Fibre-reinforced polymer composite materials are fast gaining ground as preferred materials for construction of aircraft and spacecraft. In particular, their use as primary structural materials in recent years in several technology-demonstrator front-line aerospace projects worldwide has provided confidence leading to their acceptance as prime materials for aerospace vehicles. This paper gives a review of some of these developments with a discussion of the problems with the present generation composites and prospects for further developments. Although several applications in the aerospace sector are mentioned, the emphasis of the review is on applications of composites as structural materials where they have seen a significant growth in usage. The focus of the paper is especially on the developments on the Indian aerospace scene. A brief review of composites usage in aerospace sector is first given. The nature of composite materials behaviour and special problems in designing and working with them are then highlighted. The issues discussed relate to the impact damage and damage tolerance in general, environmental degradation and long-term durability. Current solutions are briefly described and the scope for new developments is outlined. In the end, some directions for future work are given.

Over the last decade, applications of fibre-reinforced composites using polymer matrices have seen tremendous growth. In spite of the complexity of their behaviour and the unconventional nature of fabrication and other aspects, the usage of such composites, even for primary loadbearing structures in military fighters and transport aircraft, and satellites and space vehicles has been beneficially realised. Most of such usage constituted structural applications (such as in airframe) where service temperatures are not expected to he beyond 120 'C. Attention is now focussed on expanding the usage of such composites to other areas where temperatures could be higher-in the range 200400 "C. The intended applications are structural and non-structural parts on or around the aero-engines and airframe components for supersonic or hypersonic aircraft. The development of polymer matrices-such as bismaleimides, polyimides, cyanates, and liquid crystalline polymers and others-has brought such applications within the realm of practicability. The associated problems have been in terms of suitable processing technologies and in balancing the requirements of the performance with those of the processing. This paper describes briefly such developments and reviews the potential application scenario.

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