Reliability Analysis of Rotorcraft Composite Structures

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Abstract
This paper develops a probabilistic analysis framework to predict the fatigue reliability of laminated composites and applies it to tapered composites used in rotorcraft structures. The method combines finite-element analysis, composite laminate analysis, fatigue failure modeling, and first-order reliability analysis to achieve this objective. This methodology is demonstrated on a composite helicopter rotor hub test specimen with thick, thin, and tapered regions. The specimen is subjected to centrifugal and oscillatory bending loads. The failure mechanism observed for this type of fatigue loading is an initial tension crack followed by internal delamination at the thick-to-taper transition, where internal ply drop-offs occur. The proposed method predicts the probability of delamination initiation for such rotor hubs. The method is validated using full-scale test results.