Local stiffness-density correlations for polycarbonate structural foams

Most studies on the mechanical properties of foams have focused on correlating pointwise, through-thickness elastic modulus and density variations. These local property correlations have then been used to predict the tensile and flexural moduli of foam bars. However, there is some question as to the meaning of a pointwise local density for a cellular material, and the dependence of local modulus on the local density is difficult to measure. This paper is concerned with correlating the density and tensile moduli of structural foams over a 12.7-mm scale. Data obtained from tests on 6.35-mm- and 4-mm-thick polycarbonate foam plaques, molded at nominal density reductions of 5, 15 and 25%, are used to show that the local average tensile modulus of the material correlates linearly with the local average density of the material.