Carbon fiber is a polymer and is sometimes known as graphite fiber. It is a very strong material that is also very lightweight. Carbon fiber is five-times stronger than steel and twice as stiff. Though carbon fiber is stronger and stiffer than steel, it is lighter than steel; making it the ideal manufacturing material for many parts. These are just a few reasons why carbon fiber is favored by engineers and designers for manufacturing.
Carbon fiber is composed of carbon atoms bonded together to form a long chain. The fibers are extremely stiff, strong, and light, and are used in many processes to create excellent building materials. Carbon fiber material comes in a variety of "raw" building-blocks, including yarns, uni-directional, weaves, braids, and several others, which are in turn used to create composite parts. The properties of a carbon fiber part are close to that of steel and the weight is close to that of plastic. Thus the strength to weight ratio (as well as stiffness to weight ratio) of a carbon fiber part is much higher than either steel or plastic. Carbon fiber is extremely strong. It is typical in engineering to measure the benefit of a material in terms of strength to weight ratio and stiffness to weight ratio, particularly in structural design, where added weight may translate into increased lifecycle costs or unsatisfactory performance.
Carbon fibers or carbon fibres are fibers about 5-10 micrometres in diameter and composed mostly of carbon atoms. Carbon fibers have several advantages including high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion. These properties have made carbon fiber very popular in aerospace, civil engineering, military, and motorsports, along with other competition sports. However, they are relatively expensive when compared with similar fibers, such as glass fibers or plastic fibers.
Classification and types
Based on modulus, strength, and final heat treatment temperature, carbon fibers can be classified into the following categories:
Based on carbon fiber properties, carbon fibers can be grouped into:
- Ultra-high-modulus, type UHM (modulus > 450 Gpa)
- High-modulus, type HM (modulus between 350-450 Gpa)
- Intermediate-modulus, type IM (modulus between 200-350 Gpa)
- Low modulus and high-tensile, type HT (modulus < 100 Gpa, tensile strength > 3.0 Gpa)
- Super high-tensile, type SHT (tensile strength > 4.5 Gpa)
Composite materials
Carbon fiber is most notably used to reinforce composite materials, particularly the class of materials known as carbon fiber or graphite reinforced polymers. Non-polymer materials can also be used as the matrix for carbon fibers. Due to the formation of metal carbides and corrosion considerations, carbon has seen limited success in metal matrix composite applications. Reinforced carbon-carbon (RCC) consists of carbon fiber-reinforced graphite, and is used structurally in high-temperature applications. The fiber also finds use in filtration of high-temperature gases, as an electrode with high surface area and impeccable corrosion resistance, and as an anti-static component. Molding a thin layer of carbon fibers significantly improves fire resistance of polymers or thermoset composites because a dense, compact layer of carbon fibers efficiently reflects heat.
The increasing use of carbon fiber composites is displacing aluminum from aerospace applications in favor of other metals because of galvanic corrosion issues.
Carbon fiber can be used as an additive to asphalt to make electrically conductive asphalt concrete. Using this composite material in the transportation infrastructure, especially for airport pavement, decreases some winter maintenance problems that led to flight cancellation or delay due to the presence of ice and snow. Passing current through the composite material 3D network of carbon fibers dissipates thermal energy that increases the surface temperature of the asphalt, which is able to melt ice and snow above it.
Textiles
Precursors for carbon fibers are polyacrylonitrile (PAN), rayon and pitch. Carbon fiber filament yarns are used in several processing techniques: the direct uses are for prepregging, filament winding, pultrusion, weaving, braiding, etc. Carbon fiber yarn is rated by the linear density (weight per unit length; i.e., 1 g/1000 m = 1 tex) or by number of filaments per yarn count, in thousands. For example, 200 tex for 3,000 filaments of carbon fiber is three times as strong as 1,000 carbon filament yarn, but is also three times as heavy. This thread can then be used to weave a carbon fiber filament fabric or cloth. The appearance of this fabric generally depends on the linear density of the yarn and the weave chosen. Some commonly used types of weave are twill, satin and plain. Carbon filament yarns can also be knitted or braided.
Microelectrodes
Carbon fibers are used for fabrication of carbon-fiber microelectrodes. In this application typically a single carbon fiber with diameter of 5–7 μm is sealed in a glass capillary. At the tip the capillary is either sealed with epoxy and polished to make carbon-fiber disk microelectrode or the fiber is cut to a length of 75–150 μm to make carbon-fiber cylinder electrode. Carbon-fiber microelectrodes are used either in amperometry or fast-scan cyclic voltammetry for detection of biochemical signaling.
Flexible heating
Known for their conductivity, or lack thereof, carbon fibers can carry very low currents on their own. When woven into larger fabrics, they can be used to reliably deliver infrared heating in applications requiring flexible heating elements and can easily sustain temperatures past 100 °C due to their physical properties. Many examples of this type of application can be seen in DIY heated articles of clothing and blankets. Due to its chemical inertness, it can be used relatively safely amongst most fabrics and materials; however, shorts caused by the material folding back on itself will lead to increased heat production and can lead to a fire.
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