Very stiff fibres woven into history – very personal recollections of some of the British scene

COMPOSITES

Composites Science and Technology 65 (2005) 2285–2294

SCIENCE ANDTECHNOLOGY

www.elsevier.com/locate/compscitech

Very stiff fibres woven into history – very personal recollectionsof some of the British scene

Anthony Kelly *

Churchill College, Cambridge CB3 0DS, UK

Department of Materials Science, and Metallurgy University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK

Received 4 May 2005; accepted 4 May 2005Available online 10 August 2005

Abstract

A personal memento is given concerning how the author became interested in the ideas of fibre reinforcement in 1960 and how hewatched as a close consultant the invention of very stiff fibres at Farnborough by Watt and Phillips. Some account is also given ofthe early work at Farnborough both before during and after the second world war and the part played by de Bruyne and then byJ.E. Gordon and his team. The early development of the materials science of composites by the author and his colleagues and thediscovery and enunciation of the principles of how all brittle materials can show appreciable works of fracture are dealt with.

Some short remarks follow on the part played by academics in the development of a new technology.� 2005 Elsevier Ltd. All rights reserved.

Keywords: Composites; Carbon fibres; Toughness

1. First researches

I read physics for my first honours degree and inthose days great attention was paid to teaching practicalskills – we measured the charge on the electron by Mil-likan�s method for instance. The domain structure in aferromagnetic was a modern development and we exam-ined Bitter patterns – the designs formed by iron filingson the surface of a ferromagnet. This last led me as anundergraduate to an interest in what were called sub-grains in metals. I heard of these through reading thewonderful Physics of Metals by Fred Seitz [1].

I applied to enter the Cavendish Laboratory at Cam-bridge – at that time widely regarded as the foremostacademic physics laboratory in the world. Prospectiveresearch students then were not molly coddled with sug-gestions by prospective supervisors eager for graduate

0266-3538/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.compscitech.2005.05.010

* Tel.: +44 1223 363691; fax: +44 1223 33456.E-mail address: [email protected].

students but were expected to indicate a real problemon which they would like to work. I was lucky to havementioned subgrains in metals since this was a burninginterest of the Cavendish Professor Laurence Bragg (ofBragg�s law) and so he was to be my official supervisorwhen I was accepted by the Cavendish and also by Trin-ity College. At Cambridge one enters the Universitythrough one of its colleges. I worked on detecting sub-grains in metals and through that route became a metal-lurgist. Bragg, during my time at the Cavendish, lostinterest in metals and turned passionately to encourag-ing the elucidation of the structure of biological materi-als by means of X-ray diffraction. It was that interestwhich enabled Crick and Watson to meet and to workout in a spectacular and intuitive fashion the structureof DNA – the secret it seems of the genetic code – thephysical means by which hereditary features are trans-mitted from generation to generation [2]. I was in noway involved but enjoyed a spectator�s grandstand viewof the personalities involved in this wonderful scientificachievement.

mailto:[email protected]

2286 A. Kelly / Composites Science and Technology 65 (2005) 2285–2294

Having been converted to Metallurgy I fell under thespell of Alan Cottrell; he examined my PhD Thesis andlater offered me a job, or suggested that I apply for a jobat Cambridge some years later. I left the Cavendish Lab-oratory in 1953 and worked in the United States withPaul Beck at Illinois – where I met and came greatlyto admire Fred Seitz who was in the Physics Departmentand whose brilliant lectures based on his massive textbook Modern theory of Solids [3] I humbly attended.During that period I also met Bardeen, of course whowas in both Electrical Engineering and in Physics andearning his second Nobel Prize. Heissenberg passedthrough on his first (?) visit to the United States afterthe war and I did some very preliminary work withKoehler, Seitz and Baluffi. The Metallurgy departmentof Illinois was suddenly modernised by the influx of agroup from Columbia under Tom Read who had pub-lished the first US papers on dislocations with Seitzand Read [4]. Illinois was a lovely place to work in thosedays as solid state science had its origins and expanded.

I returned to England briefly for the calendar year of1955, became engaged to be married and then returnedto the USA having been recruited by Morrie Fine toteach X-ray crystallography to students of a newlyformed department of Metallurgical Engineering in theTechnological Institute of Northwestern University inEvanston Illinois – just north of Chicago and the homeof the Women�s Christian Temperance Union one of theforceful progenitors of the move to prohibit the sale ofalcohol within the USA after World War I.

Fine was and still is, now well into this ninth decade,a very forward-looking man in his science. Before com-ing to Northwestern he had taken part in the Manhattanproject (the making of the first atomic bomb) at the Uni-versity of Chicago and subsequently at Los Alamos.Through him and others at Northwestern I met Oppen-heimer – the father of the fission bomb – whom Iremember as a wise and kindly man who much encour-aged me in my researches with well-spoken words ofpraise.

Fine it was who led our department at Northwesternto attach to its name the study of Materials Science in1957. We could rightly claim to be the first departmentin the world to adopt this in our title. So our horizonswere broadened from the study of metals to includeplastics or polymers, at that time the fastest growingof the materials producing industries. Of course, we al-ready knew a little about ceramics – the third majorcomponent of materials science – through the use ofthese as refractories for furnace linings and as tundishes,etc.

Cottrell accepted the Goldsmiths Chair of Metallurgyat Cambridge and went there from the Atomic EnergyResearch Establishment at Harwell in September 1958.In 1956, he had mentioned to me the great likelihoodof this occurring and had asked me whether I would join

him there if he could secure a lectureship – a post notlightly created at Cambridge in those years. I treasuredthis thought in the intervening years at Northwesternbut when the opportunity finally arose I was sad to leaveEvanston.

