Porous metals are often used as shock absorbers due to their high energy absorption capabilities. The characteristic plateau region of porous metals under compressive loading is important for the practical use of porous metals and should thus be investigated. Especially the relationship between the deformation behavior and the initiation of the plateau region should be clarified. In this study, the deformation of porous metals with aligned unidirectional pores compressed in the direction perpendicular to the pore direction was modeled to investigate the mechanism of the plateau region initiation. The criteria for the plateau region initiation was investigated by studying the distribution of strain and stress during compression obtained by digital imaging (digital image correlation -DIC) and computational simulations using the finite element method (FEM).
Porous A6061 specimens with aligned unidirectional pores (size: 25×25×25mm^3, pore diameter: 3mm, center distance of pores: 4.8mm, porosity: 29.2%) were prepared by machining. The specimens were compressed in the direction perpendicular to the pore orientation in accordance with the ISO 13314 standard. The distribution of equivalent plastic strain was investigated by the DIC during the compression tests. Furthermore, the distribution of equivalent stress and equivalent plastic strain was obtained by the FEM.
The compressive stress increased with increase of the compressive strain in the range from 0 to 3 %. From 3 to 30 % strain the increase of the compressive stress was suppressed. The quasi-static computational model, which also considered the local deformation of porous metal in terms of bending and shear deformation of the cell walls, showed the local plastic collapse occurred when compressive strain reached approximately 3 %. The stress distribution obtained by DIC and FEM analysis showed an excellent comparison. It was therefore revealed the plateau region is initiated by the local plastic collapse of the porous metal with aligned unidirectional pores.