Wear in mechanical systems is undesired stochastic process which is a consequence of another stochastic process - friction.

In the majority of mechanical systems friction is an unwanted side effect of other main operating processes. However, since it enables kinetic energy reduction i.e. vehicle deceleration, or power transmission, high friction is appreciated in automotive friction mechanisms (such as brakes and clutches).

Unfortunately, high friction causes excessive wear of these mechanisms which disables them to operate properly. This is why it is important to understand the processes of friction and wear in these mechanisms and to predict their behavior under different service conditions. Even though friction and wear occur simultaneously in one tribo-mechanical system, tribology considers them independently from one another, each of them under the same influencing factors.

Knowing “why” influencing factors cause one tribo-mechanical system to behave in a certain manner would allow engineers to predict behavior of these systems under given service condition.

Both theory and practice show that variations in friction and wear in friction mechanisms are caused by a large number of influencing factor. That is how it has been shown that the rating and character of deviations in friction and wear cannot be explained only by the “direct” action of influencing factors, but certain “indirect” influences also need to be considered

These “indirect” influences are called “tribo-mutations”. They should represent the portion of variation of friction and wear in friction mechanisms induced by inter-related influences of main influencing factors between each other.
These inter-relations are shown in Figure below.