A constitutive model for amorphous shape memory polymers based on thermodynamics with internal state variables

Shape memory polymers (SMPs) are a class of smart materials which can recover a large pre-deformed shape in response to external stimulus. A thermoviscoelastic finite deformation constitutive model incorporated with structural and stress relaxation to capture the material behavior in the vicinity of the glass transition is developed for thermally activated amorphous SMPs in the paper. The incorporation of the Adam-Gibbs model for structure relaxation and the modified Eying model for viscous flow into a thermoviscoelastic finite deformation modeling framework is the main feature of the model. Differing from the traditional phenomenological fictive temperature modeling approach, an internal state variable modeling approach developed recently based on thermodynamics is used in the model. Besides, the temperature dependence of the model parameters is studied in the research. Comparisons between the simulation results and the experimental data show good agreement. Furthermore, the predictability of the model is examined by a parametric study and the results also demonstrate the validity of the model.