A Material to be Studied

A Material to be Studied Aircraft Engineering TH E MONTHLY ORGAN OF THE AERONAUTICAL ENGINEERING PROFESSION VOL XXVIII No 324 FEBRUARY 1956 modulus is enough to make it unlikely that wings will be made from these materials, but in the case of fuselages the stiffness is not so HE fourth annual Aircraft Production Conference at South­ often critical. The scatter in the material properties at present calls ampton was held shortly before we closed for press with this for an unfavourable safety factor, and the possibility of improving Tissue, too late for an adequate report to be prepared. A full techniques to give more consistent results needs investigating. Per­ report will however appear in our March issue, and we defer until haps the most important property, however, is fatigue strength, and then also any editorial discussion of the general points raised. on this the evidence, such as it is, seems to be conflicting. If it could One of the functions of these conferences is to spread knowledge be shown reliably that reinforced plastics had a high resistance to of new techniques, methods and materials. There was this year some fatigue (and since they do not have a crystalline structure in the sense mention of the use of reinforced plastics for airborne structures, but that metals do it seems at least possible that this might be so) there not in connexion with what has for some time seemed to us to be the would be a very strong case for their use, particularly as the way they most promising major application of these materials. We refer to the lend themselves to design with a minimum of stress concentration structure of pressure cabins. In his paper on Pressure-cabin Fatigue would also help with the problem of fatigue. in the January issue, DR P. B. WALKER went to some length to explain the peculiarities of the pressurized fuselage from the stressing point of view. There is, of course, the 2:1 ratio between hoop and Types in Use longitudinal stress in a thin-walled cylinder; also the pressure loads can be carried by a light-alloy skin much too thin to provide stable Most experience to date with reinforced plastics has been with glass fibre reinforced polyester resins and long-fibre asbestos panels for the resistance of compression stresses due to bending reinforced phenolics. The former are good for secondary structures, moments, and the necessary supporting structure of frames and and are cheap. The latter are very strong, have a fairly high elastic stringers complicates the stressing problems of the shell. The design modulus, but are inclined to be brittle, and the grade of asbestos of cut-outs and their reinforcement is also often a critical problem. needed is scarce. Perhaps the most promising for primary structures are the epoxy resins; in the aircraft industry the most familiar of Advantages of Laminates these is Araldite, manufactured in this country by Aero Research Limited. These resins produce strong laminates, have very good To what extent could these problems be simplified by the use of adhesion to metals and other materials, and compare favourably reinforced plastics? There seems to be at least a prima facie case for with light alloys for strength at high temperature. their use for the following reasons: the reinforcement can be placed so as to give the desired directional strength properties; the extra thickness of a laminated skin would reduce or eliminate the need for Research Needed stabilizing stringers and frames; the building up of skin thickness round cut-outs and at highly stressed attachment points is easily We feel that it would be of great interest if tests were to be carried achieved; and the moulding process is one which is at its best when out on the properties of materials of this type (if indeed they are not, applied to production runs of a few score to a few hundred—typical unknown to us, already in progress). It would, for example, cost com­ aircraft production runs of today. paratively little to produce a group of small fuselages in glass- Experience with magnesium alloys, particularly in the U.S.A., has reinforced epoxy resin, and subject them to tank tests comparable shown the savings in structural complication achieved by the use of a with those described by D R WALKER. Much work would need to be material of lower density and strength in thicker gauges, and done before it could be certain that such materials were economical reinforced plastics are materials with still greater potentialities for and entirely reliable, and it is therefore important that work on them use in this way. should be pressed forward as early as possible. Our assessment of these materials may be over-optimistic, but we have yet to see any evidence which suggests that this is so, and we feel that it would be Possible Drawbacks of advantage to the aircraft industry if the material suppliers, the aircraft manufacturers or the Ministry of Supply establishments, or The reinforced plastics have received rather hesitant acceptance better still all these in collaboration, were to set out to make a for aircraft primary structures, on account of their low elastic reliable assessment of their promise for this application. modulus, and of variability in properties in production. The low http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aircraft Engineering and Aerospace Technology Emerald Publishing

A Material to be Studied

Aircraft Engineering and Aerospace Technology, Volume 28 (2): 1 – Feb 1, 1956

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Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
0002-2667
DOI
10.1108/eb032657
Publisher site
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Abstract

