Uniaxial deformation of microcellular metals

The Young’s modulus and uniaxial flow stress of pure aluminium (99.99%) open-cell sponges produced using the replication process with preforms of 400 μm diameter NaCl particles are measured in tension and compression. Cold isostatic compaction is used to increase the salt preform density prior to infiltration under a fixed pressure, enabling controlled variations in relative density from 13% to 33%. Data from the present sponges and from the literature are compared to predictions of continuum micromechanics for the Young’s modulus of two-phase composite materials specialized to porous materials under uniaxial deformation. The plastic flow stress of the foams is predicted using the variational estimate of Ponte Castañeda, equivalent to the modified secant modulus method, simplified here for metal foams in a manner that renders the models fully analytical. Comparison of data with theory shows that the elastic modulus and plastic flow stress of the present replicated open-cell aluminium sponges are best predicted using Roberts and Garboczi’s Gaussian random field model of open-cell solids; investment cast sponges perform better, coming near the Gibson–Ashby predictions for these quantities.