Simulation of the material behaviour of metal powder during compaction

This article describes a direct numerical homogenization method for investigating the deformation mechanisms in, and the material behaviour of metal powder during and after compaction. An assembly of elasto-plastic spherical particles in frictional contact with one another is considered, and the stress response to some prescribed deformation history as well as the resulting yield surface of the aggregate is computed with the finite-element method. This is done by applying periodic boundary conditions to the assembly, in a manner that allows arbitrary stress or strain control, and by monitoring the dissipated energies during re-loading simulations with prescribed stress space directions. Closed die and isostatic compaction are considered in particular; the resulting yield surfaces are compared and the role of plastic deformation and frictional sliding on the micro-scale is investigated. Significant deviations from isotropic phenomenological models are found and the development of anisotropy is demonstrated.