A Recursive Approach for Remaining Fatigue Life Predictions of Monitored Structural Systems

Fatigue-induced damage is one of the most uncertain and extremely unpredictable failure mechanisms for a large variety of mechanical and structural systems subjected to cyclic loading during their service life. A field-deployable system capable of (i) monitoring the critical components of these structural systems through non destructive evaluation (NDE) inspections, (ii) assessing their structural integrity, (iii) recursively predicting their remaining fatigue life (RFL), and (iv) updating a cost-efficient condition-based maintenance (CBM) plan is therefore ultimately needed. In contribution to these objectives, the first part of the paper provides an overview of a comprehensive reliability-based fatigue damage prognosis methodology — previously developed by the authors — for predicting the RFL of critical structural elements in aerospace structures. In the second part of the paper, a set of experimental fatigue test data published in the literature is used to provide an experimental validation of the proposed framework at the local component level. The results obtained from this study demonstrate (i) the importance and the benefits of a continuous NDE monitoring system, (ii) the computational efficiency of the proposed recursive Bayesian updating scheme, (iii) the accuracy in predicting (after each NDE inspection) the most probable damage propagation trajectory for a given damage mechanism evolving at a given damage location, and (iv) the robustness of the proposed framework in recursively updating and improving the RFL predictions.