Modeling shape-memory effects in amorphous polymers

The time-dependent behavior of glass transition can be used to achieve shape-memory behaviors in amorphous polymers. Thus, modeling the shape-memory effect in amorphous polymers requires considering the viscoelastic/viscoplastic behaviour across the glass transition region. Here, we discuss our past efforts to develop constitutive models for the glass transition behavior of amorphous polymers to predict the shape-memory behavior under a variety of conditions. We first demonstrate that a viscoelastic model with multiple relaxation processes can describe the temperature memory effect and multiple shape-memory effect in amorphous thermosets and thermoplastics. The viscoelastic model is further extended to a viscoplastic model. Comparison with experimental results shows that the viscoplastic model can accurately predict the partially constrained shape recovery of polymers programmed below the glass transition temperature. Finally, we present a constitutive model to describe the effect of solvent absorption on the thermomechanical properties and shape-memory behavior of amorphous polymers. We derive an explicit function to describe the influence of solvent concentration on viscosity and implement the model for finite element analysis. The thermo-chemo-mechanical coupled model is able to describe the isothermal recovery of programmed SMPs in water. (C) 2019 Elsevier Ltd. All rights reserved.