Characterization of friction force and nature of bifurcation from experiments on a single-degree-of-freedom system with friction-induced vibrations

• Performed experiments on a laboratory set-up representing a friction-induced system.
• Analyzed the nature of friction-induced oscillations.
• Obtained subcritical Hopf bifurcation from experiments.
• Obtained friction force-relative velocity curve from experiments.
• Friction characteristics show significant hysteretic behavior.

Experimental investigation is performed on a test set-up representing a single-degree-of-freedom friction-induced system. The experimental set-up consists of a rigid mass (oscillator) connected to a fixed support through a spring and the mass in frictional contact with a moving belt. The major objectives of the experiments are to characterize (i) the nature of friction-induced oscillations, (ii) the nature of bifurcation associated with frictional instability in the system, and (iii) the nature of friction force that is responsible for the oscillations observed from the experiment. The phase portrait of the system shows significant overshoot of the oscillator velocity above the belt velocity indicating the existence of hysteretic loop around zero relative velocity (pre-sliding regime). The bifurcation diagram clearly demonstrates the subcriticality of the Hopf bifurcation associated with the system negating all empirical friction models which yield supercritical Hopf bifurcation. The friction force-relative velocity curve shows significant hysteretic behavior, both in the pre-sliding as well as in the pure sliding domains. This observation hints towards a dynamic or an acceleration-dependent friction model as an appropriate choice for representing the friction force obtained from our experimental set-up.