Instability of systems with a frictional point contact—Part 3: Experimental tests

In two earlier papers, a new formalism was derived which led to the prediction of instability for two linear systems in sliding contact at a single point. In Duffour and Woodhouse [Instability of systems with a sliding point contact. Part 1: basic modelling 271 (2004) 365–390], predictions were obtained using a friction law featuring a constant coefficient of friction. This formalism was generalised in Duffour and Woodhouse [Instability of systems with a sliding point contact. Part 2: model extensions 271 (2004) 391–410] to include all possible linear routes to instability. This paper presents results from the experimental investigation carried out to test the validity of the theoretical results obtained in the first of the two papers. The rig is of the pin-on-disc type. An instrumented pin was specially designed so that the quantities necessary for the prediction could be measured. It emerged that incipient squeal frequencies observed experimentally could be predicted in 75% of the cases using the simplest formalism presented in Duffour and Woodhouse (2004). The presence of unpredicted squeal frequencies points towards the importance of other effects, such as the disc nominal rotation speed and the value of the normal preload. This study also reveals that the ever-changing nature of friction-induced noises can, to a good extent, be explained by the slight structural variations undergone by any mechanical system.