Carbon fiber reinforced plastic

Carbon fiber reinforced plastic (CFRP or CRP), is a very strong, light and expensive composite material or fiber reinforced plastic. Similar to glass-reinforced plastic, sometimes known by the genericised trademark fiberglass, the composite material is commonly referred to by the name of its reinforcing fibers (carbon fiber). The plastic is most often epoxy, but other plastics, such as polyester, vinyl ester or nylon, are also sometimes used. Some composites contain both carbon fiber and other fibres such as kevlar, aluminium and fiberglass reinforcement. The terms graphite-reinforced plastic or graphite fiber reinforced plastic (GFRP) are also used but less commonly, since glass-(fibre)-reinforced plastic can also be called GFRP.

It has many applications in aerospace and automotive fields, as well as in sailboats, and notably in modern bicycles and motorcycles, where its high strength to weight ratio is of importance. Improved manufacturing techniques are reducing the costs and time to manufacture making it increasingly common in small consumer goods as well, such as laptop computers, tripods, fishing rods, paintball equipment, racquet sports frames, stringed instrument bodies, classical guitar strings, and drum shells.

Composite

Materials produced with the above-mentioned methodology are often generically referred to as "composites". The choice of matrix can have a profound effect on the properties of the finished composite. One method of producing graphite-epoxy parts is by layering sheets of carbon fiber cloth into a mold in the shape of the final product. The alignment and weave of the cloth fibers is chosen to optimize the strength and stiffness properties of the resulting material. The mold is then filled with epoxy and is heated or air cured. The resulting part is very corrosion-resistant, stiff, and strong for its weight. Parts used in less critical areas are manufactured by draping cloth over a mold, with epoxy either preimpregnated into the fibers (also known as "prepreg"), or "painted" over it. High performance parts using single molds are often vacuum bagged and/or autoclave cured, because even small air bubbles in the material will reduce strength.

Process

The process in which most carbon fiber reinforced plastic 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 of which relatively few copies are needed, (1–2 per day) a vacuum bag can be used. A fiberglass, carbon fiber 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 called a wet layup, where the two-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 evenly spread the resin throughout the fabric. Wire loom works perfectly for a tube that requires holes inside the bag. Both of these methods of applying resin require hand work to spread the resin evenly for a glossy finish with very small 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 (prepreg) 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 the least amount of resin waste and can achieve lighter constructions than wet layup. Also, because larger amounts of resin are more difficult to bleed out with wet layup methods, prepreg parts generally have fewer pinholes. Pinhole elimination with minimal resin amounts generally require the use of autoclave pressures to purge the residual gases out.

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 carbon fiber reinforced plastic 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, so that the fiberglass and resin are mixed on the spot. The resin is either external mix, where the hardener and resin are sprayed separately, or internal, where they are mixed internally, which requires cleaning after every use.

For difficult or convoluted shapes, a filament winder can be used to make pieces.

Automotive uses

Carbon fiber reinforced plastic is used extensively in high end automobile 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. Racecar 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 omnidirectional 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 racecars.

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.

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 have started to use CFRP in everyday road cars.

Use of the material has been more readily adopted by low-volume manufacturers who used 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 used for the majority of their products.

Often street racers or hobbyist tuners will purchase a carbon fiber reinforced plastic hood, spoiler or body panel as an aftermarket part for their vehicle. However, these parts are rarely made of full carbon fiber. They are often just a single layer of carbon fiber laminated onto fiberglass for the "look" of carbon fiber. It is common for these parts to remain unpainted to accentuate the look of the carbon fiber weave.

Civil engineering applications

Carbon fiber reinforced plastic has over the past two decades become an increasingly notable material used in structural engineering applications. Studied in an academic context as to its potential benefits in construction, it has also proved itself cost-effective in a number of field applications strengthening concrete, masonry, steel and timber structures. Its use in industry can be either for retrofitting to strengthen an existing structure, or as an alternative reinforcing (or prestressing material) to steel from the outset of a project.

Retrofitting has become the increasingly dominant use of the material in civil engineering, and applications include increasing the load capacity of old structures (such as bridges) that were designed to tolerate far lower service loads than they are experiencing today, seismic retrofitting, and repair of damaged structures. Retrofitting is popular in many instances as the cost of replacing the deficient structure can greatly exceed its strengthening using CFRP. Due to the incredible stiffness of CFRP, it can be used underneath bridge spans to help prevent excessive deflections, or wrapped around beams to limit shear stresses.

When used as a replacement for steel, CFRP bars are used to reinforce concrete structures. More commonly they are used as prestressing materials due to their high stiffness and strength. The advantages of CFRP over steel as a prestressing material, namely its light weight and corrosion resistance, enable the material to be used for niche applications such as in offshore environments.

