TY - JOUR A1 - Marwitz, Christian A1 - Stegemann, B. A1 - Breitkreiz, Maxim A1 - Spaltmann, Dirk A1 - Kloß, Heinz A1 - Woydt, Mathias A1 - Sturm, Heinz T1 - Correlation of adhesion force and electrical conductivity in Magnéli-type vanadium oxides and highly oriented pyrolytic graphite N2 - A correlation of adhesion force and electrical conductivity is established for a vanadium oxide and highly oriented pyrolytic graphite (HOPG). Adhesion forces were determined by analysis of pull-off forces obtained from force–distance curves with atomic force microscopy in ultrahigh vacuum, on clean surfaces and with defined contact conditions. The investigated samples include (i) different stoichiometries of Magnéli-type vanadium oxides (V3O5, V4O7, V6O11, and V7O13), which undergo metal-insulator-transitions as a function of temperature, (ii) the (0001) basal plane and the (10–10) prism plane of highly oriented pyrolytic graphite (HOPG), which differ in their respective perpendicular-plane electrical conductivities by several orders of magnitude, and (iii) the (100) surfaces of pure metal single crystals, i.e., silver (Ag), copper (Cu), iron (Fe) and gold (Au). It is shown, that the vanadium oxides as well as the graphite exhibit significantly lower adhesion forces in their electrical conductive state than in their non-electrical conductive state. The values obtained for the electrical conductive states are quantitatively confirmed by the measurements on the single crystal metals. KW - Adhesion force KW - HOPG KW - Vanadium oxide KW - Magnéli phases KW - Single crystal metals KW - Atomic force microscopy PY - 2011 U6 - https://doi.org/10.1016/j.susc.2011.04.014 SN - 0039-6028 VL - 605 IS - 13-14 SP - 1271 EP - 1274 PB - Elsevier CY - Amsterdam AN - OPUS4-23953 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kloß, Heinz A1 - Woydt, Mathias A1 - Willmann, G. T1 - Temperaturberechnung an den Artikulationsflächen beim künstlichen Hüftgelenk KW - Hüftgelenkersatz KW - Aluminiumoxid KW - Zirkondioxid KW - Blitztemperatur KW - Tribologie KW - Oberflächentopographie PY - 2001 SN - 0933-5137 SN - 1521-4052 VL - 32 IS - 2 SP - 30 S. PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-917 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kloß, Heinz A1 - Santner, Erich A1 - Dmitriev, A.I. A1 - Shilko, E.V. A1 - Psakhie, S.G. A1 - Popov, V.L. T1 - Simulation of material behavior in tribological contacts on the basis of movable cellular automation method PY - 2003 UR - http://www.sciencedirect.com/science/journal/10299599 SN - 1029-9599 VL - 6 IS - 5-6 SP - 57 EP - 62 PB - Inst. of Strength Physics and Materials Science SB RAS CY - Tomsk AN - OPUS4-3708 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meine, Kerstin A1 - Kloß, Heinz A1 - Schneider, Thomas A1 - Spaltmann, Dirk T1 - Adhäsion an strukturierten Oberflächen N2 - Das tribologische Verhalten wird neben den chemischen und physikalischen Eigenschaften der Reibpartner auch von deren Oberflaechentopographie bestimmt. Um deren Beitrag auf die Reibkraft zu untersuchen, wurden daher definierte Rauheitsstrukturen in Siliziumwafer geaetzt. Reibversuche mit einem Mikrotribometer [1, 2] gaben Aufschluss ueber den Einfluss dieser Strukturen auf das Deformationsverhalten im Kontaktbereich. Mit Hilfe der gewonnenen Daten wurde ein Deformationsmodell entwickelt, das eine Abschaetzung der Reibkraft in Abhaengigkeit von der Rauheit erlaubte. Treten starke Adhaesionskraefte im Reibkontakt auf, ist ein inverter Einfluss der Rauheit auf die Reibkraft zu verzeichnen. Um diesen Verlauf weiter zu charakterisieren, wurden mit einem UHV-AFM Adhaesionsmessungen an strukturierten Siliziumwafern durchgefuehrt. Diese zeigen den Verlauf der Adhaesionskraft in Abhaengigkeit von der Groesse der Kontaktflaeche auf. Ein Vergleich dieser experimentell gefundenen Korrelation mit den klassischen Kontaktmodellen machte dabei den Einfluss der Oberflaechenrauheit auf die Groesse der Adhaesionskraft deutlich. Danach ergab sich, dass bei gleicher Kontaktflaeche, aber unterschiedlicher Rauheit sich die Adhaesionskraefte um bis zu einem Faktor 3 unterscheiden. [1] K. Meine, T. Schneider, D. Spaltmann, E. Santner, Wear, 253, 2002, 725-732 [2] K. Meine, T. Schneider, D. Spaltmann, E. Santner, Wear, 253, 2002, 733-738 T2 - Frühjahrstagung des Arbeitskreises Festkörperphysik bei der DPG CY - Dresden, Deutschland DA - 2003-03-24 PY - 2003 UR - http://old.dpg-tagungen.de/archive/2003/o_6.html SN - 0420-0195 SN - 0372-5448 SN - 0343-9216 IS - O 6.2 SP - 382 