歪制御低サイクル疲労における累積被害(第1報) : 60キロハイテンの2段2重重複繰返し法による累積被害に及ぼす繰返し数比の影響

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This paper describes the two step low cycle fatigue tests on hourglass shaped specimens of a 60 kg/mm^2 high strength steel. Strain controlled tension-compressino fatigue tests were performed to study the damage processes in low cycle fatigue. The cycle ratio in the first step was varied in five conditions.It was found that original material of the 60 kg/mm^2 high strength steel showed in the general the similar behaviors to the 80 kg/mm^2 high strength steels which were studied in the previous report. The relation between longitudinal plastic strain amplitude and crack initiation life for original material indicated the linear relationship in the log-log plot. The materials which were damaged by the first step strain cycling of longitudinal true strain amplitude of 0.05 with the cycle ratio of 0.19,0.38 and 0.57 on the crack initiation basis, showed the knuckled line relations of ε-N_c curves. The knuckle point was found on the strain level in the first step. The value of index in the Manson-Coffin equation for materials damaged by the first step strain cycling is smaller than that for original material in the case of step-up test. For step-down test little difference was found between the indices for the original and the damaged materials.The mean value of the usage factor on the crack initiation basis was 0.82 to 1.09,and that on the failure basis was 0.93 to 1.01. Cycle ratio in the first step scarecely affected the static fracture ductility of damaged materials. On the contrary significant decreasing tendency of the cyclic fracture ductility was observed for damaged materials with increasing cycle ratio in the first step as a parameter, where the cyclic fracture ductility was defined as the product of total true strain amplitude and kth power of cycles to crack initiation in the second step. The cyclic fracture ductility for materials tested by step-down method was always higher than that for specimens tested by step-up method.
社団法人日本船舶海洋工学会の論文

歪制御低サイクル疲労における累積被害(第1報) : 60キロハイテンの2段2重重複繰返し法による累積被害に及ぼす繰返し数比の影響

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