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| 2. |
- Lyu, Yezhe, 1987-, et al.
(author)
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A pin-on-disc study on the tribology of cast iron, sinter and composite railway brake blocks at low temperatures
- 2019
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In: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; , s. 48-52
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Journal article (peer-reviewed)abstract
- Most freight wagons in the EU use cast iron brake blocks. Cast iron brake blocks have a stable braking capability in different environmental conditions, but wear down the wheel tread quickly. Therefore, there is a need to understand the tribology of other brake block materials. A pin-on-disc tribometer placed in a temperature-controlled chamber is used to investigate the tribology of cast iron, sinter and composite railway brake blocks at low ambient temperatures. Pins made from different brake blocks are tested with discs made from steel wheels. Both friction coefficient and wear are evaluated at five different temperatures from + 10 to − 30 °C. The cast iron block demonstrated the greatest wear at − 10 and − 20 °C, due to the ductile-to-brittle transition at low temperatures. The worn graphite from cast iron is likely to become a solid lubricant, reducing the friction at − 10 and − 20 °C. For the composite brake block, a gradual decrease in friction with decreasing temperature was found. The sinter brake block was not sensitive to changes in ambient temperature. The sliding speed in the current study is relatively low and further study at higher speed is suggested in order to evaluate the tribological performance of different brake blocks.
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| 4. |
- Riva, Gabriele, et al.
(author)
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A Multi-Scale Simulation Approach to Investigate Local Contact Temperatures for Commercial Cu-Full and Cu-Free Brake Pads
- 2019
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In: Lubricants. - Basel : MDPI. - 2075-4442. ; 7:9
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Journal article (peer-reviewed)abstract
- Copper from vehicles disc brakes is one main contributor of the total copper found in the environment. Therefore, the U.S. Environmental Protection Agency (EPA) and the automotive industries started the Copper-Free Brake Initiative. The pad friction material is essentially composed of a binder, fillers, reinforcing fibres and frictional additives. Copper and brass fibres are the most commonly used fibres in brake pads. There is a need to understand how the contact temperature distribution will change if copper-based fibres are changed to steel fibres. The aim of this work is, therefore, to investigate how this change could influence the local contact temperatures. This is done by developing a multi-scale simulation approach which combines cellular automaton, finite element analysis (FEA) and computational fluid dynamics (CFD) approaches with outputs from inertia brake dyno bench tests of Cu-full and Cu-free pads. FEA and thermal-CFD are used to set the pressure and the temperature boundary conditions of the cellular automaton. The outputs of dyno tests are used to calibrate FEA and CFD simulations. The results of the study show lower peaks in contact temperature and a more uniform temperature distribution for the Cu-free pad friction material.
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| 5. |
- Riva, Gabriele, 1988-, et al.
(author)
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An FEA approach to simulate disc brake wear and airborne particle emissions
- 2019
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In: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 138, s. 90-98
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Journal article (peer-reviewed)abstract
- Emissions from disc brake wear adversely affect the air quality in cities. Finite Element Analysis (FEA) approaches focussing on the macroscopic wear of pads and rotors can be found in the literature, but none of these take the wear and emission dependence of the local contact pressure and sliding speed into account. The aim of the present study is to further develop an FEA approach for simulation of macroscopic wear and airborne emission to include the dependences of local contact pressure and sliding speed by implementing wear and emission maps obtained by pin-on-disc tribometer tests. Results from a dyno bench test are compared with simulated results. The simulated rotor and pads wear, and airborne emissions are in line with the measured values.
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| 6. |
- Riva, Gabriele, et al.
(author)
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Simulation of Contact Area and Pressure Dependence of Initial Surface Roughness for Cermet-Coated Discs Used in Disc Brakes
- 2019
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In: Tribology in Industry. - : Faculty of Engineering, University of Kragujevac. - 0354-8996 .- 2217-7965.
