The Nature of the Static and Kinetic Coefficients of Friction

Abstract

Experiments have been carried out to determine the transition between static and kinetic conditions when stationary metal surfaces are set into motion, a simple method being used which measures the energy that has to be given to one of the bodies to start it moving. The method is confined to cases in which the static coefficient exceeds the kinetic. Using a load of 1 kg and metal surfaces of various kinds, it is found that the static coefficient persists for distances of the order of 10−4 cm, and then gradually falls off to values corresponding to the kinetic coefficient. This behavior is shown to be consistent with a simple model based on the assumption that the friction force is needed to shear metallic junctions formed between the metal surfaces. The action of boundary lubricants is discussed, and it is shown that they can act either by diminishing the metallic interaction directly, or by preventing its increase during the sliding process.

Friction Models and Friction Compensation

“…The relation between friction and displacement as found by [44]. The experimental results suggested that friction should be described as a function of displacement and not velocity.…”

“…Rabinowicz addressed the transition between sticking and sliding in [44]. He investigated friction as a function of displacement.…”

Are there reliable constitutive laws for dynamic friction?

“…A classical experiment involves a block on an inclined plane: the maximum slope that permits sticking to continue gives directly the static coefficient of friction, while the smallest slope that allows sliding to continue once started gives the dynamic coefficient. Rabinowicz [39] extended this experiment by applying calibrated impulses to the block and documented an intermediate range where the block would start to slide but then stop. He argued that the results were consistent with a model involving a 'critical slip distance', beyond which the static coefficient of friction reduces to the dynamic value.…”

Conceptual and physical clarification of rate and state friction: Frictional sliding as a thermally activated rheology

“…The detailed facts such as the time-dependent increase of static friction during stationary contact [Dokos, 1946;Dieterich, 1972], the continuous reduction of friction from static friction to dynamic friction with ongoing slip displacement [Rabinowicz, 1951 ], the velocity dependence (particularly velocity weakening) of steady state friction, and the continuous change of friction with slip when velocity is changed, all had been discovered and incorporated in the friction law [e.g., Dieterich, 1978] before the work by Dieterich [1979]. Even the concept of memory of the interface, which would be generalized as state variable later [Ruina, 1983], had already been recognized [Rabinowicz, 1958] by then.…”