The Development of Carbon Fibres and Their Applications in Composite Materials

Carbon fibre is a material composed of threads of mainly carbon at 5 to 10 nanometers in diameter. These carbon atoms are bound parallel to the direction of the thread making it very strong for its size and easily scalable. These threads can be woven together into ropes and clothes or coated in resin to take a certain shape. Its high strength to weight ratio, durable qualities and applications in composite materials such as CFRP and CFRC make it popular despite relatively high production costs.

![](/content/images/2015/09/intro-1.jpg) Weaved carbon fibres.

Development

The first carbon fibres were created by Tomas Edison[1] when he heated cotton threads or bamboo silvers to carbonise them, then passed a current through them causing these filaments to glow. These raw materials were natural carbon "threads" composed of cellulose, which were heated to remove any non-carbon atoms and produce a strong, durable thin strand of carbon. Soon after, carbon fibres were produced from rayon, a synthetic cellulose fibre that was widely used in clothing. These carbonised rayon threads were formed into clothes and tows and were used as insulation and non-reactive filters.

In 1956, Roger Bacon, in an experiment to discover the triple-point of graphite, stumbled upon the "whiskers", threads of pure carbon. Hence, the true potential of these strands were realised and utilised in industry.

A decades later, Japanese researchers discovered the use of polyacrylonitrile(PAN) precursors, which allowed for an even greater modulus and strength. However, due to material limitations, heating PAN or rayon can never achieve the 100% pure carbon fibre. This was resolved when two Australian scientists realised that they would make pitch into a fibre in their liquid-crystal mesophase. The result was a breakthrough in material strength and thermal conductivity.

![](/content/images/2015/09/poly_50.jpg) SEM image of PAN threads.

The most widely used precursor in carbon fibre production, polyacrylonitrile is synthesised with acrylonitrile powder and another acrylate plastic[1:1]. They undergo a polymerisation reaction to form the polyacrylonitrile. This is then treated with other chemicals to form strands by passing through small jet nozzles. They are then cleaned and elongated to reach the required diameter.

To maximised the efficiency of the carbonisation process, the strands are first altered to become more thermally stable. This is either done by heating the strands suspended in air or passing them through heated rollers. They are then heated in a furnace at 1000$^\circ$C-3000$^\circ$C. Lastly, the surface is once again treated to be easily bonded both chemically and mechanically. The thread is slightly oxidised in preparation for use in composite materials. For commercial purposes, the thread is woven into yarn and various other forms.

Applications

Carbon Fibre Reinforced Polymer (CFRP)

Composed of carbon fibre as reinforcement and a polymer resin as the matrix, CFRPs exhibit a directional strength property that is not observed in isotropic materials such as steel and aluminium[1:2]. It also has such a high strength to weight ratio that, despite not having a definable fatigue endurance limit, it remains popular for many applications, especially those in aerospace and automotive engineering.

The commercial airplane, Airbus A350 XWB is made of 52% CFRP[1:3]. With the Boeing 787 Dreamliner made 50% of CFRP and the Airbus A400M being the first to have wing spars composed of CFRP, it's easy to see how important this material is to the industry. Other applications in the aerospace industry involving ultralight aircrafts for recreational purposes rely much more heavily on the use of carbon fibre reinforced composite materials in order to fit under the weight limit.

For the same reasons, CFRP is used extensively in high-end sports cars[1:4]. Its low weight allowed for a smaller chassis, leading to a larger passenger space and lower overall weight. Monocoque chassises are developed to have omnidirectional threads, giving its directional strength for every orientation. In the future, it is preferable that all steel is replaced with carbon fibre materials. This would reduce the weight of the mass majority of cars by 60%[1:5]. This would inevitably allow for lower and more efficient fuel consumption and possibly another boost in the development of electric or hybrid automobile engines.

Another application for CFRP is in retrofitting. This can be done to increase the load capacity of bridges or to repair damaged structures. Its unique strength means that not much of the material has to be used and that it has a large impact on the strength of its application structure.

Ceramic Matrix Composite (CMC)

Carbon fibre reinforced ceramics were developed to have a high crack resistance. As industries found that conventional ceramics such as alumina, silicon carbide and aluminium nitride easily fracture under thermal-mechanical loads[1:6]. While CMCs offered a much larger fracture-resistance, thermal shock resistance and high dynamic load capacity. The most important property is its thermal resilience. Combined with its low weight and shock resistance, it is favoured in heat shields for space vehicles, components in jet or combustion engines, brake discs and other high temperature devices.

![](/content/images/2015/09/flaps_50.jpg) Steering flaps made of carbon fibre reinforced ceramics.

CMCs were first introduced into re-entry heat shields when previous attempts would completely destroy the surface of the vehicle upon re-entry. Carbon fibre reinforced ceramics offered the industry 30 re-entry cycles, low weight and high thermal resistance. It was also used in steering flaps so as to better control the re-entry trajectory.

The use of carbon reinforced ceramics was a vast improvement in automobile and aeroplane brake disks. These can easily last a car's whole lifetime of around 300,000km. They have high corrosion resistance and are only 40% the mass of the original metal disk[1:7].



  1. R. Renz W. Krenkel. Cmcs for friction applications. Ceramic Matrix Composites, 2008. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