ISSN 1068-3666, Journal of Friction and Wear, 2016, Vol. 37, No. 6, pp. 513–516. © Allerton Press, Inc., 2016. Original Russian Text © N.K. Myshkin, I.G. Goryacheva, 2016, published in Trenie i Iznos, 2016, Vol. 37, No. 6, pp. 665–669.
Tribology: Trends in the Half-Century Development1 N. K. Myshkina, * and I. G. Goryachevab aV.A.
Belyi Metal-Polymer Research Institute of National Academy of Sciences of Belarus, ul. Kirova 32A, Gomel, 246050 Belarus b Institute for Problems in Mechanics, Russian Academy of Sciences, pr. Vernadskogo 101, Moscow, 119526 Russia *e-mail:
[email protected] Received August 25, 2015
Abstract—The paper treats in brief trends in development of tribology (a concept formulated by Peter Jost) in the half-centennial period, setting a stress on the research history of friction, lubrication and wear processes along with their role in engineering and social life. Actuality of the new tribological trends is stated in economy of energy and materials, intensified usage of friction joints in modern engineering, including aerospace, biology, medicine and ecology. The scale factor significance in tribology and nanotechologies is underlined. Keywords: friction, tribology, energy-saving, scale factor, biotribology, ecotribology DOI: 10.3103/S106836661606009X
A remarkable date was celebrated in March, 2016 – the 50th anniversary since publication of the report on the problems of friction, wear and lubrication prepared by the Working Group set up by the GB’s Government and headed by Prof. Peter Jost [1]. In this report Peter Jost has placed emphasis on the economic importance of the problem of friction and proposed several solutions in this connection, namely, formulation of the scientific concept able to generalize all aspects involving interactions between solids and their relative motion. The Peter Jost Working Group has put forward the definition: “Tribology” (from the Greek word “tribos”–rubbing): the science and technology of interacting surfaces in relative motion and of related subjects and practices. Introduction of this term is a reflection of a new synthetic approach to the problem having millennial roots. Indeed, the ancient man has learned to make fire by rubbing dry wood or striking bits of flint. Generation of fire has given the possibility to bake food and warm up the man enabling him to explore large territories. Engineering decisions of friction and lubrication problems by the ancient civilizations have led to the appearance of ski and the wheel, transforming the sliding friction into the rolling one. Creation of the first lubricants based on vegetable and animal products, as well as numerous other inventions have made possible the technological progress and evolution of the mankind [2]. We know from the history of engineering how huge stone blocks of colossal structures were moved, carriages and chariots were created. The mankind got dressed and shoed thanks to friction 1 The article was translated by the authors.
because it hinders fibers and threads from falling apart in the clothes and boots. Then, the people started seafaring on ships also because the ropes and rigging could not work without friction. Evolution of the mankind poses still new problems for the scientists and engineers at each stage of development. Friction is guilty in one of most acute problems of the contemporary world – wear of machines and mechanisms. The expenses due to rehabilitation of the worn out machine parts are enormous, whereas increase of their lifetime is the same as to put into service a new commercial production. High energy losses are associated with friction in machine joints; what is more, the larger share of the fuel consumed by the cars, locomotives, and other vehicles is spent on overcoming resistance to friction in the machines and their contact with the road. In general, the losses connected with friction and wear in machines are estimated in 3—5% of the gross national product, besides, about a quarter of the energy input in industry is spent on overcoming friction forces [3]. Tribological applications have surmounted the frames of engineering, proving social significance of tribology in its biological and medical aspects, in learning friction in the wildlife and adoption of results for promoting technology. Completely new sectors in tribology have sprung and are developing rapidly during these 50 years, e.g., nanotribology, about which existence we could not even suspect some time ago. A special role plays in today’s social life so-called “green tribology” caused by the pressing problems in contamination of the biosphere. Drop of the losses on friction and energy saving, wear reduction in machines and mechanisms together with economy in materials,
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Basics
Basic notions
Physics Chemistry Metallurgy Mechanical engineering
Technologies
Knowledge transfer
Scientific and technical developments Technologies of materials/ Technologies of surface treatment Mechanical systems Lubrication and lubricants Tribomonitoring/ Tribodiagnostics
Application
Results
80% Designing
Innovations Reliability Energy saving Ecology
20% Operation
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National competitiveness Increase of productivity in industry
Fig. 1. Transfer of tribological knowledge into industry [4].
