Further Discussion On The Correlation Between Friction-Induced Squeal And Surface Topography With And Without Squeal Under Metal Reciprocating Sliding

Experimental investigations are carried about friction-induced noise emitted by a flat specimen rubbing against a ball specimen under metal reciprocating sliding in this dissertation. Two kinds of pad materials that are generally applied in railway vehicles were subjected to squeal-forming tests. Different velocities or waveforms of reciprocating sliding are applied. Detailed observations of the worn scars after interrupting the tests are conducted by means of a laser confocal scanning microscope (LCSM) and optical microscope. Dynamic signals of the vibration acceleration and sound pressure of friction-indued noise are picked up and analyzed.At the first, signals of friction-induced noise from the beginning to cycle 5 000 under different test conditions are recorded and analyzed. The result shows that the sliding speed has a distinct influence on the sound pressure of friction-induced noise and that friction materials, reciprocating sliding displacement waveform and other test parameters have a very limited influence on the number of cycles when the friction-induced noise is initially generated.Secondly, Detailed observations of the surface topography of the worn scars of the flat specimen with squeal and matched ball specimen formed under different test conditions are performed, which is mainly introduced in the 4th chapter. The relation between the topography characteristics such as plowing grooves and adhesive asperities and sound pressure level of friction-induced noise is investigated. Significantly, it is found that there is a protruding crack strip in the vicinity of the centre of ball specimen scar and that there is a clear difference in surface topography between two sides of the strip. This difference seems to be applied to explain the cause why the squeal only occurs in the end of the upward-stroke under reciprocating sliding.In this dsssertation, the friction-induced noise phenomena and surface topography related to sine waveforms of reciprocating sliding displacement are compared with those corresponding to triangle waveforms. The noise and topography formed by using different flat specimen materials are alsoinvestigated. The result shows that different waveforms of reciprocating sliding displacement only have an influence on the number of cycles when squeal initially occurs. Whereas the sound pressure level seems not to be correlated with waveforms of reciprocating sliding displacement and flat specimen materials. However, when thses conditions are changed, it is found that there is a clear change in the surface topography.Lastly, the formation mechanism of the special topography of ball specimens and its effect on squeal only occuring in the end of the upward stroke are discussed and explained in view of tribo-thermo dynamics.