Multi-axial yield behaviour of polymer foams

The yield behaviour of two densities of a ductile PVC foam manufactured by Divinycell have been investigated for a range of axisymmetric compressive and tensile stress states. The yield surface is found to be described adequately by the inner envelope of a quadratic function of mean stress and effective stress and a maximum compressive principal stress criterion. Under tensile loadings the deformation of these foams is governed by cell wall bending, and the uniaxial and hydrostatic tensile strengths have comparable magnitudes. Under compressive loadings the foams deform by elastic buckling of the cell walls, and the uniaxial and hydrostatic compressive strengths are again nearly equal.