Corrosive fatigue of structures with dimple holes under spectrum loading

Experimental investigation and life prediction are made for structures with straight holes and dimple holes in both laboratory ambient conditions and 3.5% NaCl solution under spectrum loading. With the aid of acoustic emission, label loading and fractography technique, the crack-growth data are obtained in both environments. Stress-intensity factors for the corner crack emanated from the dimple hole are evaluated by three-dimensional (3D) finite element (FE) method. Life prediction of the tested structures is made by using the modified FASTRAN-II code on the basis of corresponding fatigue crack-growth rate curves. It is shown that once the initial defect size a₀ is determined by one set of test data, it can be used together with the 3D crack-growth method in order to provide accurate life prediction in alternative structure and loading condition. By comparison, life prediction by the traditional local strain method is also made which is shown to be less reliable than the 3D crack-growth method.