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because of good structural properties and toughness allows a thin shell design and passive cooling by thermal radiation. The limiters consist of 24 U-shaped segments in a 5- to 6-ft-diameter toroidal arrangement with the base of the U-shaped segments facing inward. The CC limiter is based on a 0-90°, 2-D composite using staple fiber PAN yarn as a knit cloth. The width of the U-shaped segment is 21 cm and the leg height is approximately 6 cm with a wall thickness of 1 cm. The CC limiters must function at approximately 3990°F with short-duration spikes of 5000°F to 6000°F (ref. 17). Carbon-carbon is being considered for containers in which nuclear wastes are stored because of the high temperature that might be generated. Good thermal stability also makes CC attractive for use on laser shields to protect space-based satellite systems from the heat of high-powered laser beams in a space defense scenario. In a completely different environment, the compatibility of carbon with body tissues makes CC an interesting bone replacement in areas such as the hip instead of the currently used stainless steel (ref. 14).

Carbon-carbon is used in fuel cells in a commercial application that is related to electric power generation. The basic fuel cell system consists of a fuel processor that converts raw material fuel into hydrogen-rich gas, fuel cells that directly convert chemical energy into electrical energy, and a power conditioner to convert the fuel cell dc current into ac current. In practice, many individual fuel cells are connected in series to form fuel cell stacks; the power generator consists of many modules of these stacks. Currently, the most developed system is based on a phosphoric acid electrolyte with CC electrodes and other structural components. The cells operate at 400°F and generate from 200 kW to 11 MW of electrical energy. The CC functions well because of its relatively high thermal and electrical conductivity and its resistance to the fuel cell environment (ref. 18).

Carbon-carbon use in glass container forming machines as an asbestos replacement for hot-end glass contact applications illustrates its potential commercial growth. A typical machine arrangement is shown in figure 11, where K-Karb 2-D CC from Kaiser Aerotech is used as pushout pads, stacker bars, ware transfer pads, and machine conveyor ware guides (ref. 19). The CC material showed wear characteristics from 100 to 300 times greater than asbestos for these applications, and because it does not get wet by molten glass and does not require external cooling or frequent replacement, it is a cost-effective replacement for asbestos.

Additional commercial applications of K-Karb CC include vanes for rotary vane compressors and vacuum pumps, in which the CC replaces other composite and graphite parts to increase service life; nuts, bolts, and fittings to assemble major graphite elements in vacuum furnaces and increase working life over formerly used amorphic graphite parts; and

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Figure II. Section of glass container forming machine showing CC applications (Kaiser Aerotech).

flat and cylindrical heating elements for hot isostatic presses to increase work life up to 10 times over amorphic graphite, provide consistent resistance numbers to minimize power source adjustments, and allow increased working temperatures to 4000°F (2200°C). Other commercial applications include sintering trays for carbonizing and carbiding furnaces in which toughness of the CC tolerates rough shop usage better than brittle graphites; clutch disks for racing and other high-performance cars to provide high-temperature stability; and planar bearings in which temperatures are too high for Teflon or similar materials and in which graphite suffers from catastrophic failures (R. Jensen, Kaiser Aerotech, personal communication, August 1989).

The applications and ultimate markets for CC materials are continually developing for both military and commercial use. New domestic and foreign suppliers have contributed to the acceptance of this unique and versatile material through the use of improved high-modulus and highstrength carbon fibers, the development of high-char organic polymers, improved pitch matrix precursors, new rapid processing CVI technology, a better understanding of fiber-matrix interface phenomenology, and ever-increasing production capabilities. The applications discussed here indicate the variety of roles that CC can fulfill; it is hoped that they will lead to additional future uses.

References

1. Carroll, T. J.; and Connors, D. F.: Final Report for Rapid Densification of 2D Carbon-Carbon Preforms. Textron Specialty Materials Report, Dec. 1989.

2. Curry, Donald M.; Latchem, John W.; and Whisenhunt, Garland B.: Space Shuttle Orbiter Leading Edge Structural Subsystem Development. AIAA-83-0483, Jan. 1983.

3. Curry, Donald M.: Carbon-Carbon Materials Development and Flight Certification Experience From Space Shuttle. Oxidation-Resistant Carbon Carbon Composites for Hypersonic Vehicle Applications, Howard G. Maahs, ed., NASA CP-2051, 1988, pp. 29-50.

4. Martin, Jim: Creating the Platform of the Future NASA—The National Aerospace Plane. Def. Sci., vol. 7, no. 9, Sept. 1988, pp. 55-61.

5. Industry Observer Brief. Aviation Week & Space Technol., Aug. 15, 1988, p. 11."

6. Hordonneau, A.; and Grenie, Y.: Multi-Direction in Carbon-Carbon. Aerosp. Compos. & Mater., Autumn 1988, p. 17.

7. Dixon, G. A.: Large Rib-Stiffened Composite Panel. Super-Temp News Release, B.F. Goodrich, May 1989.

8. Covault, Craig: X-30 Technology Advancing Despite Management Rift. Aviation Week & Space Technol., Mar. 7, 1988. pp. 36-43.

9. Sheehey, P.: LTV Turbine Rotor Exceeds Test Objectives. News Release M88-21, LTV Corp., Aug. 23, 1988.

10. Processing Materials and Fabrication Improvements Puts CarbonCarbon Technology Ahead. Adv. Mater., vol. 10, no. 18, Oct. 24,

1988.

11. Marsh, G.: Braving the Heat. Aerosp. Compos. & Mater., vol. 1, no. 4, Summer 1989, pp. 28-32.

12. Taylor, Allan: Fabrication and Performance of Advanced CarbonCarbon Piston Structures. Fiber-Tex 1988, John D. Buckley, ed., NASA CP-3038, 1989, pp. 375-395.

13. Taylor, Allan H.: Lightweight Piston. U.S. Patent 4,683,809, Aug. 1987.

14. Holusha, J.: Withstanding 3,000-Degree Heat. The New York Times, Nov. 23, 1988, p. C-6.

15. West, P.: Weight Saving Carbon-Carbon Brakes Gaining Favor on Commercial Aircraft. Adv. Mater., vol. 10, no. 20, Nov. 28, 1988.

16. DeMario, William F.: New World for Aerospace Composites. Aerosp. America, vol. 24, Oct. 1985, pp. 36-40, 42.

17. Labik, G. W.; Bialek, J.; Owens, T. K.; Ritter, R.; and Ulrickson, M.: 77-77? Carbon-Carbon Composite RF Limiters. Plasma Physics Lab., Princeton Univ., 1987, pp. 125-128.

18. Rastler, D.: Electric Power Research Institute Fuel Cell Program. EPRI Tech. Brief, Electric Power Research Inst., Mar. 29, 1988.

19. Report on the Economies Achieved by Replacing Asbestos With K-Karb Carbon-Carbon. Kaiser Aerotech Tech. Bull., 1980.

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Carbon-fiber-reinforced carbon matrix (carbon-carbon) composites have received increasing emphasis over the past 15 years. These materials have been used primarily in the aerospace and automotive industries. Carboncarbon composites can be made in a wide variety of forms from one- to n-dimensional using unidirectional tows, tapes, or woven cloth. Because of the multiformity. their mechanical properties can be readily tailored Carbon materials have high strength and stiffness potential as well as high thermal and chemical stability in inert environments. These material systems must, however, be protected with coatings and/or surface sealants

when used in an oxidizing environment.

This document contains papers that discuss the major areas of expertise relating to carbon-carbon materials and composite fabrication. Topics presented arc fiber manufacture, carbon textile preforms, matrix material. engineering mechanics, manufacture and design. coatings. and applications of carbon-carbon composites.

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Fiber manufacture: Composite design: Unique carbon fibers; Coatings on fibers: 286 Carbon preforms Coatings on composites: Matrix materials: Mechanics and prop- IT PRICE cope ertie-Applications A13

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