Influence of mechanical properties and loading conditions on the recovery of shape memory polymers

Abstract

This work presented a parameter study to investigate the influence of material properties and loading conditions on the recovery performance of amorphous shape memory polymers using a recently developed thermoviscoelastic model. The model incorporated the time-dependent effects of both structural relaxation - using a nonlinear Adam-Gibbs model-and viscoelasticity. The model can predict well the unconstrained strain recovery response and stress evolution during constrained recovery process. The materials properties and the loading parameters, including the cooling rate, the annealing time, and the heating rate, were varied one by one to compare the effects on the start and end temperatures and recovery time of the unconstrained recovery response and on the stress hysteresis of the constrained recovery response. The results confirmed experimental observations that unconstrained strain recovery response was mostly influenced by viscoelasticity, while the constrained recovery response resulted from the interaction of many different mechanisms, including structural and stress relaxation, thermal expansion, the modulus of rubbery and glass state. The results also showed that the cooling and heating rates had the largest influence on both recovery responses.