Cottrell asked me (I knew very little of Metallurgy atthe time) to give a set of lectures on ceramics. I came toMetallurgy at Cambridge with the first Instron tensiletesting machine imported to Britain and set about pre-paring these lectures. I did this by reading Slater�s Quan-

tum Theory of Matter [5] while crossing the Atlantic byship. Other people lecturing on ceramics would havescoffed at that but, as it happened, it stood me in verygood stead. I discovered in the literature rather littlematerials science of ceramics. There was a wealth ofchemistry but less material relating structure to proper-ties. I persevered and discussed with the undergraduatesthings like the physical interpretation of Mohs hardnessscale, the difficulty of moving dislocations in materialssuch as sapphire, why silicon carbide sintered slowlyand, following Slater, why covalent solids are stiff andof low density, since the atoms are held apart by spa-tially directed bonds. We discussed a host of otherthings not usually dealt with in ceramics courses. I waspleased afterwards to discover that the graduates whowent into such industries as the steel industry foundmy lectures very useful, even though I had not dealt inexcruciating detail with how furnace linings wererammed into place.

2. Fibre reinforcement

It is difficult to appreciate nowadays that in thoseyears some very obvious data were missing from the liter-ature, e.g., the elastic constants of boron, or even of fullydense graphite. At Cambridge I started some work onceramics, notably, for what comes later, on the investiga-tion of graphite single crystals and on magnesium oxide.My own special interest was in precipitation hardening ofmetals and I discovered that, in aluminium–copper andcopper–beryllium and such like, precipitation hardenedalloys in the overaged condition developed very strongrates of work-hardening.

Cottrell, at the time, was becoming a very fashionableyoung scientist and was invited to give lectures such asthe Royal Society�s Bakerian, and discourses to the Roy-al Institution, Royal Society of Arts, etc. He often usedto give me the text of these lectures to read before deliv-ering them.

In a discourse delivered to the Royal Institution on15 June 1960 [6] he enunciated the principle of fibre rein-forcement. I quote what he said:

No, the practical approach is to admit the existence ofcracks and notches and to try to render them innocuous.

A. Kelly / Composites Science and Technology 65 (2005) 2285–2294 2287

Suppose that we are stretching a rod. . . and. . . that itconsists of a bundle of parallel. . . fibres joined together– by some adhesive or solder. If there is a transversenotch in the rod, cutting across a number of these fibres,the forces from the cut fibres can be transmitted to thefibres at the tip only by passing as shearing forcesthrough the layers of adhesive. . . If this adhesive has afairly low resistance to shear. . . it will then be incapableof focussing the transmitted forces sharply. . . There aretremendous possibilities for developing this principle fur-ther, particularly by using fibres of materials with verystrong atomic forces, e.g., refractory oxides and carbides.

It is all there. It was new to me. And in those days inpounds per square inch!

The discourses of the Royal Institution give no refer-ences, or rather AHC gave no references, to that partic-ular talk. �Had he dreamt the principle up for himself?�,was the question I asked, �Was there some literature un-known to me?� The hint that there was an extensive lit-erature occurred in the list of exhibits in the library,listed at the end of his lecture. These were from the Roy-al Aircraft Establishment. People there had approachedstrong materials in a completely different fashion fromthat of the metallurgist. Cottrell will have learnt of thisfrom his membership of various quasi-confidential Gov-ernment committees, which abounded in that period andon which most academics interested in physical metal-lurgy sat. The situation of modern fibrous composite sci-ence at that time in Britain, and its subsequentdevelopment, paying special attention to the work atthe Royal Aircraft Establishment is well described byMcMullen [7] which I now follow in part – see also[36] for recent years.

3. Modern composites at Farnborough

The beginning of research and development on com-posites for aircraft structures began in the UK in 1937when N.A. de Bruyne, an engineering don at Cam-bridge, read a paper to the Royal Aeronautical Societyentitled ‘‘Plastic materials for aircraft construction’’[8]. It is a massive paper showing in great detail howde Bruyne, with great vision foresaw the many difficul-ties and also some solutions to these – but most impor-tantly he recognised the great promise. De Bruyne was akeen amateur airman who built his own aircraft theSnark. Doing this he recognised the importance ofstressed plywood and the necessity to orientate thematerial so that the wood fibres ran parallel to the larg-est loads. Because of his knowledge of plastics he wasemployed as a consultant by the de Havilland companyto advise on the making of propellers. Plastics as mate-rials of construction for propellers had been consideredsince the 1920s.

In 1936, de Bruyne had noted, following Meyer andLotmar [9], the theoretical properties of some cellulosicfibres in terms of their high stiffness and/or strength cou-pled with a low specific gravity. To reinforce and stiffenthe plastic a flax roving was used teased out into flatbands as a continuous reinforcement De Bruyne intro-duced a material which he called Aerolite which wasphenol–formaldehyde (Bakelite) containing aligned fi-bres of cotton ramie and other textiles. He also experi-mented with urea formaldehyde resins. De Bruyne isprincipally remembered now for his wonderful inven-tions of adhesives such as Redux, which successfullybonded wood and metal for aircraft construction.

