Materials Engineering
Carbon Fibre - High Strength Applications
An overview of how carbon fibres are manufactured and bound into high-strength forms, and their applications across pultrusion, wind energy, marine, construction and sporting goods.
Carbon fibres are a form of pure carbon that has been manufactured by carbonising an organic material to pure carbon in such a manner that its mechanical properties are changed without any change in the chemical properties of carbon — that is the characteristic by which carbon is identified. In 1960, Richard Millington of H.I. Thompson Fiberglas Co. developed a process (US Patent No. 3,294,489) for producing a high carbon content (99%) fibre using rayon as a precursor. Most carbon fibres have carbon content ranging from 85% to 99%.
When carbon fibres of about 5–10 micron diameter are processed for use, the strength of individual fibres is low, so they have to be processed by bunching them together. This can be achieved by tightly binding them mechanically so that the overall strength required for processing is achieved. However, external binding has the issue of interfering with processing, and so on.
One possible method is to use a temporary or permanent matrix that will hold the fibres together sufficiently, so that there is no slippage between fibres, and they are held together in the required geometry while maintaining the overall strength.
The matrix material can be any polymer or adhesive of sufficient strength. The quantity of matrix used has to be within a certain range or proportion. A lower proportion will not give enough adhesion between the fibres and they would separate. A higher proportion will give a low-strength layer between the individual fibres, thus reducing the overall strength. The correct proportion is between 17–22% of the carbon fibre. Thus, various shapes so created — round, flat, hexagonal — are all forms of carbon with high strength.
Carbon fibres processed in this manner retain the properties of carbon as a chemical while providing adequate mechanical strength. The shape of the final product is immaterial to the properties of the carbon fibre.
In some applications where high strength is not critical but other properties of carbon fibre are desirable and cost is a factor, a higher percentage of polymer matrix has been used.
Carbon fibre is high strength. It is low weight. It is cost-efficient. It is characterised by high stiffness. It is conductive to electricity and is one of the most corrosion- and heat-resistant materials available for commercial use.
Carbon fibre is versatile. It has the ability to work with an assortment of different materials, including other fibres, plastics, metals, wood and concrete. It can be manipulated into a variety of forms. It can be dyed, treated and augmented to meet the requirements of any application.
It is nearly impossible to list all of the potential uses of carbon fibre, but here are some.
Pultrusion is a cost-effective, continuous process for producing fibre-reinforced composite parts. Characterised by high strength, high stiffness, low density, high fibre volume, very low void content, locked-in filament alignment and corrosion resistance, pultruded profiles are pre-cured, thick-ply carbon fibre laminates ideal for structural reinforcement applications.
The specific fibre alignment achieved with pultrusion delivers consistently better overall properties in laminates than any other composite manufacturing process. Depending on the end application, these pultruded profiles are typically produced with a thermoset epoxy or vinyl ester resin.
Pultruded profiles are production-ready carbon composites for infrastructure applications, deep-sea exploration, wind energy and other applications that benefit from the unique properties of pultruded carbon fibre parts.
Carbon fibre is the industry standard for wind energy reinforcement, offering an excellent balance of strength, stiffness and cost. It allows for a more slender blade profile, resulting in higher aerodynamic efficiency and lighter, longer, stiffer and stronger wind turbine blades — an overall more efficient wind turbine providing a lower levelised cost of energy (LCOE) and higher annual energy production.
Renewable energy is increasingly being directed into various types of storage batteries that contain carbon fibre products. Such batteries can be fully charged and discharged tens of thousands of times without system degradation. Many chemical batteries utilise carbon fibre in the form of graphitised felt and paper as membranes separating conductive solutions, and as bipolar carbon plates.
The next generation of yachts, cruisers and racing vessels will be lighter and stronger when made with carbon fibre composites. Tough, durable carbon composite material stands up to the extremes of marine environments. The high specific stiffness of carbon fibre lends itself well to applications such as masts, hulls and propellers, resulting in better speed and fuel efficiency and increased cost-effectiveness in the marine manufacturing process.
Carbon fibre fabrics are often used in the repair or upgrade of concrete structures including bridges, columns and beams, offering cost and scheduling benefits through minimally invasive repair methods and using non-corrosive materials with outstanding fatigue performance. The fabrics are saturated with epoxy and applied to the concrete structure using a wet layup process. The fabrics, in combination with appropriate saturating resins, are referred to as fibre-reinforced polymer (FRP) systems.
Carbon fibre has taken sporting goods to the next level of performance. Golf shafts, racquets, skis, snowboards, hockey sticks, fishing rods, bats and bicycles have all been advanced through carbon fibre reinforcement. The deepest penetration of carbon fibre in sports equipment can be seen in tennis rackets — players can hit a faster ball with a lighter racket and control the ball better with a larger hitting area. In short, the applications of carbon fibre are limited only by imagination and the technical skill required to manipulate it.