Study On Mechanical Behavior Of Hydrogels Based On Open Source Finite Element Code

This study mainly focuses on the field theory of polymeric gels based on nonequilibrium thermodynamics,and a modification by considering a recently proposed scaling law between the modulus and polymer volume fraction during swelling and deswelling.A series of interesting phenomena of hydrogels and gel structures have been studied by implementing the field theory on an open source finite element platform,FEniCS.This thesis first reviews the non-equilibrium thermodynamics of gel swelling and the derivation of the governing equation for the continuum field theory,which was used to implement a finite element code on FEniCS.Secondly,a recently proposed scaling law between the elastic modulus and the polymer volume fraction of swelling and deswelling hydrogels is extended into a free energy function,and then implemented into the finite element code.The open source finite element platform,FEniCS,was applied to study the swelling and deformation of polymeric gels.Several examples are used to verify the numerical code and to demonstrate the applications of the model:(1)swelling and deswelling process by applying a model consistent with the scaling law;(2)the wrinkling instability in a double-layer gel structure;(3)the kinetics-induced peculiar bending phenomenon of a 3D-printed hydrogel strip with asymmetric section.FEniCS is suitable for multi-physics multi-field coupled problems.Major advantages of FEniCS include the support of high-performance parallel computation and a variety of built-in solvers.The open-source platform and user-friendly language allow researchers to focus more on the physical problems,and are very suitable for research as well as teaching.Over the past decade,a large number of researchers have focused on improving the mechanical performance of hydrogels,and developing applications in biomedical,flexible electronics,sensors and actuators.The theoretical studies on the behaviors of hydrogels and physics-based models and numerical tools are essential to the development of these applications.Scientists are committed to improving the mechanical properties of hydrogels,designing and manufacturing more practical structures,introducing some new functions,and to promoting engineering applications of hydrogels by combining the advanced technologies from different fields.