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- Third body (7)
- Tribofilm (5)
- Movable cellular automata (4)
- Dry friction (3)
- MCA-modelling (3)
- Sliding simulation (3)
- Automotive braking (2)
- Friction layer (2)
- Modelling (2)
- Nanocomposite (2)
- Pin-on-disc test (2)
- Automotive Brakes (1)
- Automotive brake system (1)
- Ball milling (1)
- Brake disc (1)
- Brake pad (1)
- Brake pad formulation (1)
- Bremse (1)
- Coefficient of friction (1)
- Composite material (1)
- Copper (1)
- Copper particles (1)
- Cross-sectional TEM (1)
- Dritter Körper (1)
- Dynamic Modelling (1)
- Friction (1)
- Friction Mechanisms (1)
- Friction control (1)
- Friction film (1)
- Friction films (1)
- Friction materials (1)
- Friction-induced vibrations (1)
- Hybrid composite (1)
- MCA model (1)
- MCA-model (1)
- MCA-modeling (1)
- Mechanically Mixed Layer (1)
- Mechanically mixed layer (1)
- Method of movable cellular automata (1)
- Modellierung (1)
- Molecular dynamics (1)
- Movable Cellular Automata (1)
- Nanocharakterisierung (1)
- Nanoparticles (1)
- Nanostructure (1)
- Nanotribology (1)
- Noise propensity (1)
- Numerical simulation (1)
- Primary contact (1)
- Raman spectroscopy (1)
- Raw materials (1)
- Reibung (1)
- Silica nanoparticle (1)
- Silicone oil residue (1)
- Simulation (1)
- Stressstrain behavior (1)
- TEM (1)
- Ultra-mild wear (1)
- Verschleiß (1)
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.
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.
The method of movable cellular automata (MCA) and method of molecular dynamics (MD) were applied to simulate the friction and sliding behavior of model-tribofilms formed from a nanocomposite consisting of an epoxy matrix, 10 vol % micron-sized carbon fibers and 5 vol. % silica nanoparticles. Whereas MCA considered the tribofilm as an agglomerate of silica nanoparticles released from the composite and mixed with graphite particles, MD simulated the sliding behavior of an amorphous silica layer supported by stiff crystalline substrates on both sides. The MCA model provided reasonable quantitative results which corroborate experimental findings at moderate stressing conditions. The very low coefficient of friction observed experimentally under severe stressing conditions was not explained by this model. This could be attributed to the lack of mechanical data at the high temperature expected under these conditions. Although based on a simpler assumption of the tribofilm composition, MD-modelling could be easily applied to the expected high flash temperature and was able to predict friction reduction and smooth sliding under these conditions.
The composition and nanostructure of a beneficial tribofilm formed during sliding of a hybrid nanocomposite against steel were characterized comprehensively. A similar nanostructure was produced by high energy ball milling of the three identified tribofilm constituents: silica, hematite and graphite. By supplying powders to a pin-on-disc test it has been shown that neither silica, nor hematite, nor a mixture of both provide the low coefficient of friction (COF) observed for the hybrid composite. Only if graphite was blended with the oxides, the low COF was obtained. Thus, a film of finely dispersed stable inorganic wear products containing 15 vol% graphite provides low friction and wear in the considered case.