In 1938, J.E. Gordon a young man just trained as amarine engineer was hired at Farnborough and askedto evaluate new non-metallic materials. Among thesewas Gordon-Aerolite (flax fibre-reinforced phenolic re-sin) invented by M.F. (Malcolm) Gordon, J.E.�s name-sake – but no relation – working at Aero ResearchLtd., a firm founded by de Bruyne. It was Malcolm Gor-don one of de Bruyne�s students who, because he had aconnection with a Belfast linen mill, (in the charge of hisfather) suggested the use of flax as reinforcement. A sup-ply of unbleached flax thread was impregnated with phe-nolic resin, wound into a skein and hot-press mouldedto form what was probably the first example of a highperformance composite. M.F. Gordon went on to be-come managing director of a spinning company andan honoured Engineer/Industrialist in Northern Ireland.We know that M.F. and J.E. met but I know no more ofany interaction between them.

Gordon [10] as the first to point out that, if compositeswere to be used for structures, they had to be used as effi-ciently as possible in order to be competitive with metals.To this end, he drew attention again to the need for thehighest possible degree of fibre orientation in each layerof material and the requirement then for the layers to becrossed at appropriate angles – to meet the applied loads.This required careful calculation and the early mathe-matics of fibre orientation date from this time and isattributable to Cox of NPL [11] and Gordon and Bishopof RAE [12].

One of the first composite components of any conse-quence tested by J.E. Gordon was an experimental full-scale main wing spar made by de Bruyne�s company forthe �Blenheim� bomber. This was of lattice constructionusing Gordon-Aerolite but was designed like conven-tional metal structures, and so was a misuse of this novelmaterial. A similar abortive exercise involving a �Spitfire�fuselage was conducted at the outset of the war (WW-2)when there was a temporary shortage of aluminium al-loys in Britain. A Gordon-Aerolite replica of the realthing was made but the structure was hopelesslyoverweight.

Throughout World War II, cellulose fibre compositeswere developed with moderate priority and with some


real success. Aircraft drop tanks saw service, while wingtip tubes and ducting were in production and a compos-ite seat was made for the �Spitfire�.

Work at the RAE on cellulose fibre-reinforced plas-tics ceased in 1946 and, although only a partial success,enough had been demonstrated and learned to justifyfurther composites R&D. It was realised, for example,that the reinforcing fibre had to be inherently inert to cli-matic changes, it had to be possible to give it a high de-gree of orientation and it had to be possible to achieve agood bond between it and phenolic resins – the onlytypes available at that time. The resin/fibre pre-impreg-nate had to have a good �shelf-life� and it had to be pos-sible to mould it at low pressures in low-cost tooling andthe resulting laminates had to develop a high proportionof the properties of the fibre.

The work on cellulose fibre composites also led to thebeginnings of the understanding of fibre orientation the-ory, the realization of the importance of strict control ofmoulding conditions and the appreciation that thesenew materials would require the development of newmethods of test. In short, much of the technologylearned in this early work formed the basis of all thatfollowed.

At the end of the RAE work on cellulose fibres in1946, samples of glass fibre obtained from the USA wereexamined as a possible reinforcement for plastics for pri-mary structures. By comparison with cellulose fibresthey are heavy and thus their specific stiffness is abouthalf that of flax – one of the best of the cellulose fibres– but they have an enormous advantage in strengthand can of course be highly oriented.

Earlier developments of GRP (c 1943) owed much tothe invention of radar and the urgent need for radomes -these are radar housings and contain E glass which is aglass fibre free from ions which lead to absorption atmicrowave frequencies (cf. Stealth aircraft today). Inview of the very poor bond between glass fibres andthe phenolic resins of the time and with no immediateprospect of improving this, glass fibres as reinforcementfor major structural plastics were abandoned in 1946 atRAE.

The years from 1952 saw, however, an enormousgrowth in the glass-reinforced plastics (GRP) industrydue to the advent of polyester and epoxy resins. Dueto their prior developed expertise RAE were well placedto take advantage of this especially when glass fibres,stiffer than E glass became available in the late 1960s[13]. Glass is relatively heavy and no stiffer than alumin-ium and so its use for aircraft primary structures is verylimited. However, for rocket motor cases stiffness is lessimportant and strength paramount [14]; glass then be-comes very useful.

The filament winding technology developed by RAEin conjunction with Bristol Aerojet Ltd. and ImperialMetal Industries Ltd. led to successful firing trials of

all-plastic rocket motors in 1951/1952 and to equallysuccessful flight trials of guided weapon boost-motorssoon afterwards.

The Admiralty Research Establishment in Dunferm-line pioneered the use of glass fibres in mine huntersunder the direction of CS (Charles Stuart) Smith(1936–1991). Of course, fibreglass boats were displacingwooden boats. The Admiralty made the very coura-geous decision to displace wood with grp in large vessels(ships rather than just boats) with greater than 500 ton-nes displacement – see for example [15]. The successfulintroduction of HMS Wilton, the prototype, led to theHunter and Sandown class of mine hunter, the largestin the world in the early 1980s. Interestingly, the firstvessels were no lighter than the competition becausethey had to be over-designed owing to the notoriousplastics factor – see below. Smith and his team did muchto reduce both this and, very effectively, the cost ofproduction.

When RAE work on cellulose-reinforced plasticsceased in 1946, a search began for other, stiffer and moreinert fibre reinforcements. There was interest in thepotential of asbestos as a reinforcing fibre and it was ahappy coincidence that in 1947 Turner BrothersAsbestos Company produced Durestos – a chrysotileasbestos fibre-reinforced phenolic resin. In temperatureresistance for example, it can readily out-performGRP and aluminium and can be used for the venturiiof short burning time rocket motors. The great disad-vantage of this material is the health hazard associatedwith asbestos.

