Carbon fiber | Wikipedia audio article


Carbon fiber reinforced polymer (American
English), Carbon fibre reinforced polymer (Commonwealth English), or carbon fiber reinforced
plastic, or carbon fiber reinforced thermoplastic (CFRP, CRP, CFRTP, or often simply carbon
fiber, carbon composite, or even carbon), is an extremely strong and light fiber-reinforced
plastic which contains carbon fibers. The spelling ‘fibre’ is usual outside the
USA. CFRPs can be expensive to produce but are
commonly used wherever high strength-to-weight ratio and stiffness (rigidity) are required,
such as aerospace, superstructure of ships, automotive, civil engineering, sports equipment,
and an increasing number of consumer and technical applications. The binding polymer is often a thermoset resin
such as epoxy, but other thermoset or thermoplastic polymers, such as polyester, vinyl ester,
or nylon, are sometimes used. The composite material may contain aramid
(e.g. Kevlar, Twaron), ultra-high-molecular-weight polyethylene (UHMWPE), aluminium, or glass
fibers in addition to carbon fibers. The properties of the final CFRP product can
also be affected by the type of additives introduced to the binding matrix (resin). The most common additive is silica, but other
additives such as rubber and carbon nanotubes can be used. 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).==Properties==
CFRPs are composite materials. In this case the composite consists of two
parts: a matrix and a reinforcement. In CFRP the reinforcement is carbon fiber,
which provides the strength. The matrix is usually a polymer resin, such
as epoxy, to bind the reinforcements together. Because CFRP consists of two distinct elements,
the material properties depend on these two elements. Reinforcement gives CFRP its strength and
rigidity; measured by stress and elastic modulus respectively. Unlike isotropic materials like steel and
aluminum, CFRP has directional strength properties. The properties of CFRP depend on the layouts
of the carbon fiber and the proportion of the carbon fibers relative to the polymer. The two different equations governing the
net elastic modulus of composite materials using the properties of the carbon fibers
and the polymer matrix can also be applied to carbon fiber reinforced plastics. The following equation, E c=V m E m + V f E f {\displaystyle E_{c}=V_{m}E_{m}+V_{f}E_{f}}
is valid for composite materials with the fibers oriented in the direction of the applied
load. E c {\displaystyle E_{c}}
is the total composite modulus, V m {\displaystyle V_{m}}
and V f {\displaystyle V_{f}}
are the volume fractions of the matrix and fiber respectively in the composite, and E m {\displaystyle E_{m}}
and E f {\displaystyle E_{f}}
are the elastic moduli of the matrix and fibers respectively. The other extreme case of the elastic modulus
of the composite with the fibers oriented transverse to the applied load can be found
using the following equation: E c=( V m E m + V f E f ) −
1 {\displaystyle E_{c}=\left({\frac {V_{m}}{E_{m}}}+{\frac
{V_{f}}{E_{f}}}\right)^{-1}} The fracture toughness of carbon fiber reinforced
plastics is governed by the following mechanisms: 1) debonding between the carbon fiber and
polymer matrix, 2) fiber pull-out, and 3) delamination between the CFRP sheets. Typical epoxy-based CFRPs exhibit virtually
no plasticity, with less than 0.5% strain to failure. Although CFRPs with epoxy have high strength
and elastic modulus, the brittle fracture mechanics present unique challenges to engineers
in failure detection since failure occurs catastrophically. As such, recent efforts to toughen CFRPs include
modifying the existing epoxy material and finding alternative polymer matrix. One such material with high promise is PEEK,
which exhibits an order of magnitude greater toughness with similar elastic modulus and
tensile strength. However, PEEK is much more difficult to process
and more expensive.Despite its high initial strength-to-weight ratio, a design limitation
of CFRP is its lack of a definable fatigue limit. This means, theoretically, that stress cycle
failure cannot be ruled out. While steel and many other structural metals
and alloys do have estimable fatigue or endurance limits, the complex failure modes of composites
mean that the fatigue failure properties of CFRP are difficult to predict and design for. As a result, when using CFRP for critical
cyclic-loading applications, engineers may need to design in considerable strength safety
margins to provide suitable component reliability over its service life. Environmental effects such as temperature
and humidity can have profound effects on the polymer-based composites, including most
CFRPs. While CFRPs demonstrate excellent corrosion
resistance, the effect of moisture at wide ranges of temperatures can lead to degradation
of the mechanical properties of CFRPs, particularly at the matrix-fiber interface. While the carbon fibers themselves are not
affected by the moisture diffusing into the material, the moisture plasticizes the polymer
matrix. The epoxy matrix used for engine fan blades
is designed to be impervious against jet fuel, lubrication, and rain water, and external
paint on the composites parts is applied to minimize damage from ultraviolet light.The
carbon fibers can cause galvanic corrosion when CRP parts are attached to aluminum.==Manufacture==The primary element of CFRP is a carbon filament;
this is produced from a precursor polymer such as polyacrylonitrile (PAN), rayon, or
petroleum pitch. For synthetic polymers such as PAN or rayon,
the precursor is first spun into filament yarns, using chemical and mechanical processes
to initially align the polymer chains in a way to enhance the final physical properties
of the completed carbon fiber. Precursor compositions and mechanical processes
used during spinning filament yarns may vary among manufacturers. After drawing or spinning, the polymer filament
yarns are then heated to drive off non-carbon atoms (carbonization), producing the final
carbon fiber. The carbon fibers filament yarns may be further
