Lattice Curvature, Shear Bands, and Electroplastic Effect

Аннотация

In a solid under severe plastic deformation, strain localization develops through shear bands with alternating translations and plastic rotations induced by high lattice curvature. The charge in such plastic rotations is split, forming new electronic states, and stress concentrators arise in their regions due to entropy production via convection. For removing such stress concentrators as a source of cracks, materials can be exposed to rf pulses to destroy charges localized in plastic rotations, provide stress relaxation, and preclude cracking. Here we consider the separation of intrinsic charges in shear bands and the relaxation of mechanical stresses under plastic deformation in a high-frequency pulsed electric field. Expressions are presented for the charges and stresses in plastic rotations, and the stress relief responsible for electroplasticity is explained in the context of the Portevin-Le Chatelier effect and convection currents in applied electric fields. The study shows that crystals with polarization in charge separation zones come under the action of induction and displacement currents which arise in variable external fields, inducing a magnetic field in plastic rotations. The magnetic field creates a self-electric field and displacement current, and associated entropy production changes the mechanical stresses in plastic rotations as a polar electroplastic effect. The estimates made agree with the observed electroplastic effect in the order of magnitude and in the behavior of stress-strain curves.