Last edited 20 Oct 2016

Carbon fibre


[edit] Introduction

Carbon fibre is fibre made of carbon. But, these fibres are only a base. What is commonly referred to as carbon fibre is a material consisting of very thin filaments of carbon bound together with plastic polymer resin by heat, pressure or in a vacuum. The resulting composite material both strong and lightweight.

Much fabrics, the strength of carbon fibre is in the weave. The more complex the weave, the more durable the composite will be. It is helpful to imagine a wire screen that is interwoven with another screen at an angle, and another at a slightly different angle, and so on, with each wire in each screen made of carbon fibre strands. Now imagine this mesh of screens drenched in liquid plastic, and then pressed or heated until the material fuses together. The angle of the weave, as well as the resin used with the fibre, will determine the strength of the overall composite. The resin is most commonly epoxy, but can also be thermoplastic, polyurethane, vinyl ester, or polyester.

Alternatively, a mold may be cast and the carbon fibres applied over it. The carbon fibre composite is then allowed to cure, often by a vacuum process. In this method, the mold is used to achieve the desired shape. This technique is preferred for uncomplicated forms that are needed on demand.

Carbon fibre material has a wide range of applications, as it can be formed at various densities in limitless shapes and sizes. Carbon fibre is often shaped into tubing, fabric, and cloth, and can be custom-formed into any number of composite parts and pieces.

It is common to find carbon fibre in:

  • Aeronautics and aerospace industries
  • Oil and gas industry
  • Unmanned aerial vehicles
  • Formula 1 cars
  • Satellites
  • Musical instruments
  • Furniture
  • Art
  • Structural elements of buildings
  • Bridges
  • Wind turbine blades

Carbon fibre is an incredibly useful material used in composites, and it is likely to continue to grow manufacturing market share. As more methods of producing carbon fibre composites economically are developed, the price is likely to continue to fall, and more industries will take advantage of this unique material.

[edit] History of carbon fibre

The 20th century saw a roller coaster ride in the demand for carbon fibre. Threats to peace increased the demand for carbon fibre for defense purposes in the middle of the century. A downturn in defense needs then resulted in a reduction in production of carbon fibre toward the close of the century. By the beginning of the 21st century, new applications and new markets sent the production of carbon fibres on an upswing. Despite the downturn in 2007-2008, worldwide demand increased to approximately 40,000 metric tons in 2010.

Carbon fibres have revolutionised the technology of materials. The National Academy of Engineering voted carbon fibres one of the 20 top engineering achievements of the 20th century and the American Chemical Society named the development of high performance carbon fibres a National Historic Chemical Landmark in September 2003.

[edit] Historical Timeline of Carbon fibres

  • Late 1800s - Thomas Edison carbonised cotton and bamboo to make filaments for his early incandescent light bulbs.
  • Late 1950s - Rayon made high tensile strength carbon fibres. Rayon later replaced by pitch and polyacrylonitrile (PAN).
  • Early 1960s - First practical commercial uses of carbon fibres. With high performance, light weight, and high stiffness and strength, the use of carbon fibres resulted in lighter and faster aircraft. Aircraft were better able to withstand the extremely high temperatures of atmospheric re-entry because of the heat resistance of carbon fibre.
  • 1960s, 1970s, and 1980s - Carbon fibres were produced mainly for defence. Carbon fibres were also used in NASCAR and Formula 1 cars to make them lighter and more efficient.
  • Late 20th century - Reduced defence needs following the end of the Cold War and the collapse of the Soviet Union resulted in a decrease in the demand for carbon fibre.
  • Early 21st century - Carbon fibre production expanded significantly due to increased demand in industrial, sporting goods, energy, aerospace, and wind energy industries. Production capacities expanded in Asia, the United States, and Europe.
  • 2008 - Technical problems and global recession slowed plans for expanding manufacturing of carbon fibre.

[edit] Outlook for Carbon fibres

Despite the economic slowdown, particularly around 2008-2009 , the outlook for carbon fibres is positive.

The automotive industry currently uses carbon fibre almost exclusively in the manufacturing of high performance vehicles. Forecasters expect the industry to expand its use of carbon fibre materials to general production vehicles in the near future. Ford Motor Company will soon be using lightweight carbon fibres to reduce the weight of its vehicles in order to meet strict fuel efficiency goals. German automotive manufacturer BMW plans to expand its use of carbon fibres in conventional vehicles, and General Motors has announced plans of developing carbon fibre composites for mass production.

Additionally, China is expected to promote carbon fibre use in the field of civil engineering, which has been reluctant to embrace carbon fibre as a replacement for steel.

