Tribology is the science and engineering of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear. Tribology is highly interdisciplinary in nature and draws upon several academic areas including: physics, chemistry, materials science and engineering.
The word tribology derives from the Greek root ????- of the verb ?????, tribo, "I rub" in classic Greek and the suffix -logy from -?????, -logia "study of", "knowledge of". It was coined by Peter Jost in 1966, who produced an eponymous report which highlighted the cost of friction, wear and corrosion to the UK economy.
Video Tribology
History
Early History
Despite the relatively recent naming of the field of tribology, quantitative studies of friction can be traced as far back as 1493, when Leonardo da Vinci first noted the two fundamental 'laws' of friction. According to da Vinci, the frictional resistance was the same for two different objects of the same weight but making contacts over different widths and lengths. He also observed that the force needed to overcome friction doubles when the weight doubles. However, da Vinci's findings remained unpublished in his notebooks.
The two fundamental 'laws' of friction were first published (in 1699) by Guillaume Amontons, with whose name they are now usually associated, they state that:
- the force of friction acting between two sliding surfaces is proportional to the load pressing the surfaces together
- the force of friction is independent of the apparent area of contact between the two surfaces.
Although not universally applicable, these simple statements hold for a surprisingly wide range of systems. These laws were further developed by Charles-Augustin de Coulomb (in 1785), who noticed that sliding (kinetic) friction is independent of the sliding velocity.
In 1798, Charles Hatchett and Henry Cavendish carried out the first reliable test on frictional wear. In a study commissioned by the Privy Council of the UK, they used a simple reciprocating machine to evaluate the rate wear of gold coins. They found that coins with grit between them wore at a faster rate compared to self-mated coins. In 1953, John. F Archard developed the Archard equation which describes sliding wear and is based on the theory of asperity contact.
Other early pioneers of tribology research included Australian physicist Frank Philip Bowden and British physicist David Tabor, both of Cavendish Laboratory. Together they authored the seminal textbook 'The Friction and Lubrication of Solids' (Part I originally published in 1950 and Part II in 1964). Michael J. Neale was another leader the field of tribology during the mid-to-late 1900's. He specialized in solving problems in machinery design by applying his knowledge of tribology. Neale was respected as an educator with a gift for integrating theoretical work with his own practical experience to produce easy-to-understand design guides. The Tribology Handbook, which he first edited in 1973 and updated in 1995, is still used around the world and forms the basis of numerous training courses for engineering designers.
Duncan Dowson surveyed the history of tribology in his 1997 book History of Tribology (2nd edition). This covers developments from prehistory, through early civilizations (Mesopotamia, ancient Egypt) and highlights the key developments up to the end of the twentieth century.
Stribeck Curve
The "Stribeck curve" or "Stribeck-Hersey curve" is named after Richard Stribeck, and Mayo D. Hersey who developed it during the first half of the 20th century. It describes the variation in friction between two liquid-lubricated surfaces as a function of a dimensionless lubrication parameter (the Hersey number). The Hersey number can be defined as: ?N/P, where ? is the dynamic viscosity, N is the sliding speed, and P is the load.
Stribeck curves describe the transition between different lubrication regimes with increasing speed for liquid-lubricated sliding surfaces, these can be broadly categorized as:
Richard Stribeck's research was performed in Berlin at the Royal Prussian Technical Testing Institute (MPA, now BAM). Similar work was previously performed around 1885 by Adolf Martens at the same institute, and also in the mid-1870s by Robert Henry Thurston at the Stevens Institute of Technology in the U.S. The reason why the form of the friction curve for liquid lubricated surfaces was later attributed to Stribeck, although both Thurston and Martens achieved their results considerably earlier may be because Stribeck published in the most important technical journal in Germany at that time, Zeitschrift des Vereins Deutscher Ingenieure (VDI, Journal of German Mechanical Engineers). Martens published his results in the official journal of the Royal Prussian Technical Testing Institute, which has now become BAM. The VDI journal was one of the most important journals for engineers and provided wide access to these data and later colleagues rationalized the results into the three classical friction regimes. Thurston did not have the experimental means to record a continuous graph of the coefficient of friction but only measured it at discrete points. This may be the reason why the minimum in the coefficient of friction for a liquid-lubricated journal bearing was not discovered by him, but was demonstrated by the graphs of Martens and Stribeck.
The graphs of friction force reported by Stribeck stem from a carefully conducted, wide-ranging series of experiments on journal bearings. Stribeck systematically studied the variation of friction between two liquid lubricated surfaces. His results were presented on 5 December 1901 during a public session of the railway society and published on 6 September 1902, They clearly showed the minimum value of friction as the demarcation between full fluid-film lubrication and some solid asperity interactions. Stribeck studied different bearing materials and aspect ratios D/L from 1:1 to 1:2. The maximum sliding speed was 4 m/s and the contact pressure was limited to 5 MPa, conditions relevant to railway wagon journal bearings.
