COMPOSITES: INDUSTRIAL INNOVATION VIA NEW MATERIALS

COMPOSITES: INDUSTRIAL INNOVATION VIA NEW MATERIALSAuthor(s): ANTHONY KELLYSource: Journal of the Royal Society of Arts, Vol. 134, No. 5364 (NOVEMBER 1986), pp. 794-803Published by: Royal Society for the Encouragement of Arts, Manufactures and CommerceStable URL: http://www.jstor.org/stable/41374249 .

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COMPOSITES:

INDUSTRIAL INNOVATION

VIA NEW MATERIALS

I Л paper by I

I ANTHONY KELLY, FEng, FRS I

V ice-Chancellor , University of Surrey, given to the Society on Wednesday 14th May 1986, with R. E. J. Roberts, FEng, F I Mech E, F I Prod E,

Managing Director, GKN Group, in the Chair

THE CHAIRMAN: After a distinguished early career with strong international connections, Dr Kelly took up the office of Vice-Chancellor of the University of Surrey in October 1975. He was elected a Fellow of the Royal Society in 1973 and of the Fellowship of Engineering in 1979. He received the Medal of Excel- lence from the University of Delaware for his work on composite materials in 1984 and in that year was a founder of the European Association for Composite Materials. He maintains his scientific interest in the

science of the deformation of solids, in the long-term mechanical properties of materials and in the pro- cesses of fabrication of inorganics by low temperature routes. He pioneered the elucidation of the principles of fibre reinforcement of solids and the computer calculation of the ideal strength of materials. Technological change through innovation with new materials is one of his principal interests, and he maintains his connection with industry through various consultancies and directorships.

The following paper, which was illustrated, was then given.

FIGUREI construction. used at the

shows present Metals

the main time are

types

strong for engineering

of

and

material

stiff, FIGUREI used at the present time for engineering construction. Metals are strong and stiff,

and many have high melting temperatures but few are of low density; nearly all metals have the inestimable advantage of toughness. Ceramics are also stiff and may be very strong; but high strength in a ceramic requires exceptional conditions. They are, however, always hard and they also have high melting points. Ceramics tend to fracture easily because they lack toughness. Plastics are soft, can be malleable like metals, are very easily formed and replace metals in many objects because of this ease of formability. Rubbers are very closely related to plastics, as are (inorganic) glasses to ceramics.

Composites are a recent addition to the dia- 794

gram. They are new in concept but in some cases old in practice; wood is a composite. Com- posites are essentially mixtures of two materials put together in order to achieve a quite unique combination of physical properties.

Historically, high performance composites arose because of the aircraft designer's need for strong lightweight structures of high stiffness; plastics have very low densities and are easily moulded to complex aerodynamic shapes but generally lack both strength and stiffness. Man found stiff fibres in nature and then invented substitutes for these with much improved properties. He put them into resin; this led to high- performance composite structures.

Once the principle is appreciated and has been adequately explored, we may look for many new



NOVEMBER 1986 COMPOSITES: INDUSTRIAL INNOVATION VIA NEW MATERIALS

FIGURE 1

types of composite. For instance, we can lighten the weight of a material by introducing pores into it, which could be looked upon as making a composite with air. Inorganic foams, for instance, produce the best thermal insulators. One also realizes, with hindsight, that the rubber/steel combination of the motor car tyre is an excellent example of a composite.

Glass polymer composites make boats in what is called glass-reinforced plastic, a material now used for certain types of leaf spring in motor cars. There are many other examples of such composite materials; for instance, vehicle side- guards, road vehicle body panels, radio antennae lattice structures, as well as marine buoys and many storage tanks. They are all made from easily moulded plastics containing judiciously chosen inorganic reinforcement, which is often glass.

Concurrently with the advance of the composite principle there has come an important educational exchange of information. To make composites, practitioners from the classically separate industries and disciplines of metallurgy, ceramic technology and polymer science and technology have learnt from one another because it is necessary to do so in order to make an effective composite. This has meant that it can be said with some truth that the very boundaries between the classically separate classes of materials, viz., metals, ceramics and polymers, may no longer be drawn. It is possible, nowadays, to make polymer molecules in an aligned form as stiff as steel, on a weight for weight basis, and as strong. High strength and high stiffness carbon fibre may be equally well regarded as either the ultimate in making a stiff organic polymer - eliminating all the atoms except carbon - and arranging the carbon atoms in regular array; or,

it may be regarded as the ultimate in a ceramic of high melting temperature.

