Yield function parameters for metal powder compaction based on unit cell studies

A new method based on the micromechanics of powder particle deformation for evaluating the yield function parameters is attempted. Two-dimensional particles in close packed arrangements with two different starting relative densities are considered. These unit cells are studied under plane strain conditions for basic densification response using rate independent large strain finite element analysis. The densification range addressed in this approach is 0.78-0.98 in terms of relative density. Macroscopic values of stresses and the relative densities are recorded for different loading paths. The basic form of the Shima and Oyane yield function (Int. J. Mech. Sci. 18, 285 (1976)) is reduced to plane strain conditions and the material parameters are computed. The yield function parameters thus computed are found to be in good agreement with the experimental results reported for pure copper, iron and aluminium powders. Initial pore shape, loading path, material hardening and inter particle friction are found to influence the yield function parameters and hence the yield surface at a given relative density. It is also observed that a single function in terms of relative density cannot adequately represent the variation of the yield function parameters for the entire compaction density range. Based oil the yield function parameters thus obtained, yield surfaces are constructed. These yield surfaces are found to compare well with the yield surfaces reported by Shima and Oyane based on experiments in the relative density range of 0.82-0.95. (C) 1977 Acta metallurgica Inc.