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Journal article (peer-reviewed)abstract
- Friction, wear, and emission performance strongly depend on the contact pressure and area at the interface of the pad and disc. The contact situation at the pad-to-disc interface can be explained by the formation and destruction of mesoscopic sized contact plateaus on the pad surface. Experimental studies report that the initial surface roughness of cermet-coated discs strongly affects friction, wear and emission performance. This is explained by the formation of secondary plateaus on the disc surface. The aim of this work is to extend an existing cellular automaton approach to include the formation of secondary plateaus on the disc surface in order to explain experimental results reported in the literature. First, to investigate the validity of the novel simulation approach, a cermet-coated cast iron disc is tested against a low-met pad material with a pin-on-disc tribometer. The same conditions are used as input in a simulation. Then, the initial disc roughness influence on contact pressure and area of the same cermet-coated disc is compared with results reported in the literature. The topographies of the measured and simulated disc surfaces are qualitatively in line. An initial rougher disc surface results in a considerably lower contact area than does a smother surface.
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| 7. |
- Tu, Minghui, et al.
(author)
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A comparison of airborne wear particle emission models based on metro station measurements
- 2019
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In: Proceedings of 10th International Scientific Conference BALTTRIB 2019. - : Vytautas Magnus University. - 2424-5089. ; , s. 150-157
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Conference paper (peer-reviewed)abstract
- The main sources of non-exhaust particles around metro systems are the wear from wheel-rail contact, brake contact and the contact between mechanical parts in electric power systems. In order to predict the PM10 levels on underground metro platforms, the relation among time, train frequency and PM10 level should be investigated. Two types of particle emission models have previously been published to determine the PM10 level on underground train platform; these are the linear model and the conservation model. The aim of this study is to compare the results from the two models with a set of field measurements PM10. In 2016, a set of field measurements are performed on four underground metro platforms in Stockholm. The predicted PM10 values from the two models are compared with the measurement data. The accuracy of the two models is analysed and the behaviours of the two models in high and low train frequency regions are separately discussed.
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| 8. |
- Tu, Minghui, et al.
(author)
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Towards a two-part train traffic emissions factor model for airborne wear particles
- 2019
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In: Transportation Research Part D. - : Elsevier Ltd. - 1361-9209 .- 1879-2340. ; 67, s. 67-76
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Journal article (peer-reviewed)abstract
- In 2017 a new railway tunnel containing two stations opened in Stockholm, Sweden. A series of field measurements were carried out on the platforms in this tunnel before and after it was opened for normal traffic. These measurements were used to investigate the contribution of airborne particle emissions from wear processes to total train emissions. This field data was used to develop a two-part train traffic emission factor model for PM10. The two parts are the accumulative effect term (relating to operating distance such as wheel-rail contact and overhead electric line sliding contact) and a brake effect term (relating to the number of braking operations such as brake disc and brake pad contact). The results show that operating a single trial train at a higher than normal frequency on an otherwise empty platform increases the platform particulate concentration until the concentration reaches a steady value. The model suggests that brake emissions account for about 50% of the total emissions measured in the tunnels.
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| 9. |
- Wahlström, Jens, PhD/Docent, 1979-
(author)
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A pin-on-disc tribometer study of friction at low contact pressures and sliding speeds for a disc brake material combination
- 2019
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In: Results in Engineering. - : Elsevier. - 2590-1230. ; 4
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Journal article (peer-reviewed)abstract
- Disc brake creep groan is a stick-slip phenomenon which results in a low frequency noise in road vehicles that could occur at low vehicle speeds and brake torques. Simulation approaches are used predict the stick-slip phenomena for disc brakes. These approaches depend on the friction model used. Tribometers can be used to map how the local coefficient of friction (CoF) depends on the contact pressure (p) and sliding speed (v). A CoF pv-map can be used as friction model in simulation approaches. There is a lack of CoF maps at low contact pressures and sliding speeds are reported in the literature. The aim of the presented study is to map the CoF for a disc brake material combination at low contact pressures (0.03–0.28 MPa) and sliding speeds (0–3.8 mm/s). The result shows that the friction decreases with increased contact pressure and sliding speed for the specific material combination tested and the test conditions used. More studies are needed to further investigate the validity of the results.
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