Numerical simulation of die pressing and sintering-development of constitutive equations

This paper summarizes recent studies on solid-state sintering with the goal of developing constitutive equations for use in finite element simulations of the sintering process. The assumed transport mechanisms are grain boundary diffusion and surface diffusion. Separate models are described for the three sintering stages - (1) initial neck formation, (2) open porosity with (near-) equilibrium surfaces, (3) closed porosity. Densification can be accompanied by grain coarsening. Some of the predictions of the models are confirmed by experiments, e.g. the dependence of the bulk viscosity on the density, while the sintering stress and the ratio of shearto-bulk viscosity are not predicted correctly.