Local approach to fatigue cracks bifurcation

A "local approach" of bifurcation based on the application at the crack tip of two critical-plane fatigue criteria predicting either tensile-stress-dominated or shear-dominated fracture and on the choice of the fastest damage mode is proposed. In pure mode II, this approach is shown to successfully predict a transition from bifurcation, as predicted by usual criteria, to coplanar crack growth, when ΔK_II increases, which usual criteria fail to predict. It is also shown that the deceleration and final bifurcation of cracks propagating in shear-mode is not due to a stress/strain redistribution as the crack propagates through its plastic zone but can really be attributed to a friction-induced decrease in effective ΔK_II. The proposed approach may also be used for unconstrained plasticity or non-proportional loading and it is sensitive to the loading path. An application to sequential mode I and II is presented. The synergy of mode I and mode II in that case is captured.