Mechanism of high energy absorption by foamed materials-foamed rigid polyurethane and foamed glass

Abstract

Energy absorbability of foamed rigid materials, polyurethane and glass, was studied under a compressive load. The brittle materials were proved to absorb much energy in a manner similar to ductile materials. A mechanism for such high energy absorption was proposed, based on a fracture model in which crushing of cells initiates at the weakest cell followed by propagation to cells lying in the layer containing the weakest one and lying in a direction perpendicular to the compressive force; then the crushing propagates to another layer under the compressive force after the completion of the first layer crushing. In the period of one layer crushing, the strain energy stored in the period of compression prior to the crushing is temporarily released, and it is stored again in the period of compression after the crushing. The store and release of strain energy is assumed to be repeated until all cell layers are crushed. This mechanism of layer-by-layer crushing allows the cells to absorb strain energy repeatedly, and causes high energy absorption in the brittle foamed material. The calculated energy based on the mechanism agrees well with the observed one.