Multiple relaxation mechanism-based thermo-mechanical constitutive model describing cyclic shape memory effect of shape memory polyurethane

As an inherent property of the shape memory polymers (SMPs), relaxation plays a crucial role in their mechanical deformation and shape memory effect (SME). During the shape memory processes, relaxation behavior can be divided into short-, medium-, and long-term mechanisms that collectively contribute to the multiple relaxation mechanisms. In this study, based on the multiple relaxation mechanisms, we establish a thermo-mechanical constitutive model for the thermo-induced shape memory polyurethane (TSMPU) within the finite deformation framework. Additionally, the effect of temperature on mechanical deformation is further optimized by considering the change of viscosity with temperature. To further characterize the cyclic transition behavior between the rubbery and the frozen phases, we employ the storage strain ratio to describe the storage and release of deformation during the cyclic SME. The proposed cyclic thermo-mechanical model effectively captures the cyclic SME of TSMPU as demonstrated through comparison with the experimental results at various strain amplitudes and strain rates.