD) XXI, 2019
Soft robotics research has been motivated in part by the versatility and functionality of human m... more Soft robotics research has been motivated in part by the versatility and functionality of human muscle. Researchers have tried to mimic the speed and performance of human muscle by using soft fluid actuators; however, these actuators are often slow and bulky. Research conducted in the use of dielectric elastomers has proven to be promising. These dielectric elastomers can produce large strains using high voltage electrical input. However, the development of these dielectric elastomer actuators has been inhibited due to their susceptibility to dielectric breakdown and electrical aging. One recent technology that can solve these issues and advance the field of soft actuators, is that of the hydraulically amplified self-healing electrostatic (HASEL) actuator. Such actuators are comprised of a liquid dielectric enclosed in an elastomer shell with electrodes on either side of the shell. Incorporating a liquid dielectric dramatically reduces the impact of dielectric breakdown on the performance of HASEL actuators and allows for hydraulically-coupled modes of actuation. However, the voltages that are required to operate these actuators are still challenging for commercial applications. Our work uses a simulation-driven approach to determine design parameters for donut HASEL actuators that provide a high actuation strain at a reduced pull-in voltage. We outline a modeling approach that is comprised of calibrating the properties of a multiphysics finite element model using actual HASEL actuator experimental data. The model is validated using a donut-shape HASEL actuator from literature. The model is then applied to determine the optimal electrode size and fluid dielectric permittivity for achieving a low operating voltage. This simulation-driven design assists in the fabrication of soft actuators with potential application to a variety of industries.
AIAA SCITECH 2022 Forum, 2022
Advanced Engineering Materials, 2021
Discontinuous Fiber-Reinforced Composites, 2020
Discontinuous Fiber-Reinforced Composites, 2020
Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation, and Control of Adaptive Systems; Integrated System Design and Implementation, 2018
Stretchable strain sensors with large strain range, high sensitivity, and excellent reliability a... more Stretchable strain sensors with large strain range, high sensitivity, and excellent reliability are of great interest for applications in soft robotics, wearable devices, and structure-monitoring systems. Unlike conventional template lithography-based approaches, 3D-printing can be used to fabricate complex devices in a simple and cost-effective manner. In this paper, we report 3D-printed stretchable strain sensors that embeds a flexible conductive composite material in a hyper-plastic substrate. Three commercially available conductive filaments are explored, among which the conductive thermoplastic polyurethane (ETPU) shows the highest sensitivity (gauge factor of 5), with a working strain range of 0%–20%. The ETPU strain sensor exhibits an interesting behavior where the conductivity increases with the strain. In addition, an experiment for measuring the wind speed is conducted inside a wind tunnel, where the ETPU sensor shows sensitivity to the wind speed beyond 5.6 m/s.
Discontinuous Fiber-Reinforced Composites, 2020
Preface examples covering compression molding, injection molding, hybrid structures, and joining.... more Preface examples covering compression molding, injection molding, hybrid structures, and joining. The case studies of practical examples take the readers through all the steps necessary to arrive at a full structural model of a component and compare the predictive models to actual measurements. Some of the work presented here started in 2012 when the Toyota Research Institute North America (TRINA) began to develop know-how to design lightweight components for automotive applications using discontinuous fiber-reinforced composites. Realizing many fundamental technical challenges, TRINA approached Professor Tim Osswald from the Polymer Engineering Center (PEC) at the University of Wisconsin-Madison for help. What followed was an outstanding collaboration between industry and academia, resulting in significant improvements in the know-how to design using discontinuous fiber-reinforced composites, which is the essence of this book. The authors would like to acknowledge the invaluable help of many during the preparation of this manuscript. We would like to thank Dr. Huan-Chang Tseng, Dr. Jim Hsu, and Dr. Anthony Yang of CoreTech System for contributing the chapter on process simulation (Chapter 7) and other members of the CoreTech team for their continuous support in many other areas. We are grateful to Tobias Mattner for his outstanding job in not only drawing the figures, but also making excellent suggestions on how to present the information more clearly. We would like to offer special thanks to Prof. Noboru Kikuchi, president of Toyota Central R & D Lab, for the unceasing encouragement to write this book. Takeshi Sekito, Hidetoshi Okada, Masaya Miura, and Yoshinori Suga of Toyota Motor Company for serving as sounding boards and for their technical input. Prof. Uday Vaidya and his group at the University of Tennessee are thanked for their help with the processing technology. We are grateful to Dr. Vlastimil Kunk, from Oakridge National Laboratory, for the help in the characterization of compression molded parts. Dr. Suresh Shah of the Society of Plastics Engineers is thanked for sharing many practical insights and suggestions, and Dr. Danil Prokhorov from TRINA for his continuous cheering and support. Dr. Roger Assaker and his team at e-Xstream Engineering are thanked for their valuable assistance with multiscale modeling. Thanks are due to Dr. Mark Smith and Dr. Julia Diaz Luque of Carl Hanser Verlag for their valuable expertise in editing this book, as well as Jörg Strohbach for his support throughout this project. Above all, the authors would like to thank their families for their continued support of their work and their input throughout the writing of this book.
