Abstract
Small defect gives a substantial effect on the fatigue limit. The effects of mean stress and hardness on the fatigue limit of a small defect are quite different from those of a long crack nor a plain specimen. Fatigue tests with a small defect were performed under a wide range of mean stress for three kinds of steels with different hardness. The crack closure of a short crack was measured. It was shown that the crack closure was strongly dependent on the material hardness at low stress ratio. This behavior of crack closure resulted in peculiar fatigue limit properties of a small defect.
