Thermo-mechanical behavior prediction of shape memory polymer based on the multiplicative decomposition of the deformation gradient

During the service of shape memory polymer (SMP), the thermal-mechanical cycle is a necessary process. Meanwhile, the influence of the viscoelastic properties of SMP, such as rate-dependent behaviors, can not be ignored during the application. Consequently, a constitutive model based on the multiplicative decomposition of the deformation gradient is proposed in this work, which can clearly describe the viscoelastic behavior and capture the thermal-mechanical cycle process of SMP. By introducing the "phase transition" concept, SMP is assumed as a composite composed of glassy phase and rubbery phase, and the volume fractions of each phase vary with temperature. Furthermore, according to the different mechanical behaviors of the glassy phase and rubbery phase, two different constitutive structures that can describe the strain sensitivity of SMP are developed to represent the mechanical response. The developed model was verified by simulating a series of experiments, including strain sensitivity tests and thermal-mechanical cycle experiments.