Structural Design Against Fatigue Failure for Composite Rotor Blades

摘要

A new design procedure is developed for blade structural design and applied to a hingeless rotor. The procedure includes blade cross-sectional, nonlinear aeroe-lastic response, rotor trim and fatigue/durability analyses. The optimization also includes stiffness, weight, and frequency constraints. The sectional analysis is carried out using VABS to generate equivalent one-dimensional sectional properties from a three-dimensional blade model. The resulting cross-sectional properties are then used in a finite element based aeroelastic analysis with unsteady aerodynamics to compute the trim condition and the loads on the rotor given a forward flight condition. In order to improve the optimization efficiency, coupling of the aeroelastic and trim procedures is not conducted unless the stiffness and frequency constraints are satisfied. The resulting steady-state loads are used to predict fatigue life employing VABS for 3-D stress recovery over the cross-section and a strength-based fatigue model, in which fatigue failure occurs when the residual strength is equal to the applied stress. Failure is defined by the Tsai-Wu failure criterion, which accounts for the interaction of all stress components. The relations of residual strength are characterized in terms of unidirectional S-N data, laminate static strength, and the Weibull function. Preliminary results indicate that this approach is promising for blade structural design against fatigue failure.