Chrysotile is very stiff and strong, inert to the effectsof moisture and is well bonded by phenolic and otherresins. The big drawback in 1947 was the absence oftechnology for highly orientating the fibre. In the years1948–1954, J.E. Gordon�s section at RAE demonstratedbeyond doubt the feasibility of making large high per-formance composite structures.

The main demonstrator structures were delta wingsfor the Fairey experimental E10/47 aircraft. A descrip-tion is contained in the proceedings of the Third An-glo-American Aeronautical Conference 1951 [16].When the demonstrator exercise was terminated in1955 the wings had been developed to the stage wherethey could sustain test loads well in excess of the 12 gload required of the metal ones. They had weight inhand – but they had not sustained the loads derivedfrom the required use of the notorious 1.5 �plastics fac-tor�, i.e., 12 · 1.5 = 18 g. Because of relative ignoranceof the behaviour of the materials compared to theknowledge base concerning the properties of aluminium,a plastics factor of 1.5 was introduced. In other words,the composite had to be 50% better than the stated de-sign figure before its use would be considered. This situ-ation is reminiscent of that regarding performance underfatigue conditions today, when lack of a predictive capa-


bility comparable to that found with metallic structureinhibits the use of composites in some applications.

Nevertheless these developments during the 1950swere a significant milestone in the development of air-craft composite structures and showed beyond anydoubt the potential advantages to be gained. Above allthey demonstrated that composites for aircraft primarystructures would have to have specific stiffness proper-ties substantially greater than aluminium alloys ifworthwhile structure weight savings were to be achieved.At that time (c 1954) this meant only one thing: new,stiff, lightweight fibres had to be invented.

This was the approximate position when I first heardof the field in 1960. The principles of fibre composite sci-ence/engineering were known but not widely and the fi-bres being considered were whisker crystals, asbestosfibres, glass and possibly metal wires.

4. The field as I entered it

In the late 1950s and very early 1960s the ideas forcontrolling cracks following the ideas of fracturemechanics were only slowly being used in practice.There was a great and understandable fear of using allbrittle systems in load bearing applications based onthe experience of the spectacular Liberty ship failuresin World War II [17] and the Comet disaster [18]. Fibrecomposites appeared to be in the class of such all brittlestructures and so even if high strength were to be ob-tained many people thought that they would not be use-ful especially under any conditions of impact.

My associates and I were very fortunately placed inthe early 1960s in that we were elucidating the principlesof the strengthening of metals and yet were lucky en-ough to spot the advantages of non-metallic solids asthe major strengthening agents, because I was lecturingon ceramics.

In the summer of 1961 Phillip Bowden, Cottrell andothers organised a closed conference at Caius CollegeCambridge, financed by the National Research Devel-opment Corporation (a forerunner of the British Tech-nology Group), which discussed fibre reinforcementand we at Cambridge learnt, through our colleaguesfrom Oxford, of work on directional solidification ofeutectics, both in the USA and at Oxford. Work startedat Cambridge on this topic. I mentioned the high ratesof work hardening of alloys in the overaged condition,which appeared to support the idea of fibre reinforce-ment with a metal matrix. This was because we knewthat particles of a strong solid within the metal werebeing elastically strained as a result of the motion of dis-locations in the metal. The dislocations being unable toshear the strong particles, piled up around them andconsequently the metal appears to become very muchstronger as plastic strain is increased [19].

I immediately asked Bill Tyson (who joined mewith an Athlone Fellowship from Canada) to investi-gate the validity of Cottrell�s idea with a metallic matrixas the adhesive or solder. We tried to produce alignedrods of a very hard phase in a metal by cold workingand by directional solidification of a eutectic and othermeans, since whisker crystals were difficult to useexperimentally.

This Bill did but without exciting results. What reallygot us going was a review by Gene Machlin fromColumbia [20], and through it, coming across the workof McDanels, Jech and Weeton [20]. This latter gaveus an excellent model system to work on. They hadintroduced aligned very strong tungsten wires into softductile copper, noting that strong wires of many refrac-tory metals are insoluble in the noble metals. Machlinhad already recognised the importance of the fibre rein-forcement of metals.

Tyson went to work with a will and we produced in arelatively short time a set of principles, which could be,called the colligative mechanical properties of an alignedfibre-reinforced system. We could explain adequatelythe strength of the system in terms of the strengths ofthe two components and how it depended upon volumefraction and on the relative elongation of the two com-ponents; on the length of the fibres and more important,the ratio of length to diameter. We explored the idea ofminimum and critical volume fraction. I remember withsurprise the work being described as being elegant, but Ithought it was rather straightforward, but necessary toestablish the principles. In the course of doing it wemade one of the fundamental discoveries needed. Wefound a new means of dissipating energy. The fibrouscomposite, of course, broke. Since we were workingwith metals and were aware of the emerging conceptsof fracture mechanics, we were able to recogniseimmediately the significance of pull-out at a fracturesurface.

Tyson found that when a fibrous composite breaks allthe fibres in the fracture plane do not break at once. Thisis particularly pronounced with brittle fibres. The frac-ture surface, therefore, had a jagged appearance andthe sliding apart of the two faces or the pull-out of thefibres from holes in the matrix, dissipates a lot of energyand provides a quasi-ductile form of behaviour. Thatwas the discovery and that this would dissipate energywas the natural suggestion. Cottrell and I (I do notremember whether Tyson was present) discussed thefinding before the Royal Society meeting on New Mate-rials in 1963. With his wonderful facility for doing thephysics immediately with simple algebra Alan Cottrellproduced the first formula for estimating the work offracture due to pull-out. He altered his original draftof the introductory paper to the Conference in orderto include it. His simple formula was much quoted fora few of the succeeding years.


