Equivalent Stress Transformation for Efficient Probabilistic Fatigue-Crack Growth Analysis under Variable Amplitude Loadings

A general probabilistic fatigue-crack growth prediction methodology for accurate and efficient damage prognosis is proposed in this paper. The methodology is based on an equivalent stress transformation and the inverse first-order reliability method (IFORM). The equivalent stress transformation aims to transform the random variable amplitude loading to an equivalent constant amplitude loading spectrum. The proposed transformation avoids the cycle-by-cycle calculation under general random variable amplitude loadings. An IFORM is used to evaluate the probabilistic fatigue-crack growth behavior and to further enhance the computational efficiency. The computational cost of the proposed study is significantly reduced compared with the direct Monte Carlo simulation. Thus, the proposed method is very suitable for real-time damage prognosis because of its high computational efficiency. Numerical examples are used to demonstrate the proposed method. Various experimental data under variable amplitude loadings are collected for model validation.