Composite materials in the construction of modern aircraft

One of the important applications of technological progress to modern aircraft is the use of composite materials in their construction. Moulded into an epoxy resin matrix, they have produced extremely tough and stable materials that are replacing aluminum and aluminum alloys.

Advances in technology have had an enormous impact on the shape, performance, reliability and composition of modern aircraft and fly-by-wire flight control systems (FCS). Propulsion systems also have improved and advances in structural technology have influenced the way aircraft are designed, produced and maintained.

Until the late 1960s, almost all tactical aircraft were composed primarily of aluminum and its alloys. High-speed aircraft used a sizeable amount of titanium, but high cost and the demanding production requirements of this material limited it to moderately high temperature applications. Consequently the latest tactical aircraft incorporate many non-metallic composite materials. Sixteen per cent of the structural weight of the Boeing F/A-18E/F and Lockheed F/A-22 are made up of about 20 per cent of composite material. Future military aircraft such as the F-35 joint strike fighter are expected to have a composite content of at least 35 per cent.

Composite material is made up of two or more separate components that when combined result in property changes that differ from the original materials. Composites most widely used in combat aircraft are composed of high-strength fibres of glass, boron, plastic or carbon that are embedded in an epoxy resin matrix. The fibres have very high strength, a uniform structure and lack flaws. The epoxy resin bonds with the fibres in the curing process to produce an extremely tough and stable material.

The most widely used composite material in tactical aircraft is a carbon fibre/epoxy mix. Carbon epoxy has eclipsed boron-based composites because it is much cheaper to produce, easier to machine and drill, and can be formed into complex shapes to produce structural members such as spars and ribs. Other fibres typified by Dupont's Kevlar also are being used in aircraft production. Kevlar is less dense than carbon fibres but has inferior mechanical properties. It is used in pressure vessels, for ballistic protection and as lightweight fibreglass non-structural parts.

Big advantage of composites is that they are relatively insensitive to flaws. Fatigue testing of composite structures demonstrated their high resistance to cracking and that fractures generally do not propagate. Composite materials are very stable and so are not subject to corrosion as are metallic structures. However, in the design process, careful attention must be paid to composite/metal interaction because through galvanic action some metals will corrode when in contact with carbon fibre/resin laminate.

However, composites do require new skills. Design, production and quality-control personnel have had to adjust to the way they operate in order to take full advantage of the potential of these materials and to produce it economically. The computer has been a major ally in the move to composites. Computer-aided design (CAD) has made it much easier to develop composite structures and to understand their relationship with other elements of an aircraft more thoroughly.

Composites have already had a major impact on military aircraft design and manufacture concepts and also have been used extensively in the latest generation of commercial aircraft. As this technology continues to expand its applications metal aircraft and missiles will be seen as a throwback to an earlier era. New techniques call for new skills and computer and materials science now lead the way in aerodynamics. Just as metal planes replaced wire and wood, designers are adjusting to the new realities and possibilities available with computers and composite materials.

 

Vocabulary

1. resin [`rezιn] - смола, канифоль

2. fly-by-wire flight control systems - системы дистанционного управления полётами

3. рropulsion systems - движительная система, силовая установка

4. embed - заделывать, заливать

5. spar - (авиац.) лонжерон

6. rib - (авиац.) нервюра

7. ally[`ælaι] - друг, помощник

 

Vocabulary development