This behaviour is not confined to metals and, fromTyson�s work, sitting on the numerous quasi-confiden-tial committees I have mentioned, I remember sayingthat this would probably happen with forms of fibrouscomposites made from all-brittle systems and wouldprovide an energy absorbing mechanism. A little later,Leslie Phillips (see below) said, �and it broke, just likeDr. Kelly said it would�.

This may seem all very obvious to people nowadays,but at the time it was something genuinely new. Otherpeople had described types of pull-out but no one recog-nised its importance as a source of dissipating energyaround a crack. We announced our results at the RoyalSociety meeting in 1963 to which I refer again below.

J.E. Gordon left RAE in 1954 and went to TI Re-search Laboratories, where I met him for the first time.He worked principally on whiskers with C.C. Evans andN.J. Parratt. He returned to what is now the DERA foldin 1962 at ERDE Waltham Abbey. There, he and hiscolleagues developed methods of growing and handlinglarge quantities of whiskers, principally of Si3N4 butalso of SiC, as well as short fibres of glass carbon andvarious varieties of asbestos. SiC whiskers in aluminanow provide a very effective cutting tool. The methodsdeveloped at ERDE are very important for the develop-ment of composites containing short fibres, since com-posites with only long fibres may lack mouldability;they are what is called boardy. A summary of much ofthe work at TI and subsequently at Waltham Abbey iscontained in the book by Parratt [21].

5. Carbon fibres

Remember that at this stage we are still looking for afibre stiffer than steel (200 GPa) and of much lowerdensity.

Talley, working in the research laboratory of the Tex-aco Company for the Office of Naval research inventeda method of making boron fibre – depositing boronfrom the vapour phase onto a tungsten wire in 1958.The stiffness was 460 GPa and the strength 2.3 GPa[22]. The invention was described by a general of theUS Airforce as the biggest breakthrough in materialssince the Stone Age! This fibre is not easily handleabledue to a relatively large diameter, however, and thereally modern fibres (the various carbons and aramids)are more closely related to textiles.

I became a member of the graphite community for afew years in the early 1960s due to my interest in ceram-ics. High stiffness carbon fibres were invented almostsimultaneously in the UK, USA and Japan at about thattime and I was familiar with much of the relevant workin those three countries.

My early work on ceramics stemmed from Cottrell�sobtaining funds from the Atomic Energy Authority for

work in support of the high temperature atomic reactor –the Dragon project. And three of my research studentsworked directly on graphite. Earl J. Freise who followedme from Northwestern was the first of these – a mostdedicated man who obtained a PhD at Cambridge in re-cord time. He went on to become a University adminis-trator finally in a high position at Caltech. Clive Baker– the twin brother of Colin, who later did seminal workat Alcan on metal matrix composites, studied radiationdamage in graphite and Murray Gillin who came toCambridge in 1962 and investigated the mechanicalproperties of graphite at very high temperatures.

Gillin came from the Australian government researchcentre at Fisherman�s Bend near Melbourne and whenhe finished his PhD in early 1965 he had seen as an avidspectator, as had I, the invention of high performancecarbon fibres at Farnborough. This knowledge he tookback to Australia and being a government employeewas able to influence and initiate Australian researchin composites. Gillin has cited this experience in a num-ber of publications [23].

My three students worked with me on single crystalsof graphite – large naturally occurring single crystals.Freise and I were able to obtain these because I hadworked at Northwestern on a US Airforce contract(AP 1438 if I remember correctly) and so had contactsin that organisation. Through these, and they gave readyhelp, we obtained natural crystals from the pyroxenebearing rocks at the Lead Hill Lead mine in Ticonde-roga New York.

Freise published the definitive work on twinning [24]of crystals of graphite and carried out deformation stud-ies on kish crystals and on pyrolytic graphite and oncommercial grades of polycrystalline graphite.

Baker�s studies of the change of stiffness of graphitecrystals when irradiated led me to urge him to carryout and for me to interpret the results of one of thepieces of work of which I am most proud [25]. We deter-mined directly for the first time the elastic modulus C44

of graphite. This is the modulus governing shear on thebasal plane which has an extremely low value: we founda value of <100 MPa. And to do this we had to amplifyLord Rayleigh�s equations for the bending of a cantile-ver beam; one should include both shear and rotaryinertia, both of which Rayleigh had neglected.

Gillin constructed a unique apparatus for carrying outtensile tests at temperature as high as 3000 �C. The de-tailed results still remain unpublished, though an accountof the construction of the machine has appeared [26]. Hedeformed specimens of natural graphite and of commer-cial grades of polycrystalline graphite and of an excitingform known as pyrolytic graphite. This last is obtained bythe decomposition of methane gas at a temperature ofsay 2100 �C onto a commercial graphite substrate. Thematerial consists of individual graphite sheets which areusually wrinkled but of density 2.14 – hence close to that


of pure graphite, 2.26. The wrinkling arises due to thevery low thermal conductivity normal to the layer planesso that the individual layers are deposited in a very strongthermal gradient.

As a result of these researches I got to know WillieWatt at Farnborough who was working on pyrolyticgraphite. Gillin and I obtained specimens of the materialfrom him. The Atomic Energy Authority also supportedWatt and our association lasted until his death in 1985. Ibecame a consultant at RAE.

