Characterization of friction force dynamics

Friction modeling has been steadily gaining in interest over the last two decades. Despite persistent and painstaking efforts, however, no satisfactory, comprehensive, practicable friction model that captures all of the experimentally observed aspects of friction force dynamics in one formulation is available. Friction comprises multiscale processes requiring multiscale theories. This article presents an example of comprehensive model building, which, starting from the generic mechanisms behind friction, leads to the construction of a model that explains observed macroscopic friction behavior. Effective physics-based models at multiple scales can facilitate future work on the inter-relationships among models by furthering the understanding of emergent, collective frictional properties. Moreover, predictive physical models facilitate the derivation of simple models for control purposes. An example is the generalized Maxwell-slip (GMS) model, which is discussed in this article. Considering friction as a mechanical system, a close examination of the sliding process reveals two friction regimes, namely, the presliding regime and the gross sliding regime. In the presliding regime the adhesive forces owing to asperity contacts are dominant, and thus the friction force is primarily a function of displacement rather than velocity. The reason for this behavior is that the asperity junctions deform elastoplastically, thus behaving as nonlinear hysteretic springs.