Statistical relationship between fatigue crack initiator size and fatigue life for a cast aluminum alloy

The variability in fatigue life for a cast aluminum alloy has been investigated under both high-cycle and low-cycle fatigue. The fatigue cracks have initiated mostly near the surface from pores or oxide inclusions. The size of the initiation sites has been evaluated for all specimens and the statistical distribution has been determined. In addition, probabilistic fatigue life regression models have been used to characterize the observed scatter in fatigue life. The cumulative density function (CDF) of fatigue life was found to be approximately equal to the complementary value of the CDF of the near surface fatigue initiator size. Therefore, it has been concluded that the observed scatter in fatigue life is directly related to the distribution of casting defects within the alloy.