Velocity Accommodation in Friction

Abstract

Velocity accommodation across rubbing surfaces lubricated with thick films is well understood and can be determined from fluid dynamics theory. The situation is not the same in “dry” friction as the question is not usually formulated in the same terms. This paper shows that in “dry” friction, velocity can be accommodated through 20 different mechanisms (5 sites and 4 modes per site) known as velocity accommodation mechanisms. The situation is therefore more complex than that found in thick film lubrication where only one such mechanism (shear) exists. Friction and wear are shown to depend on the acting mechanism. Examples are given for each mechanism. The factors that control these mechanism are identified. Visualisation studies show that more than one mechanisms can act simultaneously and that the mechanisms can change during a test.