Investigation of yield surface of monolithic and composite powders by explicit finite element simulation

In this study, explicit FEM was used to simulate monolithic and composite powders consisting of periodic cells, and the macroscopic yield surfaces of the powder compacts were obtained using the probing technique. It was found that the macroscopic yield surface of monolithic or composite powders depends on not only the relative density of the powder, but also the inter-particle cohesive strength and particle arrangement. Powder compacts with no cohesive strength show nearly zero yield strength without confining pressure. With increasing cohesion, the yield surface expands in the tensile mean stress direction and, at full cohesion, the yield surface is about twice the size of the surface without cohesion. Increasing friction slightly increases the size of yield surface, but the effect is relatively minor. For monolithic hexagonal powders, the yield surface is close to isotropic. A yield function was proposed which accounts for the inter-particle cohesion and gives satisfactory description of the obtained yield surfaces.