Unsteady Friction in the Presence of Vibrations

In this paper, results from the authors’ recent work on the vibrations of sliding contacts in the presence of dry friction are summarized. We examine some idealized models of smooth and rough contacts, in which the assumed sliding conditions, the kinematic constraints and the mechanism of friction, i.e., the adhesion theory of friction, in this case, are well-defined. Instantaneous and average normal and frictional forces are computed. The results are compared with experiments. It appears that when contacts are in continuous sliding, quasi-static friction models can be used to describe friction behavior, even during large, high-frequency fluctuations in the normal load. However, the dynamics of typical sliding contacts, with their inherently nonlinear stiffness characteristics, can be quite rich and complex, even when the sliding system is very simple. A three degree-of-freedom vibratory model of a rough block in sliding contact with a planar moving countersurface, from which some preliminary results have been obtained, is used to illustrate some of these complexities.

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