Friction and wear

Friction and wear

Gardos - Self-lubricating composites for extreme environment applications print of any further studies of extreme environment (or for that fact, any o...

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Gardos - Self-lubricating composites for extreme environment applications print of any further studies of extreme environment (or for that fact, any other kind of) self-lubricating composites.

10. Tanaka K., Uchiyluna Y. and Toyooka S. The Mechanism of Wear of Polvtetrafluoroethylene. Wear, 1973, 23. 153

For now, however, we must apply what we do know. We owe this to imoroved productivity and the designers of future space and high power aensity terrestrial mechanisms who now cheerfully substitute Xs and TBDs (To Be Determined) on drawings next to where the bearings should be. We must be scientific, but science is in the eye of the beholder. As a friend of mine once said, " . . . fundamental is what we don't understand".

11. Uchiyama Y. and Tanalm K. Wear Laws for Polytetrafluoroethylene. Wear, 1980, 58(2), 223-235 12. Fwaro R.L. Tribological Properties and Thermal Stability of Various Types of Polyimide Films. Paper presented at the 1981 ASLE-ASME Lubrication Conference, 5 - 7 Oct. 1981, New Orleans, LA. ASLE Preprint No. 8 1 - L C - 4 A - 2


13. BilowN. and Gardos M.N. Heavy Metal Chalcogenide Polyimide Lubricative Components. US Patent No. 4,075,111 14. Makinson K.R. and Tabor D. The Friction and Transfer of Polytetrafluoroethylene. Prec. Roy. Soc. (London), 1964, A281,49

The author is indebted to Messrs C.R. Meeks of Hughes Aircraft Company and B.D. McConnell of the US Air Force Wright Aeronautical Laboratories Materials Laboratory for the privilege of cooperative work in producing and interpreting some of the data herein. The permission of Hughes Aircraft Company for publishing this paper is also gratefully acknowledged.

15. Brainard W.A. and Buckley D.H. Adhesion and Friction of PTFE in Contact with Metals as Studied by Auger Spectroscopy, Field Ion and Scanning Electron MicroscopyxWear, 1973, 26, 75-93


17. Buekley D.H. Surface Films and Metallurgy Related to Lubrication and Wear. NASA- TM-8264 5, July 1981

16. BucHey D.R. and Brainard W.A. The Atomic Nature of Polymer-Metal Interactions in Adhesion, Friction and Wear in Advances in Polymer Friction and Wear, Vol. 5,4, Lieng-Huang Lee (Ed), Plenum Publishing Corp., New York, NY, 1975, 315-328

1. Gardos M.N. Theory and Practice of Self-Lubricated, OsciUatory Bearings for High Vacuum Applications, Part I - Selection of the Self-Lubricating Composite Retainer Material. L ub. Eng., 1981, 37, 641

18. Fusaro R.L. Effect of Atmosphere and Temperature on Wear, Friction and Transfer of Polyimide Films. ASLE Trans. 1978, 21(2), 125-133

2. MeeksC.R. Theory and Practice of Self-Lubricated, Oscillatory Bearings for High Vacuum Applications, Part II - Accelerated Life Tests and Analysis of Bearings. Lub. Eng., 1981, 37, 657 3. Gardos M.N. and MeConnell B.D. Development of a High Load, High Temperature Self-Lubricating Composite - Part I: Polymer Matrix Selection. Paper presented at the ASLE-ASME Lubrication Conference, 5 - 7 Oct. 1981, New Orleans, LA. ASLE Preprint No. 8 1 - 3 A - 3 4. ibid, Part II: Reinforcement Selection. ASLE Preprint No. 81-3A-4

20. Burkstrand J.M. Metal-Polymer Interfaces: Adhesion and X-ray Photoemission Studies. J. A ~I. Phys., 1981, 52(7), 4 795-4800

