Crack Propagation of Corrosion Fatigue under Service Loads

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  • 実働荷重下における腐食疲労き裂の進展
  • ジツドウ カジュウ カ ニ オケル フショク ヒロウ キレツ ノ シンテン

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The effects of stress history and corrosive environment on fatigue crack propagation under stress amplitude, both constant and continuously varying, respectively, are hereunder discussed, and the following facts have been made clear: In air the crack rate under the continuously decreasing stress becomes smaller than the expected one based on the linear cumulative damage hypothesis. This is due to the deceleration effect corresponding to the delay in crack propagation found under the high-low two-step stress history. On the other hand, there is no effect of stress history to be observed on the crack growth under the continuously increasing stress. Accordingly, ∫(dn/N)>1 is concluded under the stress varying up and down periodically because of the deceleration effect of the crack propagation. In saline the same deceleration effect is observed under the continuously decreasing stress as is in air. On the other hand, when the stress amplitude is increased, the acceleration effect of the crack propagation is observed, though it tends to diminish at a smaller increasing rate of the stress amplitude under the continuously increasing stress. In consequence, ∫(dn/N)>1 is concluded under the stress varying up and down with the long period because of the more effective deceleration effect than the acceleration effect, whilst ∫(dn/N)≈1 is obtained under the stress up and down with the short period because of the mutual offset of the acceleration effect and the deceleration effect.

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