Modulus anisotropy of low-density cellular plastics: an aggregate model

Abstract

A structural model of low density (< 50 kg m −3) cellular plastics based on an aggregate approach is presented. The model is specifically designed to quantify the modulus anisotropy arising from uniaxial cellular orientation. Relationships are presented which express the five independent foam moduli in terms of the modulus of the solid polymer matrix weighted by the polymer volume fraction and specific orientation parameters. Predictions of the model for isotropic foam systems are discussed and comparisons made with independent experimental data on both the foam Poisson's ratio and density dependence of Young's modulus. A theoretically derived invariant relationship linking the oriented foam Young's moduli to the isotropic value is presented.