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Aviation History
1968
1968 - 2417.PDF
BJ6HT«*"•*"»'. M Ocu>ber l968 669 THE NEW STEEL Carbon-fibre-reinforced plastics: the materials that may revolutionise aircraft design An article in the September 1968 issue of "Design Engineering" by its assistant editor, Mr D. M. Peters, provides a most valuable up-to-date review of progress with carbon-fibre-reinforced plastics, the new structural materials which have evolved during the past five years as an extension of the technology of glass-reinforced plastics. The following summary, based on Mr Peters' article, outlines this development and its implications for the future. CARBON-FIBRE-REINFORCED PLASTICS offer every prospect ofbringing about as great a revolution in many branchesof engineering as did aluminium alloys when they first appeared in practical form 60 to 70 years ago. As was the case with aluminium and its alloys, the aerospace industry is the most important initial field of application and the rate at which these new materials are introduced in this industry and later elsewhere will largely depend on their cost, which is itself more a function of the method of manufacture and of the volume of production than of the availability of the basic new materials. The tremendous growth in the use of glass-reinforced plastics led to the search for a reinforcing fibre of greater rigidity than glass. To achieve mechanical properties superior to metal alloys, materials formed from light atoms with strong bonding forces between them were required. Ceramics are suitable but brittle unless used as a fibre reinforcement in a plastic or metal matrix in exactly the same way as glass fibre in glass-reinforced plastics. The light-atom materials with the necessary chemical bonding characteristics are the oxides, nitrides, borides, carbides and boron and carbon. A great deal of research into new structural materials has been in progress in all the technologically advanced countries during the past decade and, in 1963, the RAE began to concentrate on carbon filaments. In the autumn of that year, work started at Farnborough on methods of producing carbon fibres with machanical properties suitable for use in reinforced plastics. In about six months carbon fibres made from poly- acrylonitrile fibres of a specific modulus of about ZOxlOTb/sq in had been achieved. At this time, information on similar work undertaken in Japan in 1961 by Akio Shindo became available and the RAE workers realised, from their own experience, that the Japanese results could be improved upon. Efforts at RAE were therefore redoubled and, in about another six months, a process was evolved which, using the same starting material, gave strength and moduli at least double those obtained by Shindo. These indicated an ultimate tensile strength of 300x lO^lb/sq in, a Young's modulus of 60 x 10*lb/sq in and a specific gravity of 2. The essential part of the RAE process was controlling the orientation of the carbon fibres during manufacture. Based on previous work on graphite for the nuclear power programme, W. Watt and W. Johnson produced carbon fibres from man-made polyacrylonitrile using a three-stage batch system. In the first stage, oxidisation takes place in air at 200/300°C, in the second at about l,000°C and in the third there is final conversion to graphite at 2,000/3,000°C. This is a costly and time-consuming method of manufacture, but it produced sufficient carbon fibres for testing and development These first carbon fibres had twice the strength of glass fibres. The next step was to impregnate them with a suitable matrix. L. U. Phillips was responsible for development of the composite. The result was a material with several times the strength of steel but only a quarter of its weight. British Patent No 1,110,791 for this composite material was applied for in April 1964 in the joint names of Johnson, Phillips and Watt. The National Research and Development Council now came into the picture to negotiate commercial exploration of the new material. Licences were granted to Courtaulds and to Morganite Research and Development to expand the work started at Farnborough. AERE at Harwell developed a con- tinuous process system of manufacture and was soon supplying Rolls-Royce—who had also been working independ- ently of, and in parallel with, RAE on the same problem— Tm irm of waif ht laving W Nose section (not radome section) in CFRP would reduce weight by 20 per cent. (B) Door stiffen- •? >nd internal facings would save approximately "percent in weight. (C) Stringers: RAE Farnborough "ave constructed CFRP stringers with 25 per cent nip Mvm«- (D) Internal low-stressed panels in J-w would save 20-30 per cent of the weight. iVo •"'">»«<! 31b could be lifted from each of '« seats. Total weight saving 3841b. (F) Greatest »»in| will be in tail section; CFRP/steel skin also used ""undercarriage doors. (G) LP compressor bladini Mnni?r comPonents could be replaced (parallel to «"ll-Hyfil development). (H) Nose movement 2EU mc.y.lindert in CFRP «ould save 50 per cent .:!• "> u"«'»'Wriii« hydraulic cylinders filament- itid in CFRP would save considerable weight. "Vingtip sections can be spun in approximatelyd m*ulliltd «°Min*» would possibly be The shaded components represented in this drawing illustrate applications of CFRP to Concorde. For the sake of clarity, only ten items are shown, but there ore many other components where weight saving is made possible by the use of such materials. A weight reduction of between 20 and 25 per cent is claimed, and this could be an influential factor in any consideration of a "stretched" Concorde
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