Efficient methods for time-dependent fatigue reliability analysis

Two efficient methods for time-dependent fatigue reliability analysis are proposed in this paper based on a random process representation of material fatigue properties and a nonlinear damage accumulation rule. The first method is developed by matching the first two central moments of the accumulated damage to a well-known probability distribution, thus facilitating direct analytical solution of the time-dependent fatigue reliability. The second method uses the first-order reliability method (FORM) to calculate the reliability index based on a time-dependent limit state function. These two methods represent different trade-offs between accuracy and computational efficiency. The proposed methods include the covariance structure of the stochastic damage accumulation process under variable amplitude loading. A wide range of fatigue data available in the literature is used to validate the proposed methods, covering several different types of metallic and composite materials under different variable amplitude loading.