微小欠陥材の疲労限度に及ぼす平均応力と硬さの影響

抄録

A small defect gives a substantial effect on the fatigue limit. The effects of mean stress and hardness on the fatigue limit of material with a small defect are quite different from those of a long crack nor a plain specimen. The following questions have been arisen. (1) Why does a harder material have a higher fatigue limit in case of material with a small defect? It is not a case in a long crack. (2) Is the mean stress effect on the fatigue limit of material with a small defect the same as that on the ΔK_th of a long crack? Fatigue tests were performed under a wide range of mean stress for two kinds of steels with different hardness using specimens with small defects. The crack closure of a short crack was measured. It was shown that the build up of the crack closure was affected by the material hardness and mean stress. This behavior of crack closure resulted in peculiar properties of fatigue limit in case of material with a small defect.