A method is proposed for estimating the hazard rate and reliability function of structural components under the fatigue environment including random overloads. The fatigue crack propagation process is stochastically analyzed by the use of a Markov approximation method in consideration of the retardation effect due to the overloads. The retardation effect is expressed by the probability distribution of the total delay time for the crack propagation process. Firstly, the theoretical approach on the random crack growth is applied under the condition of random occurrence of overloads. The hazard rate of structural components with respect to the ductile failure as well as the fatigue failure is secondly investigated with the aid of the numerical calculation known as the importance sampling simulation. The reliability function for the failure of structural component is shown as the result of the hazard rate. One of the interesting results is that the possibility of failure by overloads is more dominant than the retardation effect of crack growth due to overloads in the high reliability range.
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