Critical use of video-imaging to rationalize computer sintering simulation models

Sintering, a thermally activated diffusion process, is used to densify particulate materials. During the densification process, there is concomitant volumetric shrinkage of the powder compact to the final desired part shape. Additionally, shear deformation can occur in response to deviatoric stresses in the body, such as gravity, thermal stresses, and stress gradients due to internal density differences. Finite element modeling of sintering deformation can greatly aid in reverse engineering green part shapes, thus improving dimensional precision of final parts. However, the constitutive equations that govern the rheological response of a porous body during sintering are notoriously difficult to characterize. In situ video-imaging of a simply supported beam, deforming under its own weight during sintering, has been effectively employed in determining the apparent viscosity of the densifying material. This paper describes this experimental technique and the implementation of the results in a finite element analysis. It demonstrates the efficacy of the characterized constitutive equations by a finite element simulation example using 316L stainless steel with 0.2% boron addition.