LOCAL FATIGUE DAMAGE ACCUMULATION AROUND NOTCH ATTENDING CRACK INITIATION

The subsequent recrystallization technique was used to study the process of local damage accumulation around a notch under conditions of low-cycle fatigue. A 0.8-in. compact tension specimen of 304 stainless steel with a notch radius of 1 mm was used. The accumulated plastic zone around notch increases with the number of cycles N. The accumulated plastic strain within the zone also increases with N, producing the strain gradient (damage gradient). A fatigue crack initiates when the accumulated plastic strain at the notch root reaches a critical value equal to the fracture strain of the material; that is, when the accumulated plastic work at the crack initiation site becomes critical. The fatigue crack emanating from a notch root grows through the pre-existing damaged zone. It is shown that this local damage accumulation approach can explain the fast growth of a short crack from a notch.