Dry friction between two bodies under relative movement is crucial in some technical fields. The most common application areas are certainly the various braking systems of vehicles, as well as the clutches in vehicles with combustion engines. Also sliding bearings for rotation and linear movement, which work without any external or internal liquid lubrication are widespread. While the coefficient of friction at braking systems and clutches should be mainly constant and rather high at all operating points, the development target of sliding bearings is normally a low coefficient of friction. Further requirements for all of this application areas are: low wear and especially for braking systems: a very high mechanical and thermal safety.
So far, there is no theoretical basis to forecast the coefficient of friction of two solid bodies moving relative to each other without any tests. Up to now the state of art has developed from empirical values and tests. It is the target of this publication to offer this theoretical basis, so that further calculations can be build upon it.