749 SP 処理 ADI 材の高サイクル疲労における内部起点破壊に関する研究

概要

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Rotating bending fatigue tests were carried out on austempered ductile cast iron (ADI) with shot-peening (SP) treatment, and influences of the SP treatment on fatigue property and fracture morphology were investigated. As results, the fatigue strength of shot-peened ADI specimens was improved in the region of under (10)^7 cycles. But, the S-N curve of shot-peened ADI and that of non shot-peened ADI crossed at near (10)^8 cycles, and the fatigue strength of shot-peened ADI specimens was lower than that of non shot-peened ADI in the region of over (10)^8 cycles. In order to investigate the causes, the hardness distribution and the residual stress distribution in the surface layer of the SP treated specimens was measured and the fracture surfaces of all failed specimens were observed using a field emission scanning electron microscopy (FE-SEM) after the fatigue test. The stress at the crack initiation point was calculated in consideration of the stress gradient and the residual stress for shot-peened ADI specimen. The fatigue facture mechanism was discussed in detail.
2002-09-20