elimination of harmful ejections, use of ecologically friendly lubricants and other topics are now a part of the tribology subject. In Jost’s opinion, in the course of its half-centennial development, the notion of tribology has penetrated in all the fields of human activities and natural phenomena connected with friction processes. A general scheme presented in Fig. 1 illustrates interrelation between advancement in tribological problems and the industrial efficiency (taken from Peter Jost’s report at the Jubilee Conference in London devoted to the scientific, economic and social aspects of advancement in tribology for the last 50 years). One of most applicable methods of friction and wear reduction is the use of a lubricant separating the rubbing bodies by a thin layer of the material with a low resistance to shear. In a number of tribojoints in machines it is possible to realize a hydrodynamic mode of lubrication exercising sliding in a liquid layer, so resistance to sliding is determined mainly by its viscosity. The development of the theory of lubrication has built the basis for design methods of the hydrodynamic and elasto-hydrodynamic lubrication [5, 6]. It is considered most promising today to create new lubricants and additives that combine high efficiency with a possibility to use different materials in the friction pairs and provide ecological safety [5]. Biotribology is now one of the most rapidly developing fields of tribology [7]. Nature has created perfect tribosystems and has fit the man and animals with the joints functioning in fact without any wear for many years. Besides, it used the benefits of rolling before sliding in motion of the living beings on their limbs that look like spokes in a virtual wheel. The development of artificial joints in orthopedics, use of implants, reproduction of natural preferences in technical devices, application of the materials imitating surface layers of the plants and animals, and etc. are all the achievements of biotribology. Amelioration of
sports outfit, shoes, and clothes, running and skating track pavements has multiplied the number of records in sports. Plentiful growth in computer techniques, cell phones and other devices has forced specialists to study tactile interactions of the human skin with the interface. A call and the answer—this is how the whole history of engineering is developed. To each challenge sent to tribology it has found a response. The space technology is a prominent example to this situation: when it the traditional fluid lubrication turned to be unfit for extreme conditions, the attention of the researchers switched over to the solid lubricants [8]. A valuable finding for the space engineering was molybdenum disulfide that resembles graphite by its properties with a very useful exception, i.e., lubricity in vacuum even under high temperatures. Along with molybdenum disulfide there exist other dichalcogenides of refractory metals that have antifriction properties. Some coatings from such plastic metals as indium, cadmium, lead, silver, gold, and tin are also widely applied as solid lubricants. Aside from space engineering, metallic coatings are also used in hostile media, in conditions of cryogenic temperatures, in sliding electric contacts and connectors where together with the reduction of power losses they protect against sticking and welding [8]. Such polymers as polytetrafluoroethylene are often used as solid lubricants as well. The mechanism of PTFE friction is explained by the transfer of a very thin film to the counter surface, this film playing the role of lubricant. In a pure state it is rarely used, being more often applied as a friction additive to various composite materials, e.g., sintered powder materials and coatings. Its metallic matrix provides for strength and heat removal from the friction surfaces, while the polymer ensures low friction. Self-lubricating polymer composites are intensively used in engineering today. By introduction of dispersed fillers it is possible to vary
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TRIBOLOGY: TRENDS IN THE HALF-CENTURY DEVELOPMENT
Scale
fatigue erosive environment
nano
Types of wear
deformation
surface forces
10–9
micro
mechanical properties
10–6
macro
topography
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Friction model
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abrasive adhesive adhesion
Fig. 2. The factors affecting friction and wear.
their physico-mechanical properties, as well as reduce or increase the friction coefficient. The phenomenon of self-lubrication is employed also in designing the metallic alloys for plain bearings. A significant progress was achieved in materials science of composites with adoption of nanotechnologies. When the dispersion of the fillers equals to tens of nanometers, even if their concentration constitutes a tenth share of percent, their amount is so large that they are found in the matrix at a distance from each other commensurable to their size and the whole volume of the material actually presents a layer “reinforced“ by molecular forces acting between the boundary phases. Among more available at present polymer nanocomposites are the ones containing metal particles and those of their compounds, their size being commensurable to macromolecules. Great interest is attracted nowadays to inexpensive polymer-clay nanocomposites since their raw material is extracted in the natural clay fields. Fullerenes and carbon nanotubes are employed to monitor the properties of the composites; discovery of graphene has stimulated a new wave of investigations in this field. In the 1970-ies the tribologists have encountered the problems of friction and wear at the microlevel, in part as a result of the rapid development of computer techniques, robotics and precision mechanisms. The role of the scale factor is illustrated schematically in Fig. 2 [8]. This scheme shows how different factors are interrelated depending on the scale of the process in question. Friction and wear at the micro- and nanolevels occur on the very smooth contact areas comparable to a given system size, therefore, the role of adhesion and surface forces is negligible. Miniaturization of the friction contact models needs a transfer from the volume properties of the materials to their surface features evaluated by the atomic force microscopy, measureJOURNAL OF FRICTION AND WEAR
