Experimental determination of the mechanical effects of mass density gradient in metallic foams under large multiaxial inelastic deformation

Mass density gradients at the scale of the cell size are an inherent property of metallic foams. Sandwich specimens are prepared from a continuous foam slab and then subjected to large combined compression and shear loads. The characteristic crushing nucleation envelope and the crushing plateau stress interaction surface which determine the amount of energy absorbed during crushing have been measured. In addition to ideal crushing which involves the continual collapse of the solid network structure, fracture-dominated crushing has been observed. The later mechanism occurs under large shears strains and involves the frictional sliding and interlocking of separated surfaces. The wide spread in the measured mechanical properties is only partially related to the density gradient at the microscale denoting that it is not enough to normalize the measured quantities with mass density functions. Other effects such as morphological changes and local variations in cell wall strength should be taken into account.