A theoretical investigation of the effect of material properties and cavity architecture/shape on ductile failure during the hot tension test

Abstract

The effect of material properties and cavity architecture, shape, and orientation on ductile failure behavior during hot tension testing was established using a numerical analysis of the deformation of a representative “microspecimen.” The microspecimen consisted of two regions, or slices, one containing the cavities and the other comprising a uniform, cavity-free area. The cavities were assumed to be spherical or cylindrical and to form a simple cubic (sc), body-centered cubic (bcc), or face-centered cubic (fcc) network; tensile loading was taken to be parallel to either the cube edge, face diagonal, or body diagonal. By invoking load equilibrium, expressions describing the relation between the deformations in the uniform and cavity-containing regions were derived. The principal material-related coefficients in these equations were a geometry factor G, whose value depended on the specific cavity architecture and tensile loading direction, the strain-hardening and strain-rate sensitivity exponents n and m, and the parameter η, used to describe the (volumetric) cavity growth kinetics. For cyclindrical cavities, the pertinent void-growth parameter was deduced to be the area cavity growth rate ηA. Failure was predicted to be either retarded or accelerated when ηA is less than or greater than 2η/3, respectively. The simulations were used to quantify the microscopic strain localization kinetics and, thus, to identify those deformation regimes in which void growth vs void coalescence (i.e., “internal necking”) predominates during the ductile failure process. Model predictions of tensile elongation were validated by comparison with experimental measurements for cavitating materials found in the literature.