The influence of corrosion pit-pit spacing on the pit-to-crack transition and fatigue lifetime

The influence of separation distance between pre-induced corrosion pits on both crack initiation and fatigue lifetimes is studied in an air environment by testing specimens containing pit pairs in the low-stress, high cycle fatigue regime. The results of these tests are compared with equivalent tests with samples containing similar sized single pit. Within the scope of pit sizes and separation distances investigated, when the separation distance is below a threshold, decreasing the separation distance between pits leads to earlier onset of crack initiation and decreased fatigue lifetimes; this threshold being dependent on the applied stress and relative pit sizes. When the separation distance is above this threshold, multiple pits tend to behave independently of each other. The implication of the results from the viewpoint of structural integrity assessment of components containing flaws such as corrosion pits in close proximity is discussed.