From non-planar dislocation cores to non-associated plasticity and strain bursts

In non-close-packed crystalline lattices, e.g. of bcc metals and intermetallic compounds, the stress-state dependence of the Peierls barrier for the motion of a screw dislocation violates Schmid’s law and leads to non-associated plastic flow at the continuum level. Plasticity models based upon distinct yield and flow functions are developed for both single crystals and polycrystalline aggregates that build upon atomic-level simulations of single dislocations. For a random polycrystal, isotropic forms for those functions are proposed and used to study mechanisms of macroscopic deformation. Non-associated flow is shown to have a significant effect on strain localization. Intermittent strain bursts are predicted to arise as a consequence of non-associated flow, particularly for deformations close to the plane strain state and for nearly rate-insensitive response.