Saturday, 23 June 2012

Start a Carbon-Fiber-Reinforced Polymer

  


(337). Start a Carbon-Fiber-Reinforced Polymer



Carbon-fiber-reinforced polymer or carbon-fiber-reinforced plastic (CFRP or CRP or often simply carbon fiber), is a very strong and light fiber-reinforced polymer which contains carbon fibers. The polymer is most often epoxy, but other polymers, such as polyestervinyl ester or nylon, are sometimes used. The composite may contain other fibers, such asKevlaraluminium, or glass fibers, as well as carbon fiber. The strongest and most expensive of these additives, carbon nanotubes, are contained in some primarily polymer baseball bats, car parts and even golf clubs where economically viable.
Although carbon fiber can be relatively expensive, it has many applications in aerospace and automotive fields, such as Formula One. The compound is also used in sailboats, modern bicycles, and motorcycles, where its high strength-to-weight ratio and good rigidity 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 laptops, tripods, fishing rods, hockey sticks, paintball equipment, archery equipment, tent poles, racquet frames, stringed instrument bodies, drum shells, golf clubs, helmets used as a paragliding accessory and pool/billiards/snooker cues.
The material is also referred to as graphite-reinforced polymer or graphite fiber-reinforced polymer (GFRP is less common, as it clashes with glass-(fiber)-reinforced polymer). In product advertisements, it is sometimes referred to simply as graphite fiber for short.
The properties of CFRP depend on the layouts of the carbon fiber and the proportion of the carbon fibers relative to the polymer.

The types of carbon fibers are as follows:
  • UHM (ultra high modulus). Modulus of elasticity > 65400 ksi (450GPa).
  • HM (high modulus). Modulus of elasticity is in the range 51000-65400 ksi (350-450GPa).
  • IM (intermediate modulus). Modulus of elasticity is in the range 29000-51000 ksi (200-350GPa).
  • HT (high tensile, low modulus). Tensile strength > 436 ksi (3 GPa), modulus of elasticity < 14500 ksi (100 GPa).
  • SHT (super high tensile). Tensile strength > 650 ksi (4.5GPa).

Carbon fibers are also classified according to the manufacturing method:
1. PAN-based carbon fibers (the most popular type of carbon fibers).
In this method carbon fibers are produced by conversion of polyacrylonitrile (PAN) precursor through the following stages:
  • Stretching filaments from polyacrylonitrile precursor and their thermal oxidation at 400°F (200°C). The filaments are held in tension.
  • Carbonization in Nitrogen atmosphere at a temperature about 2200 °F (1200°C) for several hours. During this stage non-carbon elements (O,N,H) volatilize resulting in enrichment of the fibers with carbon.
  • Graphitization at about 4500 °F (2500°C).
2. Pitch-based carbon fibers.
Carbon fibers of this type are manufactured from pitch:
  • Filaments are spun from coal tar or petroleum asphalt (pitch).
  • The fibers are cured at 600°F (315°C).
  • Carbonization in nitrogen atmosphere at a temperature about 2200 °F (1200°C).
The most popular matrix materials for manufacturing Carbon Fiber Reinforced Polymers (CFRP) are thermosets such as epoxy, polyester and thermoplastics such as nylon (polyamide).
Carbon Fiber Reinforced Polymers (CFRP) materials usually have laminate structure, providing reinforcing in two perpendicular directions.
Carbon Fiber Reinforced Polymers (CFRP) Properties:- 


Manufacture

The process by which most carbon-fiber-reinforced polymer 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. In addition, the choice of matrix can have a profound effect on the properties of the finished composite.

Molding

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 pre-preg) 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.

Vacuum bagging

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 and 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.

Compression molding

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.

Filament winding

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

Structure

Many carbon-fiber-reinforced polymer parts are created with a single layer of carbon fabric that is backed with fiberglass. A tool called a chopper gun is used to quickly create these composite parts. Once a thin shell is created out of carbon fiber, the chopper gun cuts rolls of fiberglass into short lengths and sprays resin at the same time, so that the fiberglass and resin are mixed on the spot. The resin is either external mix, wherein the hardener and resin are sprayed separately, or internal mixed, which requires cleaning after every use.
The primary element of CFRP is a fibre. From these fibres, a unidirectional sheet is created. These sheets are layered onto each other in a quasi-isotropic layup, e.g. 0, +60, −60 degrees relative to each other. From the elementary fibre, a bidirectional woven sheet can be created, i.e. a twill with a 2/2 weave.