According to The Future of Carbon fibre to 2017: Global Market Forecasts, this is what the future looks like for the carbon fibre market:

  • Annual growth rate of 17 percent through 2017.
  • Production of 118,600 metric tons with a market value of $7.3 billion by 2017.
  • For carbon fibre-reinforced plastics, annual growth rate of 16 percent through 2012.

Global demand for high-strength, light-weight and durable fibre is growing; with typical applications in:

  • Portable power.
  • Rechargeable batteries and fuel cell electrodes.
  • Fibre reinforced plastics, FRP.
  • Energy production; windmill blades.
  • Building and construction materials: concrete and asphalt reinforcements, soil erosion barriers.
  • Electronics, composite materials for automotives and general transportation.
  • Specialty and niche markets.

[edit] Short carbon fibre reinforced concrete

Short carbon fibre reinforced concrete was an area of intense activity in Japan. Although carbon fibres are still used in cement slurry and concrete, this area is no longer being pursued as aggressively as it once was, primarily due to economics and codes that do not take into account the higher levels of performance. Although concrete is good in compression, it lacks toughness, tensile capacity and flexural strength.

Although steel reinforcement (rebar) is conventionally used in reinforced concrete to provide tensile reinforcement, there are a number of applications such as curtain walls, fascia panels, panelling for access ducts, barriers, and so on in which cement mortar by itself could be used if tensile strength, flexural capacity and toughness could be improved. Asbestos fibres traditionally have been used as reinforcement in chopped fibre form for applications such as thin sheet-like materials or boards (where reinforcing bars cannot be used due to thickness constraints), structural and architectural panels that must withstand high loads and/or deformations, and structural components where the fibres are added to obtain toughness and prevent cracking. The overall use of asbestos prior to the determination of it as a health hazard has been estimated to be as high as 2.5 to 3 million tons. Potential replacements for asbestos have ranged from steel fibres, polypropylene, nylon and polyethylene to glass, carbon and aramid fibres. A potential replacement for asbestos must be able to match most of the attributes that made asbestos a useful additive to cement mortar. These attributes are:

  • strain to failure significantly higher than that of concrete mortar
  • small fibre diameter
  • hydrophilic surfaces that lend to good dispersion and bonding
  • long term durability in an alkaline environment (fresh concrete can have a pH as high as 13)
  • high strength and modulus
  • overall durability in a harsh external environment

As developed in Japan, CFCC (carbon fibre cement concrete) has little resemblance to conventional concrete. It contains no coarse aggregate and typically contains between 3 to 15 percent by volume chopped and short carbon fibre elements. Three types of carbon fibre are used in CFRC (carbon fibre reinforced concrete) in Japan: pitch-based carbon fibre, polyacrlonitrile-based carbon fibre, and Mitsui Mining form.

The first two materials are well known to the composites industry. The last was developed by the Mitsui Mining Co. as a cheaper material form with affinity for concrete slurry. A major concern in the addition of fibres to concrete is the bonding between the two. The resulting fibre has a "fuzzy" form with a strong affinity for concrete. The outcome is due to a combination of factors including the surface fuzziness and surface chemistry obtained by skipping the stabilisation stage during pyrolysis.

In its use in polymer concrete, as with fibre reinforced concrete, the optimum form of the fibre may well be different from that used in aerospace applications. Further, the different requirements for civil engineering applications could result in the viability of lower cost fuzzy forms that could not be used previously in composites. Not all production is used in concrete and often special varieties are produced for use in CFCC for chemical stability, bonding and economics.

Based on the specific needs for a commercially viable form usable in concrete, Mitsubishi Kasei introduced the DIALEAD chopped fibre form made of pitch some years ago. Due to improved surface characteristics, it can be mixed in a normal top loading mixer without the need for special additive or a special mixer.

Although the performance levels of the fibre used in concrete are lower, they are at levels sufficient to show significant improvement in the performance of concrete. In addition to the direct improvements in performance in tensile and flexural strengths, the use of chopped carbon fibres in concrete results in other generic advantages, especially in building construction.

[edit] Carbon reinforced concrete

Reinforced concrete is cement in which bars ("rebars") or fibres have been incorporated to strengthen a material that would otherwise be brittle. Nearly all cement used in construction today is reinforced.

The most widely-accepted form of enhancement is welded-wire fabric, a mesh of steel wires that is placed in cement. Synthetic-fibre can also be used and can reduce the labour costs and difficulty in placement of the welded-wire mesh. These reinforcing methods are incorporated into the cement when it is made.

But when structures crack, begin to fail, or the initial construction did not account for additional strength needed for unpredictable circumstances, such as wind loads, rebar or other synthetic reinforcing materials cannot be added to existing structures.