Chopped fibers reinforced polymer composites are considered for use in many automotive applicatio... more Chopped fibers reinforced polymer composites are considered for use in many automotive applications. Commonly used structural design software have difficulties predicting manufacturing parameters and constituent properties of short or long fiber reinforced polymer composites to meet mandated design requirements. A computational method is introduced for the virtual simulation of performance of chopped fibers in polymer composites. This new approach did lead to the development of a specialized Multi-Scale Material Characterization of composite system comprising of: a) chopped fiber based on Eshelby and Mori Tanaka failure theory, b) micro-macro mechanics, and damage failure theory, c) tensor stiffness averaging technique; and d) optimizer as part of the durability analysis software GENOA. The material model established in MCQ-Chopped is used in FEA interface with GENOA Multi Scale Progressive Failure Analysis (MS-PFA). The crush modeling of composite crushed tube was test validated us...
INTER-NOISE and NOISE-CON Congress and Conference Proceedings, 2021
Cone disc springs exhibit quasi-zero stiffness behavior that is useful in isolating objects from ... more Cone disc springs exhibit quasi-zero stiffness behavior that is useful in isolating objects from low frequency vibrations. However, the stroke of a single disc spring is too low for most applications, and springs are stacked to increase the displacement. A method to contain the isolator stack then becomes critical for practical uses. Many challenges in developing these containment methods have been identified and can be collectively described as how to appropriately contain the stack without affecting isolation performance. In this work, three designs are considered: a retaining ring design, tube and shaft design, and zero poisson ratio sleeve design. Disc spring stacks with containment method are built, and load-deflection curves are measured and compared with standalone stacks. Under quasi-static compression testing, each containment method has minimal effect on the standalone stack load-deflection curve. However, significant differences in isolation performance are observed in vi...
Journal of Composites Science, 2018
Its high-specific strength and stiffness with lower cost make discontinuous fiber-reinforced ther... more Its high-specific strength and stiffness with lower cost make discontinuous fiber-reinforced thermoplastic (FRT) materials an ideal choice for lightweight applications in the automotive industry. Compression molding is one of the preferred manufacturing processes for such materials as it offers the opportunity to maintain a longer fiber length and higher volume production. In the past, we have demonstrated that compression molding of FRT in bulk form can be simulated by treating melt flow as a continuum using the conservation of mass and momentum equations. However, the compression molding of such materials in sheet form using a similar approach does not work well. The assumption of melt flow as a continuum does not hold for such deformation processes. To address this challenge, we have developed a novel simulation approach. First, the draping of the sheet was simulated as a structural deformation using the explicit finite element approach. Next, the draped shape was compressed using fluid mechanics equations. The proposed method was verified by building a physical part and comparing the predicted fiber orientation and warpage measurements performed on the physical parts. The developed method and tools are expected to help in expediting the development of FRT parts, which will help achieve lightweight targets in the automotive industry.
Composites Part A: Applied Science and Manufacturing, 2018
There has been great interest in using fiber-reinforced polymer composites to develop lightweight... more There has been great interest in using fiber-reinforced polymer composites to develop lightweight components for automotive applications. Compression molding of carbon fiber (CF) reinforced thermoplastic is one of the preferred processes, as it offers the opportunity to maintain a longer fiber length and higher volume production. We have developed a unique computer aided engineering (CAE) method by utilizing viscoelastic structural analysis to accurately predict the warpage behavior of fiber-reinforced thermoplastic material under the compression molding process from a bulk charge format. A prototype structure with complex geometry was designed and manufactured for validation purposes. The fiber orientation and warpage results from both the CAE and actual part were compared to verify the accuracy of the CAE method. Additional studies related to the charge footprint effect were also conducted for the compression molding process on the same materials. The developed method and tools are expected to help in expediting the development of lightweight carbon fiber-reinforced thermoplastic parts.