Oscillations in sliding with dry friction. Friction reduction by imposing synchronised normal load oscillations

Abstract

Frictional sliding occurs in many engineering and natural systems across the scales. Often observed stick slip (jerking) movement is commonly believed to be a consequence of friction rate dependence (static friction is higher than the kinetic one). Using a simple model of a frictionally sliding block connected to a spring we show that even for constant friction the intrinsic velocity oscillations produce the movement pattern resembling stick slip. The rate dependence of friction, while changing the numbers produces qualitatively similar type of movement. The model also suggests that contrary to the common belief the rate dependence of friction is not a mechanism of sound production in bow musical instruments. Furthermore, the rate dependence reduces the clearness of sound producing unwanted harmonics. The alternating nature of the stationary and kinematic phases of stick-slip movement suggests a method of reducing energy dissipation rate. This can be achieved by applying synchronised normal oscillations such that the increases in the normal load fall on the stick phases of the sliding.