New viscoplastic model to simulate hot isostatic pressing

Most of the numerical simulation software on the hot isostatic pressing (hipping) process is based on viscoplastic modelling of densification, such as the well known Abouaf's model. These constitutive equations are generally obtained from a viscoplastic potential depending on Green's equivalent stress. An implicit coupling between isotropic and deviator parts is therefore only defined by an equivalent stress. A new viscoplastic formulation proposed by Stutz introduces an explicit coupling between isotropic and deviator parts of the stress state, allowing then more flexibility to take into account the experimental results achieved from isotropic, die compaction, and creep tests. This paper deals with the presentation of this new formulation which has been implemented in the finite elements software PreCAD, and the subsequent changes observed in numerical simulations. These simulations achieved with PreCAD software, are compared with an experiment on a complex part manufactured by CEA Grenoble.