Doctor of Philosophy
Mechanical and Materials Engineering
Featured by biocompatibility, high compliance and capacity in sustaining large deformation, dielectric elastomers (DEs) and hydrogels have gained extensive research popularity for their potential applications in the fields of soft robots, biomimetics, tissue engineering, drug delivery, and energy harvesting. The design of such soft and smart material-based devices and structures requires deep understanding and accurate simulation of their constitutive behaviors, which is challenged by their nonlinear material properties due to unique microstructures and multi-physics coupling. Meanwhile, in different application contexts, those structures are also susceptible to different failure modes, imposing further challenges in simulating and predicting their performance. To fulfill the potential applications and maintain the structural integrity of these soft and smart material-based devices, it is essential to develop accurate and robust numerical models to simulate their complex deformation behaviors and investigate the potential failures.
As the first step, a general finite element (FE) framework is established to simulate the nonlinear viscoelastic behaviors of elastomers by developing a user-defined material (UMAT) subroutine in Abaqus, which is capable of adopting most constitutive models for hyperelasticity and thermodynamics evolution laws for viscoelastic materials. Combining the developed FE framework and the nonlinear field theory for electromechanical coupling, a highly customized user-element subroutine (UEL) in Abaqus is developed to numerically investigate various failure modes of DEs including electric breakdown, buckling, wrinkling and crumpling. The effects of nonlinear material viscosity and loading conditions on different failure modes are identified to further unveil the failure mechanisms of DEs. The mechanical rupture of such polymeric materials are also simulated by incorporating the phase field modeling (PFM) into the proposed FE framework. For the first time, the driving force to the fracture of viscoelastic elastomers is identified, and the micro-mechanism of the material viscosity is further elucidated with the consideration of polymer chain breakage based on polymer dynamics. Furthermore, the dynamic breaking-healing kinetics of self-healing hydrogels is numerically investigated based on a generalized recursive integration algorithm, which is expected to act as a general avenue to numerically simulate the time/history-dependent constitutive behaviors of polymeric materials.
To conclude, this thesis aims at developing a FE framework to provide a general approach for deformation simulation and failure analysis of polymeric materials. This numerical framework can further function as a universal platform to accurately predict the performance of soft and smart material-based devices with the capability of implementing different multi-physics coupling mechanisms and time/rate-dependent constitutive models.
Summary for Lay Audience
Different from hard materials like metals, polymeric materials such as elastomers and hydrogels are featured with softness and capabilities of sustaining large deformation. Some of those materials are also responsive to external stimuli, including electric field, pH, magnetic field, and etc. Those properties make them attractive for some trending applications in the fields of soft robots, biomimetics, tissue engineering, drug delivery, and energy harvesting. To fulfill the potential applications and maintain the structural integrity of these soft and smart material-based devices, it is essential to have a better understanding on their deformation behaviors. Meanwhile, polymeric materials are susceptible to various failure modes in their service, which will affect the originally designed functionality of the devices. With these considerations, there is an urgent need to establish a computational framework to accurately and efficiently evaluate the performance of polymeric materials under different loading conditions. In this thesis, the finite element method is adopted to provide a computational platform to predict the performance of polymeric materials. The complex deformation behaviors are simulated considering their unique microstructures. On this basis, some common failure behaviors are also investigated. This proposed computational framework will help to facilitate novel design and optimization of the soft and smart material-based devices and structures in engineering applications.
Feng, Heng, "Numerical modeling and simulation on deformation and failure behaviors of polymeric materials" (2023). Electronic Thesis and Dissertation Repository. 9458.