Plastic response of open cell aluminum foams of highly uniform architecture under different quasi-static combined biaxial compression-torsion loading paths

Abstract

The aim of this new experimental work was to understand the effect of loading biaxial combined compression-torsion complexity on the plastic response of three aluminum foams having porosities of 93%, 85% and 78% and nominal relative densities of 7%, 15% and 22%, respectively. An investigation was made of the biaxial plastic response of these open-cell foams, which have a highly uniform architecture with a spherical porosity. These foams were tested under quasi-static complex loading paths using a patented rig, called ACTP. Biaxial combined compression-torsion loading paths were then applied with different torsional component rates. The key responses to be examined were yield stress, stress plateau, energy absorption capacity, and densification strain. It was revealed that the greater the density of the foam, the higher the loading complexity, and the greater the yield strength and the energy absorption capacity. The highest foam strength was thus recorded under the most complicated loading path (i.e., biaxial 60°) for the densest foam (i.e., 78% porosity). However, the foam with a porosity of 93% demonstrated a lower strength under biaxial loading compared to its uniaxial response. This was due to its small cell wall thickness, which was easily damaged. The effect of the loading complexity on the pore closure mechanism of the deformed foams was studied using an image analysis that targeted the axial and the transverse sections. For the 85% and 78% foams, the loading complexities of biaxial-37° and biaxial-45° provided the highest pore closure compared to the other loading complexities. This analysis supported the interpretation of the densification strain results.