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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)
The tribological properties of nanostructured surface films formed during dry sliding, for example during
automotive braking, were determined by modelling using the method of movable cellular automata.
Starting from a basic model structure, consisting of magnetite with 13% graphite inclusions, the impact of
additional soft and hard particles of different size and volume fraction was studied systematically. It was
revealed that agglomerates of soft particles decomposed and finally mixed with the oxide in the same
way as single nanoparticles. On the other hand, agglomerates of hard particles mixed with the other
components without decomposing. Whereas increasing the amount of soft components in the third body
lowered the coefficient of friction, the opposite occurred with the hard particles. The boundary conditions
for obtaining smooth sliding conditions with minor fluctuations between friction forces at successive time
steps could be defined. In addition to features of the nanostructure, the applied normal pressure
impacted modelling results. Within the parameter range of smooth sliding behaviour, increasing pressure
induced thicker granular interface layers, which lead to a slight decrease of the coefficient of friction.
Changing the amount of soft or hard particles did not change this pressure dependency but only the
friction level.
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.
In part 1 it was shown that tribofilms usually are 100 nm thick and exhibit a multiphase nanocrystalline structure. The objective of our modelling efforts was to obtain a better understanding of the sliding behaviour and associated friction properties and to study the impact of internal and external parameters on these properties. The method of movable cellular automata (MCA) was used. The third bodies were considered as aggregates of linked nanoparticles which may decompose and form a layer of granulär material, the so-called mechanically mixed layer (MML), if certain fracture criteria are fulfilled. The basic model structure which consists of Fe3Ü4 nanoparticles with 13 % graphite inclusions was used. In order to assess the robustness of the model the following parameter studies were performed. The pressure ränge at an asperity contact was varied between 15 and 50 MPa. The mechanical properties of the oxide were varied between brittle and ductile behaviour corresponding to room temperature and high temperature behaviour. The mechanical properties of the soft ingredient were varied + 50 % of the properties of graphite. The influence