Simulation of pressing and sintering of powders.

Inhomogeneities in green density or in the temperature distribution during sintering may cause cracking, internal stresses or distortions of the sintered specimen. As a prerequisite for a numerical simulation of these processes, constitutive equations of porous materials are derived from a micromechanical model. It is assumed that the prevailing transport mechanism is grain boundary diffusion. Grain growth is taken into account. The resulting constitutive equations contain the limiting cases of pure sintering or hipping (if the deviatoric stress component is zero) and Coble creep (if no pores are present). As a special feature of the theory unequal pore sizes are admitted and described by a size distribution function. The constitutive equations are examined with respect to the stability of homogeneous sintering as opposed to a bifurcation into sintering and de-sintering regions under tensile constraints. The constitutive equations are implemented in the finite-element program ADINA. Nu merical examples for the sintering of a less dense cylinder onto a denser core are shown, and the results are compared with those of other models of porous solids.