Dokument-ID Dokumenttyp Autoren/innen Persönliche Herausgeber/innen Haupttitel Abstract Auflage Verlagsort Verlag Herausgeber (Institution) Erscheinungsjahr Titel des übergeordneten Werkes Jahrgang/Band ISBN Veranstaltung Veranstaltungsort Beginndatum der Veranstaltung Enddatum der Veranstaltung Ausgabe/Heft Erste Seite Letzte Seite URN DOI Lizenz Datum der Freischaltung OPUS4-38933 Beitrag zu einem Tagungsband Dmitriev, A. I.; Österle, Werner Sliding simulation of automotive brake primary contact with variable amounts of copper and graphite nanoparticles 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. 2016 ADVANCED MATERIALS WITH HIERARCHICAL STRUCTURE FOR NEW TECHNOLOGIES AND RELIABLE STRUCTURES 2016 1783 International Conference on Advanced Materials with Hierarchical Structure for New Technologies and Reliable Structures Tomsk, Russia 19.09.2016 020044-1 020044-4 10.1063/1.4966337 2017-01-11 OPUS4-38548 Zeitschriftenartikel Dmitriev, A. I.; Österle, Werner Modelling the sliding behaviour of tribofilms forming during automotive braking: impact of loading parameters and property range of constituents 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. Springer 2014 Tribology Letters 53 1 337 351 10.1007/s11249-013-0274-z 2016-12-05 OPUS4-35597 Zeitschriftenartikel Dmitriev, A. I.; Österle, Werner Österle, Werner; Zhang, G. The role of solid lubricants for brake friction materials 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. Basel, Switzerland MDPI 2016 Lubricants special issue "tribofilms and solid lubrication" 4 1 5 26 urn:nbn:de:kobv:b43-355973 10.3390/lubricants4010005 http://creativecommons.org/licenses/by/3.0/de/deed.de 2016-03-30 OPUS4-44936 Zeitschriftenartikel Dmitriev, A. I.; Nikonov, A. Y.; Österle, Werner Molecular dynamics modeling of the sliding performance of an amorphous silica nano-layer - The impact of chosen interatomic potentials The sliding behavior of an amorphous silica sample between two rigid surfaces is in the focus of the present paper. Molecular Dynamics using a classical Tersoff's potential and a recently developed ReaxFF potential was applied for simulating sliding within a thin film corresponding to a tribofilm formed from silica nanoparticles. The simulations were performed at different temperatures corresponding to moderate and severe tribological stressing conditions. Simulations with both potentials revealed the need of considering different temperatures in order to obtain a sound interpretation of experimental findings. The results show the striking differences between the two potentials not only in terms of magnitude of the resistance stress (about one order of magnitude) but also in terms of friction mechanisms. The expected smooth sliding regime under high temperature conditions was predicted by both simulations, although with Tersoff's potential smooth sliding was obtained only at the highest temperature. On the other hand, at room temperature Tersoff-style calculations demonstrate stick-slip behavior, which corresponds qualitatively with our experimental findings. Nevertheless, comparison with a macroscopic coefficient of friction is not possible because simulated resistance stresses do not depend on the applied normal pressure. Basel MDPI 2018 Lubricants 6 2 43, 1 11 urn:nbn:de:kobv:b43-449366 10.3390/lubricants6020043 https://creativecommons.org/licenses/by/4.0/deed.de 2018-05-17 OPUS4-35596 Zeitschriftenartikel Dmitriev, A. I.; Häusler, Ines; Wetzel, B.; Zhang, G.; Österle, Werner Modeling of the stress-strain behavior of an epoxy-based nanocomposite filled with silica nanoparticles The method of movable cellular automata (MCA) was applied to simulate the stress-strain behavior of a nano composite consisting of an epoxy matrix and 6 vol. % silica nano particles. The size of the elements used for modelling was fixed at 10 nm, corresponding approximately to the diameter of the filler particles. Since not only the stress-strain response of the two constituents but also debonding of neighboring particles and granular flow was taken into account, plastic deformation as well as crack initiation and propagation could be simulated with the model. Modelling results were compared with tensile test results of both, pure epoxy as well as the epoxy-6 vol. % SiO2 composite. Since assuming bulk properties of the two constituents did not yield satisfactory results, slight modifications of the nanoparticle response functions and nanostructures were tested numerically. Finally, it was observed that only the assumption of slightly increased strength properties of the epoxy yielded good correlation between experimental and modelling results. This was attributed to an increased cross linking of the epoxy caused by the presence of silica nano particles. Elsevier 2016 Materials and Design 89 950 956 http://dx.doi.org/10.1016/j.matdes.2015.10.038 2016-03-30