応力集中部にき裂を有するばね鋼の単一過大曲げモーメント負荷による疲労限度向上およびき裂の無害化

概要

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This study describes an investigation of the effect of over bending moment (Mp) on the fatigue limit of spring steel containing a crack in the stress concentration zone. 3-point bending specimens with a notch were prepared for fatigue test. An artificial semi-circular slit was made into the bottom of the notch, and subsequently Mp was loaded. Next, bending fatigue tests were carried out. The following results were obtained. (1) The fatigue limits of specimens increased with increasing value of Mp. (2) In case of specimens containing a slit of 0.2 and 0.3mm in depth, the fatigue limits of the Mp-loaded specimens were improved up to around twice those of the specimens without Mp loading. (3) A slit of 0.05mm in depth was rendered harmless by the loading of Mp, because the Mp-loaded specimens with a slit of 0.05 mm in depth showed the fatigue limits about the same as that of specimens without slit. (4) Results of calculation by FEM showed that the loaded Mp induces a large compressive residual stress in the stress concentration zone.