STOCHASTIC AND DETERMINISTIC ASPECTS OF STRAIN LOCALIZATION DURING CYCLIC PLASTIC-DEFORMATION

A phenomenological model of slip patterning in fatigued metals is deve loped. The localization of slip in persistent slip bands (PSBs) is rel ated to the existence of a region of negative slope in the saturation- stress vs local strain-amplitude graph and an internal length scale as sociated with dynamical dislocation interactions that governs the widt h of the bands. Statistical characteristics of the slip patterns are d erived from a stochastic dislocation dynamics approach. This not only allows the determination of the value of the plateau stress in the cyc lic stress-strain curves, but also demonstrates certain limitations of the analogy between matrix-PSB patterns and two-phase systems in ther modynamics. The internal length scale considered yields a second-order gradient of the logarithm of the strain amplitude that allows the det ermination of the shape and width of the persistent slip bands. The re sults of the stochastic and gradient approaches are found to be mutual ly consistent and in good agreement with experimental findings. (C) 19 98 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All right s reserved.