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Lyu, Y., Bergseth, E., Tu, M. & Olofsson, U. (2018). Effect of humidity on the tribological behaviour and airborne particle emissions of railway brake block materials. Tribology International, 118, 360-367
Open this publication in new window or tab >>Effect of humidity on the tribological behaviour and airborne particle emissions of railway brake block materials
2018 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 118, p. 360-367Article in journal (Refereed) Published
Abstract [en]

A pin-on-disc tribometer placed in a one-way ventilated chamber was used to investigate the effect of relative humidity on the tribology and airborne particle emission of three commercial railway brake block materials (grey cast iron, organic composite, and sintered). Cast iron showed the highest friction coefficient, particle emission and wear loss and organic composite exhibited the lowest. The generation of oxide layers on the worn cast iron surface resulted in a decrease in friction, particle emission and wear. Moisture adsorption by the organic composite leads to decreased friction coefficient and particle emission with increasing humidity. Relative humidity does not affect the friction coefficient of the sintered brake block, whose particle emission and wear loss significantly decline with increasing relative humidity.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Airborne particles, Brake block, Humidity, Pin-on-disc
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:kth:diva-218916 (URN)10.1016/j.triboint.2017.10.011 (DOI)000423004700035 ()2-s2.0-85032008346 (Scopus ID)
Note

QC 20171201

Available from: 2017-12-01 Created: 2017-12-01 Last updated: 2018-04-03Bibliographically approved
White, B. T., Nilsson, R., Olofsson, U., Arnall, A. D., Evans, M. D., Armitage, T., . . . Lewis, R. (2018). Effect of the presence of moisture at the wheel-rail interface during dew and damp conditions. Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, 232(4), 979-989
Open this publication in new window or tab >>Effect of the presence of moisture at the wheel-rail interface during dew and damp conditions
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2018 (English)In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 232, no 4, p. 979-989Article in journal (Refereed) Published
Abstract [en]

Incidents involving low levels of adhesion between the wheel and rail are a recurrent issue in the rail industry. The problem has been mitigated using friction modifiers and traction enhancers, but a significant number of incidents still occur throughout the year. This study looks at the environmental conditions that surround periods of low adhesion in order to provide an insight into why low adhesion events occur. Network Rail Autumn data, which provided details on the time and location of low adhesion incidents, were compared against weather data on a national and then local scale. Low adhesion incidents have often been attributed to contamination on the rails, such as organic leaf matter, but these incidents also occur when no contamination is visible. The time, date and location of incidents were linked to local weather data to establish any specific weather conditions that could lead to these events. The effects of precipitation, temperature and humidity on rails were analysed in order to further the understanding of low adhesion in the wheel-rail contact, which will lead to adopting better methods of mitigating this problem.

Place, publisher, year, edition, pages
Sage Publications, 2018
Keywords
Wheel-rail interaction, tribology, railways, low adhesion, dew
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:kth:diva-226778 (URN)10.1177/0954409717706251 (DOI)000429914700003 ()
Note

QC 20180504

Available from: 2018-05-04 Created: 2018-05-04 Last updated: 2018-06-04Bibliographically approved
Cha, Y., Abbasi, S. & Olofsson, U. (2018). Indoor and outdoor measurement of airborne particulates on a commuter train running partly in tunnels. Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, 232(1), 3-13
Open this publication in new window or tab >>Indoor and outdoor measurement of airborne particulates on a commuter train running partly in tunnels
2018 (English)In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 232, no 1, p. 3-13Article in journal (Refereed) Published
Abstract [en]

Wear processes from mechanical braking, rail/wheel contact, the railway electrification system and re-suspended materials due to the turbulence of passing trains in tunnels and stations have been suggested to be the main contributors to particulate matter levels inside trains. In this study, onboard monitoring was performed on a commuter train stopping at underground and aboveground stations. The concentration and size distribution of particulates were monitored for both indoor and outdoor levels. The results show that the levels of PM10 and PM2.5 inside the train were about one-fifth of the outdoor levels. Significant increases in indoor particulate number concentrations were observed in tunnel environments and there was a slight increase when the doors were open. Differences in the size distributions of micro- and nano-sized particulates could be identified for different tunnels.

