UBC Theses and Dissertations
Friction induced vibrations in a hydraulically driven system Johannes, Veikko Ilmari
A study has been made of the behaviour of a hydraulic-ally driven system subject to friction induced oscillations. An experimental apparatus consisting of a heavy mass driven by a hydraulic ram was constructed. A mathematical model for the system was derived, and its validity was shown by comparison with experimental results. Studies were subsequently carried out with the mathematical model to determine the effects of varying system parameters and to verify the validity of simplifications in the governing equations. It was found that in general the effect of leakage at the piston should be negligible, and that the variation in behaviour with piston location can be predicted by a simple system stiffness correction. The effect of changing most parameters is to change the rate of tangential load application for a given average velocity of traverse, and the resulting behaviour can be predicted from the static friction relationship that has been proposed. A detailed study was made of the nature of the friction forces in effect during a stick-slip process. A relation, for the variation of the static coefficient of friction which appears more accurate than previous time of contact dependent formulations has been found. In the case of the kinetic coefficient of friction, a gradual decrease from the static value was found at the inception of slip. This has been observed before but generally it has not been recognized by investigators of stick-slip. Simple models have been given for both the static and kinetic friction behaviour. These may be useful as guide in further research into the fundamental nature of friction.
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