A carbon fibre is a long, thin strand of material about 0.0002-0.0004 in (0.005-0.010 mm) in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the long axis of the fibre. The crystal alignment makes the fibre incredibly strong for its size. Several thousand carbon fibres are twisted together to form a yarn, which may be used by itself or woven into a fabric. The yarn or fabric is combined with epoxy and wound or moulded into shape to form various composite materials. Carbon fibre-reinforced composite materials are used to make aircraft and spacecraft parts, racing car bodies, golf club shafts, bicycle frames, fishing rods, automobile springs, sailboat masts, and many other components where light weight and high strength are needed.
Carbon fibres are classified by the tensile modulus of the fibre. The English unit of measurement is pounds of force per square inch of the cross-sectional area or psi. Carbon fibres classified as “low modulus” have a tensile modulus below 34.8 million psi (240 million kPa). Other classifications, in ascending order of tensile modulus, include “standard modulus,” “intermediate modulus,” “high modulus,” and “ultrahigh modulus.” Ultrahigh modulus carbon fibres have a tensile modulus of 72.5 -145.0 million psi (500 million-1.0 billion kPa). As a comparison, steel has a tensile modulus of about 29 million psi (200 million kPa). Thus, the strongest carbon fibres are ten times stronger than steel and eight times that of aluminium, not to mention much lighter than both materials, 5 and 1.5 times, respectively. Additionally, their fatigue properties are superior to all known metallic structures, and they are one of the most corrosion-resistant materials available when coupled with the proper resins.
Thirty years ago, carbon fibre was a space-age material, too costly to be used in anything except aerospace. However today, carbon fibre is being used in wind turbines, automobiles, sporting goods, and many other applications. Thanks to carbon fibre manufacturers who are committed to the commercialization concept of expanding capacity, lowering costs, and growing new markets, carbon fibre has become a viable commercial product.