treated to improve handling qualities, then wound on to bobbins. From these fibers, a unidirectional sheet
is created. These sheets are layered onto each other in
a quasi-isotropic layup, e.g. 0°, +60°, or −60° relative to each other. From the elementary fiber, a bidirectional
woven sheet can be created, i.e. a twill with a 2/2 weave. The process by which most CFRPs are made varies,
depending on the piece being created, the finish (outside gloss) required, and how many
of the piece will be produced. In addition, the choice of matrix can have
a profound effect on the properties of the finished composite. Many CFRP 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. Manufacturing methods may include the following:===Molding===
One method of producing CFRP 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. An alternative to the autoclave method is
to use internal pressure via inflatable air bladders or EPS foam inside the non-cured
laid-up carbon fiber.===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 three ways to apply the resin to
the fabric in a vacuum mold. The first method is manual and 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 one is done by infusion, 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 (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 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, pre-preg 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 aluminum or steel that is pressed together with the fabric and resin
between the two. The benefit is the speed of the entire process. Some car manufacturers, such as BMW, claimed
to be able to cycle a new part every 80 seconds. However, this technique has a very high initial
cost since the molds require CNC machining of very high precision.===Filament winding===
For difficult or convoluted shapes, a filament winder can be used to make CFRP parts by winding
filaments around a mandrel or a core.==Applications==
Applications for CFRP include the following:===Aerospace engineering===The Airbus A350 XWB is built of 52% CFRP including
wing spars and fuselage components, overtaking the Boeing 787 Dreamliner, for the aircraft
with the highest weight ratio for CFRP, which is 50%. This was one of the first commercial aircraft
to have wing spars made from composites. The Airbus A380 was one of the first commercial
airliners to have a central wing-box made of CFRP; it is the first to have a smoothly
contoured wing cross-section instead of the wings being partitioned span-wise into sections. This flowing, continuous cross section optimises
aerodynamic efficiency. Moreover, the trailing edge, along with the
rear bulkhead, empennage, and un-pressurised fuselage are made of CFRP. However, many delays have pushed order delivery
dates back because of problems with the manufacture of these parts. Many aircraft that use CFRP have experienced
delays with delivery dates due to the relatively new processes used to make CFRP components,
whereas metallic structures have been studied and used on airframes for years, and the processes
are relatively well understood. A recurrent problem is the monitoring of structural
ageing, for which new methods are constantly investigated, due to the unusual multi-material
and anisotropic nature of CFRP.In 1968 a Hyfil carbon-fiber fan assembly was in service on
the Rolls-Royce Conways of the Vickers VC10s operated by BOAC.Specialist aircraft designers
and manufacturers Scaled Composites have made extensive use of CFRP throughout their design
range, including the first private manned spacecraft Spaceship One. CFRP is widely used in micro air vehicles
(MAVs) because of its high strength to weight ratio.===Automotive engineering===CFRPs are extensively used 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. 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 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 race-cars. The first carbon fiber monocoque chassis was
introduced in Formula One by McLaren in the 1981 season. It was designed by John Barnard and was widely
copied in the following seasons by other F1 teams due to the extra rigidity provided to
the chassis of the cars.Many supercars over the past few decades have incorporated CFRP
extensively in their manufacture, using it for their monocoque chassis as well as other
components. As far back as 1971, the Citroën SM offered
optional lightweight carbon fiber wheels.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.===Civil engineering===CFRP has become a notable material 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 pre-stressing)
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 the cost of 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. If a column is circular (or nearly so) an
increase in axial capacity is also achieved by wrapping. In this application, the confinement of the
CFRP wrap enhances the compressive strength of the concrete. However, although large increases are achieved
in the ultimate collapse load, the concrete will crack at only slightly enhanced load,
meaning that this application is only occasionally used. Specialist ultra-high modulus CFRP (with tensile
modulus of 420 GPa or more) is one of the few practical methods of strengthening cast-iron
beams. In typical use, it is bonded to the tensile
flange of the section, both increasing the stiffness of the section and lowering the
neutral axis, thus greatly reducing the maximum tensile stress in the cast iron. In the United States, pre-stressed concrete
cylinder pipes (PCCP) account for a vast majority of water transmission mains. Due to their large diameters, failures of
PCCP are usually catastrophic and affect large populations. Approximately 19,000 miles (31,000 km) of
PCCP have been installed between 1940 and 2006. Corrosion in the form of hydrogen embrittlement
has been blamed for the gradual deterioration of the pre-stressing wires in many PCCP lines. Over the past decade, CFRPs have been utilized
to internally line PCCP, resulting in a fully structural strengthening system. Inside a PCCP line, the CFRP liner acts as