Carbon-fibre kevlar technology, has been used in a wide range of applications to provide reinforcement to existing structures. Concrete reinforcement with carbon-fibre sheet straps is a time-proven and tested method of reinforcing existing concrete and masonry structures for the purposes of repair or to strengthen the integrity and load tolerance of existing structures.

[edit] Carbon reinforced asphalt

Fibre reinforcement of concrete has been very popular and a common method used to increase the strength and cracking resistance of the material. Although fibre reinforcement has been extensively studied for concrete pavements, these pavements only make up a small portion of the United States infrastructure system. In comparison, hot-mix asphalt (HMA) accounts for approximately 94% of the paved roadways in the United States and the trend is similar for airfield pavements. This type of paving material can provide a cost-effective method of surfacing roads, airfields and improving the world’s transportation infrastructure system. However, like any type paving material, HMA is subject to distress mechanisms which lead to deterioration and failure over time.

Distresses are the result of one or more factors, including magnitude of load, type of load, climatic conditions, material characteristics and material interactions. Major pavement distresses that challenge pavement engineers include permanent deformation (rutting), fatigue cracking, thermal cracking and raveling . Hoping to minimise or slow these pavement distresses, research has explored mixture modification through the use of fibres. Inclusion of fibres in paving materials serves to reinforce the material by adding additional tensile strength to the material that results from interconnection between aggregates. This interconnection may allow the material to withstand additional strain energy before cracking or fracture occurs.

Researchers have experimented with many different types of fibre reinforcement, including polyester, asbestos, glass, polypropylene, carbon, cellulose, Kevlar and recycled waste fibres. In addition, fibre-reinforcement of HMA has evolved to include a blend of different fibres to achieve different performance characteristics.

[edit] Fibre reinforced polymers

FRPs are typically organised in a laminate structure so that each lamina (or flat layer) contains an arrangement of unidirectional fibres or woven-fibre fabrics embedded within a thin layer of light polymer matrix material . The fibres, typically composed of carbon or glass, provide the strength and stiffness. The matrix, commonly made of polyester, Epoxy or Nylon, binds and protects the fibres from damage, and transfers the stresses between fibres.

The strength properties of FRPs collectively make up one of the primary reasons for which civil engineers select them in the design of structures. A material's strength is governed by its ability to sustain a load without excessive deformation or failure. When an FRP specimen is tested in axial tension, the applied force per unit cross-sectional area (stress) is proportional to the ratio of change in a specimen's length to its original length (strain). When the applied load is removed, FRP returns to its original shape or length. In other words, FRP responds linear-elastically to axial stress.

The response of FRP to axial compression is reliant on the relative proportion in volume of fibres, the properties of the fibre and resin, and the interface bond strength. FRP composite compression failure occurs when the fibres exhibit extreme (often sudden and dramatic) lateral or sides-way deflection called fibre buckling.

FRP's response to transverse tensile stress is very much dependent on the properties of the fibre and matrix, the interaction between the fibre and matrix, and the strength of the fibre-matrix interface. Generally, however, tensile strength in this direction is very poor.

Shear stress is induced in the plane of an area when external loads tend to cause two segments of a body to slide over one another. The shear strength of FRP is difficult to quantify. Generally, failure will occur within the matrix material parallel to the fibres.

Among FRP's high strength properties, the most relevant features include excellent durability and corrosion resistance. Furthermore, their high strength-to-weight ratio is of significant benefit; a member composed of FRP can support larger live loads since its dead weight does not contribute significantly to the loads that it must bear. Other features include ease of installation, versatility, anti-seismic behaviour, electromagnetic neutrality, excellent fatigue behaviour, and fire resistance.

However, like most structural materials, FRPs have a few drawbacks: high cost, brittle behaviour, susceptibility to deformation under long-term loads, UV degradation, photo-degradation (from exposure to light), temperature and moisture effects, lack of design codes, and lack of awareness.

FRPs have been used widely by civil engineers in the design of new construction. Structures such as bridges and columns built completely out of FRP composites have demonstrated exceptional durability, and effective resistance to the effects of environmental exposure. Pre-stressing tendons, reinforcing bars, grid reinforcement, and dowels are all examples of the many diverse applications of FRP in new structures.

One of the most common uses for FRP involves the repair and rehabilitation of damaged or deteriorating structures. Several companies across the world are beginning to wrap damaged bridge piers to prevent collapse and steel-reinforced columns to improve structural integrity and to prevent buckling of the reinforcement.

Architects have also discovered the many applications for which FRP can be used. These include structures such as siding/cladding, roofing, flooring and partitions.

In Canada, engineers have integrated fibre optic sensors into numerous FRP-reinforced systems to ensure that adequate supervision of the systems is provided.

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