Spectral analysis of fatigue crack propagation resistance and its application to evaluation of the distribution of crack propagation fatigue life.

Fatigue crack propagation can be represented by a stochastic process such as a Markov process, which accounts for the distribution of crack propagation fatigue life. However, since we normally are able to obtain only limited information about the actual stochastic properties of the fatigue crack propagation process, it is necessary to represent the process by an appropriate model. This paper presents a new stochastic model which treats the material's resistance against fatigue crack growth as a spatial stochastic process evolving along the path of the crack. To obtain the stochastic properties of the fatigue crack propagation process, constant ΔK tests were conducted for several ΔK cases, and the parameters of the model were calculated by a spectral analysis using the maximum entropy method (MEM), which accounts for the statistical correlation that has been observed between adjacent fatigue crack growth rates. Using a proposed random crack propagation model, Monte-Carlo simulations were also performed and satisfactory agreement with the results of experiments were obtained.