Carbon in this form is black because it has (almost) free electrons and so is like a metal. Do we then regard it as a strong stiff conductor, very like a metal but which happens to sublime rather than melt as a metal does, or do we call it the ultimate high-strength ceramic or the most logically designed plastic?

HIGH PERFORMANCE COMPOSITES The latest version of the Harrier aircraft, the Mark V Harrier II or AV8 B, has 25 per cent of the airframe weight made in composite materials with a total weight saving per aircraft over the all-metal version of more than a quarter of a ton. The ill-fated Space Shuttle had 23 per cent of its doors made in carbon fibre composite instead of in aluminium. An all-composite aircraft has been designed and an all-composite car engine. These are high-performance applications. At the other end of the scale lightweight aircraft are only possible because of the production of extremely stiff, low density solids. Gossamer Albatross, the first aircraft flown across the Channel by one man using his own power, was only possible because of composite materials. And another example of human endeavour: the last three feet have been added to the world's pole vault record because of the use of glass- reinforced plastic poles in place of aluminium.

First let me recite a little European history. Before World War II aircraft designers had in mind the use of plastics in aircraft primary structures (a primary structure is one which must not fail since, if it does, the aircraft crashes). Table I shows some of the fibres available before the war and compares these with modern aluminium. It is interesting to see how strong and stiff certain

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JOURNAL OF THE ROYAL SOCIETY OF ARTS PROCEEDINGS TABLE I

SOME PROPERTIES OF VARIOUS FIBROUS REINFORCEMENTS AND THEIR COMPOSITES AVAILABLE BEFORE 1960

Ultimate Young's tensile Specific

modulus, E strength , gravity, E/SG UTS/SG Fibre or composite (GPa) UTS (MPa) SG ( GPa ) (MPa)

Flax 103 690 1.50 69 460 Unidirectional flax/phenolic resin ('Gordon-Aerolite') 34 345 1.35 25 256

Hemp (wet) 34 - 1.50 23 (air dried) 57 - 1.50 38 (dried under tension) 85 - 1.50 57 -

Ramie (wet) 19 - 1.50 13 - (air dried) 51 758 1.50 34 505 (dried under tension) 90 - 1.50 60

Wood fibre 72* 896 1.50 48 597 Kraft paper/phenolic resin 13 138 1.35 10 102 Asbestos (chrysotile) 159 1379 2.60 61 530 Asbestos/phenolic resin ('Durestos') partially aligned fibres 17 138 1.27 13 109

'E' glass (Ca-Al-borosilicate) 69 3447 2.54 27 1357 Unidirectional 'E' glass/epoxy resin 41 1241 2.05 20 605 Aluminium alloy 70 600 2.8 25 214 * Deduced from the properties of laminates made with these fibres.

From P. McMullen, Composites, 15, 222 (1984) natural materials are, particularly when the properties are compared on a weight-for-weight basis. Flax reinforced phenolic resins and various forms of partially aligned asbestos, particularly that called Durestos, were introduced into resins to form composites and were flown in combat conditions during World War II. After the war the intensive development of aluminium alloys and very high-strength steels took place and competitively stiff materials based on inorganic solids were not known.

It is difficult to realize nowadays that during the '50s and '60s even the basic elastic properties of such common but intractable materials as the carbons, the carbides, the borides and elemental boron were not established and that little was known of the fundamental mechanical properties of such things as silicon carbide, aluminium nitride, or beryllium oxide. Lately the properties of these materials have been explored and it is established that the strongest and stiffest solids, on a weight-for-weight basis, are those made of the early elements in the periodic table, namely, beryllium, boron, carbon, nitrogen, oxygen, magnesium, aluminium, silicon and perhaps phosphorus. The compounds of these elements, 796

and these elements by themselves, give the strongest and stiffest solids, which are also the least dense because the atoms are held apart by spatially directed atomic bonds. Such materials possess high melting points, small coefficients of thermal expansion, show little friction when rubbed upon one another, and in many cases are widespread on the surface of the Earth, not being found solely in highly prized lodes, like metals. They are natural materials and generally, though not always, non-toxic (with the notable exception of beryllium).

Although these materials are strong and stiff they are also intractable. Many sublime instead of melting. They form highly viscous liquids when they do melt, and crystallization from these is slow.

