A yield function for copper powder in compaction

A powder conglomerate, consisting of loose metal particles, yields by shear stress as well as by hydrostatic stress. Strength of the conglomerate in tension is negligible. Thus, the yield surface of such a material can be described as an ellipse in the space defined by J1 axis and View the MathML source axis, which is shifted toward the negative direction in the J1 axis. In the present investigation, the parameters used in the yield function were determined by uniaxial strain and hydrostatic compression tests of Cu powder under the assumption that they are functions of relative density. Flow rules were obtained by imposing the normality condition to the yield function and they were applied to predict pressures required in uniaxial strain, plane strain and hydrostatic compressions. The predictions are in good agreement with the experiments.