What is Composites?

Composite materials (or composites for short) are engineering materials made from two or more components. One component is often a strong fibre such as fiberglass, quartz, kevlar, Dyneema or carbon fibre that gives the material its tensile strength, while another component (called a matrix) is often a resin such as polyester or epoxy that binds the fibres together, transferring load from broken fibers to unbroken ones and

between fibers that are not oriented along lines of tension. Also, unless the matrix chosen is especially flexible, it prevents the fibers from buckling in compression. Some composites use an aggregate instead of, or in addition to, fibers. In terms of stress, any fibers serve to resist tension, the matrix serves to resist shear, and all materials present serve to resist compression, including any aggregate. Shocks or repeated cyclic stresses can cause the fibers separate from the matrix, a condition known as delamination.

Graphite-reinforced plastic or carbon fibre reinforced plastic (CFRP or CRP)
Acrylonitrile -> Precursor ->Oxidized Fiber ->Carbon Fiber Yarn.
An important reinforcing fiber known for its light weight, high strength, and high stiffness that is produced by pyrolysis of an organic precursor fiber in an inert atmosphere at temperatures above 1,800 F. The material may also be graphitized by heat treating above 3,000 F.

It is a very expensive composite material or fibre reinforced plastic. Like glass-reinforced plastic, the composite material is commonly referred to by the name of its reinforcing fibers (carbon fiber), an example of part-for-whole metonymy. The plastic is most often epoxy, but other plastics, like polyester or vinylester, are also sometimes used.

It has many applications in aerospace and automotive fields, as well as in sailboats, and notably in modern bicycles, where these qualities are of importance. It is becoming increasingly common in small consumer goods as well, such as laptops, tripods, model accessories and fishing rods.

Synthesis
Each carbon filament is made out of long, thin sheets of carbon similar to graphite. A common method of making carbon filaments is the oxidation and thermal pyrolysis of polyacrylonitrile (PAN), a polymer used in the creation of many synthetic materials. Like all polymers, polyacrylonitrile molecules are long chains, which are aligned in the process of drawing fibers. When heated in the correct fashion, these chains bond side-to-side, forming narrow graphene sheets which eventually merge to form a single, jelly roll-shaped filament. The result is usually 93-95% carbon. Lower-quality fiber can be manufactured using pitch or rayon as the precursor instead of PAN.

Glass-reinforced plastic (GRP),
It is a composite material or fibre reinforced plastic made of a plastic reinforced by fine fibers made of glass. Like graphite-reinforced plastic, the composite material is commonly referred to by the name of its reinforcing fibers (fiberglass), an example of part-for-whole metonymy. The plastic is most often polyester or vinylester, but other plastics, like epoxy (GRE), are also sometimes used. The glass is mostly in the form of chopped strand mat (CSM), but woven fabrics are also used.

GRP/GRE is a versatile material with many uses. Although GRP was originally developed in the UK during the Second World War as a replacement for the molded plywood used in aircraft radomes (GRP being transparent to microwaves) its first main civilian application was for building of boats, where it gained acceptance in the 1950s, and now plays a dominant role. But its use has broadened over the years, and it is used extensively within the automotive and sport equipment sectors, although its use there is being taken over by carbon fiber because of its lower weight. GRE is also used to make hot tubs, pipes for drinking water, sewers, chemicals, and so on.
Interesting fact: Thorpe Park's 'Tidal Wave' ride uses reinforced GRP for its 4 tonne boats.

Kevlar,
It is also known as Twaron and poly-paraphenylene terephthalamide, is a synthetic fibre that is five times stronger than steel, weight for weight. Kevlar is very heat resistant and decomposes above 400 C without melting. It is usually used in bulletproof vests, in extreme sports equipment, as dental floss, and for composite aircraft construction. It is also used as a replacement for steel cords in car tires, in fire suits and as an asbestos replacement. Kevlar was invented by the DuPont corporation in the early 1960s, following the work of Stephanie Kwolek. Kevlar is a registered trademark of E.I. du Pont de Nemours and Company.

Kevlar is a type of aramid that consists of long polymeric chains with a parallel orientation. Kevlar derives its strength from intra-molecular hydrogen bonds and phenyl stacking interactions between aromatic groups in neighboring strands. These interactions are much stronger than the van der Waals interaction found in other synthetic polymers and fibers like dyneema. The presence of salts and certain other impurities, especially calcium, would interfere with the strand interactions and has to be avoided in the production process. Kevlar consists of relatively rigid molecules, which form a planar sheet-like structure similar to silk protein.

These properties result in its high mechanical strength and its remarkable heat resistance. Because it is highly unsaturated, i.e. the ratio of carbon to hydrogen atoms is quite high, it has a low flammability.

Kevlar molecules have polar groups accessible for hydrogen bonding. Water that enters the interior of the fiber can take the place of bonding between molecules and reduce the material's strength, while the available groups at the surface lead to good wetting properties. This is important for bonding the fibers to other types of polymer, forming a fibre reinforced plastic. This same property also makes the fibers feel more natural and "sticky" compared to non-polar polymers like polyethylene.

Kevlar's main weaknesses are that it decomposes under alkaline conditions or when exposed to chlorine. While it can support great tensile stress, like all fibers it tends to buckle in compression. In structural applications, Kevlar fibers can be bonded to one another or to other materials to form a composite.

G-10
A fiberglass based laminate. Layers of fiberglass cloth are soaked in resin and are compressed and baked. The resulting material is very hard, lightweight, and strong. Surface texture is added in the form of checkering. G-10 is an ideal material for tactical folders because of its ruggedness and lightweight. It is usually available in black.