The high strain compression of closed-cell polymer foams

Abstract

A compressed closed-cell polymer foam was modelled using a BBC lattice model of tetrakaidecahedral cells, loaded in the [001] direction. The contributions of cell face tensions and edge bending were analysed, assuming that the faces act as membranes, for a linearly-elastic, or a yielding material. The moduli and tensile yield stresses of highly oriented polymer films were measured to provide data for modelling, and the amount of polymer in the foam cell faces found to be high. Tensile face strains are predicted to reach 40% of the foam compressive strain. The predicted Youngs moduli are slightly low, because compressive face stresses are ignored, but Poissons ratio is correctly predicted. The compressive foam yield stress is predicted to depend on tensile yielding of the cell faces. Predicted values are close to experimental values for polyethylene foams, but half those of polystyrene extruded foams. The latter foam may collapse in compression when face yielding commences, rather than by the collapse mechanism of the model.