5. ibid, Part III: Additives Selection. ASLE Preprint No. 81-3A - 5 6. ibid, Part IV: Formulation and Performance of the Best Compositions. ASLE Preprint No. 81-3A - 6 7. Bayer R.G. (Ed) Wear Tests for Plastics: Selection and Use. ASTM STP 701, January 1980 8. Taber R.D. and Fuchsluger J.H. Filled PTFE Materials for Piston Rings and Seating Rings - Problems of Quality Control. Lub. Eng., 1975, 31(2), 75-80 9. Fucflfluger J.H. and Tuber R.D. Quality Control Methods Pay Off in Producing High Quality Piston Rings Using Filled PTFE Materials. Presented at the Fall Conference of American Society for Quality Control, Chemical Division, Charlotte, NC, October 1976

19. Fusaro R.L. Tribological Properties and Thermal Stability of Various Types of Polyimide Films. Paper presented at the ASLE-ASME Lubrication Conference, 5 - 7 Oct. 1981, New Orleans, LA. ASLE Preprint No. 8 1 - L C - 4 A - 2

21. Clerico M. Tribological Behaviour of Polyacetals. Wear, 1980, 64(2), 259-272 22. Rhee S.K. Wear Equation for Polymers Sliding Against Metal Surfaces. Wear, 1970, 16, 431 23. Pooley C.M. and Tabor D. Friction and Molecular Structure: The Behaviour of Some Thermoplastics. Prec. Roy. Soc. (London), 1972, A329, 251 24. Lancaster J.K. et al Effects of Amplitude of Oscillation on the Wear of Dry Bearings Containing PTFE. Paper presented at the A SLE-ASME Lubrication Conference, 5 - 7 Oct. 1981, New Orleans, LA. ASME Preprint No. 81-Lub-6 25. Risdon TJ. and Logan R.D. Effect of Molybdenum Disulphide on the Wear Rates of Polymer Composites. Prec. 2nd Intl. Conf. on Solid Lubr., ASLE-SP-6, 1978, 230 26. Theberge LE. et al. Predicting Wear in Reinforced InternallyLubricated Thermo-plastics. Plastics World, 1976, 34(10), 46-49

Friction and Wear Calculation Methods I.V. Kragelsky, M.N. D o b y c h i n and V.S. K o m b a l o v Translated by N. Standen Professor Kragelsky is a Russian engineer who has been engaged in research on friction and wear for over forty years. His work is k n o w n to nonPublished, 1982, by Pergamon Press Ltd, Headington Hill Hall, Oxford, UK, 0)(30BW at US $100 or £45. ISBN 0080254616

TR I B O L O G Y international October 1982

Russian readers through the English translation, published in 1965, of an earlier book on this subject. This book by Professor Kragelsky and two of his colleagues is a translation of a new book which has a similar title but a somewhat different aim. Whereas the

earlier book was concerned with general ideas and mechanisms, this work carries these ideas forward into a more practical area: it shows how areas • of real contact may be calculated from surface topography, how this may be applied to the calculation of the friction of real surfaces, and to the wear of machine elements in various regimes of wear. The rmal chapter describes


experimental methods of evaluating the frictional properties of materials. Although the book was written for Russian readers and contains over 450 references to Russian work, there is a very full bibliography (nearly 300 papers) of research published in nonRussian journals. The coverage is indeed extensive. However, I found that when papers were discussed describing work with which I was not familiar, it was not always easy to understand the cryptic accounts given. On the other hand, when the authors describe their own work they are clear and even though the reader may have to make some effort, the communication is effective. The authors are given greatly to the development of equations, as is not infrequently the case with Russian publications. However, these equations are meant to be used and examples are given of how one may apply them to practical situations. Furthermore, mirabile dictu, all the symbols are clearly defined and are used consistently throughout the book so that surface parameters employed in Chapters 9, 10 and 11 on the calculation of wear are the same as those derived in Chapter 2 on the characteristics of surface topography. Professor Kragelsky's views of the mechanism of friction and wear are familiar to workers in the field. Friction is due to adhesion at the regions of real contact and to the deformation of the softer surface by asperities on the harder. These two components are referred to by Kragelsky as the 'molecular' and 'mechanical' components respectively. The shear strength s of the interface is found experimentally to vary with contact pressure and to follow an equation Of the form S=So ÷ap where p is the true contact pressure. This provides the basis of Kragelsky's strong support for the two-term or binomial law of friction, a concept which seems to occupy a sancrosanct status in Russian friction studies. However, his final equations of friction are not, in fact, binomial but contain at least three terms involving So, ap, and the deformation or mechanical term as well as factors influencing the area of real contact. Indeed, in a flippant


