Isotropic constitutive models for metallic foams

The yield behaviour of two aluminium alloy foams (Alporas and Duocel) has b een investigated for a range of axisymmetric compressive stress states. The initial yield surface has been measured, and the evolution of the yield su rface has been explored for uniaxial and hydrostatic stress paths. It is fo und that the hydrostatic yield strength is of similar magnitude to the unia xial yield strength. The yield surfaces are of quadratic shape in the stres s space of mean stress versus effective stress, and evolve without corner f ormation. Two phenomenological isotropic constitutive models for the plasti c behaviour are proposed. The first is based on a geometrically self-simila r yield surface while the second is more complex and allows for a change in shape of the yield surface due to differential hardening along the hydrost atic and deviatoric axes. Good agreement is observed between the experiment ally measured stress versus strain responses and the predictions of the mod els. (C) 2000 Elsevier Science Ltd. All rights reserved.