Yielding Behaviour in Axial Compression of Cylindrical Metal Powder Assembles Under High Pressure.

Abstract

We present the method of constructing a pressure sensitive yield function which accounts for the porosity, incorporating the data from the compression of cylindrical metal powder assembles. The load paths consist of fluid hydrostatic pressure loading up to a set value, followed by the addition of an increasing mechanical axial load. The yield function (yield curve) for less than fully dense states is represented in the relation of deviatoric stress q to hydrostatic stress p. In powder metal assembles the curve which gives the relation between p and q at constant density has been frequently used as yield curve. However, it does not seem to have been examined experimentally whether the constant density curves are consistent with the yield curve. For the prediction of yield function two quantities are required, for example, axial stress and volumetric strain developing with an increasing axial strain. Here, the data obtained by Jin and Cristescu and by Gurson and McCabe are used. Our results indicate that several current models proposed for powder metal deformation do not represent actual constitutive behaviour under the assumption that associated flow rule is valid and yield curve expands in a similar shape with compressive deformation.