Experimental analysis of deformation mechanisms in a closed-cell aluminum alloy foam

The evolution of plastic deformation in a cellular Al alloy upon axial comp ression is monitored through a digital image correlation procedure. Three s tages in the deformation response have been identified. The first involves localized plastic straining at cell nodes, It occurs uniformly and leads to a nominal loading modulus appreciably lower than the stiffness, The second comprises discrete bands of concentrated strain containing cell membranes that experience plastic buckling, elastically constrained by surrounding ce lls. In this phase, as the loading increases, previously formed bands harde n, giving rise to new bands in neighboring regions. The localized bands exh ibit a long-range correlation with neighboring bands separated by 3-4 cells along the loading direction. This length scale characterizes the continuum limit. Thirdly, coincident with a stress peak, sigma(o), one of the bands exhibits complete plastic collapse. As the strain increases, this process r epeats, subject to small stress oscillations around sigma(o). (C) 2000 Else vier Science Ltd. All rights reserved.