But the proportions of these materials have changed. As you can see from Figure1, the 1994 Boeing 777 have increased the use of composites such as carbon fibres, graphite, epoxy resins etc. by 10 % in comparison to the 1969 Boeing 747.

Figure 1

For modern military aircraft such as F-22 and the Eurofighter, they have a third of their structure made by composites as shown id figure 2.

From the six materials selection parameters, composites could satisfy them for use for aerospace structures. The most important one is bulk mechanical properties of composites are strength, low density, stiff and tough which are vital and ideal for the safety of an aircraft. On the other hand, metals such as aluminium, has a higher density, less strength and stiffness.

Another important selection parameter is the economical property of composite. Even though manufacturing composites could be reasonably expensive in comparison to metals, but for the long run, due to its low density, fuel could be diminished for each flight hence a much larger reduction in cost could be achieved.

Thirdly the manufacturing property of composite is again expensive as well as difficult as they normally require tape or fabric form and then put in a mold under heat and pressure during production. Again metals such as aluminium can be easily manufactured with low cost which means the production is cheaper. But an advantage of composites during production is that they can be layered and have the fibres positioned at a different direction which could provide a different behaviour for the designated structure.

The aesthetic property is not an important factor for both composites and metals as they are only used on aircraft structures as it is used as the core of the aircraft wings, fuselage, floors etc. which will be fabricated over by different materials.

Composites have a very good surface property, which means it is difficult for it to be wear and tear or corroded. Also as it is not a metal, it is impossible to oxidized, therefore its chemical property is very consistent throughout period that it is used. But certain composites do have an advantage as they absorb moistures which will alter its mechanical properties causing it to reduce its strengths, stiffness etc. But as composites are used for the core interior of aircraft structure, there will be no opportunity for it to come in contact with water. On the other hand, some metals oxidizes and they also go through wears and tears.

For non mechanical property, composites again have an advantage as it is not magnetic, thermal or electrical. These are important as during flights, the amount of static caused from the frictions between the aircraft and air can produce static which is dangerous. Also the friction will produce heat which could alter certain operations if it reaches too high.

For conclusion, the increase use of composites from metals such as aluminium is necessary as it provides a range of advantages such as reduction of weight, cost, as well as better mechanical properties. But metals are still the major materials used as it has a more suitable property for the exterior parts of the aircraft.