What are composite materials?

Composites are defined as materials, which are consisted of two or more compovents variant physical and chemical properties. The wholly new material with unique properties develops from connection of fibres and resin. These properties can not be obtained by any component alone neither simple simulation. Significant types of composites are plastics reinforced by different kinds of fibres. They can be distributed into two groups according the length of fibres. Syntetic materials reinforced by short fibres so-called shortfibrous (the rate of length/average L/D<100) and syntetic materials reinforced by long fibres so-called longfibrous (L/D>100 i.e. fibres with length equal dimensions of whole section).

The shortfibrous composites are used for gouted moulding and plastics extrudates. The longfibrous composites are used for a big constructutions as ships, pressure tanks, wings of wind turbines. The principle of self fibrous reinforcement is following. The fibrous reinforcement has about one till two ranks higher strength and stiffness than matrix. These fibres are deformed less than polymeric resin. In so far that on the on the interface between fibre/polymer generate shear forces, which faciliate transfer of entire strain from infirm matrix to fibres in case of adhesion between both components. Fibres are able to support entire strain applied on composite section, so that infirm but deformablematrix is in practice without strain.

The weight is markedly decreased by using of composites against traditional materials such as steel. It results from low weight of composite, specific properties of individual components and possibility to make composite for given purpose. Because it is concerned a material combination, composites can be proposed with regard to specific properties, which carry range of advantages in comparison to traditional materials, e.g. chemical resistance, electrical and thermal insulation and so on.

Raw materials

Polyesters

Unsaturated polyester are the most used matrix for reinforced plastics composites, especially in combination with glass fibres. Polyester resins have good mechanical, electrical and chemical properties.

Methyl-methacrylates

Modified methyl-methacrylate resins have famous properties and are the most used in combination with highly quality fibres such as carbon. It is possible to load these resins with flame retardants, therefore they are excellent solution for applications, in which the fire resistance is demanded.

Epoxies

Epoxies have excellent mechanical and electrical propeties. These resins are usually used with carbon or glass fibres, if the amount of reinforcement is very high. They have good electical insulative properties in wide range of temperatures and considerable chemical resistance.

Vinyl esters

Vinyl esters combine the best properties of polyester and epoxides resins. They are acid and alkaliproof, especially at high temperatures. Glass-fibre reinforced vinylester profiles are good electrical and thermal insulants. 

Carbon fiber

 (alternately called graphite fiber) is a material consisting of extremely thin fibers about 0.0002-0.0004 inches (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 fiber. The crystal alignment makes the fiber incredibly strong for its size. Several thousand carbon fibers are twisted together to form a yarn, which may be used by itself or woven into a fabric. Carbon fiber can be combined with a plastic resin and wound or molded to form composite materials carbon fiber reinforced plastic (also referenced as carbon fiber) to provide a high strength-to-weight ratio material. The density of carbon fiber is also considerably lower than the density of steel, making it ideal for applications requiring low weight. The properties of carbon fiber such as high tensile strength, low weight, and low thermal expansion make it very popular in aerospace, military, and motor sports, along with other competition sports. The unique appearance of carbon fiber also makes it popular for stylistic purposes.

 
¼ micron  diameter carbon filament (running from bottom left to top right) compared to a human hair.

Fiberglass

 (also called fiberglass and glass fiber) is material made from extremely fine >fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer (FRP) or glass-reinforced plastic (GRP), is called “fiberglass” in popular usage.

 Aramid=Kevlar

  Aramid fibers are a class of heat-resistant and strong synthetic fibers. They are used in aerospace and military applications, for ballistic rated body armor fabric, and as an substitute .They are fibers in which the chain molecules are highly oriented along the fiber axis, so the strength of the chemical bond can be exploited.
 Kevlar is the registered name of Aramid.

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