Although the volumes of composites used for aircraft applications is a relatively small percentage of total use, the materials often find their most sophisticated applications in this industry. In aerospace the performance criteria placed upon materials can be far greater than in other areas – key aspects are light weight, high strength, high stiffness and good fatigue resistance. Composites were first used in military aircraft in significant quantities. The first applications were in radomes and then in secondary structures and internal components. The modulus of glass, however, is low compared with that of metals and so it was not until the introduction of boron and carbon reinforcements that primary composite structures were developed. Nowadays, composites are widely used and this has been the result of a gradual direct substitution of metal components followed by the development of integrated composite designs as confidence has increased.
The Airbus 320 uses a whole range of components made from composites, including the fin and tailplane. This has allowed a weight-saving of 800 kg over its equivalent in aluminium alloy. Composite materials comprise more than 20% of the A380’s airframe. Carbon-fibre reinforced plastic, glass-fibre reinforced plastic and quartz-fibre reinforced plastic are used extensively in wings, fuselage sections (such as the undercarriage and rear end of fuselage), tail surfaces, and doors.
Examples include: Airbus Industries A 320 and A380 , Harrier AV-8B, European Fighter Aircraft (EFA), aircraft propellers, helicopter airframes , helicopter rotor blades and helicopter rotor hubs.
The successful application of composites in missiles has led to the development of primary structures for space vehicles. In fact, space applications lend themselves in many ways to the utilisation of new materials. For satellites, for example, the timescales from concept to manufacture can be as little as two years and due to the short product runs normally involved, the materials element in the final cost is often relatively low. Also, in many applications no other material is suitable for technical reasons.
Launch details normally determine the design requirements for satellite components, for example, for a conventional rocket launch, loading would be 7 g in the axial direction with 1 g in the lateral direction, whereas for a space shuttle launch, the loading is more uniform with approximately 5 g in both directions. Once in orbit, mechanical loads are comparatively low. Environmental conditions can be extreme and severe thermal cycling can occur. The effects of high vacuum and erosion through atomic oxygen or micrometeroid impacts can also be significant.
Glass fibre composite (also commonly referred to as GRP) is used in applications where thermal insulation is important, for example in local bracketry. The material is also used in some antenna reflectors.
Carbon fibre composite (also commonly referred to as CFRP), however, is most often associated with space applications. The potential for very high stiffness and excellent thermal stability over a wide temperature range make CFRPs ideal. Examples of their application include: fairings, manipulator arms, antennae reflectors, solar array panels and optical platforms and benches. They have also recently been used for primary structure applications. In the past the need for a combination of stiffness and strength, and for thermal and electrical conductivity have favoured metals. However, the constant pressure for weight reduction means that now some satellites have been built with a predominantly composite structure sub-system.
Courtesy of Composites UK