A plasticity model for metal powder forming processes

In this paper, a double-surface plasticity model, based on a combination of a convex yield surface consisting of a failure envelope, such as a Mohr–Coulomb yield surface and, a hardening cap model, is developed for the nonlinear behaviour of powder materials in the concept of a generalized plasticity formulation for the description of cyclic loading. This model reflects the yielding, frictional and densification characteristics of powder along with strain and geometrical hardening which occur during the compaction process. The solution yields details on the powder displacement from which it is possible to establish the stress state in the powder and the densification is derived from consideration of the elemental volumetric strain. A hardening rule is used to define the dependence of the yield surface on the degree of plastic straining. Finally, an adaptive finite element model (FEM) analysis is employed by the updated Lagrangian formulation to simulate the compaction of a set of complex powder forming processes.