Shape recovery of polymers with inclusions under multi-axial stress

Abstract

This paper presents a two-phase composite model for predicting the shape memory and recovery behaviors of polymeric and particle-loaded polymeric composite parts. The shape recovery behavior is simulated using a homogenized material model with the matrix exhibiting the strain storage behavior and the inclusions adding to the stiffness and conductivity of the material. An electrically conductive reinforcement in the matrix enabled the activation of shape recovery with Joule heating. The shape recovery model for the matrix is adapted from literature and extended to include a three-dimensional stress state. Inclusions are assumed linearly elastic, and the matrix is elastic at the low-temperature glassy phase and elastic-incompressible at the high-temperature rubbery phase. The incompressibility is modeled using a temperature-dependent Poisson’s ratio that approaches close to 0.5 for the rubbery phase. A methodology for characterizing model parameters from experimental observations of shape recovery is also discussed. Correlations with experimental observations calibrate the model as well as validate it. The formulated two-phase shape recovery model was implemented into the 3D nonlinear finite element analysis. Simulations of shape recovery arbitrarily shaped 3D parts under multi-axial stress states and thermo-mechanical loading cycles are described.