Carbon fiber, also known as graphite fiber or carbon graphite, consists of thin strands of the periodic element called carbon. Carbon fibers have a high tensile strength and are very strong for their size, in fact, carbon fiber is the strongest material there is.
Each fiber is between 5-10 microns in diameter. Just to give you an idea of how small that is, one micron is about 0.000039 inches. A single strand of a spider's web is about 3-8 microns in diameter. Carbon fiber is 5 times stronger and twice as stiff as steel, it is highly chemically resistant and has a high-temperature tolerance with low thermal expansion.
Carbon fiber plays an important role in manufacturing engineering materials, high-performance vehicles, the aerospace industry, sporting equipment as well as musical instruments. The raw carbon fiber materials are made from organic polymers which consist of long strings of molecules held together by carbon atoms. Almost 90% of carbon fibers are made from the polyacrylonitrile (PAN) process, while the remaining 10% is manufactured from rayon or the petroleum pitch process. Materials, gases and liquids that are used in the carbon fiber manufacturing process determine the quality and grades of the carbon fiber, the highest grade with the best modulus properties are used in applications such as aerospace.
Carbon fibers were produced for the first time back in 1860 by English physicist, chemist and inventor, Joseph Swan, who used these fibers in light bulbs. Thomas Edison carbonized cotton threads and bamboo silvers at very high temperatures into an all-carbon filament, using them in one of the first-ever incandescent light bulbs to be heated by electricity. The American inventor Lewis Latimer developed a reliable carbon wire filament for the incandescent light bulb heated by electricity in 1880. In 1958 Roger Bacon created high-performance carbon fibers; they were manufactured by heating strands of rayon until they carbonized, however only 20% carbon fiber was found in the fibers created, they also had low strength and stiffness properties.
Dr. Akio Shindo developed a process in the early 1960s using polyacrylonitrile (PAN) as a raw material. 55% of carbon fiber was produced using this process. In 1960 a man called Richard Millington of H.I. Thompson Fiberglas Co. developed a process for producing a high carbon content (99%) using rayon as a precursor. The Carbon fiber produced from this process had sufficient strength to be used as a reinforcement for composites, having a high strength to weight property and was resistant to high temperatures.
Carbon fiber's high potential strength was realized in 1963 in a process developed by W.Watt, L.N. Phillips and W. Johnson at the Royal Aircraft Establishment in Farnborough, Hampshire. The newly developed process was patented by the UK Ministry of Defence and was then licensed to three companies, one of them which was Rolls-Royce. Rolls-Royce took advantage of the new material's properties to break into the American market with its RB-211 aero-engine with carbon fiber compressor blades. The RB-211's compressor blades were however proved vulnerable to damage from bird impact. This caused Rolls-Royce such a setback that the company was nationalized in 1971. The carbon fiber production plant was sold off to form Bristol Composites.
Experimental work during the 1960s led to the introduction of carbon fiber made from a petroleum pitch derived from oil processing. These fibers contained up to 85% carbon with excellent flexural strength. Since the late 1970s, further types of carbon fiber yarn entered the global market with higher strength and higher elastic modulus, such as T400 with a tensile strength of 4,000 Mpa and M40, a modulus of 400 Gpa, manufactured by Japanese company Toray. Carbon fibers from companies such as Toray, Akzo, and Celanese found their way to the aerospace application from secondary to primary parts, first in military and later in civil aircraft as in McDonnell Douglas, Boeing, Airbus and United Corporation planes.
Carbon fiber is supplied in a continuous tow wound onto a reel. The tow is a bundle of thousands of continuous individual carbon filaments held together and protected by a coating such as PVA.
Carbon fiber's atomic structure is very similar to graphite, consisting of carbon atoms sheets arranged in a hexagon pattern, the only difference is the way these sheets interlock. Graphite is a crystalline material, the sheets are stacked parallel to one another. The intermolecular forces between the sheets are weak according to Van der Waals forces, thus graphite's soft and brittle characteristics.
Carbon fiber may be turbostratic or graphitic, depending on the precursor to make the fiber. In turbostratic carbon fiber, the carbon atoms are haphazardly folded together. Carbon fibers derived from polyacrylonitrile are turbostratic and carbon fibers derived from mesophase pitch are graphitic after heat treatment of temperatures higher than 2200°C. Turbostratic carbon fibers tend to have high tensile strength, heat-treated mesophase-pitch derived carbon fibers have high stiffness or resistance and high thermal conductivity.
In the manufacturing process of carbon fiber, the raw materials are drawn into long strands. They are then woven into fabric or combined with other materials that are filament wound or molded into different shapes and sizes that may be needed.
In the PAN process there are usually five segments in the manufacturing of carbon fiber; spinning, stabilizing, carbonizing, surface treating and sizing.
In the spinning segment, PAN is mixed with other ingredients and spun into fibers, washed and stretched. After the spinning process the fibers are stabilized with chemical alterations. The stabilized fibers are then carbonized by using high temperatures to form tightly bonded carbon crystals. The surface of the fibers is treated by oxidizing them to improve bonding properties. After surface treatment, the fibers are coated and wound onto bobbins, loaded onto spinning machines that twist the fibers into different sizes of yarns. Instead of fibers being woven into fabrics, they may be formed into composites to form composite materials. Heat or pressure binds fibers together with a plastic polymer to form composites.
Aircraft and aerospace, wind energy and the automotive industry have the strongest demand for carbon fiber. Carbon fiber is known to be more expensive than other materials which is a limiting factor when implementing this material into the manufacturing process, especially in the automotive industry. Carbon fiber can be 10-12 times more expensive in comparison to steel.
Besides the high costs, there are also several challenges involved when manufacturing carbon fiber, such as: health and safety issues, skin and breathing irritation, close control is required to ensure consistent quality as well as arcing and shorts in electrical equipment due to the strong electro-conductivity of carbon fiber.
Carbon fiber is considered to be the most significant manufacturing material of our generation. In the automotive industry carbon fiber is currently used for high-performance vehicles, but carbon fiber composites for mass production of automobiles are also being implemented. In the construction industry, carbon fiber is used in lightweight pre-cast concrete for earthquake protection. Carbon fiber also plays an important role in the aircraft industry for manufacturing defense and commercial aircraft. In the energy industry, carbon fiber is also implemented to manufacture windmill blades, natural gas storage, and transportation.
Among aerospace-grade materials such as titanium, aluminum alloy, and stainless steel, carbon fiber is one of the vital materials used to manufacture Super Veloce's timeless masterpieces. Due to its lightweight and high tensile strength properties, carbon fiber is an essential material utilized for components such as the engine cam covers and baseplates forming part of the authenticity and mechanical integrity of these handcrafted works of art.