Characterization of the compressive stress drop in the plateau region in porous metals with unidirectional pores

A drop in compressive stress in the plateau region is one of the issues in compressive behavior of porous metals since it has a negative effect on energy absorption efficiency. The compressive deformation behavior of porous aluminum with irregular unidirectional pores was investigated to clarify the mechanism of the drop. Compression tests of cubic specimens with various irregular circular pore geometries were performed. Digital image correlation and finite element analysis were also conducted to obtain strain and stress distribution of the surface perpendicular to the pores. Fracture of the cell walls was observed when the drop occurred. The results show that pore geometry has an effect on the number and the amount of drop in compressive stress. Measurement of an area of two nearest pores of the fractured cell walls suggests that the amount of drop in compressive stress increases as the area increases. Also, a calculation of normalized critical stress for the plastic collapse of the cell walls shows that the fractured cell walls tend to be geometrically weak. Furthermore, stress concentration occurred around the fractured cell walls, which resulted in a secondary fracture of the cell walls.