Graphite-reinforced plastic
Graphite-reinforced plastic or carbon fiber reinforced plastic (CFRP or CRP), is a strong, light and very expensive composite material or fibre reinforced plastic. Like glass-reinforced plastic, which is sometimes simply called fiberglass, 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, vinylester or nylon, are also sometimes used. Some composites contain both carbon fiber and fiberglass reinforcement.
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 laptop computers, tripods, fishing rods, racquet sports frames, stringed instrument bodies and classical guitar strings.
Composite
The choice of matrix can have a profound effect on the properties of the finished composite. One common plastic for this application is graphite epoxy, and materials produced with this methodology are generically referred to as composites. The material is produced by layering sheets of carbon fiber cloth into a mould in the shape of the final product. The alignment and weave of the cloth fibres is important for the strength of the resulting material. In professional applications all air is evacuated from the mould, however in applications where cost is more important than structural rigidity, this step is skipped. The mould is then filled with epoxy and is heated or air cured. The resulting stiff panel will not corrode in water and is very strong, especially for its weight. If the mould contains air, small air bubbles will be present in the material, reducing strength. For hobby or custom applications the cloth can instead be draped over a mould, and the epoxy is "painted" over it, however because of the resulting lack of strength, this is usually only used for cosmetic details.
The large amount of (often manual) work required to manufacture composites has hitherto limited their use in applications where a high number of complicated parts is required.
The chemistry and manufacturing, techniques for thermosetting plastics like epoxy are often poorly-suited to mass-production. One potentially cost-saving and performance-enhancing measure involves replacing the epoxy matrix with a thermoplastic material such as nylon or polyketone. Boeing's entry in the Joint Strike Fighter competition included a Delta-shaped carbon fiber reinforced thermoplastic wing, but difficulties in fabrication of this part contributed to Lockheed Martin winning the competition.
Process
The process in which most CFRP is made varies, depending on the piece being created, the finish (outside gloss) required, and how many of this particular piece are going to be produced.
For simple pieces that relatively few copies are needed of (1-2 per day) a vacuum bag can be used. A fiberglass, or aluminum mold is polished, waxed, and has a release agent applied before the fabric and resin are applied and the vacuum is pulled and set aside to allow the piece to cure (harden). There are two ways to apply the resin to the fabric in a vacuum mold. One is a wet layup, where the 2 part resin is mixed and applied before being laid in the mold and placed in the bag. The other is a resin induction system, where the dry fabric and mold are placed inside the bag while the vacuum pulls the resin through a small tube into the bag, then through a tube with holes or something similar to spread the resin throughout the fabric fairly evenly. Wire lume works perfect for your tube that requires holes inside the bag. Both of those methods of applying resin require hand work to spread the resin evenly for a glossy finish, without pin-holes. A third method of constructing composite materials is known as a dry layup. Here, the carbon fiber material is already impregnated with resin (pre-preg) and is applied to the mold in a similar fashion to adhesive film. The assembly is then placed in a vacuum to cure. The dry layup method has least amount of resin waste and can achieve lighter constructions than wet layup.
A quicker method uses a compression mold. This is a two piece (male and female) mold usually made out of fiberglass or aluminum that is bolted together with the fabric and resin between the two. The benefit is that, once it is bolted together it is relatively clean and can be moved around or stored without a vacuum until after curing. However, the molds require a lot of material to hold together through many uses under that pressure. Many CFRP parts are created with a single layer of carbon fabric, and filled with fiberglass. A chopper gun can be used to quickly create these types of parts. Once a thin shell is created out of carbon fiber, the chopper gun is a pneumatic tool that cuts fiberglass from a roll, and sprays resin at the same time, the fiberglass and resin are mixed on spot. The resin is either extenal mix, where the hardener and resin are sprayed separately, or internal, where they are mixed internally, which requires cleaning ever every use.
For difficult or impossible shapes (such as a tube) a filament winder can be used to make pieces.
