The effect of pitting corrosion on fatigue life

Fatigue testing of pre-pitted 2024-T3 aluminium alloy specimens is performe d in laboratory air at 22 degrees C and 40% RH to characterize the effect o f pitting corrosion on fatigue life. Specimens, pre-corroded in a 0.5 M NaC l solution from 48 to 384 h, have fatigue lives that are reduced by more th an one order of magnitude after 384 h pre-corrosion as compared to those of uncorroded specimens. The reduction in fatigue life is interpreted in term s of the influence of the time of exposure to the corrosive environment or pit size. The crack-nucleating pit sizes, ranging from 20 to 70 mu m, are d etermined from post-fracture examinations by scanning electron microscopy. Fatigue lives are estimated using a fracture mechanics approach and are sho wn to be in good agreement with the actual data. A probabilistic analysis s hows that the distribution of fatigue life is strongly correlated to the di stribution in nucleating pit size.