The high strain compression of closed-cell polymer foams

A compressed closed-cell polymer foam was modelled using a BBC lattice mode l of tetrakaidecahedral cells, loaded in the [001] direction. The contribut ions of cell face tensions and edge bending were analysed, assuming that th e faces act as membranes, for a linearly-elastic, or a yielding material. T he moduli and tensile yield stresses of highly oriented polymer films were measured to provide data for modelling, and the amount of polymer in the fo am cell faces found to be high. Tensile face strains are predicted to reach . 40% of the foam compressive strain. The predicted Young's moduli are slig htly low, because compressive face stresses are ignored, but Poisson's rati o is correctly predicted. The compressive foam yield stress is predicted to depend on tensile yielding of the cell faces. Predicted values are close t o experimental values for polyethylene foams, but half those of polystyrene extruded foams. The latter foam may collapse in compression when face yiel ding commences, rather than by the collapse mechanism of the model. (C) 199 9 Elsevier Science Ltd. All rights reserved.