Numerical and experimental study on the optimization of overload parameters for the increase of fatigue life

Fatigue life and crack growth retardation due to periodic tensile overloads, which are superposed on constant amplitude cycles, have been investigated in the present study. In the numerical analyses, the Walker equation with the generalized Willenborg model has been used. The analyses and experiments have been performed on C(T) specimens made of 7075 aluminium. The periodic overloads have been induced at two different periodicities and the effect of overload ratio and overload periodicity on the fatigue life has been studied. The results of the experiments and analyses reveal that the normalized fatigue life versus overload ratio curve has a maximum point, which indicates that there are greater retardation effects in the intermediate overload ratio values. Also, the numerical and experimental results indicate that at the occurrence ratios (the ratio of the number of overload cycles to the number of constant-amplitude cycles between overloads) of 1/50 and 1/500, the maximum interaction occurs at the overload ratios of 1.5 and 2.0, respectively.