Even if made in large monolithic, perfect pieces, such solids would, although stiff, only be strong if well protected from surface damage. It follows that their usable, high strength form is that of a fibre, or perhaps in very special cases, in the form of very thin sheets. Fibres of carbon of sufficient stiffness to attract the engineer's attention were first produced by the late Willie Watt together with Johnson and Phillips at



NOVEMBER 1986 COMPOSITES: INDUSTRIAL INNOVATION VIA NEW MATERIALS TABLE II

SOME PROPERTIES OF VARIOUS FIBROUS REINFORCEMENTS AND THEIR COMPOSITES AVAILABLE SINCE 1960

Ultimate Young's tensile Specific

modulus , E ' strength > gravity , E/SG UTS/SG Fibre or composite (GPa) UTS (M Pa) SG (GPa) (MPa)

'S' glass (magnesium silicate) 86 4481 2.49 35 1780 Unidirectional 'S' glass/epoxy resin 52 1793 2.08 .25 862 Boron (boron on W substrate) 379 2758 2.69 141 1025 Unidirectional boron/epoxy resin 269 1345 1.97 137 683 Carbon (high modulus) 379 1724 2.0 189 862 Unidirectional С fibres/epoxy resin 207 1034 1.60 129 646 Carbon (medium modulus) 234 2992 1.71 137 1750 Unidirectional С fibres/epoxy resin, 60% fibre volume 131 1517 1.55 85 979

Carbon (medium modulus) chopped and aligned/epoxy resin, 55% fibre volume (Ex PERME) 110 1110 1.50 73 740

Asbestos (chrysotile) 159 1379 2.60 61 530 Aligned/epoxy resin (Ex PERME) 93 689(F) 2.0 46 344 Aromatic polyamide ('Kevlar' 49) 117 2758 1.45 81 1902 Unidirectional Kevlar 49/epoxy resin 83 1931 1.35 61 1430 (F) Figures derived from flexural tests

From P. McMullen, Composites , 15, 222 (1984)

Farnborough in 1964. Stiff fibres of boron were first made by Talley working for the Texaco Company in 1959, and after the discovery of these two, stiff fibres of aluminium oxide, silicon carbide and silicon nitride were made. It is interesting that the method to make the carbon fibre, that of using a polymer in the form of a fibre and gently converting it to pure carbon in an aligned form, is also now being followed for silicon carbide and some of the other stiff fibres. These, with aluminium oxide (important because of its already oxidized nature) and certain stiffer glasses are the main fibres which attract attention. These can be coupled nowadays with the American invention of very well aligned poly- meric substances based on the benzene ring, notably polyparabenzamide and related products known as the fibre Kevlar. This consists of benzene rings linked by strong, non-rotating peptide-like and related linkages. The material is again intractable and rather expensive methods must be used to spin the fibres.

The basic disadvantage of the natural fibres shown in the first table was that they reacted with water and swelled. Furthermore, natural fibres need sorting, alignment and characteriza- tion. The alignment problem for things like

asbestos and some of the natural fibres posed a problem, lately solved, but too late in fact for the extensive use of materials such as Durestos.

Table II shows the properties of some fibres and of those composites which have become available since I960;

The modern fibre, including the stiffer glasses, must be produced under highly controlled conditions and continuous fibres are the best. If continuous fibres are available they may be impreg- nated with resin and wound into the required shapes. If the required shape is a simple cylinder, then it is made by a process of filament winding, and many rocket motor cases are made in this way; the fibre, being coated with resin, wound on to a former and the resin allowed to cure.

Most of us possess in our pockets a handker- chief which illustrates some of the salient mechanical properties of fibre-reinforced materials. It is stiff in the direction of the warp and the weft but shears easily, as I demonstrate. Because of this the material is highly directional in its properties. In fact, for high performance composites (e.g. carbon fibre), woven forms of good quality have only recently become available. The uni-directional material is used to demonstrate the advantages. It is very strong and stiff

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JOURNAL OF THE ROYAL SOCIETY OF ARTS

parallel to the fibres but much weaker in a direction normal to these. It also shears easily parallel to the fibres. In order to make a material which is strong in other than one direction one therefore laminates. Lamination is stacking together composite sheets, each of which is aligned, but choosing the number of sheets in the particular directions in order to match the expected tensile stresses and strains there.

