O’zbekistоn respublikasi оliy va o’rta maxsus ta`lim vazirligi

1.3 Historical outline. The main stages in the development of tribology and tribology

One should not think that the science of friction began with P. Jost. More than 2 thousand years ago, Aristotle in the mechanics of sublunar (ie, terrestrial) bodies wrote about the resistance of the external environment to the movement of bodies. However, no even simple

calculations using its mechanics could not be done. At the turn of the 16th and 17th centuries, Galileo Galilei (1564-1642) discovered the law of inertia and showed that resistance to movement is exerted by the mass of a body, and in conditions of uniform movement, only the force of friction. He was the first to clearly distinguish between two fundamentally different types of resistance of bodies to movement: resistance associated with the inertia of the body, and resistance due to friction. Friction and wear in machines were first taken into account by Leonardo da Vinci. He is the author of the first designs of rolling bearings, plain bearings and gears. The description of Leonardo's inventions, from drive mechanisms to machine guns and flying machines, reflects an entire era in the development of technology.
In 1699 G. Amonton (1663-1705) discovered the law of linear dependence of friction on the load F = f N, where F is the friction force, N is the load along the normal to the friction surface, f is the coefficient of friction. Despite its apparent simplicity, this law is nontrivial. It follows from this that the friction force is independent of the area of the friction surface. Those. the friction of a brick moving on a flat base is the same, whether we put it flat, turn it on its side, or put it on the end. The physical meaning of this law remains the subject of discussion today. In 1750, Leonhard Euler (1707-1783) established the laws of friction in uniformly accelerated sliding. He was the first to note that the friction force during the transition of a friction pair from a state of rest to motion is always greater than the friction force during sliding.
The French physicist Charles Coulomb (1736-1806) is considered the creator of the science of friction. In 1781, for his work in the field of friction, he was awarded the Prize of the French Academy of Sciences. This is the same Coulomb who established the laws of electrical and magnetic effects and laid the foundations of modern electrostatics. He studied three main aspects of friction: resistance to sliding, rolling and breaking away. When setting up experiments, he proceeded mainly from practical problems related to the requests of the fleet: launching ships along the stocks, determining the friction forces in hoists and other rigging systems, resistance to the rotation of the compass needle on the tip, etc. In those days, no one (including Coulomb) was interested in the transition of mechanical energy into heat. And the very concept of “energy” did not yet exist. The tasks were practical: when dragging weights, it was necessary to determine the total effort, and then the required number of people and horses. Coulomb refined Amonton's law and proposed a two-term law of friction, and also established patterns of breakaway depending on the duration of static contact. The two-term Coulomb's law has the form: F = fN + A, where A takes into account the adhesion of friction surfaces. Coulomb possessed the powers of observation of a scientist and the practicality of an engineer. He was the first to understand that friction is caused by many factors, which can only be taken into account approximately, based on empirical relationships.
The transformation of the mechanical energy of friction into heat was described by Baliani in a letter to Galileo in 1614. He noted that when a rapidly rotating metal disk immersed in water rubbed against the wall of an iron vessel, the water boiled. However, this experience until the middle of the XIX century. remained unknown. M.V. Lomonosov (1711-1765) studied thermal phenomena during friction, using an emery wheel, which was rubbed against a flat counterbody fixed on a lever loading system (. 1754 г). The first person who truly understood that mechanical energy does not disappear during friction, but turns into heat, was B. Thompson (1753-1814), known in the history of science under the name of Count Rumfoord. He was engaged in drilling cannon barrels and set up experiments in which a workpiece processed with a blunt drill was placed in water. After a while the water boiled. In a report to the Royal Society of London, he wrote: "The source of heat arising from friction in these experiments is, apparently, inexhaustible." It seemed completely unexpected at the time.
This problem in its modern form was solved in the middle of the 19th century , when in 1842 Robert Mayer (1814-1878) and in 1843 James Joule (1818-1889 ) put forward the principle of equivalence of mechanical energy and heat, and in 1847 Hermann Helmholtz ( 1821-1894) introduced the fundamental concept of energy and formed the law of its conservation in the most general form. Later, the German physicist Rudolf Clausius (1822-1888) laid the foundations for the mechanical theory of heat and introduced the concept of entropy . This term is important for understanding the nature of friction and its place in the physical picture of the world. The physical meaning of this initially mysterious concept was revealed at the end of the 19th century. creator of static thermodynamics Ludwig Boltzmann (1844-1906). He showed that entropy is the degree of disorder in a system. Under normal conditions, there are always more opportunities for the transition of an isolated system (in particular, a friction unit) to disorder than the options for which the system is ordered or at least retains its previous state. This is the most important consequence for tribology of the second law of thermodynamics, one of the most general laws of nature.
Further, the most important events in the history of friction are as follows. In 1804, Leslie put forward a hypothesis about the dissipation of energy during friction as a result of the irreversible deformation of irregularities on friction surfaces. Earlier (1734) Desaguliers discovered seizing during friction of polished metal specimens. A century and a half later, Leon Briluin (1889-1969) showed the possibility of energy dissipation during friction as a result of the formation and rupture of adhesive bonds (adhesion - sticking, cohesion). Thus, the adhesion theory of friction acquired a physical basis.
Already in our time, the idea of energy dissipation ( dissipation ) during the exchange of adhesive bonds between friction surfaces was developed in various theories of friction by V.D. Kuznetsov (1887-1963). These theories have been criticized for not explaining the many deviations from Amonton's law. However, the experimental technique of the 1930s did not allow their direct verification. Research methods developed in the 1950s and 1960s made it possible to carefully study the relief and microstructure of friction surfaces. These were the years of the formation of the molecular-mechanical theory of friction , which was created by the efforts of I.V. Kragelsky (1908-1989), English tribologists F. Bowden and D. Tabor. According to I.V. Kragelsky, the friction force is composed of two components: the resistance due to the deformation of the material during the introduction of irregularities, as well as the resistance of adhesive bonds to rupture.
The friction mode is determined by the absence or presence of a lubricating layer between the elements of a friction pair. In the latter case, a liquid lubricant is installed , obeying the laws of hydrodynamics. The founders of the theory of liquid lubrication are the Russian engineer N.P. Petrov (1836-1920) and English scientist Oscar Reynolds (1842-1912). Now, on the basis of this harmonious theory, it is possible to calculate the thickness of the oil layer and predict friction modes. N.E. Zhukovsky (1817-1921), S.A. Chaplygin (1869-1942), M.V. Korovchinsky and others.
The laws of friction with a lack of lubricant are disclosed in the works of F. Bowden, B.V. Deryagin, our contemporary R.M. Matveevsky and others. A number of friction pairs operate without lubrication. The works of M.M. are devoted to “dry” friction. Khrushchev, I.V. Kragelsky, S.B. Ainbinder and others.
In the process of friction, the parts wear out, which leads to a gradual failure of the friction pairs. Wear patterns are considered in the works of M.M. Khrushchev, I.V. Kragelsky, B.I. Kostetsky, A.V. Chichinadze, N.B. Demkin and others.
A significant contribution to tribology was made by V.A. Bely (1922-1994) is the founder of the Belarusian tribological school, whose works devoted to the friction of polymers are known all over the world.