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-Co ulomb yield surface and, a hardening cap model, is developed for the nonlin ear behaviour of powder materials in the concept of a generalized plasticit y formulation for the description of cyclic loading. This model reflects th e yielding, frictional and densification characteristics of powder along wi th strain and geometrical hardening which occur during the compaction proce ss. 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 harden ing rule is used to define the dependence of the yield surface on the degre e of plastic straining. Finally, an adaptive finite element model (FEM) ana lysis is employed by the updated Lagrangian formulation to simulate the com paction of a set of complex powder forming processes. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.