When carbon fibre reinforced plastics are made with woven fabric rather than non-woven material, distortion of the load-carrying fibres parallel to the applied stress reduces the tensile strength, stiffness and toughness. When, however, woven fabric is oriented at 45° to the load direction these properties compare favourably with those for non- woven + 45° material. Indeed, the residual strengths after impact can be greater. At present between one-third and one-half of the market consists of woven fabric; the rest of aligned material.

Here is a completely new feature in engineering design. We have materials which are non- isotropic and the non-isotropy can be varied; in fact it is possible now to place the fibres precisely where they are needed in a structure. In fact it is also possible along the length of a beam, for instance, to vary the amount and stacking of the fibres in various directions so as to vary the stiffness and torsional rigidity of the material.

This is precisely what is needed in helicopter rotor blades, and within a few years' time all rotor blades except perhaps those for heavy lift helicopters will be made from GRP or combina- tions of GRP or carbon-fibre-reinforced plastics; this despite the fact that such composites were not applied to helicopter blades until the mid- 1960s. Looking at the AV 8B, the new version of the

Harrier, one finds composites used in torque boxes, auxiliary flaps, the forward fuselage and cone structure, horizontal stabilizers, ammuni- tion and gun pods.

It would be impossible to make use of inherent advantages of anisotropic material such as carbon- reinforced plastic without the invention of computer-aided methods. Reiterations and the number of the variables require computer programmes both to relate the properties of the in- dividual laminae to the properties of the fibres and also to take into account the interactions in terms of bending, twisting coupling between the various laminae. Initially of course these com- 798

PROCEEDINGS

plications were viewed as a great disadvantage in the material, since the engineer was not happy with anisotropy. Now he has learnt to use it and to make a virtue not so much out of necessity but of supposed vices. The latest Grumman X29 aircraft makes use of bending, twisting coupling so that as the loads on an aircraft wing increase the structure can deform but remain tuned to the aerodynamic requirements. The material possesses almost a form of 'gearing', so that it changes its shape automatically without the need for levers and sensors to bring this about.

COMPOSITES FOR EVERYMAN High performance composites use fibres in order to attain the inherent properties of the fibre, coupling this with a judicious choice of the matrix so that toughness and impact damage is not lost.

Strong fibres, whether they be stiff or not, have the great advantage of restraining cracking in what are called brittle matrices. It is this use of fibres which is often referred to when quotations from the Bible are made, such as that from the Book of Exodus, Chapter V, verses 6 et seqq., which refer to the difficulty of making of bricks without straw. Fibres restrain cracking because they bridge the cracks. The principle is very simple. It has been used in asbestos-reinforced cement and the principle of reinforced concrete is not too far from using the same ideas. However, the incorporation of large numbers of small fibres rather than reinforcing bars leads to a composite material which people can view as a single material rather than seeing it as a two- phase one.

This judicious use of fibres enables us to think nowadays in terms of using brittle materials for construction purposes, because if they are cracked the fibres will render the cracks harmless. Build- ing panels and pipes, of course, are made of such material. Glass-reinforced cement is becoming a commonplace. However, a much greater prize appears ahead. Metals have limited high temperature capability. The ceramic materials that I described above as providing the best fibres also provide the materials of highest melting point. For the construction of prime movers at high temperature these will have to replace metals. They cannot do this as monolithic pieces because, as we have seen, these would be easily broken. However, they can resist cracking if they contain fibres. The composite principle then leads to



NOVEMBER 1986 COMPOSITES: INDUSTRIAL INNOVATION VIA NEW MATERIALS

suggesting that even fibres of the same material as the matrix may give marked resistance to cracking and fracturing. Such is true of carbon- carbon composites which are used in brakes in the Concorde and in certain ballistic missile and re-entry vehicle applications. Of course carbon oxidizes and in contrast a deal of interest centres on the use of refractory oxide glasses such as cordierite or a material of almost amorphous silicon nitride or silicon carbide for use at high temperature, containing fibres again of silicon nitride or silicon carbide. These will restrain cracking and give a usable engineering material for thousands of hours at temperatures in excess of 1 100°C. As yet these are not commercial but the aircraft engine manufacturers are making them and flying pieces of ceramics, sometimes unreinforced; but the main thrust of research is towards reinforced materials.

