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- Third body (8)
- Tribofilm (8)
- Sliding simulation (6)
- Movable cellular automata (5)
- Friction (4)
- Automotive braking (3)
- Dry friction (3)
- MCA-modelling (3)
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- Molecular dynamics (2)
- Pin-on-disc test (2)
- Polymer matrix composite (2)
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- Additive manufacturing (1)
- Amorphous silica (1)
- Automotive Brakes (1)
- Automotive brake system (1)
- Ball milling (1)
- Biomaterials (1)
- Brake disc (1)
- Brake pad (1)
- Brake pad formulation (1)
- Bremse (1)
- Carbon fibers (1)
- Coefficient of friction (1)
- Cold-welding (1)
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- Copper (1)
- Copper particles (1)
- Cross-sectional TEM (1)
- Dritter Körper (1)
- Dry sliding (1)
- Dynamic Modelling (1)
- Electrical connectors (1)
- Electro-plated nickel coatings (1)
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- Friction Mechanisms (1)
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- MCA-model (1)
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- Method of movable cellular automata (1)
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- Movable Cellular Automata (1)
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- Raman spectroscopy (1)
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- Silica nanoparticle (1)
- Silicone oil residue (1)
- Simulation (1)
- Sliding behaviour (1)
- Solid lubricant (1)
- Stress-strain behavior (1)
- Stressstrain behavior (1)
- TEM (1)
- Thin tribofilm (1)
- Ti-Nb alloy (1)
- Tribological properties (1)
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- Ultra-mild wear (1)
- Verschleiß (1)
- Wear (1)
- amorphous carbon film (1)
- amorphous silica film (1)
- dry friction (1)
- molecular dynamics (1)
- sliding simulation (1)
Organisationseinheit der BAM
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.
In the paper the method of discrete modeling (movable cellular automata method) and combined discrete-continuous description of the simulated medium are used to analyze processes occurring in the local contact of the automotive brake system. The characteristic size of the considered region is 1.5 ?m. The following contact situation is simulated: steel fiber coated by an iron oxide film as the brake pad and pearlitic steel also coated by an iron oxide layer as the disc. On the assumption of oxide layer wearing we simulate the iron oxide - iron oxide, iron oxide - metal and metal - metal contacts.
The calculation results for the friction coefficient for various contact situations give quite adequate values. For example, for the oxide - oxide system the calculated coefficient is approximately equal to 0.4, while for the metal - metal contact the obtained value varies from 0.7 to 0.9. Analysis of a set of the obtained results allows concluding that oxide is formed more rapidly than the sliding layer, which in turn makes the friction coefficient value stabilized.
The sliding behaviors of two simplified tribofilms with amorphous structure consisting either of SiO₂ molecules or C atoms were simulated by molecular dynamics modeling. The objective was to identify mechanisms explaining the experimentally observed lubricating properties of the two amorphous films. The impacts of layer thickness, normal pressure, temperature and different substrate materials were studied systematically, while the sliding velocity was kept constant at 30 m/s. While the layer thickness was not critical, all the other parameters showed special effects under certain conditions. Normal pressure impeded void formation and could even eliminate voids if applied at high temperature. Stick-slip sliding was changed to smooth sliding at high temperature due to void healing. Considering the carbon film, high friction forces and shearing of the entire film was observed with diamond substrates, whereas interface sliding at low friction forces and an amorphous layer of iron mixed with carbon was observed if the supporting substrates consisted of α-Fe. Both films show a decrease of friction forces and smooth sliding behavior at elevated temperature, corresponding well to the tribological behavior of and advanced nanocomposite sliding against a steel disc under severe stressing conditions when high flash temperatures can be expected.
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). Our previous studies show that copper as a constituent of the tribofilm formed during braking provides smooth sliding by forming a granular layer of mechanically mixed materials from the friction layers. In the present study the concentration of copper particles in a Fe3O4-matrix was varied systematically in the range 5.5-28 vol. % and compared to mixtures with the same amount of graphite nanoparticles. The sliding simulations were performed while assuming material properties at 500°C in order to assess the beneficial role of copper during severe braking conditions corresponding to fading cycles during dynamometer testing.