変動応力振幅下の疲労強度に関する確率論的一考察

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In this study authors proposed the stochastic model for the fatigue crack initiation and discussed on the estimation method of fatigue life under variable stress amplitude. The outline of the model is as follows. In fatigue test, although great many micro fatigue damages are occurred in the material, the number of cracks which can grow up to visual length is limited, because many micro cracks can not penetrate the grain boundary. Actual fatigue crack initiates from the position where the number of cycles for visual crack initiation takes the smallest value in the material. In the model, the crack initiation life,N_c, is expressed as the sum of ND and N_w, where N_D Is a number of cycles consumed by the crack propagation of transgranulars, N_w Is a number of cycles consumed by the crack penetration of grain boundaries. Since ND and N_w are different with the positions in the material. N_c takes several values. To estimate the smallest number of cycles of N_c, smallest value distribution is introduced in each variable stress amplitude. In this paper, it is considered with the conditions of constant stress amplitude and variable stress amplitude with the exponential and the uniform stress frequency distribution. Estimated results are a good agreement with the experimental results qualitatively. It is clarified that the fatigue strength under variable stress amplitude may be stochastically estimated by the consideration of fatigue damage induced by the stress below fatigue limit
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変動応力振幅下の疲労強度に関する確率論的一考察

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