Friction-induced Vibrations in an Experimental Drill-string System for Various Friction Situations

Friction-induced limit cycling deteriorates system performance in a wide variety of mechanical systems. In this paper, we study the way in which essential friction characteristics affect the occurrence and nature of friction-induced limit cycling in flexible rotor systems. This study is performed on the level of both numerical and experimental bifurcation analysis. Hereto, an experimental drill-string set-up is used. The synthesis of these numerical and experimental results confirms that friction-induced limit cycling is due to a subtle balance between negative damping at lower velocities and viscous friction at higher velocities. Furthermore, we also show that the level of positive damping in the friction at very small velocities in relation to the level of negative damping appearing for slightly higher velocities determines whether torsional vibrations with and/or without stick-slip can appear. Finally, it is shown how these essential friction characteristics depend on physical conditions such as temperature, normal forces or the type of material in the frictional contact in the experimental set-up