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Carbon-Carbon Composites
| Article
# : |
16200 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
6 / 1989 |
1,640 Words |
| Author
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Howard G. Maahs
Howard G. Maahs is assistant branch head of the Applied
Materials Branch, Materials Division, at the NASA Langley
Research Center in Hampton, Viginia. |
Conceive of a sleek, futuristically shaped aerospace vehicle racing through the atmosphere at many times the speed of sound. Molecules of air continuously bombard the surface of the vehicle, driving its temperature up. Surface temperatures reach 2,000 degrees F, 2,500 degrees F, and even higher, depending on the location on the vehicle.
An aerospace engineer engaged in designing such a vehicle would discover that light weight materials capable of extended service at these extreme temperatures are simply not available. However, an emerging class of materials called carbon-carbon (C-C) composites is presently under development to fill this need. Participating significantly in this development are the National Aeronautics and Space Administration (NASA) and the Department of Defense.
In comparison with other materials, C-C composites are relative newcomers, having been discovered by accident in the late 1950s. Since then, these materials have been developed and improved, and are currently used in a variety of specialty applications, which include friction applications as aircraft brake discs, propulsion applications as rocket nozzle throats and exit cones, and military applications as missile nose tips. Possibly the best-known use of C-C composites is on the space shuttle, where they are used to protect the nose cap and leading the edges of the wings from the searing heat of reentry into the earth's atmosphere from space. In this role, they prevent the extreme heat generated during reentry from reaching the main metallic structure of the shuttle.
Because of the high-temperature strength and low density of C-C composites, aerospace engineers would like to use these materials in even more advanced applications. One application of considerable interest is as the structure of the aerospace vehicle itself rather than simply as a protective heat shield, as on the space shuttle. But suitable forms of these materials have yet to be developed. If these can be successfully developed, advanced aerospace vehicles such as the National Aero-Space Plane (NASP) and other hypersonic vehicles will be close to becoming a reality.
What are carbon-carbon composites?
C-C composites constitute a special subclass of composite materials. In simple terms, a composite is a material that contains both a reinforcing material to provide strength and stiffness, and a matrix material, or glue, to surround and hold the reinforcement in place. Many types of
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