On the Fatigue Deformation of Steel

概要

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Metals deform plastically by the repetitions of stress of comparatively small magnitude. The yield limit under repeated stress may be determined by the same condition as that of yielding under static stress. However, the investigation concerned is scarecely found. The present study has been made for clarifying the yielding phenomena of metals under repeated stress. Results obtained are as follows;(1) The fatigue deformation, which appears in repeated bending or torsion test, enhances rapidly soon after the start of test, and then increases slowly with repetition of stress. When stress applied is over the endurance limit, the increase of deformation continues till fracture, while deformation ceases to increase after experiencing some stress cycles, provided the stress applied is less than the endurance limit.(2) For materials with apparent yield point in static test, the fatigue yield limit agrees with static one, while for other materials both yield limit are not the same, the former being considerably less than the latter. For the latter materials, therefore, the safety range in the endurance limit diagram hitherto used must be revided, that is the yield limit must be correctly lowered.(3) Prestressing due to cold working is effective for descending the fatigue deformation.
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