Investigation and Verification of Potential Impacts of Third Body Nanostructure on Tribological Properties of Conventional and Unconventional Material Combinations for Automotive Braking and Risk Assessment of Particle Emission

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Our hypothesis is that smooth sliding behaviour and a constant friction level during dry sliding is determined by the formation of a granular layer from third body films which are screening the first bodies, pad and disc in case of a disc brake system. Our method to study friction processes in detail is firstly to investigate the nanostructure of third body films and secondly to understand the function of such films by modelling on the nanometre scale. Modelling will not only help to understand the fundamentals of friction but will also provide the opportunity to check the impact of different microstructures (nanostructures) and stressing conditions on the friction behaviour. The third and fourth steps will be to implement results of an optimization process done by modelling into new brake pad formulations and show that the modified system works. The goal is not only to improve properties, but also to show how environmentally critical pad ingredients can be substituted or eliminated. Besides conventional automotive brakes, based on cast iron discs, light weight brakes based on ceramic discs (unconventional) will be considered as well. Our intention is to prove the hypothesis that optimization of the system with respect to smooth sliding behaviour and minimal wear rate will result in nanostructured surface films and the emission of either single nanoparticles or small agglomerates of nanoparticles. Therefore we have planned to perform on-line particle measurements during dynamometer tests and sampling of emitted particles during certain stages of a test procedure for further nanoscopic and nanoanalytical investigations.Risk assessment of airborne particles released from brakes during dynamometer tests is planned for a second period of the project. Two important prerequisites for this enterprise are currently installed at BAM: i) preparation of a reference material and in vitro test procedure for nanotoxicological studies with living cells, and ii) construction of an exposure system for cell cultures with airborne nanoparticles.