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 (C/Ph) 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. In addition to alternate fiber architectures carbon-carbon processing techniques can also be improved significantly using models that address pore pressures and shrinkage stresses that occur during carbonization. These processing models have been applied successfully to the recent fabrication of carbon-carbon exit cones. The goal of the Phase II effort is to develop a material design and processing method that will produce a structurally sound C-C aeroshell for prompt global strike reentry body. The development effort will address both tape wrapped and involute fabrication methods. Tape wrapping provides potentially lower processing risk, but also offers lower strengths and stiffness. Alternatively, involutes offer higher thermostructural properties, but are expected to exhibit higher processing risk. The proposed Phase II effort will be performed by a team of Materials Research & Design (MR&D), ATK Launch Systems, Southern Research Institute (SoRI), and Mr. H.O. Davis. MR&D will analyze the operational behavior of the aeroshell, exercise the processing model, design the subcomponents and manage the program. ATK will fabricate materials and perform carbonization experiments. SoRI will characterize C/Ph materials for processing properties and carbon-carbon panels for thermostructural properties. Mr. H.O. Davis will guide the process modeling, involute design, and carbon-carbon fabrication.