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

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