Chapter 4 - Properties of metal foams

Abstract

The characteristics of foam are best summarized by describing the material from which it is made, its relative density, and stating whether it has open or closed cells. The foam properties are influenced by structure, anisotropy, and defects such as wiggly, buckled or broken cell walls, and cells of exceptional size or shape.. Open-cells foams have a long, well-defined plateau stress, where the cell edges yield while bending. Closed-cell foams show more complicated behavior that can cause the stress to rise with increasing strain as the cell faces carry membrane (tensile) stresses. The plateau continues up to the densification strain, beyond which the structure compacts and the stress rises steeply. The tensile stress-strain behavior of metal foams differs from that in compression. The slope of the stress-strain curve before general yield is less than E, implying considerable micro-plasticity even at very small strains. The damping capacity of metal foam is typically five to ten times greater than that of the metal from which it is made, and they also have some capacity as acoustic absorbers. The melting point, specific heat, and expansion coefficient of metal foams are the same as those of the metal from which they are made.