1989 年 38 巻 434 号 p. 1275-1281
Single-edge-notched specimens of a low-carbon steel and an aluminum alloy were fatigued under cyclic in-plane bending. The growth behavior of a short fatigue crack formed at the notch root was discussed on the basis of the measurement of crack closure. For each material, the propagation rate of short fatigue cracks was uniquely related to the effective stress intensity range, and the relation agreed well with that obtained for long cracks. The resistance curve was constructed in terms of the threshold value of the maximum stress intensity factor which was the sum of the threshold effective stress intensity range ΔKeffth and the opening stress intensity factor Kopth. The value of ΔKeffth was constant, while Kopth increased with increasing crack length cnp in accordance with
where Kopth∞ is the Kopth value for long cracks, and c1 and c2 are the characteristic crack lengths. The ratio of Kopth∞ to (c2-c1)1/2 was independent of the material. The predicted values of the fatigue limit of crack initiation, the fatigue limit of fracture, and the non-propagating crack length agreed very well with the experimental results. A simplified method of determining the resistance curve was also proposed.