Size Effect on Rotating Bending Fatigue in Steels

概要

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Rotating bending fatigue tests were performed for forged and cast steels of which specimen sizes are in the range from 8 to 40mm in diameter. The cast steel including originally many defects exhibits a decrease of about 27% in the fatigue limit with an increase in the size from 8 to 40mm, while such a decrease is about 13% in the forged steel of comparatively homogeneous substance. The measurement of the strain during tests manifests that a plastic strain of about 80×10^<-6> is produced at the fatigue limit in the forged steel, independently of specimen size, and on the other hand, the cast steel yields no macroscopic plastic strain at the fatigue limit of this material. From these results, it is suggested that in the former the size dependent plastic strain, which is caused by the difference in the stress gradient produced in the cross section of the specimen, and in the latter the scatter in the fatigue strength induced by the defects, are the dominant factors controlling the size effect on the fatigue limit of steels.
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