Carbon Fibre Reinforced Plastic (CFRP)

CFRP (also referred to as Graphite) is a composite material, which was primarily developed to retain (or improve upon) the high strength-to-weight ratio characteristics exhibited by GFRP, but with very much greater stiffness values.

Carbon fibres are very stiff and when formed into a composite, the Young's Modulus (‘E’) value can be higher than steel. CFRP is not only six times stiffer than GFRP, but is also over 50% stronger. It also has twice the strength of high-strength aluminium alloy and three times the stiffness.

Carbon fibres are typically less than 0.01 mm (0.0004 in) in diameter and are produced by subjecting a fine thread of a suitable nylon-type plastic to a very high temperature (to decompose the polymer), and driving off all of the elements with the exception of carbon. The carbon thread is then stretched at white heat (2000ºC-3000ºC), to develop strength. Unfortunately, the process is complex and very costly.

Nevertheless, where the high cost can be justified, CFRP can offer considerable weight savings over conventional materials. CFRP components are generally made from ‘Pre-preg’ sheet (fibres impregnated with resin and a hardener, which only require heat and pressure to cure). Some specialist items are made by a laborious process called Filament Winding, in which a carbon fibre string is wound over a former in the shape of the workpiece whilst bonded with resin.

Because of CFRP's high stiffness modulus, it is also used extensively to stiffen GFRP or aluminium alloy structures.

A material known as Carbon-Carbon (where the resin is also graphitised) is used for the rotors and stators on brake units. It offers a significant weight saving, as well as high efficiency due to the fact that it dissipates the heat generated very quickly.

Replacing 40% of an aluminium alloy structure by CFRP would result in a 40% saving in total structural weight. And CFRP is used on such items as the wings, horizontal (and vertical) stabilisers, forward fuselages and spoilers of many aircraft.

The use of composites in the manufacture of helicopter rotor blades has led to significant increases in their life. In some cases, they may have an unlimited life span (subject to damage). The modern blade is highly complex and may be comprised of CFRP, GFRP, stainless steel, a honeycomb core and a foam filling.