The ceramic materials are ones of widespread abundance and they are all materials that are essentially cheap. If they can be fashioned by simple chemical means such as reacting acids with alkalis, they make phosphate-bonded materials. These again have great advantage in replacing, say, sheet steel in normal household use, again provided cracking can be restrained. Fibres will do this and if the material is not exposed to high temperature, one may use glass fibres, or even textile fibres may be employed.

INDUSTRIAL INNOVATION Composite materials form an interesting example, perhaps a paradigm, of the process of innovation via a new material. The total world production of high-performance carbon fibres approaches 3,000 tonnes per year. They were invented twenty years ago and some 30 tonnes were made in 1968-9. So in seventeen years the average growth rate is some 30 per cent. The material was invented simultaneously in the UK, the USA and in Japan. We have 7.5 per cent of the world production, Hercules in the USA 28 per cent, Toray of Japan 30 per cent and Toho 15 per cent. The British carbon fibre is probably of the highest quality but the company concerned has not invested in a massive sales programme, nor has it spent the amount on developing the material that has been spent by the Japanese competitors. It is now under threat from cheaper fibres based on pitch.

New industrial materials are of two types in my opinion. One is intrinsic materials in which the

material itself is the host of the potentially useful scientific phenomenon. The material is then a member of a restricted class possessing a rather special physical property, e.g. ferro-magnetism, piezo-electricity, photosensitivity, liquid crystal- line behaviour. When used in the intrinsic rôle the amount of material employed is not large; the selling price per unit weight is high; the material is usually used in a device and in fact constitutes the heart of the device. Under those conditions the material's specific function can often create a new product and with it a new market.

On the other hand constructional materials are what I call extrinsic. They possess properties common to all solids; for instance all solids are elastic, possess hardness, stiffness, rigidity. It is just a question of the value of the property. The property is not unique. In the extrinsic, or sup- porting, rôle materials are used to connect, control, contain, display useful phenomena, and the forms they are used in are usually connecting rods, cylinders, pistons, linkages, wings, maybe electrical connectors or simply housings.

It is true to say, as a generalization, that in this secondary rôle very few new materials have been developed in the last fifty years without extensive government involvement, usually for defence purposes. This is because the path from the concept of a new material to profitable commercialization is long and arduous and involves many stages. A novel material must be chosen by an engineer and when it is first chosen by that engineer it must be available with adequately certified and tested properties.

The engineer chooses a particular material in the extrinsic rôle, bearing in mind four important factors: - History (or fashion) - Availability (awareness) - Properties - Processability It is the user's conception of the importance of

these factors which determines the price that will be paid. The four are of course interrelated and properties and processability should not be considered separately. However, again we have an educational problem. They are usually taught quite separately. The materials scientist dwells on the properties of the material, the technologist on how the materials are fashioned. The two come together rather less than they should.

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JOURNAL OFTHE ROYAL SOCIETY OF ARTS One of the difficulties of commercialization,

particularly acute from a materials manufacturer's point of view, is the absence from the outset of a knowledge of where the profit can be taken. The new materials supplier does not generally sell directly to the consuming public. He sells to other engineers, initially to the designer. When a new material is proposed for a design it is surprising how the traditional material being used, either owing to history or fashion, has not been chosen for defined properties but because it was available. It follows that some of the less obvious properties of the presently used material must be evaluated before a new material can take its place. Doing this is expensive.

Second, the new material must be available at the right stage of the product life cycle. The . cycle is complicated and new materials can enter it at different stages. It seems best to distinguish four modes. (a) Production of a totally new product - new

to the world as well as to the company or group concerned, which is usually based on an invention; an example would be the jet engine.

(b) Developmental improvements to an existing product which may be innovative; e.g., a composite material replaces steel in a car bumper.

(c) Developmental improvements to an existing product which are evolutionary; e.g., car bumpers are shaped differently to reduce drag.

(d) Introduction of a new model or mark of an existing generic type of product which can incorporate either innovative or evolutionary changes.

Taking these in order: (a) Unless the invention centres on a new material, no one wants a new one in order to prove out an invention. The invention itself is enough to cope with.

The next three types do offer the possibility of introduction of the new material, particularly when a new mark is to be made which seeks competitive advantage.

Taking now (b), i.e. developmental improvements which may be innovative, the engineer may seek a change of mechanism, e.g. a rubbery material instead of his spring and dashpot or a vibrating diaphragm instead of, say, a cylinder. A new material may then have a great advantage. However, the introduction of a new material 800

PROCEEDINGS

must usually be accompanied by re-design . For example, composite leaf springs are not subject to fatigue in the same way as metal leaf springs.