Automotive uses

Carbon-fiber-reinforced polymer 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.
Many supercars over the past few decades have incorporated CFRP extensively in their manufacture, using it for their monocoquechassis 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 polymer they used for the majority of their products.
Use of carbon fiber in a vehicle can appreciably reduce the weight and hence the size of its frame. This will also facilitate designers and engineers' creativity and allow more in-cabin space for commuters.

Civil engineering applications

Carbon-fiber-reinforced polymer (CFRP) 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, cast iron, 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) instead of 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.
Applied to reinforced concrete structures for flexure, CFRP typically has a large impact on strength (doubling or more the strength of the section is not uncommon), but only a moderate increase in stiffness (perhaps a 10% increase). This is because the material used in this application is typically very strong (e.g., 3000 MPa ultimate tensile strength, more than 10 times mild steel) but not particularly stiff (150 to 250 GPa, a little less than steel, is typical). As a consequence, only small cross-sectional areas of the material are used. Small areas of very high strength but moderate stiffness material will significantly increase strength, but not stiffness.
CFRP can also be applied to enhance shear strength of reinforced concrete by wrapping fabrics or fibers around the section to be strengthened. Wrapping around sections (such as bridge or building columns) can also enhance the ductility of the section, greatly increasing the resistance to collapse under earthquake loading. Such 'seismic retrofit' is the major application in earthquake-prone areas, since it is much more economic than alternative methods.CFRP is a more costly material than its counterparts in the construction industry, glass fiber-reinforced polymer (GFRP) and aramid fiber-reinforced polymer (AFRP), though CFRP is, in general, regarded as having superior properties.

Sporting goods

A carbon-fiber and Kevlar canoe (Placid Boatworks Rapidfire at the Adirondack Canoe Classic)
Carbon-fiber-reinforced polymer has found use in high-end sports equipment such as racing bicycles. For the same strength, a carbon fiber frame weighs less than a bicycle tubing ofaluminum 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 allowedaerodynamic considerations into tube profiles. Carbon-fiber-reinforced polymer frames, forks,handlebarsseatposts, and crank arms are becoming more common on medium- and higher-priced bicycles. Carbon-fiber-reinforced polymer forks are used on most new racing bicycles. Other sporting goods applications include rackets, fishing rods, longboards, and rowingshells. The large majority of NHL ice hockey players use carbon-fiber sticks.
Shoe manufacturers use 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.
This material is used when manufacturing squash, tennis and badminton racquets.
Carbon-Graphite spars are used on the frames of high-end sport kites.
In 2006 a company introduced cricket bats with a thin carbon fibre layer on the back which were used in competitive matches by high-profile players (e.g. Ricky Ponting and Michael Hussey). The carbon fibre was claimed to increase the durability of the bats, however they were banned from all first-class matches by the ICC in 2007.Carbon fiber is used in the manufacture of high quality arrows for archery.

Aerospace engineering

Carbon Fibre Aerospace
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 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.
Especially aircraft of the sub-category of microlights (SSDR) take advantage of CFRP. Those aircraft, such as the E-Go, must comply with a weight less than 115 kg (254 lb) without fuel and pilot. Creating an aircraft of this class without the usage of CFRP would be really difficult.

Other applications

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 Viktorian 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 reinforced plastics are unsuitable replacements.
CFRP is used, either as standard equipment or in aftermarket parts, in high-performance radio-controlled vehicles and aircraft, e.g. for the main rotor blades of radio controlled helicopters—which should be light and stiff to perform fast aerobatic maneuvers.
Fire resistance of polymers or thermoset composites is significantly improved if a thin layer of carbon fibers is molded near the surface—dense, compact layer of carbon fibers efficiently reflects heat. IBM/Lenovo's ThinkPad laptops, Dell's XPS13 and several Sony laptop models use this technology. Carbon fiber is a popular material to form the handles of high-end knives.

End of useful life/recycling

Carbon-fiber-reinforced polymers (CFRPs) have a long 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 withdowncycled 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 polymers used even if it lacks the strength-to-weight ratio of an aerospace component.
Despite its high initial strength-to-weight ratio, one structural limitation of CFRP is its lack of a fatigue endurance limit. As such, failure cannot be theoretically ruled out from a high enough number of stress cycles. By contrast, steel and certain other structural metals and alloys do have an estimable fatigue endurance limit. Because of the complex failure modes of such composites, the fatigue failure properties of CFRP are difficult to predict. As a result, when utilizing CFRP for critical cyclic-loading applications, engineers may need to employ considerable strength safety margins to provide suitable component reliability over a sufficiently long service life.





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