Modeling the Responses of Light-activated Shape Memory Polymers
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The aim of this study is to model the macroscopic response of light-activated shape memory polymers (LASMPs) subject to mechanical loadings and exposure to light at certain wavelengths and frequencies. When exposed to external stimuli of mechanical, thermal, photochemical and other origins, polymers undergo microstructural changes, e.g., scission, crosslinking, crystallization, etc. These microstructural changes affect the macroscopic performance of the polymers. In this study, in order to incorporate the effect of microstructural changes on the macroscopic response of light-activated shape memory polymers, we formulate constitutive models based on the notion that the natural configuration of the body under consideration evolves during its response. The theoretical framework appeals to a multi-network approach consisting of two microstructural networks, which are the original network and the new network formed owing to a light activation. Firstly two different nonlinear elastic models are considered based on photo-tunable molecular crosslinks (PMC) LASMPs. The first model assumes the two networks are isotropic. The second model takes into account the directional preference owing to the anisotropy of the second network that is formed. Several classical boundary value problems involving homogeneous and inhomogeneous deformations are studied. We also investigate two nonlinear constitutive relations and different loading modes. The results highlight the differences in the responses when isotropic and anisotropic models are considered. Furthermore, with a view toward incorporating two different mechanisms and determining the effect of the viscoelasticity of the polymers, a single integral model is adopted to incorporate the viscoelastic response in the original and second networks. We study the response of viscoelastic light-activated shape memory polymers subject to uniaxial and biaxial tension. Parametric studies are carried out to obtain a better understanding of the effect of quantities such as relaxation time and the ratio of the relaxation modulus to the instantaneous modulus. Finally, the model is used to describe the stress relaxation behavior of photo-induced network rearrangement (PNR) LASMPs reported in the literature. In order to solve boundary value problems with complex geometries and boundary conditions, the constitutive models based on the multi-network configuration are implemented in user material subroutines (UMAT) within ABAQUS finite element analysis. Finite element is then used to simulate and investigate the response of the structures integrated with LASMPs, such as folding in flexible structures to mimic morphing wings and shape changes in lattice structures.
Subjectlight-activated shape memory polymers
multiple natural configurations
finite element implementation
Yuan, Zhi (2017). Modeling the Responses of Light-activated Shape Memory Polymers. Doctoral dissertation, Texas A & M University. Available electronically from