Constitutive model for shape memory polymer based on the viscoelasticity and phase transition theories

As a kind of smart materials, shape memory polymer has covered broad applications for its shape memory effect. Precise description of the mechanical behaviors of shape memory polymer has been an urgent problem. Since the phase transition was a continuous time-dependent process, shape memory polymer was composed of several individual transition phases. Owing to the forming and dissolving of individual phases with the change in temperature, shape memory effect emerged. In this research, shape memory polymer was divided into different kinds of phases including frozen and active phases for its thermodynamics properties. Based on the viscoelasticity theory and phase transition theories, a new constitutive model for shape memory polymer which can explain the above assumptions was studied. In addition, a normal distribution model, which possesses less but physical meaning parameters, was proposed to describe the variation in the volume fraction in shape memory polymer during heating or cooling process.