実働荷重疲労に対する信頼性設計手法の提唱

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A reliability-based design method has been proposed for fatigue under service loads. The method is a practical one because it does not require to conduct fatigue tests on a large number of specimens under the relevant loading condition. In order to develop such a practical method, literature survey was carried out concerning the statistical nature of the cumulative cycle ratio D≡Σn_i/N^^∿_t where N^^∿_t was the fatigue life under constant amplitude loading as given by the S-N curve. The survey revealed the following common tendencies: (1) D follows a log-normal distribution approximately, and (2) η_D, the coefficient of variation of D, is roughly equal to η_N, the coefficient of variation of the fatigue life N under constant amplitude loading. Based on (1) and (2) above, a reliability based design method was proposed. In this method, S-N^^∿/k curve is used as design fatigue curve, and Σn_i/(N^^∿_i/k)≦1 is used as a design criterion. The factor k is determined from ln 1/k=ln(μ^^^_D/√<1+η_N^2>)+[Φ^<-1>(P_a)+n^<-1/2>Φ^<-1>(γ)]√<ln(1+η_N^2)> where μ^^^_D is the estimate of the mean value of D≡Ση_i/N^^∿_i, n is the number of specimens tested to obtain μ^^^_D, 1-P_a is the reliability goal, 1-γ is the confidence coefficient, and Φ^<-1> is the inverse function of the standard normal distribution function. The above equation was derived from the condition that the reliability of 1-P_a is attained with the confidence of 1-γ. The most remarkable point in employing this design method is that fatigue tests to be conducted under the relevant loading condition is simply for obtaining μ^^^_D, hence a large number of samples are not required. A simple design diagram for obtaining k easily was also proposed.
社団法人日本材料学会の論文
1985-06-15

実働荷重疲労に対する信頼性設計手法の提唱

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