Study on coalescence probability of cracks from randomly spaced surface defects and associated fatigue life distribution.

Rotating bending fatigue tests were carried out on S50C steel specimens having four drilled holes with random distance at the critical section to investigate statistically the propagation behavior of surface cracks and their coalescence leading to the failure of specimen. The important findings in the present study are summarized as follows. It was observed that the first crack coalescence was encountered between adjacent holes with the minimum distance or second small distance. There was little difference between the number of cycles to crack coalescence and that to failure. The distribution of the number of cycles to crack coalescence has been theoretically derived on the basis of crack coalescence probability as a result of theoretical analysis with the assumption of the first crack coalescence occurring between adjacent two holes of the minimum distance or second small distance. The theoretical distribution thus derived shows a good agreement with that of experimental trends.