Fretting corrosion

Fretting corrosion

I I BOOK REVI E W S The Rheology of Lubricants 7". C, Davenport (Editor) Applied Science Publishers Ltd (1973) 148 pp, £4.50. This book contains t...

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BOOK REVI E W S

The Rheology of Lubricants 7". C, Davenport (Editor) Applied Science Publishers Ltd (1973) 148 pp, £4.50.

This book contains the eleven papers which were presented at a conference organised jointly by the Institute of Petroleum, the Institution of Mechanical Engineers and the British Society of Rheology, held at Nottingham in July 1972. It was one of the stated aims of the conference to present an authoritative review of various aspects of lubricant rheology; this aim has been admirably fulfilled in the two review papers given by J. F. Hutton and K. Waiters. Hutton's paper, on the rheology of petroleum-based lubricating oils and greases, uses as its starting point the review given by Bondi in 1960 and covers developments up to 1970/71. The first part of the review is concerned with non-polymeric materials and includes a discussion of new viscosity/temperature/pressure equations based upon the free volume and activation energy concepts. The author suggests that equations based upon these concepts deserve greater consideration by the oil industry than they have received ha the past. The second part deals with polymeric materials and reviews the development of the theories of polymer thickening at low concentrations and non-Newtonian effects at high concentrations and high shear rates. The paper ends with a brief review of work on greases. The second review paper by Waiters looks at new theoretical and experimental concepts and begins by reviewing the development of the basic constitutive equations of rheology which began in the 1950s. The content of this review is necessarily mathematical but the author has been at pains to emphasize those theoretical results which are likely to be of use to the lubrication engineer. There is much discussion in this and other papers, and in the general discussion, of normal stress effects. It seems appropriate that Walters should end his paper by citing as the most urgent question to be answered: 'What is the ratio between normal and shear stress and extensional and shear stress for lubricants under operating conditions?'. Two papers report results of rheological tests carried out on crankcase lubricants after service. The first by J. Harris and E. T. Busby, looks at the shear rate/shear stress behaviour of carbon-black filled lubricants with different de-flocculating treatments, and the second, by J. A. Spence and D. E. S. Middleton, is concerned with viscosity loss due to shear breakdown. One reservation expressed by W. C. Pike in his comments on this paper was that shear breakdown is not the only factor responsible for viscosity loss in crankcase lubricants and that, although the authors took steps to avoid it, fuel dilution may have been a significant factor affecting their results. The paper by G. R. Dobson and Anne C. Tompsett discusses the many anomalous effects that can occur in the viscometry of greases. This is also the theme of a

paper by J. F. Hutton on the cone-and-plate rheometer in which he describes the formation of a free surface within the zone of apparent shear caused by the extrusion of the grease. His comment that 'cone-and-plate rheometers should be used for the testing of greases only in very special circumstances' should obviously provide both the manufacturers and the users of these instruments with some food for thought. In their paper on the application of elastico-viscous theory to the journal bearing, M. J. Davies and K. Waiters conclude that elasticity does in fact provide a partial theoretical explanation for the improved behaviour of bearings when lubricated with polymer thickened oils. The discussion on this paper indicated, however, that engineers were not totally convinced, and one contributor to the discussion suggested that maybe the kind of situations where normal stress effects were important corresponded to speeds outside the range of engineering practice. It is a pity that the results of experiments conducted by K. L. Johnson on the theology of elastohydrodynamic lubrication films (which were touched upon during the general discussion) were not reported more fully, since his experiments using the rolling/spinning ball configuration are now generally regarded as being quite crucial in our understanding of elastico-viscous effects in this situation. Engineers are playing an increasingly important role in the alleviation of human suffering by actively cooperating with the medical profession, and the contribution made by tribologists, particularly in the field of prosthetic replacements for diseased joints, is a good example of how fruitful this co-operation can be. The paper by D. Dowson and V. Wright outlines some of the main areas of activity in the field of bio-tribology ranging from the friction of razor blades to the lubrication of red blood cells in the human body. This book is a valuable progress report upon a subject which should continue to form an important part of tribological research for a number of years. R. W. Snidle

Fretting corrosion R. B. Waterhouse Pergamon Press (1972) 253pp, £6.50

If two contacting surfaces are subjected to slight periodic relative movement of the order of 10 to 100/am, the interfacial slip may lead to a type of deterioration which is known as fretting. The main characteristic that distinguishes this from other types of wear is that there is little opportunity for the products of the fretting process to escape. If the debris produced is a chemical reactionproduct between constituents of the surface and the environment the damage is termed fretting corrosion.

