CONSTITUTIVE MODELING FOR POWDER COMPACTION AND DENSIFICATION

摘要

In this paper an internal state variable material model for powder metallurgy component design and performance prediction is developed and evaluated using finite element analysis. The constitutive modeling is introduced as a first step of ongoing research of a multiscale and multistage mathematical based concept to capture the entire history of the P/M densification process. To describe the metal powder compaction and densification processes, a pressure sensitive plasticity model is represented by a double-yield surface, based on a combination of a convex yield surface comprising of a failure envelope, such as a Mohr-Coulomb yield surface, and a hardening cap model. The formulation uses the variables of temperature, stress, hardening, relative density, strain rate, contact between metal powder particles and other microstructural and mechanical aspects. Molecular Dynamics is also introduced in this multiscale methodology as numerical experiments to study the metal compaction and sintering processes at the nanoscale level. These numerical experimental data are aimed to determine and correlate the microstructure-plasticity relationships for the macroscale formulation. To accurately describe the compaction process, some material parameters are density dependent variables as indicated from experimental data collected from the literature. Finally, the model is implemented in a finite element program and numerical results of a compaction of cylindrical geometry are presented to illustrate the capability of the model.