Effect of Prestrain Type on the Rotating Bending Fatigue Limit of Carbon Steel

概要

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The effect of the type of prestrain (tensile or torsional prestrain) on the fatigue limit of carbon steel was investigated. Annealed 0.1%, annealed 0.5%, and quenched and tempered 0.5% carbon steel specimens were subjected to monotonically tension or torsion to produce plastic strain. Fatigue tests were performed using rotating bending fatigue test machines (R=-1). The results of experiments showed that the fatigue limit of the torsional-prestrained specimen was higher than that of the tensile-prestrained specimen and the degree of cyclic softening induced by fatigue loading in the torsional-prestrained specimen was lower than that in the tensile-prestrained specimen. The results mean that the effect of the prestrain type on the fatigue limit is related to the cyclic softening and the cyclic softening depends on the relationship between prestrain type and fatigue-loading type. However, the effect was small when there is precrack formed by prestraining or artificial defect on the specimen. A method of predicting the fatigue limit of prestrained carbon steels was also discussed on the basis of the results.