HIGH TEMPERATURE STRUCTURES
One of the most important challenges in materials science is the development of high performance aeronautical structures which maintain their structural integrity at elevated temperatures. This problem is particularly important in the design of new space vehicles with greater maneuvering capability than the current space shuttle. Incorporating a sharp leading edge in the wing design would achieve this goal, but it would also increase the peak operating temperatures to 40000 F, well beyond the limits of current structural materials. Thus there is a critical need for new materials and designs for elevated temperatures.
High Temperature Material System with Active Cooling
Technical Approach
We propose to develop a materials system for the leading edge of aerospace vehicles with sharp leading edges. In order to be useful, any proposed sensor must meet several stringent criteria. In particular, prospective candidate materials must posess high specific stiffness and strength as well as creep resistance and resistance to oxidation at elevated temperatures.
Our approach is based on these specific design components:
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Carbon-Based Sandwich Composite Structure withCarbon-Carbon Skins andCarbon Foam Corev
FGM SiC-C Coatingv
Active Cooling
Composite Structure
The main component of our design is a sandwich construction with carbon-carbon composite face sheets and a porous carbon foam core. This arrangement produces a lightweight, highly efficient structure, particularly in flexure. The carbon foam core offers several significant advantages over conventional honeycomb construction both structurally as a stiffener as well as thermally as a heat exchanger. Since both core and face sheet materials are carbon, they are structurally useful at elevated temperatures provided that oxidation issues are properly addressed.Functionally Gradient Coating
The principal limitation in the use of carbon based structures at elevated temperatures is the extensive mass loss that occurs due to oxidation. A variety of oxidation resistant barriers have been utilized for these materials usually based on a ceramic coating such as silicon carbide. While this approach is moderately successful delamination and crack formation remain significant problems due to the thermal expansion mismatch between coating and substrate. Here, we propose to address that issue through the use of a coating material whose properties change through its thickness or functionally gradient materials( FGM ) . By tailoring the coating composition to vary continuously from pure carbon at the substrate interface to pure silicon carbide at the outer service, it is expected that the thermal expansion problems can be mitigated while maintaining the desired protection from oxidation of the structure.Active Cooling System
The final component of this high temperature material system is provided by active cooling. Here we rely on the porous nature of the carbon foam core and its high thermal conductivity to serve as a heat exchanger with a gas traveling through it. One possible gas for this function is helium as it is chemically inert and has excellent thermal properties In this way we hope to promote heat transfer from the wing leading edges to the remainder of the structure where it can be successfully dissipated.
