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Fiber-reinforced plastics (FRP), also known as fiber-reinforced polymers, are a category of composite plastics specifically using fiber materials to mechanically augment the elasticity and strength of the plastic. They consist of a polymer matrix – the original plastic which is usually tough but weak – which is blended with a reinforcing material to yield a final product with the desired material or mechanical properties.
The polymer matrix is developed via a step growth or addition polymerisation and is usually an epoxy, vinylester or polyester thermosetting plastic. FRP are chiefly created through molding processes, where a mold is used to place a fiber preform – containing balsalt, carbon, an aramid, or even glass - into the matrix. Occasionally asbestos, wood or paper can be incorporated instead.
After wetting and curing, the fibers and matrix take on the shape of the mold. The resulting structure has a greater mechanical strength and elasticity than the original plastic, toughened by the addition of the reinforcing fiber or filament, which plays a critical role in differentiating the parent polymer from the FRP.
The characteristics of fiber-reinforced plastics hinge upon factors such as the mechanical properties of the matrix and the fiber, the volumes of both and the length and orientation of the fibers in the matrix.
FRPs have a low weight but are incredibly strong, and have good fatigue, impact and compression properties. This makes them of great interest to the motor industry who aim to replace metal with lighter weight materials to not only make the cars stronger but more fuel efficient.
They also demonstrate 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.
The composite plastics can be manufactured cost-effectively and can be tailored to suit a wide range of performance specifications, meaning they have a wide range of uses in many industries including the automotive, aerospace, construction and marine sectors.
Glass: When combined with the matrix, glass – which acts as a good insulator – forms fiberglass or glass reinforced plastics. Plastics reinforced with glass are ideal for the power industry as they have no magnetic field and are resistant to electrical sparks. They have been incorporated into engine intake manifolds where they offer a 60% decrease in weight over cast aluminium manifolds. They also give an improved surface quality and aerodynamics.
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Glass FRPs have also been used in gas and clutch pedals in cars as they can be molded as a single unit. The fibers are oriented in such a way that they support against specific stresses, increasing durability and safety.
However, glass FRPs are not strong, rigid or brittle as carbon fiber reinforced materials and can be expensive to produce.
Carbon: Materials based on carbon fibers exhibit a high tensile strength, chemical resistance, stiffness and temperature tolerance. Carbon atoms form crystals which lie along the axis of the fiber; this serves to strengthen the materials by increasing the strength to volume ratio. Carbon fiber reinforced plastics are used in sporting goods, gliders and fishing rods for example.
Carbon FRPs have been incorporated into the rudders of the Airbus A310 where they have decreased the number of components needed to create it by 95%. The simple molded parts have reduced the production and operational costs and are 25% lighter than the sheet aluminium traditionally used, making them more fuel efficient too.
Aramids: Aramids are a class of synthetic polyamide formed from aromatic monomers – ring-shaped molecules – which demonstrate robust heat resistance. For this reason, they are used in bullet-proof and fire-resistant clothing.
As demonstrated, fibre reinforced plastics have a wide range of uses in the automotive and aviation industry. They can also be used in the construction industry to strengthen beams, columns and slabs utilised in building and bridges. KONE elevator company have also developed Ultrarope to replace steel cables in their lifts. The carbon fibres are sealed in a high-friction polymer and are designed for use in buildings that require 1km of rope, most steel cables only reach 500m.
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