疲労き裂発生モデルとモンテカルロ法によるランダム荷重下の寿命推定

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In the previous report, authors proposed a new mechanical model for the fatigue crack initiation and investigated the fatigue life properties under variable stress amplitude. In this study, using the montecarlo method the fatigue crack initiation lives were estimated for random loads with exponential, weibull and uniform density based on this model. The outline of the model is as follows. In fatigue test, although great many micro fatigue damages are occured in the material, the number of cracks which can grow up to visual length is limited, because many micro cracks among them can not penetrate the grain boundaries. 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 distribution function of the crack initiation life, N_c, is expressed as in equation(3) and(4). In the equations, f_<ΔNm> (n) is the probability density function PDF of the number of cycles consumed by the micro crack propagation of the m-th number of transgranular, f_<ΔNm>,_ω(n) is the PDF of the number of cycles consumed by the crack penetration of m-th number of grain boundaries. And symbol * signifies the convolution integral, k is the set of the number of micro fatigue damages on the material surface. The reliability system of the model is expressed as in Fig. 2. After the PDF of f_<ΔNm>(n) and f_<ΔNm>,_ω(n) are determined, the montecarlo simulations are carried out in accordance with the flow chart of Fig. 8. On the above random loads, the effects of the shape parameter, the scale parameter, the maximum stress and the minimum stress amplitude of the stress frequency distributions are considered. Estimated results are a good agreement with the experimental results obtained by authors and others qualitatively.
社団法人日本船舶海洋工学会の論文

疲労き裂発生モデルとモンテカルロ法によるランダム荷重下の寿命推定

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