Work on graphite at that time involved naturally theUnion Carbide Corporation and on a visit to the USAin 1962 I met Roger Bacon. There were clues to the pos-sibility of very stiff carbon fibres in the late 1950s andearly 1960s, which were emphasized by some of us atthe time. These were, Roger Bacon�s graphite whiskers(now fashionable again following the terrestrial manu-facture of fullerenes). Bacon made these in a carbonarc under pressure in 1960 [27] some specimens of whichhe later presented to me and I in turn to a young scien-tist working on carbon nanotubes in 2000. The whiskershad moduli of 700 GPa and strengths of 20 GPa. Theyare scrolls of graphite layer planes. Kotlensky Titus andMartens [28] in 1962 hot stretched pyrolytic graphiteand attained a modulus of 560 GPa.

The graphitization of polymers such as polyacryloni-trile can lead to a preferred orientation and Shindo in1961 [29] had produced a fibre with a modulus of 120GPa. Akio Shindo visited me in Cambridge in 1965and presented me with a print of a woodcut by KiyoshiSaito – a well-known Japanese printmaker. Hence, I wasfortunate enough to know personally all three inventorsof carbon fibre of high modulus.

In June of 1963 the Royal Society held a discussionmeeting on New Materials [30]. It was organised byJ.D. Bernal (1901–1971), Alan Cottrell (b. 1919),Charles Frank (1911–1998), and Cecil Bawn (1908–2001?) – what a panoply of talent! Both Jim Gordonand I spoke at the meeting, he on designing with brittlematerials (when he produced the very well-known dra-matic diagram of an aircraft wing illustrating the needfor stiffness). I, on the principles of determining thestrength of continuous and discontinuous aligned com-posites of fibre reinforcement. And, as I have saidemphasised that all brittle systems could be tough. Dur-ing the discussion, the lack of a stiff fibre of carbon wasmentioned. Watt (1912–85) was present at the meetingand told me later that he immediately determined tosee if he could make stiff graphite fibres.

Cottrell and I returned to Cambridge having dis-cussed stiff graphite on the train, and on that evening Iput some cotton wool in our graphite tube furnace over-night. The resulting carbonised cotton wool was not stiff– one had to be much more sophisticated. Watt, Phillipsand Johnson at the RAE succeeded. Three groups al-most simultaneously invented stiff carbon fibres in

1963-64: Bacon in the USA, Shindo in Japan and Watt,Phillips, and Johnson. Of these three original processesthat invented by the last three named became dominant[31].

The first experiments on the production of carbon fi-bres by Watt were according to Watt, stimulated by theRoyal Society Discussion Meeting. Phillips always vig-orously denied this. He said Willie Watt and Bill John-son asked for a meeting with him in order to get hisviews on the polymer chemistry connected with makingsilicon carbide. Anyway, it was Leslie who suggestedtrying black Orlon and referred Watt to the observa-tions of Houtz who had shown that, on heating a pro-prietary fibre based on PAN, viz. Orlon, in air for upto 20 h, it underwent a colour change to yellow, thenbrown, then black and became insoluble in PAN sol-vents. The key step in the process developed at RAEis the oxidation of the PAN fibre while under longitudi-nal constraint. The possibility of shrinkage was pointedout by Bill Johnson and according to his own accountLeslie Phillips banged the table and said �we must notlet it�.

Phillips� recollection at the time was that it wouldhave been relatively easy to get a high elastic moduluscarbon fibre – it depended (cf. Kotlensky) on the cokingtemperature. The difficulty was to obtain a useable highstrength, which depended on clean fibre, optimum timeand temperature of heat treatment so as to decomposethe PAN.

The initial batch process in which PAN fibres werewound on frames were made of graphite and �Meccano�and later of glass. This was to provide the tension duringthe oxidative stabilising process, which was the key tothe invention so as to stop the fibres shrinking. Ineffect they were stretched during the oxidation stage. Itwas this step which had eluded the Japanese. TheRAE fibres were some three or four times stiffer thanthose produced in Japan. Watt and Johnson actuallymade the first fibre and Phillips showed these fibres tobe compatible with epoxy and polyester resins. Afterthe invention carbon fibres were made on a pilot scaleat AERE Harwell.

The RAE patents covering the production of carbonfibre from PAN were assigned to NRDC (later BTG)and three licensees established: Courtaulds, Rolls-Royceand Morganite. Details of the invention were given in anexceptionally complete and detailed form. All threelicensees used Courtaulds PAN (a variant of their Cour-telle) as a precursor. Rolls-Royce set up productionfacilities at Hucknall to produce material for theRB211 jet engine and excellent carbon fibre prepregwas produced under the name of Hyfil [32], althoughthe material was not used in the engine.

The business passed to Bristol Composite Materials.Production ceased around 1980. Morganite madecarbon fibre under the name of Modmor, but ceased


production in the early 1970s. Courtaulds continued toproduce until 1991 when they ceased production in theUK and sold their American interests to a Japanesecompany. They continue strongly in Advanced Compos-ite Structures. A later comer, RK-Textiles, maintain acarbon fibre manufacturing capability in the UK.

During the establishment of the processes in indus-try, Phillips played a leading part in advising the licens-ees, drawing attention to the dangers (avoided) ofsodium cyanide and HCN evolution, to the need forcontrolled flow rates of all the gases and to the removalof tars [33].