TRIBOLOGY June 1973

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This monograph is 'an attempt to provide structural engineers, mechanical engineers and tribologists with a survey of the field. It is aimed particularly at the professional man who may be confronted with a typical fretting problem but it is also relevant to the scientist engaged in fundamental studies of contact phenomena. The book is well planned. It begins by describing the main features of fretting corrosion and the nature of contact between solid surfaces. It then documents a vast discordant literature on the types of fretting damage observed and the importance of various variables involved. The last three chapters deal with electrochemical aspects of corrosion, the methods of preventing fretting and finally a five page review of the mechanism of fretting. The main criticisms that I have to make of this book are five-fold. Firstly it occasionally presupposes a good deal of knowledge on the part of the reader. The chapters on the theoretical and experimental aspects of surface-contact are very good but only fully intelligible if the reader already knows the field rather well. The same applies to the chapter on electrochemistry: a mechanical engineer would find this rather tough going. Secondly the author is not always emphatic enough in pointing out the mutual contradictions that may exist between various experimental results. Consequently the reader is sometimes in doubt as to whether he has misread

a sentence or whether the sentence contains a misstatement. Thirdly the legends under the figures are often too brief so that the reader is not always sure of the test to which a particular graph refers nor of the main point that it is illustrating. This can be slightly irritating since the text and the figures are frequently out of phase, a technical issue that the publishers ought to have had the wit to resolve. Fourthly the quality of the half-tone blocks is variable - Figures 3.13 and 3.14 are particularly unsatisfactory. Finally the chapter on the mechanism of fretting is disappointingly brief though this may reflect the nature of the subject itself. Having enumerated these criticisms I would like to express my appreciation of Dr Waterhouse's effort to provide coverage of such a difficult field, containing as it does so many unresolved fundamental problems. The central body of the book from page 36 to page 181 provides an enormous store of information on the type of experiments that have been carried out and the main results (not always self consistent) that have been achieved. Material-scientists confronted with a problem of wear and corrosion between contacts will be extremely grateful to Dr Waterhouse for this thesaurus of fretting as well as for his penultimate chapter on methods of preventing it. The book is graced by a charming foreword by Dr Ulick Evans. David Tabor

CALENDAR June

July

September

3 - 6 . 75th National meeting of the American Institute of Chemical Engineers

9--13. Limits of lubrication

3rd International round table meeting on sintering

Detroit, Michigan, USA Mr G. Coustan, Dow Corning Corp, Midland, Michigan 48640, USA

London Dr A. Cameron, Mechanical Engineering Dept, Imperial College, London SW7 16--17. OECD friction and wear conference

4-8. IMAS '73. Conference London Institute of Marine Engineers, 75 Mark Lane, London EC3R 7JN

Imperial College, London Dept of Mechanical Engineering, Imperial College, Exhibition Road, London SW7 2BX

Lubrication symposium

18--19. Conference on materials for use in medicine

Evanston, Illinois, USA Meetings Dept, The American Society of Mechanical Engineers, 345 East 47th Street, New York ]0017, USA 5-8. Tribology '73 London UTP Exhibition, 36-37 Furnival Street, London EC4A 1JH 14--15. "/'ribotiogy as applied to micro-

Cambridge, England Dr K. Copeland, Dept of Biophysics, University College, Gower Street, London WC 1

August 13-- 16. Internal friction and ultrasonic attenuation in crystalline solids

Aachen, Germany Prof K. Lfieke, Institut fdr Allgemeine Besan~on, France Metallkunde und Metallphysik, TechM. Massin, CETEHOR, 39 Avenue de l'Observatoire BP 1145, 25003 Besancon, nische Hochschule Aachen, Aachen, Birkenweg 14, Germany France mechanics and chronometry

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TRIBOLOGY June 1973

Yugoslavia Dr Vojin Mikijelj, Organising Committee of III RTM (Lab 28), PO Box 522, 11001 Belgrade, Yugoslavia 1 2 - 1 4 . 14th international machine tool design and research conference

Manchester, England Professor F. Koenigsberger, Dept of Mechanical Engineering, Institute of Science and Technology, University of Manchester, PO Box 88, Manchester M60 1QD, England 13-15.

The knee joint

Rotterdam, The Netherlands The Secretariat of the International Congress of the Knee Joint, c/o Holland Organizing Centre, Lane Voorhout, The Hague, The Netherlands 17--21. 7th seminar on industrial tribology

Swansea, Wales Dr G. P. Thomas, Room 408, Physics Tower, University College of Swansea, Singleton Park, Swansea SA2 8PP