Abstract
Sharply notched specimens of structural low-carbon steel were fatigued under several ratios of maximum to minimum stresses. The growth behavior of a fatigue crack near the notch root was analysed based on the crack closure measurement. A fatigue crack first decelerated with increasing crack length, and then accelerated or became non-propagating depending on the range and ratio of the applied stress. The effective range of the stress intensity factor was found to be the single-valued parameter in describing the growth rate of small cracks near the notch root, and their relation agreed well with that obtained for long cracks. By considering the increase in crack closure stress with crack length, a quantitative method was proposed for predicting the non-propagating crack length and the fatigue strength reduction of notched specimens as a function of the applied stress and the notch geometry.
