A thermodynamics viscoelastic constitutive model for shape memory polymers

In this study, a thermodynamics viscoelastic constitutive model was developed to describe behaviors of the typical thermo-mechanical cycle experimentations. In this model, the changes of thermodynamic and mechanics for SMPs in cooling/heating process were described clearly and the irreversible deformations were calculated. A new type of microstructure of SMPs was proposed and new definitions of phases: active phase and frozen phase were set forth in the present study. The new thermodynamics viscoelastic model is series by two parts: mechanical parts and thermal parts. A new transform equation for the transformation of frozen phase was proposed, and the transform delay time and cooling/heating rate were considered in this transform equation. A transform equation based on the transformation of frozen phase was proposed to describe the change of thermal expansion coefficient of SMPs. Finally, the typical thermo-mechanical cycle experimentation processes were calculated using the new thermodynamics viscoelastic constitutive model. Through the comparison between the calculated results and experimental results, the rationality and accuracy of the new thermodynamics viscoelastic constitutive model was finally verified.