Automotive uses
CFRP is used extensively in automobile racing, most especially in Formula One and Indycar racing. The high cost of carbon fiber is mitigated by the material's unsurpassed strength-to-weight ratio, and low weight is essential for high-performance automobile racing. Race car manufacturers have also developed methods to give carbon fiber pieces strength in a certain direction, making it strong in a load-bearing direction, but weak in directions where little or no load would be placed on the member. Conversely, manufacturers developed uni-directional carbon fiber weaves that apply strength in all directions. This type of carbon fiber assembly is most widely used in the "safety cell" monocoque chassis assembly of high-performance race cars.
In 2000, Ferrari's factory Formula One racing team, long at the forefront of development of carbon fiber technology for racing vehicles, discovered a loophole in the Formula One rule book. Ferrari developed a rear wing that would deflect downward at high speed, thus changing the angle of attack of the wing in order to reduce drag. Downforce was also affected, but compensated for with design of the car's underbody and rear diffuser.
Several supercars over the past few decades have incorporated CFRP extensively in their manufacture, using it for their monocoque chassis as well as other components. Examples include the Koenigsegg CCR, McLaren F1, Bugatti Veyron, Bugatti EB110, Pagani Zonda, Ferrari Enzo and Porsche Carrera GT.
Until recently, the material has had limited use in mass-produced cars because of the expense involved — in terms of materials, equipment and the relatively limited pool of individuals with expertise in working with it. Recently, several mainstream vehicle manufacturers such as General Motors and BMW have started to use carbon fiber technology in everyday road cars.
Chevrolet is using carbon fiber in its flagship sports car, the Corvette. A special option package for the Corvette, dubbed the Z06, includes carbon fiber front bodywork for reduced weight and added rigidity.
BMW has begun studying and creating methods of producing carbon fiber reinforced plastics in its Landshut plant. To make the roof of the BMW M3 CSL, for example, 5 layers of carbon fiber cloth are placed in an 1,800 ton press, where epoxy is resin transfer moulded and heat-cured in a robot-automated process. The resulting roof is half the weight of an equivalent steel roof.
Use of the material has been more readily adopted by low-volume manufacturers like TVR who use it primarily for creating body-panels for some of their high-end cars due to its increased strength and decreased weight compared with the glass-reinforced plastic they use for the majority of their products.
Civil Engineering Applications
CFRP has recently become somewhat of a hot topic in the field of Structural Engineering, surprisingly enough, due to cost-effectiveness. Think for example, of a bridge. Many small bridges in the world were built quite a number of years ago, some actually dating to the era of horse-drawn carts. These bridges were designed to tolerate far lower service loads then they are subject to today. So compared with the cost of replacing the bridge, reinforcing it with CFRP is quite cheap. Due to the incredible stiffness of CFRP, it can be used underneath spans to help prevent excessive deflections, or wrapped around beams to limit shear stresses etc. The Westgate Bridge in Melbourne, for example, is as of 2005, the largest bridge in the world to be reinforced with carbon fiber laminates [1].
Much research is also now being done using CFRP as internal reinforcement in concrete structures, such as beams and bridge decks. The material has many advantages over conventional steel, mainly that it is much stiffer and corrosion resistant. There is, however, some hesitation among the engineering community in implementing these new materials, as more real-world evaluation must be done.
Other applications
An area where CFRP has found good use is in the manufacture of bicycles, especially road bikes. The vibration absorbing properties of CFRP make for a less harsh ride, whilst offering weight reduction compared to traditional bicycle tubing materials such as aluminum or steel. The choice of weave can be chosen so as to maximise stiffness. Expolitation of the variety of shapes CFRP can be built into has further increased stiffness and also allowed aerodynamic considerations into tube profiles. CFRP frames, forks, handlebars, seatposts and crank arms are becoming commonplace on medium- and higher-priced bicycles. CFRP forks are used on most road bikes.
Another widespread use of carbon fiber is in the manufacture of fishing rods. Its high flexibility and low weight make it ideal to feel every bite.
Recycling
An important usage concern is regarding the material's entire lifecycle, as carbon fiber reinforced plastics have an almost infinite lifetime. There exist companies [2] which are attempting to recycle this carbon fiber. The recycling strategy centers around milling, compounding or shredding the reclaimed carbon fiber, and finding use for this end product in various industrial applicantions (including for carbon fiber applications less stringent than those required by, say, the aerospace industry).