Place, publisher, year, edition, pages
Sage Publications, 2018
Keywords
Train, underground, indoor aerosol, airborne particulates, railway tunnel
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:kth:diva-185505 (URN)10.1177/0954409716642492 (DOI)000419833100001 ()2-s2.0-85040337944 (Scopus ID)
Note

QC 20180122

Available from: 2016-04-20 Created: 2016-04-20 Last updated: 2018-01-29Bibliographically approved
Cha, Y., Tu, M., Bergstedt, E., Carlsson, P., Lyu, Y., Olofsson, U., . . . Norman, M. (2018). Ombordmätningar av luftburna partiklar i X60 samt på citybanans plattformar. Kungliga Tekniska högskolan
Open this publication in new window or tab >>Ombordmätningar av luftburna partiklar i X60 samt på citybanans plattformar
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2018 (Swedish)Report (Other (popular science, discussion, etc.))
Place, publisher, year, edition, pages
Kungliga Tekniska högskolan, 2018
Series
TRITA-MMK, ISSN 1400-1179 ; 2018:02
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
The KTH Railway Group - Tribology
Identifiers
urn:nbn:se:kth:diva-221674 (URN)
Note

QC 20180122

Available from: 2018-01-19 Created: 2018-01-19 Last updated: 2018-03-13Bibliographically approved
Alemani, M., Wahlström, J. & Olofsson, U. (2018). On the influence of car brake system parameters on particulate matter emissions. Wear, 396, 67-74
Open this publication in new window or tab >>On the influence of car brake system parameters on particulate matter emissions
2018 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 396, p. 67-74Article in journal (Refereed) Published
Abstract [en]

The influence of car brake system parameters on particulate matter emissions was investigated using a pin-on-disc tribometer. Samples from a low-steel friction material and a cast iron disc were tested for different sliding velocities, nominal contact pressures and frictional powers. Disc temperatures were also measured. Their impact on total concentration, size distribution, particle coefficient and transition temperature was analysed. Results show that frictional power is the most significant brake system parameter. However, temperature, as a response parameter, is the most influential, inducing a shift towards the ultrafine particulate fraction and raising emissions. A transition temperature, independent of the system parameters, was identified.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2018
Keywords
Brake environmental design, Frictional heating, Particulate Matter, Particle Coefficient
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:kth:diva-222166 (URN)10.1016/j.wear.2017.11.011 (DOI)000422803000007 ()2-s2.0-85035047416 (Scopus ID)
Note

QC 20180207

Available from: 2018-02-07 Created: 2018-02-07 Last updated: 2018-02-07Bibliographically approved
Alemani, M., Wahlström, J., Matějka, V., Metinöz, I., Söderberg, A., Perricone, G. & Olofsson, U. (2018). Scaling effects of measuring disc brake airborne particulate matter emissions – A comparison of a pin-on-disc tribometer and an inertia dynamometer bench under dragging conditions. Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology
Open this publication in new window or tab >>Scaling effects of measuring disc brake airborne particulate matter emissions – A comparison of a pin-on-disc tribometer and an inertia dynamometer bench under dragging conditions
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2018 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305XArticle in journal (Refereed) Epub ahead of print
Abstract [en]

An important contributor to non-exhaust emissions in urban areas is airborne particulate matter originating from brake systems. A well-established way to test such systems in industry is to use inertia dynamometer benches; although they are quite expensive to run. Pin-on-disc tribometers, on the other hand, are relatively cheap to run, but simplify the real system. The literature indicates promising correlations between these two test stands with regard to measured airborne number distribution. Recent studies also show a strong dependency between the airborne number concentration and the disc temperature. However, a direct comparison that also takes into account temperature effects is missing. The aim of this paper is, therefore, to investigate how the transition temperature is affected by the different test scales, under dragging conditions, and the effects on total concentration and size distribution. New and used low-steel pins/pads were tested against cast iron discs/rotors on both the aforementioned test stands, appositely designed for particulate emission studies. A constant normal load and constant rotational velocity were imposed in both test stands. Results show that a transition temperature can always be identified. However, it is influenced by the test scale and the frictional pair status. Nevertheless, emissions are assessed similarly when an equivalent frictional pair status is analysed (e.g. run-in). Further investigations for fully run-in samples on the pin-on-disc should be performed in order to finally assess the possibility of using the tribometers for the initial assessment of different friction materials.

