Study on Coalescence Probability of Cracks Originating 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 circumferential distances in the critical section to investigate statistically the propagation behavior of surface cracks and their coalescence leading to a failure of the specimen. The important findings in the present study are summarized as follows: It was observed that the first crack coalescence occludes between adjacent holes with the minimum or second minimum distance. There was little difference between the number of cycles to crack coalescence and that to a failure. The distribution of the numbers of cycles to crack coalescence has been theoretically derived on the basis of crack coalescence probability assuming that the first crack coalescence occurs between adjacent two holes of the minimum distance or the second minimum distance. The theoretical distribution thus derived shows good agreement with the experimental result.