Deformation behaviour of closed-cell aluminium foams in tension

The mechanical behaviour of commercially available ALPORAS aluminium foam with two different densities was studied under tension loading. In addition to the common stress-strain measurements, local deformation, notch-opening displacement and damage evolution were deter-mined. The deformation characteristics deviated from those observed in aluminium foams under compression. No deformation bands or plastic instabilities could be observed in tension, which are very frequent in compression of metallic foams. Four regimes were evident in the stress-strain curves and deformation maps: the linear elastic regime, the plastic regime with no significant crack initiation and propagation, the regime of formation of a fracture process zone and, finally, the regime of fracture, where a main crack propagates through the specimen and leads to failure. The fracture strain was only a few per cent, with the higher-density foam showing a larger fracture strain, and the plastic Poisson's ratio was about 0.35. The notched specimens showed increasing fracture strengths in terms of the net section stress with increasing notch depth. It is suggested that a change in stress state, caused by a non-vanishing Poisson's ratio, in front of the notch tip creates an increase of the fracture strength similar to the behaviour in ductile bulk metals. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.