In the early days Phillips was also concerned with thetreatment by hydrogen peroxide to essentially makepores on the surface of the fibre so as to vary the adhe-sion to the resin. It was he, I believe, who made the cru-cial decision that, since carbon fibres were likely to beexpensive, they should be married with the expensiveresins and it was I think the development of carbon fi-bres which led very much to the development of im-proved properties of epoxy resins.

Watt�s main interest was in the chemistry of makinghigh performance carbon fibre and he continued towork on these until his death. I felt privileged to havebeen able to attract him to work at Surrey Universitywhere I was then the Vice Chancellor when he retiredfrom the RAE. Watt, through his position as a Fellowof the Royal Society – he was elected in 1976 – had aninterest in composites of course and organised severalsuccessful meetings.

The aerospace industry saw the potential of carbonfibres immediately but it was Phillips of the three Britishinventors who undertook the prosecution of the wide-spread application of these things not only into aero-space but also into much more fashionable andexciting artefacts, such as kayaks, golf clubs, fishingrods (he was a keen fisherman), motor car bodies, furni-ture, textile machinery and many other forms. For manyyears the body of the Maclaren racing car – a sweepingGrand Prix winner – embodied the largest piece of car-bon fibre moulding ever made. Phillips was also the manwho realised, with others, that the most important prod-uct form would be fabrics and fibre hybrids and herecognised the need for the invention of simple manufac-turing processes. He would be delighted today with theprospect of non-woven, two-dimensional arrays of fi-bres, which are becoming available. He was always con-cerned with finding widespread uses for carbon fibresand avoiding solely esoteric ones like, as he said �blackpiano keys and false teeth for soldiers on nightoperations�.

He will be particularly remembered for his efforts tointroduce carbon fibres into thermoplastics, first bycompounding and then by the invention of the filmstacking method and also of course of various types ofvacuum moulding. He said:

One should be careful to choose possible applicationswhere high initial costs can be tolerated and whereanisotropic and highly orientated composites are anadvantage rather that the reverse. These conditionsapply in the construction of helicopter blades, hover-craft propellers and in a variety of industrial fans andcompressors, subjected primarily to centrifugal forces.A somewhat similar reasoning of cost/efficiency appliesto satellite rocket bodies and other space hardwarebecause it costs a great deal to put a pound of weightinto orbit.

After the invention of carbon fibres the scientistsand engineers at RAE pioneered the proper evaluationand use of carbon fibre-reinforced plastics – principallyin epoxy resins. They developed manufacturing meth-ods, validated test methods, and carried out designstudies. They showed how to design in the presenceof fillets and notches and understood that mostimportant property and one so elusive of definition,toughness. This property-toughness under impact con-ditions – defeated the brave attempt by Rolls-Royceto introduce carbon fibre fan blades for the RB 211in 1969–1970. The names of Ham, Ewins, Potter,Dorey, Sidey, Cook, Bradshaw, Moreton, Wadsworth,Parratt and lately Bishop and Curtis have become verywell known either for work related to advanced com-posites at RAE or at other centres of British Defenceresearch.

6. Toughness again

In the early 1960s engineers were fearful (as indeedwe still are to some extent) of putting brittle materialsunder tensile load. The recognition of pullout as asource of dissipating energy around a crack went someway to assuaging this worry for fibre composites andparticularly for those with discontinuous fibres. I notedabove that we announced our results on this at the RoyalSociety meeting in 1963.

J.D. Bernal summing up at the end of the confer-ence, said the contributions on fibre reinforcementwere all obvious; he had seen it all done during thewar! As, indeed, he could claim: though I would arguethat the mode of conferring toughness he was refer-ring to is of a different type. He knew the story of�Pykrete�. �Pykrete� was ice reinforced with wood fi-bres, named after Pyke who proposed to make a float-ing aircraft carrier out of it for emplacement in themid-Atlantic during World War II [34]. I becamereally familiar with the details because the idea wasmooted again to us at NPL in the early 1970s to assistthe exploitation of oil from the North Sea. However,Pykrete was more concerned with reinforcement ofbrittle matrices than with ductile ones and hence with


the second mode of dissipating energy which I nowdescribe.

G.A. Cooper was the second of my research studentsto work on fibre reinforcement. Since we had discoveredpull-out, it was his job to professionalise that and ex-plore it as a means of dissipating energy; a task thathe did very well. He also demonstrated, most elegantly,that a crack could not extend if faced with an interfacewhich yielded easily in shear. George was (is?) a superbexperimentalist, somewhat difficult to restrain, and hediscovered while at Cambridge, though we did notinvestigate it fully until we had both gone to the NPL,the principle of multiple fracture. The actual experimentperformed by George was as follows. He strained in ten-sion a resin, of elongation to failure, 6% at room tem-perature and 1% at 77 K, containing silica fibrescoated with carbon of strain to failure 4% at both tem-peratures. At room temperature, then, the strain to fail-ure of the resin exceeded that of the fibre; at 77 K thereverse was the case. At room temperature the systemwas quite brittle but at 77 K a large extension occurred.

The load extension curve is striking [35]. One of thecomponents breaks in a series of parallel cracks whilethe other remains and bears the load. The high elonga-tion phase need not be continuous. We applied the re-sults to reinforced cement, showing that it could bequite tough. Fibre-reinforced cement had again beenstimulated by the development of a fibre, namely Cemfilglass which was alkali resistant.

