P&ted in the U.S.A. FATIGUE CRACK GROWTH RETARDATION INCONEL 600

Abstract-The effect of single-cycle overloads on the subsequent fatigue crack growth behavior of Incond 600 is studied. Overloads ranging from 10 to 50 % are applied to a sample undergoing baseline fatigue crack growth at constant AK. In all cases, the crack growth rate increases lightly immediately after the overload and then decreases rapidly to a minimum value before later returning to the pre-overload value. The plastic zone size, affected crack length and the crack growth increment at minimum crack growth rate, a’, are measured for each overload. The affected crack length is considerably larger than the overload plastic zone size for overloads greater than ZtQ. Consequently, although the minimum crack growth rate occurs within the plane stress overload plastic zone, the effect of the overload extends well beyond the overload region. Within the overload plastic zone, contact occurs between the crack faces due to the excessive deformation produced during the overload cycle. The size of the contact region agrees very well with the overload plastic zone size. Beyond the overload region, AI & remains less than the applied AK for some time due to the wedge action of the plastically deformed overload region, delaying recovery of the pre-overload crack growth rate. The crack growth rate recovers only after the crack grows out of the region of influence of the wedge