Experimental and Numerical Investigation of a Friction Oscillator

Friction induced self-sustained oscillations, also known as stick-slip vibrations, occur in mechanical systems as well as in everyday life. Examples are stick-slip motions which lead to squealing railway wheels, grating brakes, rattling machine tools or the cozy sound of a violin. The robust limit cycles of stick-slip motions can be broken up by an additional harmonic external excitation. The extended nonsmooth system of a friction oscillator including a nonsmooth friction law and an additional external excitation shows rich bifurcational behaviour. On the basis of a one-dimensional map stability analysis and the determination of Lyapunov exponents has been carried out similar to the logistic map (Oestreich et al., 1996a). The present paper focuses on the comparison of the dynamical behaviour of a simple mechanical model and the dynamics observed in experiments. Since in engineering systems the friction characteristic is often not known or is varying for different test parameters, first the friction characteristic is determined from experiments with different test conditions. In the next step the results of the simulations using the identified friction characteristics will be compared with measurements of the dynamics of the friction oscillator with pure external excitation, pure self-excitation and simultaneous self- and external excitation. An additional verification of the identified friction characteristic can be done by means of a comparison of phase curves, trajectories in the three dimensional state space and bifurcation diagrams.