Modelling High Density Powder Compaction Using Multi-Particle Finite Element Method

Multi-Particle Finite Element Method (MPFEM) is a sub-particle scale numerical approach to provide an accurate description of particle deformation, thus well suits for modelling high density compaction in which particles experience large deformation. In this work, a 3D MPFEM model was developed to investigate the structure and stress of particle compacts at high density compaction. The model was firstly developed to simulate the compression of single particles and a BCC ordered packing. An elastoplastic model was adopted in the model. The simulation results such as the stress-strain relation and the variation of packing structure were compared with previous studies to validate the model. The model was then applied to simulating the die compaction of a random packing with an initial packing state generated using the discrete element method (DEM). The results showed the relative density increased with the increasing pressure applied on the punch. During unloading, the pressure sharply dropped to zero with slight decrease in compact density. The forces between particles were analysed, showing they were mainly vertical and increased with increasing density.The model was further extended to study the softening effect of particles and the mixing of particles of different hardness on compaction. In the particle softening study, the hardness of the particles varied with temperature. With increasing temperature and decreasing hardness, the hardness affected the porosity of packing dramatically. Larger hardness led to a higher porosity under the same pressure while force orientation and coordination number showed no much difference. The results of mixture model showed that the soft particles took most responsibility of deformation and the hard particles deformed little. However, the stress in the hard particles were larger than the soft particles, indicating that the forces were transmitted in compacts mainly through the hard particles