Plastic flow anisotropy drives shear fracture.

Fracture of initially crack-free bodies often occurs due to plastic instabilities known as shear bands. Previous computer simulations advanced a myriad of mechanisms to rationalize shear banding. However, they were restricted to planar geometries. We investigate the relevance of anisotropic plasticity by picking an axisymmetric tensile test rig, in which shear localization is rarely observed. The three-dimensional finite-element simulations of shear banding in this type of specimens are the first of their kind. The micromechanical modeling covers a range of competing mechanisms believed to be responsible for such failure. We show that anisotropic plasticity can effectively trigger shear bands thereby causing failure of ductile solids. Our results enable shear fracture to be rationalized in ductile rocks and mitigated against in designing advanced materials.

Micromechanics-based constitutive relations for post-localization analysis.

Micromechanics-based constitutive relations for post-localization analysis are obtained, to be used in a multi-surface representation of porous metal plasticity. Each yield surface involves a number of internal parameters. Hence, the constitutive relations must be closed with evolution equations for the internal parameters. The latter are essential to describing the gradual loss of load-bearing capacity under shear-dominated loading. We also briefly discuss potential void closure due to void rotation and elongation in shear and show additional details regarding the simulations reported in a recent paper (A mechanism of failure in shear bands (2018) Extreme Mechanics Letters, 23, pp. 67-71.) The method can be more broadly used in a range of ductile failure problems involving combined tension and shear loadings.

Power-law creep from discrete dislocation dynamics.

We report two-dimensional discrete dislocation dynamics simulations of combined dislocation glide and climb leading to "power-law" creep in a model aluminum crystal. The approach fully accounts for matter transport due to vacancy diffusion and its coupling with dislocation motion. The existence of quasiequilibrium or jammed states under the applied creep stresses enables observations of diffusion and climb over time scales relevant to power-law creep. The predictions for the creep rates and stress exponents fall within experimental ranges, indicating that the underlying physics is well captured.