A thermoviscoelastic model incorporated with uncoupled structural and stress relaxation mechanisms for amorphous shape memory polymers

In this paper, a thermoviscoelastic constitutive model incorporating uncoupled structure and stress relaxation is proposed to capture the material behavior for thermally induced amorphous shape memory polymers. The leading particulars of this model is that the structure and stress relaxation mechanisms are not coupled but connected by the internal state variable which describes the degree of volume departure from equilibrium. Based on the internal variable, a simplified KAHR model is developed for the structure relaxation, and a new relaxation time model is proposed to describe the temperature and structure dependence of the characteristic stress relaxation. Moreover, the Eying model is modified by the new stress relaxation model to study the stress-activated viscous flow. Finally, the thermoviscoelastic constitutive model is applied to investigate the shape recovery behavior and the yielding and post-yielding behavior, and the simulation results show good agreement with the experimental data.