Modeling the mechanical behavior of crystallizable shape memory polymers: incorporating temperature-dependent viscoelasticity

Abstract

Shape memory polymers (SMPs) are soft active materials that have an ability to retain a temporary shape, and revert back to their original shape when triggered by a suitable stimulus, typically an increase in temperature. These materials are finding wide use in a variety of fields such as biomedical and aerospace engineering; hence it is important to model their mechanical behavior. Crystallizable shape memory polymers (CSMPs) is an important subclass of SMPs, and their temporary shape is fixed by a crystalline phase, while return to the original shape is due to the melting of this crystalline phase. In our earlier work, we have studied the mechanical behavior of CSMPs within a mechanical setting by considering the original amorphous network above the recovery temperature as a hyperelastic material. In this article, we extend our earlier work to incorporate the temperature-dependent viscoelasticity into the developed constitutive model to study the mechanical behavior of CSMPs. The viscoelastic behavior of the polymers at high temperature is simulated through a rate type model. Furthermore, the model of the semi-crystalline polymer after the onset of crystallization is developed based on the mixture theory and the theory of “multiple natural configurations”. In addition, we have applied the model to a specific boundary value problem, namely uniaxial extension. The shape memory cycles of the CSMPs under different stretch rates have been studied. The results are consistent with what has been observed in experiments.