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Squeal in disc brake systems are powerful acoustic emissions involving significant environmental pollution and client complaints. Recent experimental and numerical results have shown that it could be possible to investigate influence of contact localizations at pads/disc interfaces on squeal behaviour, by considering geometry variations linked to load bearing area modifications, and friction material impact on tribological circuit. In this research project, numerical simulations and experimental aspects at different scales are of interest, the purpose being to identify key parameters to introduce into multiscale simulations. The study is focused on macroscopic influent parameters, keeping in mind that microscopic scale also has an impact on squeal behaviour. A full-scale brake system provided by Hitachi Astemo is tested on a dynamometer bench with a dedicated NVH squeal matrix, and various pads geometric configurations are considered, in order to characterize acoustic emissions. Different squealing patterns are observed when changing geometries, giving consequently an industrial base than can be further analysed via a laboratory simplified configuration. A full-scale numerical model of the industrial brake is then used with Complex Eingenvalue Analyses (CEA) simulation type, having been correlated to experimental results. CEA results show that unstable frequencies are different considering pads geometries. Particularly, regarding type of geometric modification (parallel or radial chamfers, central slots, and mix of these cases), instable frequencies are not the same when really implementing these modifications or when assuming contact zone as the projection of these geometric changes. Therefore, it involves that pure interface contact influence can have a major effect on squeal depending on type of modification applied on pads lining. To study more finely contact evolution and acoustic emissions, a pin-on-disc system is then considered, equipped with a multimodal instrumentation and an in-operando surface tracking. It allows to continuously track assumed contact zone and surface evolution at pin/disc interface through braking sequences, thanks to thermal measurements via an inserted thermocouple film. Information on macroscopic contact localizations can thus be interpreted with help of a thermomechanical numerical model and CEA simulation of the pin-on-disc configuration. It is observed that macroscopic localizations indeed have an impact on squeal frequencies and evolve through time namely because of thermal expansion and wear accumulation. In the future, a deeper investigation on pads geometries and lining formulations will help understanding the mechanisms involved in disc brake squeal, by namely implementing defined key parameters, linking input characteristics to instable / squealing frequencies properties.
University of Lille: Dr. Jean-François Brunel, Dr. Philippe Dufrénoy; Hitachi Astemo: Mr. Nicolas Strubel, Mr. Thierry Chancelier, Mr. Saïd Hamdi, Mr. Yassine Waddad, Mr. Sylvain Thouviot