Aircraft Engineering TH E MONTHLY ORGAN OF THE AERONAUTICAL ENGINEERING PROFESSION VOL XXVIII No 324 FEBRUARY 1956 modulus is enough to make it unlikely that wings will be made from these materials, but in the case of fuselages the stiffness is not so HE fourth annual Aircraft Production Conference at South­ often critical. The scatter in the material properties at present calls ampton was held shortly before we closed for press with this for an unfavourable safety factor, and the possibility of improving Tissue, too late for an adequate report to be prepared. A full techniques to give more consistent results needs investigating. Per­ report will however appear in our March issue, and we defer until haps the most important property, however, is fatigue strength, and then also any editorial discussion of the general points raised. on this the evidence, such as it is, seems to be conflicting. If it could One of the functions of these conferences is to spread knowledge be shown reliably that reinforced plastics had a high resistance to of new techniques, methods and materials. There was this year some fatigue (and since they do not have a crystalline structure in the sense mention of the use of reinforced plastics for airborne structures, but that metals do it seems at least possible that this might be so) there not in connexion with what has for some time seemed to us to be the would be a very strong case for their use, particularly as the way they most promising major application of these materials. We refer to the lend themselves to design with a minimum of stress concentration structure of pressure cabins. In his paper on Pressure-cabin Fatigue would also help with the problem of fatigue. in the January issue, DR P. B. WALKER went to some length to explain the peculiarities of the pressurized fuselage from the stressing point of view. There is, of course, the 2:1 ratio between hoop and Types in Use longitudinal stress in a thin-walled cylinder; also the pressure loads can be carried by a light-alloy skin much too thin to provide stable Most experience to date with reinforced plastics has been with glass fibre reinforced polyester resins and long-fibre asbestos panels for the resistance of compression stresses due to bending reinforced phenolics. The former are good for secondary structures, moments, and the necessary supporting structure of frames and and are cheap. The latter are very strong, have a fairly high elastic stringers complicates the stressing problems of the shell. The design modulus, but are inclined to be brittle, and the grade of asbestos of cut-outs and their reinforcement is also often a critical problem. needed is scarce. Perhaps the most promising for primary structures are the epoxy resins; in the aircraft industry the most familiar of Advantages of Laminates these is Araldite, manufactured in this country by Aero Research Limited. These resins produce strong laminates, have very good To what extent could these problems be simplified by the use of adhesion to metals and other materials, and compare favourably reinforced plastics? There seems to be at least a prima facie case for with light alloys for strength at high temperature. their use for the following reasons: the reinforcement can be placed so as to give the desired directional strength properties; the extra thickness of a laminated skin would reduce or eliminate the need for Research Needed stabilizing stringers and frames; the building up of skin thickness round cut-outs and at highly stressed attachment points is easily We feel that it would be of great interest if tests were to be carried achieved; and the moulding process is one which is at its best when out on the properties of materials of this type (if indeed they are not, applied to production runs of a few score to a few hundred—typical unknown to us, already in progress). It would, for example, cost com­ aircraft production runs of today. paratively little to produce a group of small fuselages in glass- Experience with magnesium alloys, particularly in the U.S.A., has reinforced epoxy resin, and subject them to tank tests comparable shown the savings in structural complication achieved by the use of a with those described by D R WALKER. Much work would need to be material of lower density and strength in thicker gauges, and done before it could be certain that such materials were economical reinforced plastics are materials with still greater potentialities for and entirely reliable, and it is therefore important that work on them use in this way. should be pressed forward as early as possible. Our assessment of these materials may be over-optimistic, but we have yet to see any evidence which suggests that this is so, and we feel that it would be Possible Drawbacks of advantage to the aircraft industry if the material suppliers, the aircraft manufacturers or the Ministry of Supply establishments, or The reinforced plastics have received rather hesitant acceptance better still all these in collaboration, were to set out to make a for aircraft primary structures, on account of their low elastic reliable assessment of their promise for this application. modulus, and of variability in properties in production. The low

Journal

Aircraft Engineering and Aerospace TechnologyEmerald Publishing

Published: Feb 1, 1956

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