Constitutive Modeling of Metal Powder Behavior During Compaction

In this paper, a constitutive modeling of the metal powder compaction is presented as a first step of ongoing research of a multiscale and multistage mathematical based model concept for powder metallurgy component design and performance prediction using the finite element method. In recent years, techniques such as finite element analysis have received wide attention for their high applicability to powder metallurgy (PM) industry. These techniques provide a valuable tool in predicting density and stress distributions in the pressed compact prior to the actual tooling design and manufacturing process. However, the accuracy of FE prediction highly depends on the possibility to obtain appropriate experimental data to calibrate and validate the powder material model. Within the framework of continuum mechanics, the plasticity model depends on external and internal state variables such as temperature, stress, hardening, relative density and contact between metal powder particles. The material model considers different microstructural and mechanical aspects such as dislocation dynamics, friction, porosity/density evolution, pressure dependent yield surface, particle size/shape distribution, and rate effects related to press speed. To represent the powder densification, we describe a double-surface plasticity model, based on a combination of a convex yield surface consisting of a failure envelope, such as a Mohr-Coulomb yield surface and, a hardening cap model with the use of internal state variables that capture the structure of the structure-property relations. The model is aimed to be implemented in the finite element program. The 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 at the macroscale.