A finite deformation constitutive model for thermally activated amorphous shape memory polymers

A thermoviscoelastic-thermoviscoplastic finite deformation constitutive model incorporating structural and stress relaxation is developed for thermally activated amorphous shape memory polymers. In this study, the nonlinear Adam-Gibbs model is used to describe the structural relaxation. Furthermore, a modified Argon scalar equation is proposed for the viscous flow as the temperature crosses T-g. In addition, as the Arruda-Boyce eight-chain model captures the hyperelastic behavior of the material up to large stretches, it is used here to represent the partial material behavior of shape memory polymers. To further feature the macroscopic post-yield strain softening behavior, the phenomenological evolution rule is also implemented. Comparisons of numerical simulations and the thermomechanical experiments conducted on an ether-based polyurethane shape memory polymer show acceptable agreement.