Particulate pollution caused by traffic is an important socio-political issue nowadays. In addition to the engines as a source of particulate matter, non-exhaust sources of vehicles like tyre, road abrasion and the brake are moving into focus due to the improved exhaust after-treatment and electrification. Although many studies have looked into brake particle number, mass and size distribution until now, the formation of this particles and their change within the frictional contact haven't been complete revealed. However, the understanding of these mechanisms is important. This knowledge can help, for example, to identify possible reduction potentials. In order to achieve a better understanding about the mechanisms that occur between the brake pad and the brake disc, tests are carried out on a tribological brake test rig. Using a borosilicate glass disc instead of a cast iron disc, allows optical in-situ measurements with a high-speed camera equipped with a magnification lens. The microscopic system is mounted on a linear bearing and can be moved stepwise in horizontal and vertical direction. Therefor sequential observation of the entire brake pad is feasible. In addition, 3-D images provide insights into the influence of the local structure of the pad. Besides, a newly developed sampling method will be used to remove wear mass from the system and analyze it chemically. This procedure can also be applied in combination with a grey cast iron disc, which allows further validation of the described glass method. By recording of the pad surface section by section, insights about the distribution of the brake particle movement within the tribological system can be gained. Hereby it can be analyzed, whether only the location on the pad influences the occurrence of particle motion or also other influencing variables exist. For instance, the presence of primary and secondary patches, as well as deposited wear mass and the surface morphology could be important. The 3-D images in combination with the chemical analysis can shed light on the mechanisms of wear mass deposition. Therefore this study shows new findings about brake particle behavior with regard to pad location, surface structure and chemical composition. In addition, the phenomenon of deposited mass is analyzed more precisely.
Katharina Kolbeck, PhD Candidate, BMW/ TU Ilmenau; Prof. Dr. Klaus Augsburg, TU Ilmenau