| Abstract Scope |
Scalar metal memory, or isotopic work hardening, is conceptually well understood: Plastic deformation induces dislocation multiplication and intersection, which increases strength microstructurally by higher dislocation density and shorter pin spacing. Tensor metal memory, as sometimes represented macroscopically by kinematic hardening, has no such simple interpretation. Well-known and broad manifestations include the Bauschinger effect, ratcheting in fatigue, back stress in creep, and anelasticity. Recent experiments and simulations suggest that anelasticity and other tensor memory effects are the result of the concurrent operation of two mechanisms: 1) development of internal stress by GND evolution and 2) bowout of dislocation segments.
The rapidly-evolving evidence for this hypothesis, some peer-reviewed and published, some in progress or in review, will be summarized. Experimental results for complex commercial alloys as well as for single crystals and bicrystals show that directional hardening is likely significant at all length scales and for all metals. Crystal plasticity simulations with an explicitly calculated internal stress tensor field throughout the body predict the various effects, but often only approximately in terms of magnitude. Integrating dislocation bowout with the existing internal stress capability promises to complete the theory. |