Threshold stress range for short crack growth

By determining the threshold stress range, which is that just sufficient to initiate and grow a short fatigue crack, it is possible to predict the fatigue limit and depth of non-propagating cracks in smooth and notched specimens. The approach is based on assessing the non-uniformity of strains at the surface and the development of crack closure. The nominal threshold increases with crack depth and reaches a maximum value corresponding to the endurance limit. The depth of non-propagating cracks increases with applied stress range to reach a maximum at the endurance limit.