Nonmetallic materials and composites at low temperatures

Nonmetallic materials and composites at low temperatures

BoOk reviews A review of the determination of dynamic properties of polymers and composites Nonmetallic materials and composites at low temperatures ...

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BoOk reviews A review of the determination of dynamic properties of polymers and composites

Nonmetallic materials and composites at low temperatures

B.E. Read and G.D. Dean

Edited by: A.F. Clark, R.P. Reed and G. Hartwis

Adam Hilger Limited, Bristol

Plenum Press, New York, 1979

The book consists of eight chapters: a general discussion of dynamic property-structure relationships for isotropic and anisotropic materials; several chapters specifically discussing various methods of studying dynamic behaviour, including sonic and ultrasonic techniques; and a chapter on data correlation and conclusions,

Interest in non-metallic materials at low temperatures has grown steadily during the past ten years, mainly resulting from research and development of superconducting magnets at various laboratories throughout the world, and the need for lightweight structural materials for low temperature space applications.

Methods of dynamic testing are discussed in considerably more detail than many reports on the subject; emphasis being placed on the recognition of possible sources of error and methods of minimizing and/or eliminating such errors. The authors set out to provide a basic guide for workers concerned with the development of dynamic test methods or those concerned with improving the accuracy of

This book contains the proceedings of the conference sponsored by the International Cryogenic Materials Conference Board, and held in Munich, West Germany, in July 1978. That there was a need for the conference is evidenced by the fact that parallel - and sometimes duplicate - research is being carried out by different organizations.

existIng facilities. The book does not attempt to survey the whole range of commercially available dynamic test equipment but merely to describe methods of data analysis and correction which should be applicable to many of the available facilities, Chapter 2 covers the subject of the 'Forced Non-Resonance

The two opening papers constitute an excellent introduction to the subject. The first, by U.T. Kreibich, F. Lohse and R. Schmid, deals with the chemical structure of polymers and attempts to relate this to flexibility and toughness at low temperature. It is known that these properties can be improved by the addition of flexibilizers, but with undesirable increase in thermal expansion coefficients. The second paper, by G. Hartwis, summarizes information on

Method', outlining the theory, apparatus, test arrangement, methods of measurement, corrections and data processing. In chapter 3 the 'Torsion Pendulum' is discussed in a similar manner with a little more emphasis on theory and experimental determinations. 'Audiofrequency Resonance Methods' take up little space and only a brief introduction and description of the methods are given. The chapters on 'Flexural Resonance' and 'Torsional and Longitudinal Resonance' account for about one third of the book, which is not surprizing since they are probably the most versatile and well used methods of dynamic testing. 'The Ultrasonic Immersion Method' is also given good coverage in chapter 7. Data on the usual model systems are included t(~ demonstrate the performance of various test techniques and although, as the title of the book suggests, there has been no attempt to provide design information it sadly lacks in examples of the use of the techniques with less 'exotic' composite materials, which may have lower performance than those described but nevertheless can be and often are used in dynamic situations. In fact since most of the examples given are for materials such as rubber, perspex, and unidirectional carbon fibre composite it leaves the reader wondering whether or not many of the methods and corrections described can be confidently applied to other less well characterized materials, particularly randomly and hybrid reinforced composites, The book will obviously be welcomed by those working on the development of dynamic test methods and those involved in teaching the subject. It will undoubtedly become a useful source of reference on dynamic test methods, L.S. Norwood

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the mechanical and electrical properties of polymers at low temperatures. Papers on spectroscopic analysis and the relationship between valence energies and flexibility are followed by three papers on dielectric properties and one on flashover behaviour. Unfortunately, there is only one paper, by B. Kneifel, which deals specifically with fracture properties. The results confirm previous work, and indicate that work of fracture and fracture toughness tend to increase as the temperature is lowered to that of liquid nitrogen (77 K), but that further lowering of the temperature causes reductions in these properties. Because polymers tend to behave in a brittle manner at low temperatures, and fracture properties are the only real guide which the designer has for such materials, it is to be hoped that this work will stimulate further efforts in the experimentally difficult field of fracture mechanics. The effects of particle and gamma irradiation on polymers are described in two papers. Two of the most interesting applications of superconducting magnets are in connection with fusion reactors and high energy physics, where radiation doses are often high. There are three contributions on thermal Insulation; two on expanded foams, and one on balsa wood - the latter having found favour with the designers of storage tanks for liquified natural gas. Six papers on fibre reinforced and powder Filled composites demonstrate the interests and problems of the low temperature designer. Carbon reinforced epoxies are of considerable interest, one favourable feature being their low thermal

COMPOSITES. OCTOBER 1979

expansion coefficients. A paper by E.L. Stone, L.O. ElMarazki and W.C. Young describes compressive fatigue tests on glass fibre/polyester composites: such materials are considerably cheaper than the epoxy resin composites which have been favoured by superconducting magnet designers, J.W. Ekin, R.W. Schramm and A.F. Clark give the results of experiments on impregnated superconducting coils, and suggest that the phenomenon known as 'training' is due to cracking within the impregnant: this suggestion is not new, however, and has been a topic of discussion for several years, It is by no means certain that resin cracking is the only cause of training, The final section of the conference was concerned with applications of composites and polymers. Large superconducting magnets appear to provide the main justification for development of expensive high strength composites,

together with a need for better impregnating resins and low thermal conductivity support structures. The book will be of great interest to scientists and designers in the field of low temperatures. It should also prove of use to others, who may not have ready access to the large number of reports which have been issued by the laboratories involved in the subject. It is to be hoped that further research will be stimulated, and that co-operation between polymer chemists, materials scientists, and designers will result in a far better understanding of the properties of polymers at low temperatures than exists at present. It should be pointed out that the conference was almost entirely concerned with polymers and composites, and there is little mention of other non-metallic materials such as ceramics and glasses. B. Colyer

IOINTING IN

Symposium, 4-5 September 1978, Imperial College, London

materials field, from industry and from academic and research establishments, with the hope that some rather more quantitative information would emerge. The investigation reported in this book, when taken

This book contains the papers presented at a two-day Symposium organized by the Aeronautics Department of Imperial College of Science and Technology, University of London, in cooperation with the Royal Aircraft Establishment, Farnborough, England. As reinforced plastics become more widely used in structures the need for reliable methods of jointing them to each other and to metals becomes more pressing. The problem is not simple since the non-metallic materials are often wildly anisotropic. Although the ad-hoc art goes back some thirty years to the early days of glassreinforced plastics, the technology is not well documented; and methods which are established at one concern may be unknown to another.

COMPOSITES. OCTOBER 1979

together, should lead to a deeper understanding to joint behaviour, a more accurate knowledge of design allowable stresses and a greater confidence in practical application. JOINTING IN FIBRE REINFORCED PLASTICS will be essential reading for all'those working in the field of composite materials. 240 x 170mm/viii + 151 pages/illustrations/ November 1978 Paper/ISBN 0 86103 008 7/£11.00 ($28.60) further information and complete catalogue available from IPC Science & Technology Press Ltd. PO Box 63, Westbury House, Bury Street, Guildford, Surrey, England GU2 5BH

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