TY - JOUR A1 - Österle, Werner A1 - Prietzel, Claudia A1 - Kloß, Heinz A1 - Dmitriev, Andrey T1 - On the role of copper in brake friction materials N2 - Copper is a major ingredient in friction materials used for automotive braking. The purpose of this study was to find out how copper contributes to good brake performance properties in addition to providing good thermal conductivity. Microstructural investigations of copper chips at the surfaces of brake pads revealed a zone of severe plastic deformation which provides high hardness, but there is also evidence of recrystallized copper nano-particles which are incorporated into friction layers as soft ingredient once detached from the pad surface. Thus copper seems to play a dual role, firstly as reinforcing element of the brake pad providing primary contact sites, and secondly as solid lubricant by contributing to the formation of a layer of granular material providing velocity accommodation between the rotating disc and fixed pad. Confirmation for this hypothesis was obtained by modelling contact sites on the nanometre scale with the method of movable cellular automata. Results show both, the similarity of steel fibres and copper macro-particles in respect to providing primary contact sites, as well as similar sliding behaviours of friction layers containing either copper or graphite as soft inclusions. Furthermore, it is shown that not only material properties, but also the concentration of solid lubricant particles in the friction layers, determine conditions for friction force stabilization and smooth sliding behaviour. KW - Friction material KW - Friction layer KW - Copper macro-particle KW - Copper nano-particle PY - 2010 U6 - https://doi.org/10.1016/j.triboint.2010.08.005 SN - 0301-679X VL - 43 IS - 12 SP - 2317 EP - 2326 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-22342 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Prietzel, Claudia A1 - Dmitriev, Andrey T1 - Investigation of surface film nanostructure and assessment of its impact on friction force stabilization during automotive braking N2 - The unique nanostructure formed during severe as well as moderate braking on the surface of brake discs was investigated by conventional and analytical Transmission Electron Microscopy. In both cases nanocrystalline magnetite mixed with carbon nanoinclusions and minor amounts of other pad constituents were identified. On the basis of these observations the friction performance of a single micro-contact was simulated with the method of Movable Cellular Automata. Inspite of a simplified nanostructure which was examined in two dimensions only, the calculated mean coefficient of friction fitted well to the value usually demanded for automotive braking. Furthermore, the model predicts that oxide films without soft nanoinclusions are not capable of providing smooth velocity accommodation at the pad–disc interface and thus lead to unstable friction behaviour. KW - Friction KW - Third body film KW - Nanostructure KW - MCA-model KW - EFTEM PY - 2010 SN - 1862-5282 VL - 101 IS - 5 SP - 669 EP - 675 PB - Carl Hanser CY - München AN - OPUS4-22343 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Österle, Werner A1 - Bresch, Harald A1 - Dörfel, Ilona A1 - Fink, C. A1 - Giese, A. A1 - Prietzel, Claudia A1 - Seeger, Stefan A1 - Walter, J. T1 - Examination of airborne brake dust T2 - JEF 2010 - 6th European conference on braking CY - Lille, France DA - 2010-11-24 KW - Brake dust KW - Nanoparticles KW - Size-distribution PY - 2010 SP - 1 EP - 6(?) AN - OPUS4-22655 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -