A discrete dislocation model of Stage I fatigue crack growth and an analysis of Mode I to Mode II transition at low ΔK1

Simulations of dislocations nucleation and glide ahead of a crystallographic mode II crack are performed for push-pull and reversed torsion . An influence of the normal stress on the friction of crack flanks, as well as on the condition for dislocation emission is introduced.The crack growth rates are deduced from the dislocation fluxes at the crack tip. A comparison between the loading modes is made. Taking into account the presence of grain boundaries, the repeated decelerations and sometimes the arrest that characterise Stage I crack growth are described by the model. An analysis of the transition from mode I to mode II crack growth observed at low ΔK1 in single crystals is proposed