亀裂発生寿命に及ぼす切欠形状の影響

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In order to investigate the effect of notch shapes on fatigue crack initiation, the axial load controlled fatigue tests were carried out employing the double edge notched plate specimens. Materials used in this study were SM 50B, SM 58, HT80 steel plates and A 5083 aluminium alloy. SM50B butt welded joints were also tested in order to investigate the relation with the notched plates and were discussed from a viewpoint of the fatigue crack propagation and initiation. It was found from these test results that N_c depended ended on mainly the local maximum cyclic stress range of notch root as same as that proposed by Topper et. al.. Also, in the case of the notched plates, a good correlation of the normalized stress intensity parameter, ΔK_0/σ_<yc>√<πρ>, with N_c was obtained in the high cycle region and, from that, the crack initiation threshold level, ΔK_<th, ρ>, proposed by Barsom et. al. was obtained. After that, the correlation of ΔK_<th, ρ> with the crack propagation threshold level, 11Kth, was investigated and was discussed in relation with the notch shapes. And it was found that in the region of that was larger than _<th>, K_<th, > had larger values than K_<th>and so that the parameter. K_<th, >, was a useful for the design of structures. Moreover, the definition for the fatigue crack initiation was discussed by the way of investigating the fatigue crack propagation from notch root and was applied for the case of the test results of this study. And the difference of the crack initiation life was discussed for several crack lengths that had physically a meaning from a viewpoint of the fatigue crack propagation.
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亀裂発生寿命に及ぼす切欠形状の影響

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