Investigation of initiation and growth behavior of short fatigue cracks emanating from a single edge notch specimen using in-situ SEM

In-situ scanning electron microscope fatigue observations on initiation and propagation behavior of short fatigue cracks emanating from notch root of specimens were conducted for a low strength aluminum alloy. It was observed that short fatigue crack initiation was a process of acummulative slipping of surface grains near notch root and occurrence of multiple microcracks. The results also show that the early stage propagation of short fatigue crack was a process of the competition of multiple micro-cracks: one of them became a dominant propagating crack while most of them became dormant (i.e. non-propagating cracks). There was a deceleration of crack growth rate in the transition process where the dominant crack formed from the multiple microcracks.