Compaction and yield behaviour of particulate materials

Experimental and theoretical studies were carried out to improve the understanding of the compaction and yield behaviour of a wide range of different metallic, ceramic, magnetic and hardmetal powders. The research can be divided into low pressure and high pressure compaction, friction and residual stress measurement. The main topic of this thesis is the determination of the compaction and the yield response of particulate materials. The compaction behaviour of different materials was characterized and models such as Cam-Clay and Drucker-Prager were calibrated. The yield response of closed die and isostatically compacted powders with irregular and spherically shaped particles were compared for two materials: steel and copper. It was found that the yield surface of the compacts made of spherical particles can be modelled by the Fleck micromechanical model if the densification level is low. The irregular shaped materials at higher densities could be modelled by the Cam-Clay model. A full anisotropic constitutive model based on Hill's anisotropic yield expression was developed. The model was calibrated for a Distaloy AE which contained 0.5% C-UF4 and 0.6% kenolube P11. Residual stresses in a typical industrial green component were determined using neutron diffraction. Experimental validation of residual stresses predicted by different compaction models is required to help identify the most appropriate model for a given material. The technique was sensitive enough to measure residual stresses, which were found to correlate to cross sectional changes within the component. Residual stress on the edge of the compact, which was in contact with the die wall during compaction, reached 50 MPa in tension and 100 MPa in compression.