A thermoviscoelastic finite deformation constitutive model based on dual relaxation mechanisms for amorphous shape memory polymers

This paper proposes a new thermoviscoelastic finite deformation model incorporating dual relaxation mechanisms to predict the complete thermo-mechanical response of amorphous shape memory polymers. The model is underpinned by the detailed microscopic molecular mechanism and effectively reflects the current understanding of the glass transition phenomenon. Novel evolution rules are obtained from the model to characterize the viscous flow, and a new theory named an internal stress model is introduced and combined with the dual relaxation mechanisms to capture the stress recovery. The rationality of the constitutive model is verified as the theoretical results agree well with the experimental data. Moreover, the constitutive model is further simplified to facilitate engineering applications, and it can roughly capture the characteristics of shape memory polymers.