Dynamic multi‐layer models of dry friction

Abstract Determining the friction law between solids as a function of material and loading parameters remains a topical and still unsolved problem of tribology. In the rail‐wheel‐contact the law of sliding friction determines not only the maximum tractive forces but also defines the conditions for the occurrence of instabilities. Recent simulations of irreversible processes in micro‐contacts with the method of movable cellular automata (MCA) have shown that dynamic aspects do play an essential role in these processes. Inelastic processes of plastic deformation, detaching of particles and their reintegration into the surfaces as well as processes of mechanical mixing occur only in a thin surface layer called quasi‐fluid layer. Studying the properties of the quasi‐fluid layer is thus a key for understanding friction. To better understand the physical nature of the quasi‐fluid layer and especially the physical nature of the viscosity of the quasi‐fluid state, multi‐layer models of an elasto‐plastic solid have been studied. In the layer model it becomes particularly clear that the physical reason for occurrence of the quasi‐fluid layer is the bi‐stability of the friction law between layers. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)