Analysis of monotonic and cyclic crack tip plasticity for a stationary crack tip in a FCC crystal

The fields produced at the tip of a Mode I crack in a ductile single crystal have been previously investigated using theoretical, experimental, and numerical methods. Limitations in the material model complexity used in theoretical approaches and difficulties in experimentally measuring in situ crack tip fields invite consideration of numerical crystal plasticity. Prior crystal plasticity analyses of crack tip plasticity have leveraged simple phenomenological constitutive forms and investigated limited loading scenarios. The current work extends prior approaches by using a recently developed face-centered cubic (FCC) crystal plasticity model that considers dislocation substructures and complex back stress evolutions during cyclic loading in concert with a finite element model of a stationary crack tip. The model is used to i) more thoroughly understand the conditions where theoretical analyses remain valid in the context of dislocation interactions and substructure development and ii) explore potential fatigue crack growth driving forces for microstructurally small and physically small cracks. Specific observations are made regarding the observed formation of alternating bands of forward and reverse shear, unique to the present model with dislocation substructure, as well as the influence of ratcheting strain on the cyclic irreversibility of slip and associated correlative fatigue crack growth relations.