Effects of overloads on fatigue-crack propagation: aluminium alloys

AbstractThe effect of multiple-cycle overloads on the rate of fatigue-crack propagation has been investigated in an Al-4.5Zn-2.5Mg alloy in the underaged, peak-aged, and overaged condltions. The effects on-the Post-overload delay period of number of cycles of overload, alternating stress intensity during the overload, specimen thickness, mean stress, and alternating stress intensity after the overload, have been correlated with the fatigue crack propagation behaviour and the monotonic and cyclic stress/strain properties of the material in the three aged conditions. All the overload tests were conducted under conditions of constant stress intensity and, in all cases, the mean stress intensity was maintained constant before, during and after the overload.