Abstract

The behaviour of foams, lattices, and other cellular materials in compression has received much attention in the literature and the relationship between the microstructure of the cellular material and the macroscopic response has been established both experimentally and theoretically. However, the tensile response of such materials has not been explored and a number of experimentally observed phenomena are not clearly understood. In particular, it is possible to compress an open-cell foam up to very large strains (>50%) until densification. However, in tension, the same foam will fail at strains in the range 1% to 10%. It is well understood that open cell foams deform in compression by elastic and plastic bending (and buckling) of the foam struts. Since strut bending can accommodate large strains in compression, such asymmetry between tension and compression is not expected.

In this talk, I will first describe the behaviour of cellular materials in tension, specifically where the solid material undergoes ductile failure (by necking), for different two-dimensional foam geometries. The effect of relative density on the ultimate tensile strength and the ductility is explained for the case of a perfect microstructure. Various defects, such as plateau borders, cell wall misalignments and missing cell walls, are introduced in order to elucidate the low observed ductility of foams.