Experimental studies of friction-induced brake squeal: Influence of environmental sand particles in the interface brake pad-disc

The disc brake squeal is a very annoying sound which affects the customer comfort. The generation of this noise is considered as a structural dynamics and/or tribological problems of the pad-disc system. Unlike drum brake design, this system is exposed to external environmental sand particles, wear debris and water spray. Their presence into the disc and pad interface may create dynamic and physics phenomena induced by friction surface changes which lead to brake noise and vibration issues. Thus, this paper aims to investigate the effect of environmental sand particles (silica sand and road sand particles) with a range size of 100-150, 150-200 and 300-400 µm on the brake squeal noise occurrences. The sensitivity of the sand particles to produce noise is correlated with the wear scar, friction coefficient and variation of brake operational parameters. It was concluded that the primary reason for the reduced squeal noise generation was contributed to the reduced COF with the particle embedment. The analysis of the particle size influence on the squeal occurrence indicated that a small size of silica sand particle produces less squeal occurrence than that of road sand particles. However, the biggest silica and sand particles seriously damage the pad surface and reduce consequently the real contact surface, inducing a decrease on the friction coefficient.