平均応力下での切欠低微小き裂の伝ぱおよび停留挙動の予測

概要

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A resistance-curve method was proposed for predicting the growth threshold of short fatigue cracks emanating from the notch root under arbitrary stress ratio. The resistance curve was determined from the experimental result obtained from the fatigue tests of single-edge-notched plate of low-carbon steel under several stress ratios. The relation between the crack opening stress intensity factor at threshold, K_<op th>, and the nonpropagating crack length, c_<np>, was approximated by K_<op th>= K_<op th∞>[(c_<np>-c_1)/(c_2-c_1)]^<l/2>, (c_1⥶c_<np>⥶c_2), K_<op th>= K_<op th∞>, (c_2<c_<np>), where K_<op th∞> was the value for long cracks, c_2 was proportional to K_<op th∞>, and c_1 was constant. Under compressive mean stresses, the effect of notch plasticity on crack closure was superposed on the above-mentioned closure. Good agreement between prediction and experiment was obtained for the fatigue limit for fracture and the nonpropagating crack length. The fatigue limit for crack initiation of a stage II crack was almost constant, and equal to the value predicted for the case of R=-1.
一般社団法人日本機械学会の論文
1989-03-25