EFFECTS OF SHEAR-STRESS AND CHANGE IN VOID SHAPE ON DISTORTION AND DENSIFICATION OF POWDER COMPACTS

If shear streSseS are present during isostatic pressing of a powder co mpact they may distort its shape, enhance densification, or both. A fl ow surface is required to predict these effects, but those available h ave been developed for highly consolidated, porous materials. not for less consolidated particulate materials. Since both are compressible m edia, a flow surface is constructed using Beltrami's principle of cons tant total strain energy. This is applied in particular to particulate media, using a micromechanical model of densification which includes both void shape change and particle yielding and strain hardening. The theory agrees well with powder compact densification data for a wide variety of materials throughout the entire consolidation process. It i s further compared with shape changes in copper compacts where shear s tresses have been generated by the containment canister.