Low Cost Fabrication of Carbon-Carbon (C-C) Aeroshells for Hypersonic Vehicles

Future Air Force hypersonic vehicles will employ complex shapes and fly extended maneuvering trajectories. Since the flight times may increase by an order of magnitude or more, existing ablative thermal protection systems will not be practical due to their excessive surface recession and high density. The future Air Force vehicles will employ wave rider shaped carbon-carbon aeroshells over multiple insulating layers to protect the payload. The present manufacturing method employed for these aeroshells is hand lay-up of two-dimensional fabric in which substructures are tediously formed and debulked to create a carbon/phenolic precursor aeroshell. Even with this time-consuming process, the aeroshell often delaminates during carbonization so the part must be scrapped. This leads to an expensive, trial and error process to develop an acceptable carbon-carbon part. In order for carbon-carbon aeroshells to serve as a practical component for future hypersonic vehicles, it is necessary to develop less expensive fabrication methods, and more reliable, well understood processing techniques. One attractive fabrication method uses a tape-wrapping technique in which a bias-ply C/Ph tape is wrapped over a mandrel, cured, carbonized, and graphitized to form a carbon-carbon aeroshell. Tape-wrapping has been recently applied successfully to the development of erosion-resistant carbon-carbon exit cones. A second attractive fabrication technique is to replace the flat 2D lay-ups with an involute, or rosette construction. The involute plies spiral from the inner to outer diameter of the carbon-carbon part providing through-thickness reinforcement to reduce the potential for delaminations. Involute technology was used throughout the 1980s and 1990s to build carbon-carbon exit cones for Air Force missile systems such as the Peacekeeper. Furthermore, processing techniques can also be improved significantly using models that address pore pressures and shrinkage stresses during carbonization. These processing models have been applied successfully to the recent fabrication of carbon-carbon exit cones. The goal of the proposed program is to demonstrate low cost fabrication methods for carbon-carbon aeroshells that are based upon well understood, physics-based processing models. The specific objectives include definition of a representative aeroshell, development of a processing model, optimization of an involute ply pattern, design of an aeroshell subcomponent, and fabrication of two or more carbon-carbon aeroshell subcomponents. The proposed Phase I effort will be performed by a team of Materials Research & Design (MR&D), ATK Launch Systems, and Mr. H.O. Davis. MR&D will develop the process model, define the involute ply pattern, and design the subcomponents. ATK will fabricate the subscale carbon-carbon aeroshells, and Mr. H.O. Davis will guide the process modeling and involute design. This team offers a state of the art skill set, which is uniquely suited to the Phase I program.