An experimental study of the effect of surface morphology on squeal occurrence

Abstract

Squealing is a major matter of concern for environmental issues and the raised expectations for superior performances in braking systems. Squealing, as well as other types of noise nuisances, contributes to noise pollution and leads to additional expenses for phonic isolation. Brake squeal noise, which is defined as noise at frequency higher than 1000 Hz, occurs if the system has very high amplitude of mechanical vibration with sound pressure level above 80 dB. It involves instable vibrations, which are quite well understood as a result of mode couplings between the rubbing parts. These mode couplings are allowed by modal frequency shifts induced by the changes of sliding contact conditions. Nonetheless, the origin of squeal occurrence remains misunderstood as many parameters have to be taken into account, making it virtually impossible to predict when a squeal noise will appear or disappear. The strong coupling between structure and material, the continual change of the materials surfaces (chemistry and morphology), the influence of external parameters (temperature, pressure, hygrometry) all play a role in squealing. As a consequence, research on squealing is empirical by nature. Following this, one of the main goals in braking sciences is to determine the set of conditions on the parameters that provoke the start or the end of a squealing noise.