Tribology

Tribology is the science and technology of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear. The word "tribology" derives from the Greek τριβο ("tribo") meaning 'to rub', and λόγος ("logos") meaning 'principle or logic'.

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Applications

The study of tribology is commonly applied in bearing design but extends into other almost all aspects of modern technology, even to such unlikely areas as hair conditioners and cosmetics such as lipstick, powders and lipgloss.

Any product where one material slides or rubs over another is affected by complex tribological interactions, whether lubricated (e.g. hip implants and other artificial prosthesis) or unlubricated (for example, high temperature sliding wear in which conventional lubricants can no longer be used and the formation of compacted oxide layer glazes have been observed to protect against wear).

Origins

Historically, Leonardo da Vinci (1452-1519) was the first to enunciate two 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 is doubled when the weight is doubled. Similar observations were made by Charles-Augustin de Coulomb (1736-1806). The first reliable test on frictional wear was carried out by Charles Hatchett (1760- 1820) using a simple reciprocating machine to evaluate wear on gold coins. He found that compared to self-mated coins, coins with grits between them wore at a faster rate. The deciphering of da Vinci's work took several centuries, before the development of this branch of science, today called "tribology".

The term became widely used following The Jost Report in 1966, in which huge sums of money were reported to have been lost in the UK annually due to the consequences of friction, wear and corrosion. As a result several national centres for tribology were created in the UK. Since then the term has diffused into the international engineering field and many specialists now claim to be tribologists.

There are now numerous national and international societies, such as the Society for Tribologists and Lubrication Engineers (STLE) in the USA and the Institution of Mechanical Engineers' Tribology Group (IMechE Tribology Group) in the UK.

Most technical universities have a group working on tribology, often as part of their mechanical engineering departments. The limitations in tribological interactions are however no longer mainly determined by mechanical designs, but rather by material limitations so the discipline of tribology now counts at least as many materials engineers, physicists and chemists as it does mechanical engineers.

Fundamentals of Tribology

The tribological interactions of a solid surface's exposed face with interfacing materials and environment may result in loss of material from the surface. The process leading to loss of material is known as "wear". Major types of wear include abrasion, adhesion (friction), erosion, and corrosion. Estimated direct and consequential annual loss to industries in USA due to wear is approximately 1-2% of GDP.^{[citation needed]}. Wear can be minimized by modifying the surface properties of solids by one or more of "surface engineering" processes (also called surface finishing) or by use of lubricants (for frictional or adhesive wear).

Engineered surfaces extend the working life of both original and recycled and resurfaced equipments, thus saving large sums of money and leading to conservation of material, energy and the environment.

Methodologies to minimize wear include systematic approaches to diagnose the wear and to prescribe appropriate solution. Important ones include:

• Terotechnology in UK (Peter Jost , 1972), where a system approach of multidisciplinary engineering and management techniques is used to protect plant, equipment and machinery (assets) from degradation by improving performance in all the functional areas;
• Horst Czichos system approach (H. Czichos,1978) where appropriate material is selected by checking material properties against tribological requirements under operating environment
• Asset Management by Material Prognosis - a concept similar to terotechnology has been introduced recently by the US Military (DARPA) for upkeepment of key equipments in good health and start-ready condition for 24 hours. Good health monitoring system combined with appropriate medication at M&R stages have led to improved performance, reliability and extended life cycle of the assets, like advanced military hardwares and civil aircraft.

In recent years, micro- and nanotribology have been gaining ground. Frictional interactions in microscopically small components are becoming increasingly important for the development of new products in electronics, life sciences, chemistry, sensors and by extension for all modern technology.

See also

• Lubrication
• Oil analysis
• Tribometer
• Wear
• Compacted oxide layer glaze
• Surface engineering
• Surface science

Bibliography

• Surface Wear – Analysis, Treatment, and Prevention: R. Chattopadhyay, published by ASM-International, Materials Park, OH, 2001, ISBN 0-87170-702-0.
• Advanced Thermally Assisted Surface Engineering Processes: Ramnarayan Chattopadhyay, Kluwer Academic Publishers, MA (now Springer, NY), 2004.