Introductory RemarksAuthor(s): A. H. CottrellSource: Proceedings of the Royal Society of London. Series A, Mathematical and PhysicalSciences, Vol. 319, No. 1536, A Discussion on Strong Fibrous Solids (Oct. 6, 1970), pp. 3-4Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/77773 .

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Proc. Roy. Soc. Lond. A. 319, 3-4 (1970) Printed in Great Britain

Introductory remarks

By A. H. COTTRELL, F.R.S.

Cabinet Office, Whitehall, London, S. W. 1

Dr Kelly and I are very glad that today's speakers have been able to accept the invitation by the Royal Society to talk about the work they are doing in this still new field of strong fibrous solids. It is interesting to look back to an earlier Discussion Meeting of the Society, in 1963, t when New Materials were discussed. Although glass fibre was already in wide use at that time, the 1963 Discussion brought out clearly the more general significance of fibrous microstructures and also provided broad scientific principles by which such microstructures could be designed to achieve great mechanical strength and toughness in a wide range of composite materials. Strong whisker crystals of stiff, brittle, and lightweight, substances had of course already been produced in small quantities, and the idea of putting these into a softer carrier material to achieve greatly improved properties was already recognized. From a different direction of approach, the metallurgist also, by his considerations of the nature of work hardening in heterogeneous alloys, had been led to expect particularly good strengths in metals containing dispersed rod-like particles of strong solids such as carbon, boron, silicon carbide and intermetallic compounds.

A great advance since then has been the discovery of a way to make continuous fibres of strong, high modulus, carbon. The pyrolytic conversion of certain organic fibres to carbon was already known, but I believe that the 1963 Discussion played a large part in encouraging Mr Watt and his colleagues at the Royal Aircraft Establishment, Farnborough, to try to produce a really high modulus carbon fibre; and, as we all know, they achieved striking success shortly afterwards.

This carbon fibre, together with boron, silicon carbide, and alumina, has pro- vided us with a radically new class of engineering materials, made from continuous lengths of stiff, strong, and lightweight, fibres assembled in a suitable carrier substance. In addition, the price of carbon fibre is not high, compared with other advanced modern materials. Engineering components reinforced by such fibres have gone into service in recent years, particularly in aero-space applications, but also in other things such as motor vehicles. At the same time glass fibre has con- tinued to find increasing use, in boat hulls and many other applications, and its addition to cement and plaster has provided some greatly improved buiulding materials.

The science has also gone forward. The elastic properties of simple arrangements of fibres can now be predicted fairly exactly. Strength and fracture toughness are now moderately well understood. We now see that, to design advanced

t Proc. Roy. Soc. Lond. A 282 (I963).

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4 Introductory remarks

microstructures, we need not only fibres of given properties but also to be able to make them of the right diameter and to control their surfaces and coat them where necessary.

The engineering aspects are also very active. Anisotropic elasticity is now being more widely used. Many design studies of engineering structures based on stiff, brittle, lightweight, anisotropic materials are now being made and the problem of joining seems to be becoming solved.

These are all things about which we can expect to hear a good deal in this very full and attractive programme. Perhaps I might just make two remarks about wider aspects, at this stage. First, we live in a time when rising populations and rising levels of consumption are making increasingly heavy demands on world resources of traditional engineering materials. Anything which can relieve the pressure of this demand, by introducing alternative materials made from abundant substances, such as carbon, silicon, nitrogen, oxygen, etc., is thus greatly to be welcomed from this point of view. Secondly, running as a counter to this, there will be a problem of how to get rid of old products made from such materials, should these come into mass production, e.g. motor cars, refrigerator cases, etc. The term 'consumer durables' may become uncomfortably true in the future ! In fact, of course, there will be little economic incentive to do anything other than dump them since, unlike scrap mnetals which have a recovery value, the value of these sophisticated fibrous materials lies mainly in their form, not their substance. I hope that our enthusiasm for these exciting new materials will not lead us to overlook this problem.

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