1977 年 26 巻 280 号 p. 56-61
The fatigue tests were carried out under completely reversed plane bending stress using the mild steel specimens with or without chemical polishing after grinding. The fatigue limit was 17.2kg/mm2 for the specimens with work-hardened layers and was 11.5kg/mm2 for the chemically polished specimens having no hardened layers. The residual stress in the work-hardened layer was measured by X-ray diffraction technique and was found to be about 15kg/mm2 in tension. Although the tensile residual stress is generally considered to be detrimental to the fatigue limit, the present study seemed to show the opposite effect. The reason for this was followed by using two kinds of experiments, namely the fatigue tests under the mean stress and the evaluation of the strength of thin work-hardened layers by X-ray stress measurements. The results showed that the mean stress has only a slight effect on the fatigue limit. With the assumption that the effect of the mean stress is the same as that of the residual stress, the tensile residual stress in this case is estimated to decrease the fatigue limit by about 1kg/mm2. The strength of grinding surface was found to be increased nearly 50% and this was considered to be the main cause of the high fatigue limit of ground specimens.