Elastic properties of compacted metal powders

This paper describes a study of the unloading characteristics of compacts made from the uniaxial compression of metal powders in a cylindrical die. Spherical, irregular and dendritic copper powders and spherical stainless-steel powder were investigated to determine size, shape and material effects on the unloading response. This response was characterized in terms of Young's modulus and Poisson's ratio. Measures of these quantities were made at different relative densities by unloading from different peak axial stresses. With both parameters, there was a strong dependence on particle shape. The load response of lightly compressed material was found to be dominated by its particulate nature and interparticle forces. Unloading material in this condition gave values of Young's modulus that increased slightly and Poisson's ratio that decreased with increasing values of relative density. In contrast, the load response of heavily compressed material was found to be similar to that of a porous solid. Unloading material in this condition gave values of Young's modulus that increased more steeply and Poisson's ratio that increased with increasing values for the starting relative density. Transition between these two types of behaviour depended on the particle shape, and also, to a lesser extent, the particle material