comment, I once suggested a pentanomial law of friction. Once sliding occurs, the frictional process itself produces a heavily modified surface layer referred to by the authors as the third phase which often dominates the friction and wear behaviour. With metals, this could be a weakened layer or a work-hardened layer, an oxide layer or an adsorbed lubricant film. With polymers, the third phase usually consists of a degraded layer of lower molecular weight and smaller shear strength. The authors also make the general point that the most favourable condition for low friction and wear is the presence of an appropriate gradient of strength properties in moving froro the surface into the bulk. Broadly speaking, Professor Kragelsky divides the sliding and wear processes into three categories of increasing severity. The first involves predominantly elastic deformation, fatigue wear and possible delamination; the second involves plastic deformation and groov!ng of the surfaces; the third microcutting Where relatively large chips are removed during sliding. A fourth category deals with the rupture of surface films. Some of these processes are analysed in detail. For example, fatigue wear lends itself to fairly precise computation and prediction once the fatigue characteristics of the system have been established in an empirical test. There is an impressive correlation between theory and experiment over eight orders of magnitude in the wear rate (Chapter 8, Fig 15). Similarly useful equations are derived for abrasive wear, including a brave attempt to include the possibility of the fragmentation of the wear particles themselves. There are also discussions of oxidative and erosive wear. In this rather substantial part of the monograph, the authors have provided a very useful series of equations that, in conjunction with appropriate laboratory or simulated tests, can be applied to practical situations involving the wear of brakes and clutches, the wear of machine elements, seals, cams, piston-rings and similar mechanisms. Some worked examples are given, but it would be interesting to know how far these procedures are, in fact, followed in Soviet engineering design.

The translation is competent, if not inspired, and the style somewhat awkward. Sometimes the wrong alternative word is used, eg evidently instead of apparently, wear on a lattice instead of wear on a mesh, elastic restoration instead of elastic recovery. There is also the inevitable difficulty of transliterating European names from their Russian form. Thus we have Kurtel (Courtel), Eiler (Euler), Paran (Parent), Kulcn (Coulomb), Blodzhet (Blodgett). A charming example is the appendix on p. 411 giving a table of properties of metallic elements. This was originally taken from an English source (Rabinowicz's book on Wear) and rearranged to suit the Russian alphabet which runs, A, B, V, G, D, E ..... so that the first six elements given are A1, Be, Bi. Va, W, Ga. Incidentally, sur'ma is mistranslated as arsenic; it should be antimony. Finally, there are those occasional lapses which one discovers, on consulting the original, are not the fault of the translator. What is one to make of the comment (p. 12) that the energy of wetting (W = 3"1 + 3'2 - 3'12) implies that energy is expended in forming an adhesive bond, or the phrase (p. 26) stating that 'whereas in physical adsorption heat is evolved, in chemisorption heat is absorbed', or the statement (p. 249) that 'the rate of crack formation in a hard material is retarded because of the high value of the friction stress and the cohesive strength of the material'? These, however, are minor blemishes in a book of over 450 pages containing numerous figures and valuable tables as appendices. The book as a whole represents a very solid workmanlike contribution to the science and practice of tribology. There is an enormous amount of information, many thoughtful ideas and a host of equations which the authors believe can be usefully applied to the design of better machinery and to the prediction of machine life. It is not an easy book to read, but research workers and mechanical engineers who are prepared to master the text will find it valuable and stimulating. D. Tabor

Cavendish Laboratory, Department of Physics, University of Cambridge, Madingley Road, Cambridge, UK, CB3 0HE

TR IBOLOGY international October 1982