An estimate of the macroscopic yield surfaces of powder compacts using the kinematic approach of the yield design theory

The 3D compaction of a square array of spherical particles of uniform size is studied using the kinematic approach of the yield design theory. The densification is assumed to occur by plastic deformation at the mutual zone contacts between grains where the dissipation is localized. The compaction response of the array of spherical particles is considered in term of representative unit cell of the aggregate submitted to axisymmetrical loading conditions. Approximate macroscopic yield surfaces resulting from hydrostatic and closed die compaction are constructed at various stages of densifications. The size and shape of the yield surfaces depend upon the loading history as well as the relative density of the compact. Finite element simulations have also been performed in order to validate to some extent the results provided by the kinematic approach of the yield design theory and to examine the evolution of macroscopic yield surface with the degree of compaction.