疲労き裂進展に及ぼす圧縮応力成分の影響

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It has been considered that the crack propagation rate is controlled by the tensil part of stress range but not by the compressive part. However, according to the experimental results carried out by the present authors for a plane bending stress condition, the compressive part of stress range affered the crack propagation behavior and the accelerated crack propagation rate was observed, causing shorter fatigule life than that without a compressive part. To clarity the effect of the compressive stress range of cyclic amplitude on the crack propagation, push-pull fatigue tests with a constant stress amplitude two step multi-fold stress were carried out for plane sheet specimens (CCT) of low carbon steel ( the ultimate tensil strength is 517 MPa). The crack opening stress level was measured by the unloading elastic compliance method. The conclusions obtained are summarized as follows: (1) When the crack propagation rate was high, the compressive part of stress range accelerated the propagation , due to lower crack opening stress level. (2) When the compressive part of stress range, that is the absolute value of minimum stress in cyclic stress range, increased beyond a certain value, the acceleration of crack propagation rate appeared.The compressive part of stress range larger than this value showed the same acceleration effecton the crack propagation behavior. (3) The acceleration effect of the compressive part of stress on the crack propagation rate was observed in the tests where the stress ratio R_1 in one step was 0 and R_2 in another step was -0.33. (4) When the crack propagation rate was low, the comppressive part of cyclic stress range decelerated the crack propagation rate because of the oxide induced crack closure.
社団法人日本材料学会の論文
1985-10-15

疲労き裂進展に及ぼす圧縮応力成分の影響

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