Qualitative and quantitative characterizations of fracture surfaces of AL6XN super-austenitic stainless steel fatigued at different stress amplitudes

Fracture surface features of the AL6XN super-austenitic stainless steel fatigued at different stress amplitudes were observed by SEM and quantitatively analyzed by a fractal method. It was found that the morphologies corresponding to three characteristic zones of fracture surface, i.e., fatigue crack source (or initiation) zone, crack growth zone and final rapid fracture area, are more or less related with the applied stress amplitude Δσ/2. A quantitative relationship between the total fatigue life and the average fractal dimension of scanning profile of fracture surface was experimentally established. The lower the fractal dimension, the longer the fatigue life is. A similar change of fractal dimension with the applied Δσ/2 in the fatigue crack source and growth zones suggests that crack initiation and propagation lives might contribute comparably to the resulting total fatigue life of the AL6XN super-austenitic stainless steel tested under constant stress amplitude control.