A systematic experimental study of squeal initiation

A large-scale systematic experimental investigation into friction-induced vibration is described. A specially designed ‘pin-on-disc’ test rig is used, with dynamical properties which can be altered to allow different aspects of theoretically predicted behaviour to be probed. These dynamical properties have been carefully characterised, including an assessment of uncertainty in each parameter. A large volume of ‘squeal’ data has been generated, involving a sequence of different test conditions repeated over many days. The results were post-processed to extract the growth phase of instabilities and automatically assess their quality in terms of linearity and time-invariance, providing a rich source of high-quality data for several thousands of initiation events. A variety of ways to present the measured results is explored, highlighting trends and assessing repeatability. The experimental test rig exhibits a wide range of squeal behaviour, at frequencies ranging from tens of Hz to tens of kHz. At first glance the results are unrepeatable and twitchy, but the large quantity of data allows significant underlying structure to be demonstrated, shedding light on the roles of symmetry, pre-load, speed and structural perturbations, and also improving understanding of ‘repeatability’ in the context of squeal.