Here, indeed, was a very striking phenomenon; wehad produced ductility. You could produce it with themetal matrix; that is commonplace, but to produce itin an all-brittle system was magic. We had made a fullybrittle system show the sort of load extension curvewhich metallurgists were always willing to find accept-able because the material appeared to be ductile. Ofcourse, it had been done before, as Bernal would haverecognised, but we were the first to name it clearly andto analyse it. The whole subject is now covered underthe sobriquet of internal cracking in laminates.

So Tyson and Cooper had each separately discovereda totally new method of dissipating energy in a materialso that it could resist fracture: pull-out is one; what isnow called microcracking or multiple fracture another.Both will work in all-brittle systems though, as I havesaid, we discovered pull-out first in a metallic matrix sys-tem. They are both vital for understanding the materialsscience of composites and form contributions from thematerials scientist to composite science, which is other-wise a very engineering discipline.

Pull-out, as I said, represented a new mode of dissi-pating energy and gave people confidence that all brittlefibre systems would not be fragile. It has been used toproduce energy-absorbing structures and the idea devel-oped using helically conformed fibres. It is one of theprincipal means by which ceramics may be toughened.

Multiple fracture, whether of laminates, or of aligned fi-bre composites, or of planar matted composites, or ofoxide layers on a metal, or of protective coatings, is ofthe utmost importance. Under various other names, likemicrocracking, or given the initials MC, its control is vi-tal in all fibre-composite systems of brittle constituents.Control of this phenomenon determines how, for exam-ple glasses or ceramics are, or will be, used in gas turbineengines [37].

Both those two new methods of dissipating energy inor around a crack were discovered; they were not pre-dicted. I was lucky enough to be able to recognise theirsignificance and to partly and imperfectly analyse them.They illustrate to my mind together with carbon fibresand whiskers, ceramic superconductors and now carbonnanotubes the central dogma that new materials are al-ways discovered experimentally. They are not predicted.

7. The academic�s contribution

When I had written this account I fell to wonderingwhat had been the contribution to the development ofcomposite materials by an academic such as my self. I,and my associates, through our work on reinforced met-als, namely copper reinforced with tungsten wires, intro-duced the idea of fibre reinforcement to metallurgistswho were the dominant practitioners of structural mate-rials science at the time. Being academics we aimed toenunciate principles-in this case the principles of the col-ligative rules governing strength (stiffness had alreadybeen done). Secondly, we attracted bright new personsinto a new field through our teaching and researches ata well-known university. Students, those from overseasin particular, carry the ideas with them and effectively dis-seminate the knowledge – see the example of Gillin citedabove. Thirdly, we publicise the subject; and this rolecontinues today in collaboration with younger colleagueswho are at the forefront of current research [38]. And weact as consultants, and being freer than most, providedstimulus and contribution to the networking of ideas.

Acknowledgements

I am grateful to Professor A.J. Kinloch, TrinityCollege and Michael Gordon for tracing the personalityM.F. Gordon.

References

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[13] Loewenstein KL. Phys Chem Glasses 1961;2:69. 169–184.[14] Bernstein M, Kies JA. The fibreglass motor case in the Polaris

Program. In: Proceedings of the filament winding confer-ence. Azuza, CA: Society of Aerospace Materials and ProcessEngineers; 1961. p. 273–81.

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[18] HMSO (1955). Civil aircraft accident. Report of the court ofenquiry into the accidents to two comet aircraft. Heywood RB.Designing against fatigue. London: Chapman & Hall; 1962.

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metal composites. Materials Research Corporation Contract.NOW 61-0209-c pp; 1961;See also McDanels DL, Jech RW, Weeton JW. Metal Progr1960;78:118.

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[24] Freise EJ, Kelly A. Twinning in graphite. Proc Roy Soc A1961;264:269–76.

[25] Baker C, Kelly A. The effect of neutron irradiation on theelastic moduli of graphite single crystals. Phil Mag 1964;9:927–51.

[26] Gillin LM. A multipurpose high-temperature tensile-testingmachine using electron beam heating. In: Proceedings firstconference electron and ion beam science and technology,Toronto; 1964. p. 567–82.

[27] Bacon R. Growth structure and properties of graphite whiskers. JAppl Phys 1960;31:283–90.

[28] Kotlensky WV, Titus Jr KH, Martens HE. Youngs modulus ofhot worked pyrolytic graphite. Nature 1962;193:1066–7.

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[30] Bernal JD, Bawn CEH, Cottrell AH, Frank FC. A discussion onnew materials. Proc Roy Soc London A 1964;282:1–154.

[31] Watt W, Phillips LN, Johnson W. British Patent 1 110 794.[32] Standage AE, Prescott R. High elastic modulus carbon fibre.

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pykrete below 0 �C National Physical Laboratory Report H/2509;1943.

[35] Aveston JA, Cooper GA, Kelly A. Single and multiple fracture.In: Conference Proceedings. National Physical Laboratory, IPCScience and Technology Press; 1971. p. 15–25.

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[37] For example: Miller RJ. Design approaches for high temperaturecomposite aeroengine components. In: Kelly A, Zweben C,editors. Comprehensive composite materials, vol. 6. Amster-dam: Elsevier; 2000. p. 181–570 [chapter 6.10];Richerson DW. Industrial applications of ceramic �matrix com-posites�. In: Kelly A, Zweben C, editors. Comprehensive com-posite materials, vol. 6. Amsterdam: Elsevier; 2000. p. 549–70[chapter 6.28].

[38] Kelly T, Clyne B. Composite materials-reflections on the first halfcentury. Phys Today 1999:37–41.

Very stiff fibres woven into history – very personal recollections of some of the British scene

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