CFRP is a more costly material than its counterparts in the construction industry, glass fibre reinforced polymer (GFRP) and aramid fibre reinforced polymer (AFRP), though CFRP is generally regarded as having superior properties.

Much research continues to be done on using CFRP both for retrofitting and as an alternative to steel as a reinforcing or prestressing material. Cost remains an issue and long term durability questions still remain. Some are concerned about the brittle nature of CFRP, in contrast to the ductility of steel. Though design codes have been drawn up by institutions such as the American Concrete Institute, there remains some hesitation among the engineering community about implementing these alternative materials. In part this is due to a lack of standardisation and the proprietary nature of the fibre and resin combinations on the market, though this in itself is advantageous in that the material properties can be tailored to the desired application requirements.

Other applications

Carbon fiber reinforced plastic has found a lot of use in high-end sports equipment such as racing bicycles. For the same strength, a carbon-fiber frame weighs less than a bicycle tubing of aluminum or steel. The choice of weave can be carefully selected to maximize stiffness. The variety of shapes it can be built into has further increased stiffness and also allowed aerodynamic considerations into tube profiles. Carbon fiber reinforced plastic frames, forks, handlebars, seatposts and crank arms are becoming more common on medium- and higher-priced bicycles. Carbon fiber reinforced plastic forks are used on most new racing bicycles. Despite carbon fiber reinforced plastic's advantages, it has been known to fail suddenly in bicycles, causing devastating crashesFact|date=January 2008. Other sporting goods applications include rackets, fishing rods and rowing shells.

Much of the fuselage of the new Boeing 787 Dreamliner and Airbus A350 XWB will be composed of CFRP, making the aircraft lighter than a comparable aluminum fuselage, with the added benefit of less maintenance thanks to CFRP's superior fatigue resistance.

Due to its high ratio of strength to weight, CFRP is widely used in micro air vehicles (MAVs). In [http://cmr.mech.unsw.edu.au/mavstar MAVSTAR Project] , the CFRP structures reduce the weight of the MAV significantly. In addition, the high stiffness of the CFRP blades overcome the problem of collision between blades under strong wind.

CFRP has also found application in the construction of high-end audio components such as turntables and loudspeakers, again due to its stiffness.

It is used for parts in a variety of musical instruments, including violin bows, guitar pickguards, and a durable ebony replacement for bagpipe chanters. It is also used to create entire musical instruments such as Blackbird Guitars carbon fiber rider models, Luis and Clark carbon fiber cellos, and Mix carbon fiber mandolins.

In firearms it can substitute for metal, wood, and fiberglass in many areas of a firearm in order to reduce overall weight. However, while it is possible to make the receiver out of synthetic material such as carbon fiber, many of the internal parts are still limited to metal alloys as current synthetic materials are unable to function as replacements.

Nike often uses carbon fiber as a shank plate in their basketball sneakers to keep the foot stable. It usually runs the length of the sneaker just above the sole and is left exposed in some areas, usually in the arch of the foot.

CFRP is used, either as standard equipment or aftermarket parts, in high performance radio controlled vehicles and aircraft, i.a. for the main rotor blades of radio controlled helicopters -- which should be light and stiff to perform 3D manoeuvres.

End of useful life/recycling

Carbon fiber reinforced plastics (CFRPs) have an almost infinite service lifetime when protected from the sun. When it is time to decommission CFRPs they cannot be melted down in air like many metals. When free of vinyl (PVC or polyvinyl chloride) and other halogenated polymers, CFRPs can be thermally decomposed via thermal depolymerization in an oxygen free environment. This can be accomplished in a refinery in a one-step process. Capture and reuse of the carbon and monomers is then possible. CFRPs can also be milled or shredded at low temperature to reclaim the carbon fiber, however this process shortens the fibers dramatically. Just as with downcycled paper, the shortened fibers cause the recycled material to be weaker than the original material. There are still many industrial applications that do not need the strength of full-length carbon fiber reinforcement. For example, chopped reclaimed carbon fiber can be used in consumer electronics, such as laptops. It provides excellent reinforcement of the plastics used even if it lacks the strength-to-weight ratio of an aerospace component.

See also

*Carbon fibre
*Graphite
*Aramid
*Fiberglass

References

http://www.bluebird-electric.net/composites/glass_fibre_reinforced_plastic.htm

External links

* [http://www.carbonfiber.gr.jp/english/ Japan Carbon Fibre Manufacturers Association (English)]
* [http://www.pslc.ws/mactest/carfib.htm Carbon fibre page from the Department of Polymer Science at USM]
* [http://www.vtnews.vt.edu/story.php?relyear=2005&itemno=1074 Engineers design composite bracing system for injured Hokie running back Cedric Humes]
* [http://www.quickstep.com.au/ Quickstep Technologies pty ltd, Western Australia]