Some aspects of corner fatigue crack growth from holes

Abstract

The early stages of fatigue failures often involved the initiation and growth corner cracks. To assess the residual strengths and to predict the remnant lives of components containing corner cracks, the associated stress intensity factors must be known. These stress intensity factors are sensitive to crack shape as well as crack size and vary along the crack front. The complex nature of the problem often precluded analytical treatments so that numerical methods are generally employed to obtain the related stress intensity factors. Different numerical solutions exist. These solutions usually assumed the corner cracks are exactly elliptical in shape. Each solution uses its own interpolation method to arrive at the stress intensity for different crack sizes and crack shapes. There exist few experimental data to check the usefulness of these solutions. In the current work, direct observations of corner fatigue crack growth were made. It was attempted to calibrate the stress intensity factor of some corner cracks using a backtracking method. Details about the experiment are reported. The empirical stress intensity factors are compared with two published numerical solutions. The agreement is found to be reasonable and the possible causes of discrepancy are discussed.