TY - JOUR A1 - Dmitriev, A.I. A1 - Österle, Werner A1 - Kloß, Heinz T1 - Numerical simulation of typical contact situations of brake friction materials N2 - In the paper, a model typical for contact situations of automotive brakes is established based on the method of movable cellular automata. The processes taking place at local contacts in an automotive brake system are analysed. Based on microscopic and micro-analytical observations, the following contact situations were simulated: (i) a couple of ferritic steel against pearlitic steel, both covered by an oxide layer mixed with graphite nanoparticles and (ii) the same situation but without oxide layers. The results of calculated mean coefficients of friction of the oxide-on-oxide contact correspond well to expected values for a real braking system, whereas steel-on-steel contact are twice as high. This allows one to make some conclusions; for example, oxide formation will take place more quickly than friction layer elimination, and finally this is responsible for the stabilisation of the coefficient of friction. KW - Friction KW - Primary contact KW - Automotive brake system KW - Numerical simulation KW - Method of movable cellular automata PY - 2008 U6 - https://doi.org/10.1016/j.triboint.2007.04.001 SN - 0301-679X VL - 41 IS - 1 SP - 1 EP - 8 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-15841 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Österle, Werner A1 - Dmitriev, Andrey A1 - Kloß, Heinz T1 - Assessment of sliding friction of a nanostructured solid lubricant film by numerical simulation with the method of movable cellular automata (MCA) N2 - Tribofilms formed during dry sliding usually exhibit a nanocrystalline structure and complicated composition. In the present study, tribofilms consisting mainly of a solid lubricant, namely graphite nanoparticles, are considered. Systems providing such tribofilms are candidates for anti-friction applications. Since sliding action always leads to mixing of the materials at both sides of the tribological interface, it was of major interest to study the impact of different amounts of a hard constituent, SiC in the considered case, within the soft matrix systematically. Furthermore, the impact of normal pressure was considered. A mechanically mixed layer was observed for the whole range of normal pressures and SiC volume fractions. The calculated coefficient of friction decreased significantly with increasing thickness of this layer but was only marginally affected by SiC volume fraction, which is good news for anti-friction applications. T2 - WTC 2013 - 5th World tribology congress CY - Torino, Italy DA - 08.09.2013 KW - Friction KW - Third body film KW - Numerical simulation KW - Nanostructure PY - 2013 SP - 1 EP - 4 AN - OPUS4-29659 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 - JOUR A1 - Österle, Werner A1 - Dörfel, Ilona A1 - Prietzel, Claudia A1 - Rooch, Heidemarie A1 - Cristol-Bulthé, A.-L. A1 - Defallaix, G. A1 - Desplanques, Y. T1 - A comprehensive microscopic study of third body formation at the interface between a brake pad and brake disc during the final stage of a pin-on-disc test KW - Brake KW - Third body KW - Wear KW - Friction KW - Nano-scale KW - TEM PY - 2009 U6 - https://doi.org/10.1016/j.wear.2008.11.023 SN - 0043-1648 VL - 267 IS - 5-8 SP - 781 EP - 788 PB - Elsevier CY - Amsterdam AN - OPUS4-19450 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Wolter, Christian A1 - Österle, Werner A1 - Gradt, Thomas T1 - Metal sulphides as friction stabilisers under variable humidity N2 - Neben Kohlenstoff werden Metallsulfide in jeder Standardrezeptur für Bremsbeläge als Reibungsstabilisatoren verwendet. Um deren Wirkung zu untersuchen, wurden verschiedene Pulvermischungen in einer Stift-Scheibe-Anordnung tribologisch beansprucht, um künstliche dritte Körper zu erzeugen und zu testen, deren definierte Zusammensetzungen aus drei wichtigen Bestandteilen einer realen Reibschicht bestehen: Magnetit, Graphit und div. Metallsulfide. N2 - Besides carbon, metal sulphides are used in every standard brake pad formulation as friction stabilisers. In order to investigate their impact, various powder mixtures were tribologically stressed in a pin-on-disc device in order to produce and test artificial third bodies. containing the three main components of a real friction film, namely magnetite, graphite and a metal sulphide of interest. Since the sliding behaviour is influenced by the relative humidity the powder mixtures are tested at low, medium and high moisture levels. The tests revealed that the presence of graphite dominates the friction behaviour as well as the humidity sensitivity. The powders were prepared by either manual mixing or high energy ball-milling. Interestingly, all ball-milled blends provided coefficients of friction within the desired range for braking, which was attributed to the effect of zirconia particles from wear debris of the milling balls. The zirconia particles prevent the formation of solid lubricant films on the surfaces and support a homogeneous mixture of all constituents of the powder. Optimum brake performance is gained by an optimum