ON CONSTRAINED SINTERING .2. COMPARISON OF CONSTITUTIVE MODELS

Part I of this series developed a constitutive equation for an isotropic viscous material for which the strain rate is linearly proportional to the stress. The equation can be written in various forms in terms of Poisson's ratio and functions that represent the viscous response of the porous body to pure shear, hydrostatic, and uniaxial stresses. This paper examines similar constitutive equations that have been used in the analysis of constrained sintering problems such as sintering under a uniaxial load, on a rigid substrate, or with rigid inclusions. It is shown that some of those models imply that Poisson's ratio is negative, in contradiction to experimental evidence. Part III applies the models to the calculation of stresses in a matrix sintering around rigid inclusions. Very high stresses are erroneously predicted by the models for which Poisson's ratio is negative.