In the slow evolution of established products small, changes in materials specification which improve product performance and ease of manufacture contribute to product competitive- ness but seldom involve the use of a really new material. Under these conditions the introduction of a model change, as in the motor car industry, or a new airliner does offer the possibility for change.

We have to recognize that many products use standard components and the properties of these are defined by standardized test methods. Well accepted standards assist a firm to achieve material reliability and safety. Well recognized standards are the hallmark of a mature product and when applied to the specifications of materials, always inhibit the introduction of these even though it is stated that standards are supposed not to relate to 'fitness for purpose'.* This arises on a number of counts. 1. The new material's properties are usually

different from those currently used and so a new standard is needed.

2. Because the properties of the new material are different, a new test method is often required.

3. Properties of a new material must often be measured over long spans of time and in various environments.

4. Large pieces are needed for some types of test and these are expensive to produce, particularly so in a new material. Under these conditions of maturity an assembler

of components has much more freedom to make use of new materials.

It is then the man making components who, if inventive, can take the greatest advantage of the new materials because the materials can start small. He does not need to use a great deal. He can add value quickly to an existing product. For instance, a new loudspeaker material is desperately needed in the musical reproduction industry. He can sometimes make use of failures, for instance a partial adhesive can be used to make easily fixable tags. A new material which changes its shape on heating and returns to the original one on cooling can be used to maintain form in

*A striking recent example is the change of standards necessary to accommodate the use of polypropylene in place of asbestos in cement- based roofing sheets.



NOVEMBER 1986 COMPOSITES: INDUSTRIAL INNOVATION VIA NEW MATERIALS women's garments and maintain this before and after washing.

Composite materials show all these constraints and also the advantages. They quickly entered sports goòds such as cricket bats, golf clubs, tennis rackets, fishing poles. They provide lightweight stretchers. The existence of a plethora of new materials and new materials opportunities based not only on properties but, as importantly, on processing is an example, perhaps a hallmark, of a healthy manufacturing industry. To the innovator and inventive designer it is a great boon. To the materials producer it is often a headache.

The main cost of new materials development must of necessity be borne by the community,

usually not directly but via the pursuit of some well-defined technical aim in for example defence, or else stimulated by legislation in the civil field. Legislation is very important in assisting and pro- moting technical change. As an example, plastic car bumpers in a composite material have been introduced because of anti-pollution measures and safety legislation. The latter also encouraged the introduction of g.r.p. crash helmets.

Composite materials, as they grow in use and provide us with wonderful new opportunities, are an example of these central doctrines. They sprang from an unequivocal and well-articulated materials requirement for defence, as did so many of the other new materials we see around us now.

DISCUSSION

DRR.J. S. GREEN (Patents and Licensing Executive, Research Corporation Limited): Do you think that the move towards greater product liability legislation is going to cause a halt to materials development? Will engineers fall back on that piece of doggerel 'When in doubt, make it stout and of things you know a lot about'?

the LECTURER: It has already done so, and it can be inhibiting. It is particularly so with domestic con- sumer products, but of course the lawyers have a lot to answer for in mounting cases. Wasn't there the case of the lady who put her dog in the microwave oven to dry it off? She won, because the manufacturer had not put on the microwave 'Don't put your poodle in here to dry off. In many cases the legislation concerning fuel consumption in the US and the collision regulations have been beneficial to innovation and many companies, not only American, have benefited from a single-minded attack on a technical problem posed by legislation. Of course one is not sure whether the legislation will be repealed. If you know it is sensible and will be maintained, then I am sure that it can help innovation.

DR J. S. GOW (Secretary-General, Royal Society of Chemistry): Could I ask whether Dr Kelly believes that, to make further progress in composites, we shall be short of the necessary new chemistry to make the matrix; or does he believe that there are so many chemical components around now that you can get all the kinds of composite effects that you want?

THE LECTURER: That is a very technical question. The surface chemistry has hardly been explored at all, so there must be lots of opportunities there. The present method, which is to make the two materials

separately and then put them together, seems to sug- gest the opportunity of doing it all in one. There have been various ways of doing it all in one operation, e.g., the metallurgical solutions of growing the fibres; the present polymer emphasis on growing some type of stiff fibre in a nylon matrix. I am sure there is lots of important chemistry to be done, particularly in the non-mechanical applications of composites. I have only talked about mechanical applications because that is what I know most about, but there are many wonderful opportunities because the composite principle frees one from the tyranny of the periodic table and a discrete set of values for any physical property.

