き裂の発生と伝ぱを分離した疲労寿命の信頼性工学的研究

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A statistical nature of fatigue life (total life) N_f was studied by decomposing N_f into the crack initiation life N_i and crack propagation life N_p. By assuming that both N_i and N_p follow log-normal distributions and that the coefficient of variation is larger for N_i than for N_p, the distribution of N_f was derived theoretically by using Monte Carlo simulation. Mutual independence of N_i and N_p Was also assumed. It was shown that N_f followed a composite log-normal distribution approximately. In the regions left of and right of the transition point, this composite distribution was similar to that of N_p and to that of N_i, respectively (the "transition point" denotes the point at which plot of N_f breaks into two segments on log-normal probability paper) . The transition point moved downwards with an increase in the average ratio of N_i to N_p. When this ratio was significantly small or large, N_f followed actually a simple log-normal distribution similar to the distribution of N_p or to that of N_i, respectively. By combining the above results with the well-known experimental fact that the ratio of the crack initiation life to the crack propagation life increases with a men decrease in stress level, a new interpretation was presented to the stress level dependence of the fatigue life distribution. This interpretation is different from the conventional one which is based on the mixed distribution. The present theory was examined experimentally. The data on an aluminum alloy and a low carbon steel showed that both N_i and N_p followed log-normal distributions approximately and that the coefficient of variation was larger for N_i than for N_p. Furthermore, the distribution of N_f as derived by Monte Carlo simulation was in good agreement with the measured distribution of N_f.
社団法人日本材料学会の論文
1982-07-15

き裂の発生と伝ぱを分離した疲労寿命の信頼性工学的研究

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