Hybrid structures in aero engines

Abstract

The continuous increase in already high specific performance of aero engines and growing optimization demands require further innovation in the fields of materials and design of structures to reach the primarily aerodynamic driven goals. In general, the improvement of materials on its own cannot guarantee success but rather the combination of different materials offers the potential for increased performance and additional functionality. For using different material properties, an adapted hybrid design is necessary. Within this design outstanding material characteristics should be addressed, whilst the lower performance properties must not be critical and provoke faults. By combining different materials within hybrid structures, the feasible increase in performance is accompanied with the challenges of handling a lot more parameters for optimization. Three examples are described in this paper, showing hybrid design approaches for aero engine structures. The design principles can be transferred to similar structures by using the shown basic mechanisms. The first example covers a hybrid ring structure used for simultaneous movement of stator vanes within an axial compressor. BLISK technology with high aerodynamic efficiency and low structural damping requires an accurate positioning of the stator vanes to avoid dynamic excitation in transient surroundings during a complete flight cycle. Additionally, the weight of the structure should be reduced compared to conventional in-service structures. A second example shows a hybrid fan blade. Here it is demonstrated how titanium can be combined with carbon fibre-reinforced plastics to create an airfoil. This concept can be implemented in generating stator vanes and rotor blades for aero engines. A special surface treatment leads to a non-aging jointbetween the two materials. The third example explains the basics for an alternative hybrid rotor design. Three titanium rotor segments are joined together by brazing under vacuum conditions. During the manufacturing process, the inner areas of the rotor are accessible which offers the opportunity to integrate cavities as well as fibre reinforcement.