Tribology is a relatively new word, although it represents phenomena and problems that have been around since the Stone Age and extend to our present lives. The word “tribology” was introduced in 1964, when a working group chaired by Dr. H. Peter Jost CBE was invited by the UK Department of Education and Science to investigate the state of lubrication education and research, and to give an opinion on the needs of the industry. When the group introduced the report in February 1966, they proposed, for the first time, the word “tribology” to describe this field (Jost, 1966). The word comes from the ancient Greek “tribo” meaning “rubbing” and the suffix “logy” for “the knowledge of”, so the literal translation would be “the science of rubbing”. Currently, dictionaries define tribology as “the study of friction, wear and lubrication, and the design of bearings” or “the science of interacting surfaces in relative motion” (Oxford, Dictionary).
By definition, tribology is an interfacial phenomenon that is affected by physical and mechanical properties of the two interacting surfaces as well as operational conditions. Since surface interactions are highly complex aspects, their understanding requires studying a variety of fields, including mechanical engineering, material science, surface topography and fluid mechanics. Moreover, there is a further complexity due to the fact that tribology is strongly associated with a wide range of practical applications, with small possibilities of theoretical formulation for a limited range of them.
If we try to explore the principal constituents of tribology of interacting solid surfaces, we realize that friction and wear are very ancient ones. In fact, solid surfaces are in contact with each other in relative motion, that is, surfaces sliding, rolling and rubbing on each other. For effective solution of tribology problems, all three constituents should be considered carefully and equally.
Since time immemorial, efforts have been made in order to minimize wear and control friction. This has triggered the need for lubrication, in which fluids (or solids) are introduced as a lubricant film to reduce the contact between moving surfaces in order to save power and material, Fig. 1.1 represents an illustration for tribology triangle.
The word “friction” came into usage in the middle of the 16th century, it comes from the Latin frictiō, meaning “a chafing or rubbing”, and from Middle French friction as a noun of action from the past participle stem of fricare, meaning “to rub”. The first record of using friction as “resistance to motion” was in the middle of the 17th century (Oxford, Dictionary). Even though many scientific definitions were introduced in order to describe this phenomenon, most of them have the common essence that there are two regimes of friction: Static friction between non-moving surfaces and kinetic (or dynamic) friction between moving surfaces.
Friction is expressed in quantitative terms as the force generated between the two surfaces in the direction opposite to the direction of motion (for kinetic friction) or potential motion (for static friction). To easily differentiate bet...
