The yield criteria for green compacts of iron and copper powders were determined by means of the uniaxial compression and the triaxial compression tests. In the triaxial test under the condition, preventing the increase in the density of the compacts by the hydrostatic confining pressure, the decrease in the apparent Young's modulus and a large plastic deformation of the compacts with the increase in the confined pressure were observed. The yield-loci for the compacts are of a type in which the second invariant of the stress deviator decreases with the increase in the mean stress, and which is consistent with the compressive behavior of metal powder compacts.
The experimentally determined yield-loci for the copper compacts agreed very closely with those theoretically calculated by R. J. Green.
