EFFECT OF A SINGLE PEAK OVERLOAD ON PHYSICALLY SHORT FATIGUE CRACK RETARDATION IN AN AXLE‐STEEL

Experiments on the propagation behaviour of physically short fatigue cracks were conducted on an axle-steel, using a direct current potential technique. Various overload ratios (OLR=1.5, 1.7, 1.9 and 2.1) and different overload positions were employed. The experimental results show that physically short cracks are more sensitive to the overload retardation effect than long cracks. The overloads produce a beneficial effect when they are introduced early. Later overloads, although giving an increase in life, produce a smaller effect. The delay cycles N D due to the application of a single overload increase with increasing overload ratios. The experimental data, when plotted on a log-log graph of N D /N CAL (where N CAL is the number of cycles under constant amplitude loading) versus overload ratio OLR, gives a straight line relationship, namely N D /N CAL =2.81 x 10 -3 (OLR) 10.12 .