Modeling deformation induced anisotropy of light-activated shape memory polymers

Light-activated shape memory polymers (LASMPs) are a new generation of active materials that undergo phase transformations upon light irradiation at different wavelength and intensities. This type of material shows much promise in its use in adaptive and shape reconfiguration structures for applications in biomedical and aerospace engineering. LASMPs exhibit nonlinear viscoelastic behavior due to the rearrangements in the macromolecular networks of the polymers when they are mechanically deformed. The deformed configuration can have a different symmetry group than the original undeformed configuration. In this study we assume that the body has multiple natural configurations in order to incorporate the microstructural changes in the viscoelastic polymers due to mechanical loading and light irradiation. We also account for the directional preference of the new network that is formed due to stretching the polymers. In this paper, the constitutive models developed for elastic and viscoelastic LASMPs in our previous work (Yuan and Zhi, 2017; Zhi and Yuan, 2017) are modified to include the changes in the symmetry group of the new network due to mechanically stretching the polymer. The models are implemented within ABAQUS finite element (FE) through the use of user-material subroutines (UMAT).