Growth evaluation of multiple interacting surface cracks. Part I: Experiments and simulation of coalesced crack

In order to develop a procedure for assessing the growth of interacting surface cracks, the relationship between the area of the crack face and fatigue crack growth behavior was investigated. Fatigue crack growth tests were conducted using stainless steel plate specimens with surface notches. Then, finite element analyses were performed to simulate the growth behavior obtained by the experiment. It was shown that the change in area can be predicted by assuming the extension of crack front based on evaluated stress intensity factor at each position along the front. Based on experimental and analysis results, it was revealed that the growth of interacting surface cracks as well as independent cracks can be represented well by change in area and showed good correlation with the driving force based on area. It was also shown that, in the case of parallel cracks, the area on the projected plane was dominant. It was concluded that, when the magnitude of the interaction is sufficiently large, by replacing the two cracks with a semi-elliptical crack of the same area on the projected plane, the growth in area can be predicted precisely.