Influence of contact condition and sliding speed on friction-induced instability

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Conference Proceeding
ICSV 2016 - 23rd International Congress on Sound and Vibration: From Ancient to Modern Acoustics, 2016
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Brake squeal, defined as audible noise above 1 kHz, is triggered by energy provided in the contact area between the pad and the disc and friction-induced instabilities. Owing to customers' demand of reducing vehicle noise and the increasing use of light composite materials in cars, squealing brakes remain a major concern to the automotive industry because of warranty-related claims. The prediction of disc brake squeal propensity is as challenging as ever. Although friction-induced instabilities are inherently nonlinear and during squeal the brake system's operating and environmental conditions keep changing, mostly linear and steady state methods are used for the analysis of brake squeal propensity. While many different instability mechanisms have been identified, their interactions and the resulting dynamics are not yet fully understood. Linear instability predictions suffer from over- and under-predictions and have to be complemented by extensive noise dynamometer or in vehicle tests. Recent studies indicate that frictional contact is multi-scaled in nature, highly sensitive and inhomogeneous. Very high local pressures and partial contact separations in the contact interface further complicate its numerical modelling. By studying an analytical model of 3 × 3 friction oscillators using three different friction laws (Amonton-Coulomb, the velocity-dependent and the LuGre friction model) in point contact with a sliding rigid plate and incorporating uncertainties in the contact condition, robustly unstable vibration modes have been identified in our previous research. Here, the number and the combination of friction oscillators engaged in contact are randomised to model imperfect contact. In addition, the effect of the variation in the plate's sliding velocity on the in-stability analysis is investigated with randomised friction coefficient of the Amonton-Coulomb friction model. Results of instability prediction and net work calculations are used to illustrate the sensitivity of the instability to the contact modelling and sliding velocity. The potential of considering uncertainties in contact condition on improving the instability prediction for a full brake model will be discussed.
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