Effect of shear-affected zone on fatigue crack propagation mode

It is well known that the fatigue limits of some precipitation-hardened steels with a punched hole do not increase, even if the tensile strengths of base-metal increases. This study suggested that the dominant reason for this strange phenomenon is a transition from the Mode I type fatigue crack propagation due to the cyclic plastic deformation to Mode II type propagation due to the damage accumulation by a quantitative analysis of influential factors based on fracture mechanics. This result can open a probability that the fatigue limit of the punched hole with shear-affected zone can be actively quantified.