CY - Bad Honnef AN - OPUS4-2400 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - 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 - JOUR A1 - Österle, Werner A1 - Kloß, Heinz A1 - Urban, Ingrid A1 - Dmitriev, A.I. T1 - Towards a better understanding of brake friction materials N2 - This work focuses on surface changes induced by repeated brake applications and tries to provide explanations, how such material modifications might affect friction and wear properties of automotive disc brakes. Surface films were investigated locally by transmission electron microscopy (TEM) after having prepared thin cross-sections with a focused ion beam instrument (FIB). Since the observed friction layers revealed a nanocrystalline structure, modelling with the method of movable cellular automata (MCA) was performed by assuming an array of linked nanometer-sized particles. In spite of complicated material combinations at the pad surface, two very characteristic features were always observed at both the pad and disc surface, namely a steel constituent—either ferritic (pad) or pearlitic (disc), partly covered with patches of nanocrystalline iron oxide, on a zone of severe plastic deformation with fragmented grain structure. When using an automata size of 10 nm, reasonable values for the mean coefficient of friction (COF) were obtained, namely 0.35 and 0.85 for oxide-on-oxide and metal-on-metal contacts, respectively. Immediately after brake application mass-mixing and bond-breaking was observed within a narrow zone at both surfaces. KW - Brake pad KW - Brake disc KW - Composite material KW - Friction layer KW - Third body KW - MCA-modelling PY - 2007 U6 - https://doi.org/10.1016/j.wear.2006.12.020 SN - 0043-1648 VL - 263 IS - 7-12 SP - 1189 EP - 1201 PB - Elsevier CY - Amsterdam AN - OPUS4-15735 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kloß, Heinz A1 - Klaffke, Dieter T1 - Untersuchungen und Modellrechnungen für eine Verschleißprognose metallischer Werkstoffe KW - Metalle KW - Verschleißprognose KW - Kontaktmechanik KW - Oberflächentopographie KW - Scherenergiedichte PY - 2006 SN - 0724-3472 VL - 53 IS - 6 SP - 14 EP - 17 PB - Expert Verlag CY - Renningen AN - OPUS4-14798 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - 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 - Kloß, Heinz A1 - Dmitriev, A.I. T1 - Friction control during automotive braking: experimental observations and simulation at nanometer scale KW - Friction control KW - Friction film KW - Automotive braking KW - MCA model KW - Nanostructure PY - 2009 U6 - https://doi.org/10.1179/175158309X12586382418454 SN - 1751-5831 VL - 3 IS - 4 SP - 196 EP - 202 PB - Maney CY - London AN - OPUS4-20829 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Österle, Werner A1 - Dmitriev, A.I. A1 - Kloß, Heinz T1 - Does ultra-mild wear play any role for dry friction applications, such as automotive braking? N2 - Nanostructured third body films and/or storage of wear debris at the surfaces of the first bodies are deemed as prerequisites of sliding under ultra-mild wear conditions. Since such features have been observed experimentally on brake pads and discs, attempts were undertaken to study their sliding behaviour by modelling on the nanoscopic scale with an approach based on Movable Cellular Automata (MCA). The model rendered the possibility to study the influence of different nanostructures systematically and to assess the impact of different brake pad ingredients on the sliding behaviour, velocity accommodation and friction force stabilization at a sliding contact. Besides providing a review on previously published modelling results, some additional new graphs enabling better visualization of dynamic processes are presented. Although ultra-mild wear conditions were considered to be essential for achieving the desired tribological properties, transitions to mesoscopic and macroscopic wear mechanisms were studied as well. The final conclusion is that ultra-mild wear and corresponding smooth sliding behaviour play an important role during automotive braking, even though temporarily and locally events of severe wear may cause friction instabilities, surface damage and release of coarse wear particles. KW - Dry friction KW - Ultra-mild wear KW - Third body KW - MCA-model KW - Simulation PY - 2012 U6 - https://doi.org/10.1039/c2fd00117a SN - 1359-6640 SN - 1364-5498 VL - 156 IS - 0 SP - 159 EP - 171 PB - Soc. CY - Cambridge [u.a.] AN - OPUS4-26822 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -