Carbon-Fiber Reinforced Composite

any of a group of plastic materials containing carbon fibers as filler. The fibers can take the form of continuous filaments, strips, or cloth; chopped fibers are also used. The binders for these materials include such synthetic polymers as epoxy resins, polyester resins, phenol-formaldehyde resins, polyimides, organosilicon polymers (polymeric carbon-fiber composites), pyrolyzed synthetic polymers (coked carbon-fiber composites), and pyrolytic carbon (py-rocarbon carbon-fiber composites).

Articles of carbon-fiber composites can be formed by all the methods used with laminated plastics. With the most common method, the carbon filler is impregnated with a melt or solution of the binder, for example, an alcohol or hydrocarbon solution, and then dried to produce a semifinished product (prepreg). Blanks cut from the prepreg are gathered into a packet in the shape of the desired article and subjected to pressure, usually in hydraulic presses, autoclaves, or chambers fitted with rubber bags. The specific pressure here must not exceed 2.0–2.5 meganewtons per sq m (MN/m²), or 20–25 kilograms-force per sq cm (kgf/cm²), because of the extreme brittleness of the carbon fibers. Prepregs in the form of strips or filaments are also used in producing articles by a winding method. Coked carbon-fiber reinforced composites are obtained from the pyrolysis of polymeric carbon-fiber composites at temperatures of 300°-1500°C or 2500°-3000°C. In the manufacture of pyrocarbon carbon-fiber composites, the filler, which is not impregnated with a binder, is spread out in the shape of the desired article and then placed in a furnace, through which, in most cases, methane is passed. At 1100°C and a residual pressure of 2.6 kilonewtons per sq m (20 mm Hg), methane decomposes, and the pyrolytic carbon thus formed settles on the carbon fibers and acts as a binder.

Carbon-fiber reinforced composites combine a number of valuable properties. While possessing great strength and hardness, their density is low. They have a low coefficient of linear expansion (providing for good dimensional stability at elevated temperatures), a low coefficient of friction, high thermal and electrical conductivity, and high wear resistance. The composites also have good resistance to heat, chemicals, and radiation. Carbon-fiber reinforced composites are superior both to such other laminates as fiber glass reinforced plastics and asbestos plastics and to metals in terms of static and dynamic endurance, and they also have high vibration strength. For example, the fatigue strength upon bending of carbon-fiber composites having epoxy resins as a binder exceeds 400 MN/m², or 40 kgf/mm², and the vibration strength exceeds 480 MN/m², or 48 kgf/mm². The properties of carbon-fiber composites are highly anisotropic. Pyrocarbon and coked carbon-fiber composites are also distinguished by their good ablation characteristics. However, the impact strength of carbon-fiber composites is less than that of, for example, fiber glass reinforced plastics.

Carbon-fiber reinforced composites are important aircraft construction materials, allowing for a reduction in weight of parts for the fuselage, wings, and tail assembly by 15 to 50 percent. The composites are also used in making parts for spacecraft and supersonic aircraft, in manufacturing sporting goods (skis) and chemical equipment, and in shipbuilding and the automotive industry. Coked and pyrocarbon carbon-fiber composites are used for the external heat shields of returning spacecraft and as insulating materials for such internal elements of rocket engines as nozzles and combustion chambers.