Fatigue limits of shot-peened metals

The fatigue limits of shot peened 20Cr, 30CrMo: 40Cr, GC4, 45 steels and Al-alloy LC9 have been studied quantitatively. Three-point bending fatigue tests were performed in a high-frequency fatigue-test machine and the apparent fatigue limit (sigma(wa)) was determined by the up-and-down method, defined by the maximum achieved value of the applied stress at the surface. Fractographs of specimens tested at stresses just over their sigma(wa) were observed under scanning electron microscopy, when the positions of the fatigue cracks initiation sites were determined. The local stresses at the crack initiation sites were calculated, the results showing that the local stresses at the crack initiation sites are nearly equal for properly shot-peened metals. A model to predict the apparent fatigue limits of shot-peened metals has been proposed. (C) 1998 Elsevier Science S.A.