A Study of Damage Tolerant Design for Composite Bearingless Rotor System.

A helicopter rotor system which consists of rotor blades and a hub, is a primary structure. For the components made of composite materials, a safe-life design as well as a damage tolerant design method would be required. In this paper such a damage tolerant design method using fracture mechanics and FEM analysis is described. Some single small defects, such as a crack, void or delamination were assumed to be in a rotor hub component, then the energy release rate around thedefect was calculated by FEM analysis. The crack propagation in a glass fiber composite which is a main structural material for the rotor system was examined. The onset of a crack propagation under repeated loads was obtained. The test results were analyzed by FEM method and the critical energy release rate around the defect was calculated. Finally, the allowable crack size of the hub was determined and the usefulness of this method was demonstrated.