Application of Direct Current Potential Drop Method in Analysis of Fatigue Overload-induced Retardation of Steels

A new driving force model without material fitting parameters was proposed to predict crack growth rate and overload fatigue life by introducing an equivalent residual stress intensity factor ΔK_res. The crack growth length was measured by direct current potential drop (DCPD) method combined with finite element calibration, and compared with measured values to verify the accuracy of the method. On the basis of DCPD method and finite element calibration, the crack growth rate and overload fatigue life of four steels after overload were obtained by overload fatigue test to verify the accuracy of the prediction model. The results show that the overload-induced retardation appeared in four test steels after single-peak overload. The higher the overload ratio, the smaller the minimum crack propagation rate of the test steel after overload, and the lower the yield strength, the greater the retardation effect of the test steel. The relative error between crack growth length measured by DCPD method and finite element calibration and measured values was smaller than 3.75%, indicating the method had high accuracy. The trend of crack growth rate prdicted by driving force model agreed with test values by DCPD method combined with finite element calibration well, and the predicted overload fatigue life was within 2 times the error band of the test value, which verified the accuracy of driving force model.