Technology Explained – Composites

Part One Composites

The most significant types of material to gain wider application in the 1970s are fibre/epoxy composites. They are becoming and will become one of the most important materials involved in high performance aircraft technology. The development of many new configurations, such as forward swept wing (FSW) aircraft, relies wholly on materials of this kind and further progress in V/STOL technology is doubtful without them.

1. Analysis of problems and requirements

When using conventional materials, we very quickly notice their limitations in strength, as compared to their relatively large weight. The strength of the material depends on a multitude of factors, the great majority of which directly relate to the crystalline structure and its uniformity. ·An ideally uniform structure possesses a strength often an order or more greater than its non-ideal counterpart because there is no local stress concentration, thus every molecular bond is equally stressed. The strength is determined by bond strength, which can be very high. A non-ideally uniform material, as the great majority are, suffers strength limitations due to a large number of minute flaws (internal and surface) which will cause local increases in stress when loaded. If these local stresses exceed bond strength, the material fails. Corrosion accelerates the process, by creating microcracks and penetrating between crystals. Fatigue enhances the negative effects.

All of these problems can be overcome by using more or stronger material, but the penalty is weight, and weight is the number one factor in the choice of aircraft materials.

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