Abstract
According to the analysis made in this paper, squeal triggering, establishment or vanishing can be described in terms of a new index dependent on two topographic parameters; the mean radius of asperities and the standard deviation of the height distribution of asperities of the sliding surfaces. Experimental investigation of squeal noise generated from the friction sliding of a brake pad on a rotating plexiglass disc revealed that the pad surface at the beginning of squeal became glazed and that this pad abraded the disk. This means that plastic contact between asperities at the beginning of sliding caused the smoothening of the softer surface and roughening of the harder surface. Topographic analysis of the squealing surfaces has shown that, due to running in of a plastic surface (e.g. rough pad) with another smooth elastic surface (e.g. brand new disk), the mean radius of asperities of the sliding surfaces were largely increased which leads to a clear drop in the tangential stiffness of these asperities. It is believed that loading and unloading fatigue cycle of elastic asperities with weak stiffness in addition to their impact initiate cracks and lead to tearing away and separation of some asperities which causes the emission of squeal noise. Continuation of sliding process may reverse this trend due to wear debris, i.e. changing elastic contact condition to plastic one and consequently, squeal vanishes.