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ments of adhesion, micro- and nanoindentation. It is worthy to notice that in the course of mutual sliding of contacting solids, the mechanical properties of their materials may change under the action of the frictioninduced heat. The analysis of known wear modes evidences that all of them are also related to the friction force components. At the same time, the fatigue wear is conditioned mainly by deformation of the material by friction, while the adhesive wear is affected by the surface forces when the material undergoes breakage and is transferred to the rubbing bodies. Of course, it is impossible to summarize in a brief report all the variety of the goals that are under consideration today or are to be decided by the tribologists in the nearest future. Physics, mechanics, chemistry and materials science are serving the basis for further development of this synthetic scientific discipline. The achievements in the methods of solving problems in contact mechanics make possible to study interactions between solids at different scale levels [9]. Physicochemical processes in friction and lubrication have been profoundly examined and estimated analytically during this half a century. The engineering approach to the design and manufacturing technologies of the efficient tribosystems has yielded numerous beneficial results. Progress in instrument-making and tribotesting technology has given a possibility for the accelerated advanced decision-making [10]. The micro- and nanotribology required new principal approaches. For example, to reduce friction in the systems of magnetic recording, it turned expedient to use the monomolecular layers of fluorinated hydrocarbons as lubricants. The rapid pace of technologies by the end of the 20th century gave birth to a new class of the compact devices portions of millimeter in size, so-called microelectromechanical systems (MEMS) able to combine the mechanical and electric components in one device. Most often, the MEMS are functioning as sensors, e.g., gyroscopes, accelerometers, 2016
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positioners, and so on. They are present in all cars inside the air bags activated by accelerometers or in the smartphones with a turn positioner. Their design involves microelectronic technologies operating with silicon that, unfortunately displays rather high friction coefficient. To overcome this obstacle, either the superfine lubricating coatings should be applied (monolayers or polymer heterostructures), or the surface layer properties of the components should be changed by, e.g., ion alloying. When we consider the millennial advancement of tribology it is important to note that nothing is lost in its history, beginning with Egyptian chariots till the Moon and Mars rovers. From the other hand, with the development of technologies and creation of advanced materials there occurs a transfer to the novel research cycles and applications of science in practice The present authors were lucky to take part in London’s Conference which summed up the achievements in tribology for the past 50 years and in further reception in the Buckingham Palace by HRH the Prince Philip who is a patron of scientific and technical Societies in Great Britain. In his speech Prof. Jost underlined that much has been done within these 50 years. The actions undertaken by the Working Group in 1966 were realized in creation of four National Laboratories in GB, dozens of laboratories engaged in this sphere round the world, set-up of the International Council on Tribology and a net of national societies in more than forty countries. Five World Congresses in tribology were conducted, as well as many international and national conferences. The training course in tribology have been included to the graduate programs, many countries award scientific degrees in this discipline, numerous journals devoted to this subject are published, and bibliography in this area is practically unbounded [11, 12]. The community of scientists and engineers working in the field of friction, wear, and lubrication apprehends future with optimism.
ACKNOWLEDGMENTS This work was supported by the joint projects BRFFI Т16Р-054 and RFFI 16-58-000085Bel-a. REFERENCES 1. Lubrication (Tribology) Education and Research. A Report on the Present Position and Industry’s Need, Jost P. Ed., London: Dep. Educ. Sci., Her Majesty’s Stat. Off., 1966. 2. Dowson, D., History of Tribology, London: Longman, 1979. 3. Holmberg, K., Andersson, P., and Erdemir, A., Global energy consumption due to friction in passenger cars, Tribol. Int., 2012, vol. 47, pp. 221–234. 4. Jost, P., Brief notes, Int. Conf. “50th Anniversary of the “Jost Report,” London: IMechE, 2016. 5. Spikes, H., Liquid lubrication research; 1966 to the present day, Int. Conf. “50th Anniversary of the “Jost Report,” London: IMechE, 2016. 6. Fillon, M., Development of Hydrodynamic Journal and thrust bearings during the last half century, Int. Conf. “50th Anniversary of the “Jost Report,” London: IMechE, 2016 7. Cann, P., Biotribology: opportunities and challenges, Int. Conf. “50th Anniversary of the “Jost Report,” London: IMechE, 2016. 8. Myshkin, N.K and Petrokovets, M.I., Trenie, smazka, iznos (Friction, Lubrication, and Wear), Moscow: Fizmatlit, 2007. 9. Goryacheva, I.G., Contact Mechanics and Tribology, Amsterdam: Kluwer, 1997. 10. Gee, M., Measurement in tribology, Int. Conf. “50th Anniversary of the “Jost Report,” London: IMechE, 2016. 11. Sviridenok, A.I., Myshkin, N.K., and Kovaleva, I.N., Latest developments in tribology in the Journal Friction and Wear, J. Frict. Wear, 2015, vol. 36, no. 6, pp. 449– 453. 12. Encyclopedia of Tribology, New York: Springer-Verlag, 2013, vols. 1–6.
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