ON THE DEVELOPMENT OF CONSTITUTIVE RELATIONS FOR METALLIC POWDERS

This article describes the development of elastic and plastic constitu tive relations as functions of relative density for partially consolid ated - 100 mesh aluminum powder. First, measurements of yield stress a s a function of stress state and relative density are described. Measu rements of the plastic strain increments associated with yielding in u nconstrained compression tests and elastic properties, both as functio ns of relative density, are also described. The experimental results a re combined with the associated flow rule to show that the yield surfa ce is asymmetric with respect to hydrostatic tension and compression. Second, it is shown that the yield stress results can be represented b y a two-part (capped Drucker-Prager) yield surface. The consolidation yield surface moves along the hydrostatic stress axis during densifica tion, while the shear yield surface approaches the Mises yield surface . For the Al powder used in the present investigation, superposition o f shear stress on a hydrostatic stress state aids the densification pr ocess. However, the hydrostatic stress requirement was found to be red uced by only about 20 pct for relative densities below 0.98.