Systems with friction are widespread in all kinds of applications. Unfortunatelly the precise simulative prediction of the resulting friction force in frictional contacts is still an unsolved task which has led to the developement of many empirical friction laws. Nevertheless, a deeper insight into the actual contact situation and the corresponding friction force with its dependencies is necessary to improve technical systems e.g. with regard to energy efficiency and wear.
Early works on this topic by Greenwood & Williamson and Archard for the pure elastic and Bowden & Tabor for the pure plastic deformation case have at least led to a justification for Coulombs friction law. Their results indicated that the real contact area is almost proportional to the normal contact force whereby this relation can be attributed to surface roughness in both cases. Coulombs friction law can then be justified by the additional assumption that the friction force is proportional to the real contact area.
Further influences on contact forces, real contact area and friction coefficient besides surface roughness are investigated by contact simulations on microscopic scale which include for example temperature evolution and thermoelastic distortions due to frictional heat. Keeping in mind that a specific friction coefficient is always closely connected to the actual macroscopic system bevhaviour and vice versa investigations on the macroscopic system behaviour are performed as well.