A first stage in the development of micromechanical simulations of the crystallographic propagation of fatigue cracks under multiaxial loading

Simulations of the nucleation of dislocations, glide and annihilation ahead of a fatigue crack growing along a localized slip band (a 'long' Stage I crack or a Stage II crack with a K value close to the threshold) are performed for the case of push-pull or reversed torsion loadings, ignoring, in a first approach, the effect of grain boundaries. The crack growth rates are deduced from the dislocation flux at the crack tip. An influence of the normal stress on the friction between the crack flanks as well as on the condition for dislocation emission is introduced. A slower Stage I growth rate is then predicted for reversed torsion, consistent with experimental data.