DR NORMAN A. WATERMAN (Managing Direc- tor, Quo-Tec Ltd.): I wonder if you could put your educational hat on and consider how much the problem of availability of composite materials is inhibiting their use. If you cut down a tree, you have the wood and an engineer can handle it and see what he can do with it; similarly with steel. But the company that is going to be marketing composites has a bottle of resin and a handful of fibres and it requires a leap of imagination by the engineer actually to see what he can do with those. Quite recently we have seen the growth of the composite shape stockist, of people making shapes for engineers to get their hands on. Hence the virtue can be a vice if you go straight from the raw material to the end product.

THE LECTURER: That is a very important point. To make an introductory remark before answering you directly, things like the invention of the Grum- man forward-swept wing happen because of the over- coming of an educational problem. The aircraft industry regards itself as very young and dynamic even though lots of people have been in it forty years

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JOURNAL OF THE ROYAL SOCIETY OF ARTS and the fact that changes could be made would have been because young men and women have introduced the new ideas that they have learned in 'school' as they call it in America (that means in university), and they have been able to import that philosophy. It is obviously necessary for people to be aware of

the properties and how to use them and that can only come about by shortening the cycle in education. We must do something in this country about universities mounting short courses, awareness courses, not looking always inwards for the teachers but using teachers from outside the university system. That is the information technology problem at present. But we as a country are not alone in that. It is frightfully important and the universities have a rôle to play in just being aware and knowing what is going on in other countries.

MR DAVID BASHFORD, BTechHons (Research Manager, Fulmer Research Laboratories Limited): You say we need to improve basic awareness in education for the benefits of using composites. Do you see that awareness being taken up in British universities on a similar line to that of the University of Delaware, where they have a Centre for Composite Materials, which is very much orientated to the requirements of industry?

THE LECTURER: I know a little about the centre at Delaware and it has been possible because, in the richer atmosphere in the United States, they have been able to obtain industry funding for setting up sets of computer programmes and industry is undertaking to send people to the centre. This country has done well in teaching about composites in the universities and some universities have been very sensible about importing knowledge from abroad for one or two- week courses, which have been very popular and good, but what we have not done is just that sort of thing, inventing the centre concept for teaching at the frontiers of what can be regarded as in some ways rather low-level stuff. It is very important and as an educator I feel slightly ashamed that we have not done more, but it is not easy to do it unless you can approach a number of companies and obtain largish sums from them, between £50,000 and £100,000 for a year or two, so that investment in the hardware can be made.

DR N. A. SLAYMAKER, MIEE (Research Execu- tive, Defence Technology Enterprises Ltd): I was sur- prised at how much carbon fibre/epoxy composite there was in the Harrier. I cannot recall if the Harrier is a supersonic aircraft but will we see the spread of composites to aircrafts like Jumbos? They are all mainly metal at the moment, aren't they?

THE chairman: They are not all metal. You will find in a lot of aircraft now, and certainly in the genera- 802

PROCEEDINGS tion which is just beginning to be produced, that large parts of the wing sections, tail sections, stabilizers, are all using this material.

DR SLAYMAKER: I am not familiar with carbon- carbon composites. Could you say a few words about them?

the lecturer: They are made in one of a number of ways. The two principal ways are to take sets of carbon fibres woven in particular directions (they are seldom used unidirectionally) which are then either infiltrated with something like alcohol that is subsequently carbonized or else infiltrated by vapour deposition. It is really to hold the carbon fibre together that the matrix is put there. Carbon-carbon composites are very effective in reducing atmospheres.

DR SLAYMAKER: The fibres have structure, but the rest of it is amorphous?

THE LECTURER: Yes and quite pulverous and fri- able.

THE chairman: One of the problems in introducing composites is that one is frequently replicating a design in another material. It is difficult to take a leap forward and start to design for the material instead of replication. I don't know how you set about that with the design standards that we have.

THE LECTURER: There are some very interesting concepts emerging. They are certainly not in the handbooks, the idea being rather that you think of the material as being diluted to obtain effects, rather than as presently always concentrated. You think of spread- ing it and then seeing whether you need to fill in; you have the carbon fibres and then you infilter as you make a carbon-reinforced car.

