Modeling the Thermoviscoelastic Properties and Recovery Behavior of Shape Memory Polymer Composites

This work investigated the effects of stiff inclusions on the thermoviscoelastic properties and recovery behavior of shape memory polymer composites. Recent manufacturing advances have increased the applicability and interest in SMPCs made with carbon and glass inclusions. The resulting biphasic material introduces changes to both the thermal and mechanical responses, which are not fully understood. Previous studies of these effects have been concerned chiefly with experimental characterization and application of these materials. The few existing computational studies have been constrained by the limitations of available constitutive models for the SMP matrix material. The present study applied previously developed finite-deformation, time-dependent thermoviscoelastic models for amorphous SMPs to investigate the properties and shape memory behavior of SMPCs with a hexagonal arrangement of hard inclusions. A finite element model of a repeating unit cell was developed for the periodic microstructure of the SMPC and used to evaluate the temperature-dependent viscoelastic properties, including the storage modulus, tan δ, coefficient of thermal expansion, and Young's modulus, as well as the shape recovery response, characterized by the unconstrained strain recovery response and the constrained recovery stress response. The presence of inclusions in greater volume fractions were shown to lower both the glass transition and recovery temperatures slightly, while substantially increasing the storage and Young's modulus. The inclusions also negligibly affected the unconstrained strain recovery rate, while decreasing the constrained recovery stress response. The results demonstrate the potential of using hard fillers to increase the stiffness and hardness of amorphous networks for structural application without significantly affecting the temperature-dependence and time-dependence of the shape recovery response.