PROPAGATION AND NON‐PROPAGATION OF SHORT FATIGUE CRACKS AT A SHARP NOTCH

Abstract— Sharply notched specimens of a structural low‐carbon steel were fatigued under several ratios of the maximum to minimum loads. The growth behavior of a short fatigue crack near the notch tip was analyzed based on crack closure measurements. A fatigue crack first decelerates with increasing crack length, and then accelerates or becomes non‐propagating depending on the applied stress. A similar deceleration is seen when the rate is correlated to the stress intensity range. The effective stress intensity range is a unique parameter in correlating the growth rate of a short crack for all the stress levels examined, and the relation is identical to that obtained for a long crack. By considering the increase in crack closure with crack length, a quantitative method is proposed for predicting the non‐propagating crack length and the fatigue limit of notched specimens as a function of the applied stress and the notch geometry.