a barrier that controls the level of strain experienced by the steel cylinder in the host
pipe. The composite liner enables the steel cylinder
to perform within its elastic range, to ensure the pipeline’s long-term performance is maintained. CFRP liner designs are based on strain compatibility
between the liner and host pipe.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. Much research continues to be done on using
CFRP both for retrofitting and as an alternative to steel as a reinforcing or pre-stressing
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 standardization
and the proprietary nature of the fiber and resin combinations on the market.===Carbon-fiber microelectrodes===
Carbon fibers are used for fabrication of carbon-fiber microelectrodes. In this application typically a single carbon
fiber with diameter of 5–7 μm is sealed in a glass capillary. At the tip the capillary is either sealed
with epoxy and polished to make carbon-fiber disk microelectrode or the fiber is cut to
a length of 75–150 μm to make carbon-fiber cylinder electrode. Carbon-fiber microelectrodes are used either
in amperometry or fast-scan cyclic voltammetry for detection of biochemical signaling.===Sports goods===CFRP is now widely used in sports equipment
such as in squash, tennis, and badminton racquets, sport kite spars, high quality arrow shafts,
hockey sticks, fishing rods, surfboards, high end swim fins, and rowing shells. Amputee athletes such as Jonnie Peacock use
carbon fiber blades for running. It is used as a shank plate in some basketball
sneakers to keep the foot stable, usually running the length of the shoe just above
the sole and left exposed in some areas, usually in the arch. Controversially, in 2006, cricket bats with
a thin carbon-fiber layer on the back were introduced and used in competitive matches
by high-profile players including Ricky Ponting and Michael Hussey. The carbon fiber was claimed merely to increase
the durability of the bats but was banned from all first-class matches by the ICC in
2007.A CFRP bicycle frame weighs less than one of steel, aluminum, or titanium having
the same strength. The type and orientation of the carbon-fiber
weave can be designed to maximize stiffness in required directions. Frames can be tuned to address different riding
styles: sprint events require stiffer frames while endurance events may require more flexible
frames for rider comfort over longer periods. The variety of shapes it can be built into
has further increased stiffness and also allowed aerodynamic tube sections. CFRP forks including suspension fork crowns
and steerers, handlebars, seatposts, and crank arms are becoming more common on medium as
well as higher-priced bicycles. CFRP rims remain expensive but their stability
compared to aluminium reduces the need to re-true a wheel and the reduced mass reduces
the moment of inertia of the wheel. CFRP spokes are rare and most carbon wheelsets
retain traditional stainless steel spokes. CFRP also appears increasingly in other components
such as derailleur parts, brake and shifter levers and bodies, cassette sprocket carriers,
suspension linkages, disc brake rotors, pedals, shoe soles, and saddle rails. Although strong and light, impact, over-torquing,
or improper installation of CFRP components has resulted in cracking and failures, which
may be difficult or impossible to repair.===Other applications===
The fire resistance of polymers and thermo-set composites is significantly improved if a
thin layer of carbon fibers is moulded near the surface because a dense, compact layer
of carbon fibers efficiently reflects heat.CFRP is also finding application in an increasing
number of high-end products that require stiffness and low weight, these include: Musical instruments, including violin bows,
guitar picks and pick-guards, drum shells, bagpipe chanters, and entire musical instruments
such as Luis and Clark’s carbon fiber cellos, violas, and violins; and Blackbird Guitars’
acoustic guitars and ukuleles; also audio components such as turntables and loudspeakers. Firearms use it to replace certain metal,
wood, and fiberglass components but many of the internal parts are still limited to metal
alloys as current reinforced plastics are unsuitable. High-performance drone bodies and other radio-controlled
vehicle and aircraft components such as helicopter rotor blades. Lightweight poles such as: tripod legs, tent
poles, fishing rods, billiards cues, walking sticks, and high-reach poles such as for window
cleaning. Dentistry, carbon fiber posts are used in
restoring root canal treated teeth. Railed train bogies for passenger service. This reduces the weight by up to 50% compared
to metal bogies, which contributes to energy savings. Laptop shells and other high performance cases. Carbon woven fabrics. Archery, carbon fiber arrows and bolts, stock
and rail. As a filament for the 3D fused deposition
modeling printing process, carbon fiber-reinforced plastic (polyamide-carbon filament) is used
for the production of sturdy but lightweight tools and parts due to its high strength and
tear length.==Disposal and recycling==
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 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
polymers used even if it lacks the strength-to-weight ratio of an aerospace component.==Carbon nanotube reinforced polymer (CNRP)
==In 2009, Zyvex Technologies introduced carbon
nanotube-reinforced epoxy and carbon pre-pregs. Carbon nanotube reinforced polymer (CNRP)
is several times stronger and tougher than CFRP and is used in the Lockheed Martin F-35
Lightning II as a structural material for aircraft. CNRP still uses carbon fiber as the primary
reinforcement, but the binding matrix is a carbon nanotube filled epoxy.==See also==
Carbon fibers – Material fibers about 5–10 μm in diameter composed of carbon
Carbon nanotube Composite repairs
Fibre-reinforced plastic Mechanics of Oscar Pistorius’s running blades
– Blades used by South African Paralympic runner Oscar Pistorius

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