Constitutive behaviour of metal powder during hot forming. Part II: Unified viscoplastic modelling

Constitutive equations used for the finite element simulation of hot isostatic pressing should describe both plastic and viscous strains. For this purpose the unified viscoplastic theory, which has originally been developed for dense metals, has been extended to porous materials. Classical Abouaf's model, which is based on a symmetric, elliptic viscous potential, fits in with this theory ii is associated with a non-power creep law. However experimental data obtained on a lead powder and presented in the first part of this paper (Geindreau et al.) cannot be described with such model. To get a better description, a new asymmetric viscoplastic potential with linear strain hardening is thus proposed and identified. (C) Elsevier, Paris.