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Fiber-reinforced plastics (FRP) are a composite material consisting of a polymer matrix carefully combined with a supporting material or fiber which serves to enhance the mechanical strength and elasticity of the plastic. Common fibers include basalt, carbon, glass or aramid although in some cases it might include asbestos, wood or paper.
The core polymer matrix – usually an epoxy, vinylester or polyester thermosetting plastic – is manufactured using step-growth polymerization or addition polymerization. The matrix is hard but comparatively weak and the addition of powerful fibers and filaments serve to toughen it up and provide the desired mechanical and material properties to the resulting plastic.
The choice of fiber is crucial in differentiating the parent polymer from the FRP. Fiber-reinforced plastics – or fiber-reinforced polymers are they are also known – are well-suited to any design that necessitates weight saving, precision engineering, predetermined tolerances and simplification of parts in production and operation. Since FRP typically have a low weight and high strength, with good fatigue, impact and compression properties, making them attractive to a number of trades, including the automotive, aerospace and construction industries.
Carbon-fiber-reinforced plastics are strong and light, with a high tensile strength, chemical resistance, stiffness, tolerance to temperature and low thermal expansion. Although they can be expensive to manufacture, they are often found wherever a high strength-to-weight ratio is required – in aerospace, ship-building, and the automotive industry for example.
The rudder of the Airbus A310 is composed of carbon-FRP, which offers a 25% reduction in weight compared to aluminum sheeting. There is also a 95% reduction in the number of components as parts are combined into simpler molded parts, which are cheaper, quicker and easier to make than cast aluminum or steel objects, and uphold or even surpass tolerance and material strengths. The Airbus A35 XWB, for example, is 52% carbon-FRP, including its wing spars and components of the fuselage. Such measures offer an overall reduction in production and operations costs – the economy of parts results in lower production costs and weight savings, which leads to fuels savings and lowers the cost of flying the plane.
Carbon-FRPs are popular in civil engineering to strengthen concrete, masonry, steel, cast iron and timber structured either by retrofitting existing structures to improve their strength or as an alternative reinforcing material to steel.
The principle use of carbon-FRP is in retrofitting structures to improve and increase their load capacity and repair damage – bridges that carry far more traffic than there were ever intended to, for example. Carbon-FRP can be wrapped around certain areas of a structure, a column, for instance, to enhance the shear strength of its reinforced concrete.
Aluminum windows, doors and facades are also thermally insulated using plastics made of a glass-fiber-reinforced polyamide.
Carbon-FRPs are also attractive to the automotive industry where their high cost is lessened by the material’s unsurpassed strength-to-weight ratio. The lighter weight material replaces metal in the body panels of high-end cars and supercars, making the vehicles not only lighter but more fuel efficient too.
Glass-fiber-reinforced plastics, specifically glass-fiber-reinforced PA 66, are also used in the automotive industry in engine intake manifolds - the part of an engine that supplies the fuel/air mixture to the cylinders. Here, the FRP offers up to 60% reduction in weight over a cast aluminum manifold, along with an improved surface quality and aerodynamics. There is also a decrease in the number of components as parts are combined into simpler molds.
Glass-FRPs are also found in gas and clutch pedals, replacing stamped aluminum. Pedals can be molded as a single unit by combining the pedal and mechanical linkages, again streamlining production and operation. The fibers can also be oriented to reinforce again specific stresses, thereby increasing durability and safety.
Sporting and Consumer Goods
Carbon-RFPs are also making their way into sporting goods such as squash, tennis and badminton racquets; sport kite spars; hockey sticks; bike frames; fishing rods and surfboards. Paralympian Jonnie Peacock also uses a carbon FRP blade for running (and dancing in 2017 on Strictly Come Dancing), and high-performance drones often consist of carbon-FRP bodies, as do other remote-controlled vehicles and aircraft components – helicopter rotor blades for example. The material’s high strength-to-weight ratio makes it ideal for such sporting uses.
Other uses for carbon-FRP include in musical instruments – violin bows and guitar picks, for example, or the whole instrument in some cases! It is also found in firearms where it has replaced certain metal, wood and fiberglass components, and in lightweight poles such as tripods and tent poles.
Fiber-reinforced plastics have impressive electrical properties and a high-grade environmental resistance, along with good thermal insulation, structural integrity, fire hardiness, UV radiation stability and resistance to chemicals and corrosives. Those reinforced with glass are ideal for the power industry as they have no magnetic field and are resistant to electrical sparks.
Plastics reinforced with aramids - a class of synthetic polyamide formed from aromatic or ring-shaped monomers – demonstrate robust heat resistance and exceptional strength and thermals stability. As a result, they are utilized in bullet-proof and fire-resistant clothing.
Sources and Further Reading