A viscoelastic constitutive model for shape memory polymers based on multiplicative decompositions of the deformation gradient

Shape memory polymers (SMPs) are a class of polymeric smart materials that have the capacity to return from a deformed state (impermanent shape) to their original state (permanent shape) by temperature stimulus. In this work, we propose a novel phase-transition-based viscoelastic model including the time factor for shape memory polymers (SMPs), which has a clearer physical significance. To describe the phase transition phenomenon of SMPs, our new model defines different constitutive structures for above and below transformation temperature separately. As the proposed viscoelastic model is based on multiplicative thermoviscoelasticity, it can not only be used for different types of SMP materials, but also can be used to treat large strain problems. To validate the model's availability and show the model's capability of reproducing the shape memory effect (SME), two testing examples are predicted with this new constitutive model. The prediction results of the simulation are in good agreement with the available experimental results.