TY - JOUR A1 - Österle, Werner A1 - Deutsch, Cornelius A1 - Gradt, Thomas A1 - Orts Gil, Guillermo A1 - Schneider, Thomas A1 - Dmitriev, A.I. T1 - Tribological screening tests for the selection of raw materials for automotive brake pad formulations JF - Tribology International N2 - A modified pin-on-disc test was applied to determine tribological properties of typical brake pad constituents. Ball-milling of these ingredients together with iron oxide and graphite provided model materials displaying the main features of real third bodies. Solid lubricants like graphite affected the friction and wear behaviour of Fe3O4 powders considerably whereas further addition of hard nanoparticles induced only minor effects. This was corroborated by comparison with modelling results. MoS2 played a dual role. Depending on special conditions, this ingredient either reduced or increased friction. The latter could be explained, after nanoscopic characterization, by oxidation and destruction of the wear-protecting tribofilm. KW - Brake pad formulation KW - Raw materials KW - Third body KW - Pin-on-disc test PY - 2014 DO - https://doi.org/10.1016/j.triboint.2014.01.017 SN - 0301-679X VL - 73 SP - 148 EP - 155 PB - Butterworth-Heinemann CY - Oxford AN - OPUS4-30221 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Dmitriev, Andrey T1 - Some considerations on the role of third bodies during automotive braking JF - SAE International journal of passenger cars: mechanical systems N2 - Third bodies, also termed friction layers, tribofilms or secondary contact patches, are layers of more or less compacted wear debris between pads and rotor of a disc brake. Our approach of assessing the sliding behavior and friction properties induced by third bodies has been: i) structural characterization after AK-master test procedure, ii) sliding simulation of model structures similar to the observed ones but with simpler and well defined compositions, and iii) verification of simulation results by pin-on-disc tests with artificial third bodies showing the same microstructures and compositions as the model structures. The idea was to simulate structure formation during real braking conditions by high energy ball milling of appropriate powder blends. The final outcome of numerous parameter studies was that a third body containing 15 vol% soft ingredients and 0-20 vol % hard ingredients, both distributed homogeneously in a nanocrystalline iron oxide matrix, should be most desirable for braking. This general description of the optimum third body structure and several parameter studies performed by modelling enabled us to interpret a number of features of the AK-master test procedure, such as i) friction evolution during bedding, ii) the role of solid lubricants in respect to the initiation of smooth sliding behavior, and iii) friction evolution during a single braking event (in-stop behavior). KW - Tribofilm KW - Thrid body KW - Friction material KW - MCA-modelling KW - Automotive braking PY - 2014 DO - https://doi.org/10.4271/2014-01-2490 SN - 1946-3995 SN - 1946-4002 VL - 7 IS - 4 SP - 1287 EP - 1294 PB - SAE International CY - Warrendale, Pa. AN - OPUS4-31930 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 JF - Tribology Letters 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 DO - 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 - Schempp, Philipp A1 - Cross, C.E. A1 - Pittner, Andreas A1 - Oder, Gabriele A1 - Neumann, R.S. A1 - Rooch, Heidemarie A1 - Dörfel, Ilona A1 - Österle, Werner A1 - Rethmeier, Michael T1 - Solidification of GTA aluminium weld metal: Part I - Grain morphology dependent upon alloy composition and grain refiner content JF - Welding journal KW - Aluminium KW - Gas tungsten arc welding (GTAW) KW - Grain refinement KW - Columnar to equiaxed transition (CET) KW - Epitaxial nucleation KW - Duplex nucleation theory PY - 2014 SN - 0043-2296 SN - 0096-7629 VL - 93 SP - 53-s - 59-s PB - American Welding Society CY - New York, NY AN - OPUS4-30413 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -