NASA's Glenn Research Center has developed a breakthrough means of adapting strong but lightweight carbon fiber composite material to fabricate structures of complex shape such as specialized components for drive systems. Conventional methods of using discontinuous fiber composites for forming complex shapes can produce defects including a tendency toward weakness and fatigue at the cut ends of the fibers. Glenn's novel technology instead uses multiple layers of formable continuous fiber composite material, eliminating the cut ends that form a potential site for failure, as well as filler materials between plies.
Using this method, manufacturers can provide the optimum shape of the continuous plies and thus of the structure as a whole. The structure can then meet high specific strength and high cycle fatigue resistance requirements for rotor-craft gears and other applications including aircraft, power generation such as wind turbine systems, unmanned vehicles, and urban air mobility (UAM).
Designers are constantly seeking to improve the power-to-weight ratio of components in rotorcraft and other flight vehicles. One approach has involved using lightweight carbon fiber composite materials to replace gear web portions and other components that are typically made from steel. The problem with using fiber composite materials comes when more complex shapes are required. To create thickness variation and other accommodations for complex shapes, manufacturers can stack cut continuous fiber plies and/or form short, fiber-reinforced composite material to the desired shape. Unfortunately, these methods leave cut fiber ends within the structure that often become initial sites for high cycle fatigue damage in high-speed, high-power-density applications.
Glenn's new method tackles this problem with one of three approaches. The first approach is applicable to gears that are planar in shape and have a single hub and a single rim. The hub and web sections of the gear are made as an integrated structure with decreased thickness from the hub inner diameter to the web outer diameter. The thickness variation is accomplished using multiple layers of continuous fiber composite material formed to specific shapes and separated by filler materials.
The second approach is applicable to gears that have an extended gear body in the axial direction rather than a simple planar structure. In this approach, the gear body is made using multiple layers of continuous fiber composite material in the shape of a solid of revolution.
The third approach is a power transfer assembly made by combining approaches one and two. With any of these three approaches, the material can be tailored to the structure by the properties of fibers used, the number of fiber layers used, and the location of the fibers relative to the neutral axis of the structure. Glenn's innovation opens the door for carbon fiber composite materials to be used for many applications for which they were previously unsuited.