MR P. в. R. JOHNSON: All the materials you showed in Table II seemed to include epoxy resins. I imagine the life of epoxy resin to be quite adequate for the aircraft industry, but in the case of the building industry, which might, for example, require a sixty-year mini- mum life, any loss of strength could be quite critical.

the lecturer: Epoxy is having problems, but like many high-performance industries the aircraft industry wants a material that it can characterize and standardize and then use; that is what has happened essentially because of the US Air Force programmes with epoxy. Epoxy has a lot of disadvantages. It is expensive, it is not good under hot/wet conditions and there have been many interesting recent better materials such as peek which I referred to, ICI's thermoplastic material. That again is fairly expensive. Principally in the civil field one needs a cheaper material and one available in the necessary quantities.



NOVEMBER 1986 COMPOSITES: INDUSTRIAL INNOVATION VIA NEW MATERIALS DR J. w. McLEAN, OBE (Senior Research Fellow,

Eastman Dental Hospital): The origin of epoxy resin was dental and it was invented by Castan, who was employed by Amalgamated Dental of London when they made this dental filling material. It failed because it was hydrolytically unstable and Amalgamated Den- tal sold the patent to Ciba-Geigy for virtually peanuts.

MR CHRISTOPHER HYATT (Research Executive, Defence Technology Enterprises): You spoke of the ability to free yourself from the tyranny of the periodic table, which rather suggests tailoring any specific material to your specific needs. Going a stage further with the forward-swept wing, if I understand you aright, you are actually building up a totally non- linear material which has the properties you want in the places that you want it. It is an integrated structure. Having reached that stage (and, as you say, much of this work has been done in the Defence industry) you no longer have a material so you cannot say 4 Here is a particular composite that could be used for офег things'. How do you see the benefit of that type of development spinning off into the world at large?

THE LECTURER: It comes back to the Chairman's question. We conventionally thought of getting the material and then making it do certain things. Com- posites, and the rapid transmission of information combined with sensing, will mean that we will think more in terms of structures. People are building piezo- electrics into a composite so that the material almost acts as its own strain gauge and reacts to external loads by moving things about. That is what will be engineered in the future but it requires an intelligence higher than we can muster at present in design and which will come about by the use of computer-aided methods.

MR HYATT: You are actually producing techniques rather than materials?

THE LECTURER: Exactly.

MR ERIC M. BRISCOE, OBE (Chairman, Fairey Tecramics): Dr Kelly has mentioned the original composite in wood. If one looks at other instances in Nature, of shell, a platelike structure, and one then tries to solve the problem of how you would put ceramic fibres in a ceramic matrix so that when you mould them into shape you do not destroy them, one

runs into a lot of difficulties. What did Nature do, one asks, and one suddenly comes across gemstones with lots of fibres inside them. If you discover how the Almighty put those fibres in gemstones please let me know!

THE LECTURER: The composite principle offers the possibility of using composites to make materials and that is exactly what happens in certain biological structures. The hydroxy lapatite is got into place and then the structure built. There is a recent very interesting paper on making ceramics by oxidizing a metal. Having got the metal in the right shape, containing things which make it oxidize quickly, then oxidize; thus you have your oxide; a strong material in the required shape. Again referring to ICI - such an inventive company - their MDF cement is made in a way analogous to that. There is a polymer put in to make the cement grains move in the right way and then the polymer is taken out and, hey presto! it is back to cement.

THE CHAIRMAN: Have you, anywhere in the work you have done, tackled the introduction of fibres into metals?

THE LECTURER: At NPL we did a lot of work on that, and before I left Cambridge, in fact, we started with metals. We thought that what we were doing on the work hardening of aluminium alloys containing a fine precipitate was a form of fibre reinforcement. That is how I first met it and it is interesting that the whole thing has come full circle. If I had amplified the answer to the question on epoxy resins. I would have said that the resin is almost the worst carrier for the fibres; it has poor thermal conductivity, it is dimen- sionally unstable, it outgasses, etc. Metals does none of those things. There is a lot of future for metal as a matrix.

THE chairman: Ladies and gentlemen, I am sure you would wish me to thank Dr Kelly again. He has taken up the questions extraordinarily well and covered a wide field. Those of us who have had something to do with composites realize that he is grappling with everything from chemistry to mechanical engineering to bio-chemical engineering, and I am not sure that I could keep up with him for very long on this subject.

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