Deformation of epoxy shape memory polymer foam: Part II. Mesoscale modeling and simulation

Abstract

The present study focuses on how the relative density of an epoxy shape memory polymer foam affects mesostructural response to deformation. The modeled foam had relative densities of 20%, 30%, and 40%, with a glass transition temperature ( T g) near 85 °C as measured by dynamic mechanical analysis. Statistical analysis of the dynamic mechanical analyisis data showed that stiffness did not significantly vary across foam samples of the same relative density. The stress–strain response of the base polymer was obtained through tensile and compressive tests at T g +17 °C and fit to a hyperelastic material model using the ABAQUS material evaluation function. Meshes for the three relative densities were obtained through micro-CT scanning of actual foam, to accurately represent the mesostructure. Overall compression responses predicted by ABAQUS correlated well with experimental stress–strain responses. The simulations qualitatively showed a shift in mesostructure response to deformation between the 20% relative dense material and the materials with higher relative densities. Quantitatively, both the local maximum shear strain and tensile strain cumulative probability distributions within the material were analyzed and a lognormal function was fit to these distributions. The function had three parameters fit to the distribution. Two other parameters, the applied macroscale strain and the reference strain value, were considered in scaling the distributions. These lognormal distributions were then used to predict local strain distributions at applied compressive strain values larger than those simulated in the finite element modeling. The results are discussed in light of the potential local damage mechanisms in shape memory polymer foam.