The phenomenon of fatigue crack growth acceleration due to variable amplitude overloading was studied in a 2017-T3 aluminum alloy. Compact specimens were subjected to single and multiple peak applications of overloads. Striation spacings during and just after the overloads were measured. The crack tip blunting and resharpening process for each loading cycle was examined.
The fully blunted crack tip was followed by fatigue crack growth acceleration microscopically. On the other hand, no fatigue crack growth acceleration occurred if the previous crack tip was fully resharpened. These results were able to be interpreted from the view point of the transition from the fatigue crack to the ideal crack.
It should be noted, however, that the shape of the crack tip during overloading had no marked influence on the subsequent fatigue crack growth retardation macroscopically.
