Contact impingement in packings of elastic–plastic spheres, application to powder compaction

Abstract

High-density compaction of ductile powder particles is characterized by a sharp increase of the inter-particle normal contact force. This is due to both complex contact interactions and plastic incompressibility of the particle constitutive material. A DEM model (OPEN-DEM YADE) using an interaction force-law reproducing this increase has been developed to simulate high-density compaction of ductile powders. Its formulation is derived from a Finite Element Method model (ABAQUS). Macroscopic stresses resulting from compaction tests carried out on a random assembly of spherical grains were computed with both models and then compared. A good agreement between the stress–density curves confirmed the accuracy of the DEM formulation. However, the role of the grain deformation may not be well described using DEM since it is based on an assumption of overlapping rigid particles but allows low calculation costs. To highlight the role of this deformation process, a detailed FEM-based analysis of the influence of contact impingement on the normal contact force is thus presented. It explores the mechanisms of stress transmission between contact zones and quantifies the appearance of contact interactions in terms of both indentation depth and relative density. Results show that contact impingement cannot be neglected at a relative density as low as 0.7 if a local, contact-scale analysis is aimed for (such as density distribution for instance). In such a case, previous models like the one proposed by Storåkers and co-authors, should be used with care. The local solid fraction provides a correct local description of both contact interactions and plastic incompressibility of the constitutive material of the grains up to the maximum density. This would allow the DEM to be successfully applied to large-scale simulations of high-density compaction.