Micro-mechanical modelling of powder compaction

This paper compares critically a trio of models of the compaction of granular materials in processes of industrial interest. The simplest model assumes an isotropic material with a spheroidal yield surface in principal stress space. The shape of this yield surface is constant but the size is a simple function of the volume strain. The other two models attempt to capture the anisotropic nature of compaction by assuming initially spherical granules that are deformable. One anisotropic model (kinematic) assumes an affine deformation of the centres of the spheres and gives relatively poor quantitative predictions. The other anisotropic model (static) assumes a simple approximation for the values of the contact forces and can be made to give adequate simulations of the compaction of at least some granular materials. Comparison with previously published experimental results shows that at least for some powders the history of anisotropic compaction is carried, not in the overall deformation, but in the maximum force seen by the contacts. Another important new result is that for the case of proportional loading the results of the isotropic model and the static model are in close, but not perfect agreement.