combination of solid lubricants and abrasives. T2 - 57. Tribologie-Fachtagung CY - Göttingen, Germany DA - 26.09.2016 KW - Friction KW - Metal sulphides KW - Brake pad formulation PY - 2016 SN - 978-3-9817451-1-5 SP - 1.5/1 EP - 1.5/6 AN - OPUS4-37838 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Dmitriev, A. I. A1 - Österle, Werner T1 - Sliding simulation of automotive brake primary contact with variable amounts of copper and graphite nanoparticles N2 - Copper is one of the most important components in brake pads and its amount can reach up to 14%. In spite of a number of positive features copper usage in brake pad formulations has recently become the subject of considerable discussions, primarily due to concerns about potential risks related to environmental impacts of copper particles. So, for developing new pad formulations with possible replacements of copper content, it is very important to understand the functionality of copper additions to brake friction materials. In the paper theoretical investigation of the role of copper as a pad ingredient was carried out on the basis of modelling by the method of movable cellular automata (MCA). In the study the concentration of copper particles in a Fe3O4-matrix was varied. The sliding simulations were performed while assuming material properties at 500 degrees C in order to assess the beneficial role of copper during severe braking conditions corresponding to fading cycles during dynamometer testing. T2 - International Conference on Advanced Materials with Hierarchical Structure for New Technologies and Reliable Structures CY - Tomsk, Russia DA - 19.09.2016 KW - Polymer matrix composite KW - Silica nanoparticles KW - Friction KW - Wear PY - 2016 U6 - https://doi.org/10.1063/1.4966337 VL - 1783 SP - 020044-1 EP - 020044-4 AN - OPUS4-38933 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dmitriev, A. I. A1 - Österle, Werner T1 - Modelling the sliding behaviour of tribofilms forming during automotive braking: impact of loading parameters and property range of constituents N2 - The impact of pressure, sliding velocity and property variation of constituents on the sliding behaviour of a model tribofilm was studied with the method of movable cellular automata (MCA). Whereas a clear pressure dependency of the coefficient of friction (COF) was always observed and could be correlated with the structure formation in terms of varying thickness of a mechanically mixed layer, the impact of the other parameters was either negligible or rather weak. Only if a brittle-to-ductile Transition of the oxide-based tribofilm was assumed, a significant decrease in the COF level was predicted. Temperature-dependent property changes can be neglected during MCA modelling, unless this transition takes place. For magnetite-based tribofilms, the transition temperature is beyond 800 °C, i.e. a temperature leading to fading effects during braking anyway. Thus, it could be concluded that, except for very severe braking conditions, sliding simulations with the MCA method yield meaningful results without considering temperature-dependent mechanical properties. KW - Tribofilm KW - Sliding behaviour KW - Friction KW - Movable cellular automata KW - Mechanically mixed layer PY - 2014 U6 - https://doi.org/10.1007/s11249-013-0274-z SN - 1023-8883 SN - 1573-2711 VL - 53 IS - 1 SP - 337 EP - 351 PB - Springer AN - OPUS4-38548 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dmitriev, A. I. A1 - Österle, Werner ED - Österle, Werner ED - Zhang, G. T1 - The role of solid lubricants for brake friction materials N2 - This review article comprises of three parts. Firstly, reports of brake manufacturers on the beneficial impact of solid lubricants for pad formulations are surveyed. Secondly, since tribofilms were identified to play a crucial role in friction stabilization and wear reduction, the knowledge about tribofilm structures formed during automotive braking was reviewed comprehensively. Finally, a model for simulating the sliding behavior of tribofilms is suggested and a review on modelling efforts with different model structures related to real tribofilms will be presented. Although the variety of friction composites involved in commercial brake systems is very broad, striking similarities were observed in respect to tribofilm nanostructures. Thus a generalization of the tribofilm nanostructure is suggested and prerequisites for smooth sliding performance and minimal wear rates have been identified. A minimum of 13 vol.% of soft inclusions embedded in an iron oxide based tribofilm is crucial for obtaining the desired properties. As long as the solid lubricants or their reaction products are softer than magnetite, the main constituent of the tribofilm, the model predicts smooth sliding and a minimum of wear. KW - Solid lubricant KW - Friction KW - Automotive braking KW - Tribofilm KW - Sliding simulation KW - MCA-modeling PY - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-355973 UR - www.mdpi.com/journal/lubricants SN - 2075-4442 VL - 4 IS - 1 SP - 5 EP - 26 PB - MDPI CY - Basel, Switzerland AN - OPUS4-35597 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -