ショットピーニング処理後に人工ピットを導入したばね鋼の疲労特性

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The fatigue property of shot-peened specimens with a semispherical artificial pit of varied diameter was investigated. Shot peening (SP) and stress shot peening (SSP) were administered to the specimens, followed by etching hole diameter of 0.2, 0.4, and 0.8 mm. After that, bending fatigue tests were carried out on the specimens. The fatigue strength of the SP specimen was improved substantially because of the compressive residual stress generated on the surface, furthermore, the SSP specimen shows a higher fatigue strength due to the formation of greater compressive residual stress than SP.Å@In the case of shot-peened specimens and stress shot peened specimens, the specimen having an artificial pit with d=0.2mm fractured from outside the artificial pit. Therefore, d=0.2mm diameter artificial pit was acceptable in the case of SP or SSP specimen. Multiple non-propagating cracks were observed in a peened specimen after fatigue testing. It is considered that the reason why the artificial pit is acceptable is the stress intensity factor range, which is reduced by compressive residual stress by SP or SSP, becomes smaller than the threshold stress intensity factor range compared to the fatigue limit stress of un-shot peened material.
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