The Jost Report
The term tribology became widely used following 'The Jost Report', published in 1966. The report highlighted the huge cost of friction, wear and corrosion to the UK economy (1.1-1.4% of GDP). As a result, the UK government established several national centres for tribology to address tribological problems. Since then the term has diffused into the international community, with many specialists now identifying as 'tribologists'.
There are now numerous national and international societies, including: the Society for Tribologists and Lubrication Engineers (STLE) in the USA, the Institution of Mechanical Engineers' and Institute of Physics (IMechE Tribology Group, IOP Tribology Group) in the UK, the German Society for Tribology (Gesellschaft für Tribologie), the Malaysian Tribology Society (MYTRIBOS), the Japanese Society of Tribologists (JAST), and the Chinese Mechanical Engineering Society (Chinese Tribology Institute).
Technical universities all over the world have researchers working on tribology problems, often as part of mechanical engineering departments. However, tribology groups now generally include at least as many materials scientisits, physicists and chemists as they do mechanical engineers.
Worldwide Importance
Despite considerable research since The Jost Report, the global impact of friction and wear on energy consumption, economic expenditure, and carbon dioxide emissions are still considerable. In 2017, Kenneth Holmberg and Ali Erdemir attempted to quantify their impact worldwide. They considered the four main energy consuming sectors: transportation, manufacturing, power generation, and residential. The following were concluded:
- In total, ~23% of the world's total energy consumption originates from tribological contacts. Of that 20% is used to overcome friction and 3% is used to remanufacture worn parts and spare equipment due to wear and wear-related failures.
- By taking advantage of the new surface, materials, and lubrication technologies for friction reduction and wear protection in vehicles, machinery and other equipment worldwide, energy losses due to friction and wear could potentially be reduced by 40% in the long term (15 years) and by 18% in the short term (8 years). On a global scale, these savings would amount to 1.4% of GDP annually and 8.7% of the total energy consumption in the long term.
- The largest short term energy savings are envisioned in transportation (25%) and in the power generation (20%) while the potential savings in the manufacturing and residential sectors are estimated to be ~10%. In the longer term, the savings would be 55%, 40%, 25%, and 20%, respectively.
- Implementing advanced tribological technologies can also reduce global carbon dioxide emissions by as much as 1,460 metric tons of carbon dioxide equivalent (MtCO2) and result in 450,000 million Euros cost savings in the short term. In the long term, the reduction could be as large as 3,140 MtCO2 and the cost savings 970,000 million Euros.
Maps Tribology
Applications
Tribology problems range from macro to nano scales, in areas as diverse as the movement of continental plates and glaciers to the locomotion of animals and insects. Until recently, most tribology research was concentrated on transportation and manufacturing sectors, but this has considerably diversified in recent times.
Traditional Research Areas
Historically, most tribology research concentrated on the design and effective lubrication of machine components, particularly for bearings. However, the study of tribology extends into almost all other aspects of modern technology and any system where one material slides over another can be affected by complex tribological interactions.
Tribology has played an important the transportation industry, with effective lubrication of moving parts being critical to human progress. In the past, tribology research in the transportation industry focused on reliability, ensuring the safe, continuous operation of machine components. Over the last few decades, due to an increased focus on energy consumption, efficiency has become increasingly important and thus transportation lubricants have become progressively more complex and sophisticated in order to improve this.
Tribology also plays an important role in manufacturing. For example, in metal-forming operations, friction increases tool wear and the power required to work a piece. This results in increased costs due to more frequent tool replacement, loss of tolerance as tool dimensions shift, and greater forces required to shape a piece. The use of lubricants which minimize direct surface contact reduces tool wear and power requirements.
New Research Areas
Since the 1990s, new interdisciplinary areas of tribology have emerged, including the nanotribology, biotribology, and green tribology. Nanotribology and biotribology study friction, wear and lubrication in nanoscale and biological systems respectively, whilst green tribology focuses on ecological considerations, such as sustainable sourcing of lubricant feed-stocks. Nanotribology is becoming increasingly important as devices become smaller (e.g. micro/nanoelectromechanical systems, MEMS/NEMS) and research has been aided by the invention of Atomic Force Microscopy.
Recently, intensive studies of superlubricity (phenomenon of vanishing friction) have sparked due to increasing demand for energy savings. Development of new materials, such as graphene, have initiated the development of fundamentally new approaches to tribology problems.
See also
References
External links
- International Tribology Council
- tribology-abc
- Tribonet
- Tribology Group, Imperial College London
- Leonardo Centre for Tribology, University of Sheffield
- National Centre for Advanced Tribology (nCATS), University of Southampton
- The Institute of Functional Surfaces (iFS), University of Leeds
- Laboratory of Tribology, Moscow
- LaMCoS, INSA Lyon
- Tribology Research and Evaluations Group, Southwest Research Institute
- IET Tribology Network
- Neale Consulting Engineers
Source of the article : Wikipedia
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