Constitutive model for shape memory polyurethane based on phase transition and one-dimensional non-linear viscoelastic

Shape memory polymers are the most essential branches of smart materials, which can be fixed at a temporary shape and recover to permanent shape in response to environmental stimuli, such as temperature, electricity, light and magnetic field. To provide a suitable mechanism for shape memory polyurethanes (SMPU) and to predict their behavior, in this study, a nonlinear viscoelastic constitutive equation was constructed based on the viscoelasticity theory and phase transition theory. A modified three element model with Kohlrausch-Williams-Watts (KWW) stretched exponential function was used to simulate the mechanical behavior of frozen and active phases to describe the viscoelastic behavior of SMPU. A connection coefficient k, which describes the connection model of frozen and active phases, was proposed to represent the relation between the effective modulus and that of each phase.