Place, publisher, year, edition, pages
Sage Publications, 2018
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:kth:diva-224833 (URN)10.1177/1350650118756687 (DOI)
Projects
REBRAKELOWBRASYS
Funder
EU, FP7, Seventh Framework Programme, 324385EU, Horizon 2020, 636592
Note

QC 20180328

Available from: 2018-03-26 Created: 2018-03-26 Last updated: 2018-03-28Bibliographically approved
Lindholm, P., Sosa, M. & Olofsson, U. (2018). The effect of elasticity in powder metal gears on tooth loading and mean coefficient of friction. Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, 232(11), 2023-2031
Open this publication in new window or tab >>The effect of elasticity in powder metal gears on tooth loading and mean coefficient of friction
2018 (English)In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 232, no 11, p. 2023-2031Article in journal (Refereed) Published
Abstract [en]

Powder metal gears have a lower density than conventional steel gears due to their intrinsic porosity from the manufacturing process. This also results in a lower elasticity leading to larger deformations and lower contact pressure in a gear contact. By using different modelling tools (namely FEA and available commercial software), the load behavior along the line of action is studied to compare the influence of lower elasticity with standard wrought steel elasticity for FZG-C type gears. A further step is taken analyzing this effect on the mean coefficient of friction through the recalculation of the gear mesh power loss factor. Conclusions observed are differences in load distribution and marginal differences in the gear mesh power loss factor when comparing sintered and wrought steel FZG-C type gears. Sintered steel showed a marginally longer line of action and simultaneously a decrease of the single tooth contact length when compared to wrought steel, while differences in the gear mesh power loss factor proved non-essential due to the spread in previously measured experimental data.

Place, publisher, year, edition, pages
Sage Publications, 2018
Keywords
Sintered steel, gear, load distribution
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-230477 (URN)10.1177/0954406217712280 (DOI)000433922800007 ()2-s2.0-85045448151 (Scopus ID)
Note

QC 20180613

Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-06-19Bibliographically approved
Lindholm, P., Sosa, M. & Olofsson, U. (2018). The effect of elasticity in powder metal gears on tooth loading and mean coefficient of friction. Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, 232(11), 2023-2031
Open this publication in new window or tab >>The effect of elasticity in powder metal gears on tooth loading and mean coefficient of friction
2018 (English)In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 232, no 11, p. 2023-2031Article in journal (Refereed) Published
Abstract [en]

Powder metal gears have a lower density than conventional steel gears due to their intrinsic porosity from the manufacturing process. This also results in a lower elasticity leading to larger deformations and lower contact pressure in a gear contact. By using different modelling tools (namely FEA and available commercial software), the load behavior along the line of action is studied to compare the influence of lower elasticity with standard wrought steel elasticity for FZG-C type gears. A further step is taken analyzing this effect on the mean coefficient of friction through the recalculation of the gear mesh power loss factor. Conclusions observed are differences in load distribution and marginal differences in the gear mesh power loss factor when comparing sintered and wrought steel FZG-C type gears. Sintered steel showed a marginally longer line of action and simultaneously a decrease of the single tooth contact length when compared to wrought steel, while differences in the gear mesh power loss factor proved non-essential due to the spread in previously measured experimental data.

Place, publisher, year, edition, pages
SAGE PUBLICATIONS LTD, 2018
Keywords
Sintered steel, gear, load distribution
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:kth:diva-230409 (URN)10.1177/0954406217712280 (DOI)000433922800007 ()2-s2.0-85045448151 (Scopus ID)
Note

QC 20180619

Available from: 2018-06-19 Created: 2018-06-19 Last updated: 2018-06-19Bibliographically approved
Riva, G., Wahlström, J., Alemani, M. & Olofsson, U. (2017). A CFD study of a pin-on-disc tribometer setup focusing on airborne particle sampling efficiency. In: ECOTRIB 2017: . Paper presented at ECOTRIB 2017, 6th European COnference on TRIBology 7–9 June 2017, Ljubljana, Slovenia.
Open this publication in new window or tab >>A CFD study of a pin-on-disc tribometer setup focusing on airborne particle sampling efficiency
2017 (English)In: ECOTRIB 2017, 2017Conference paper, Published paper (Refereed)
Abstract [en]

One of the most important measures to evaluate air quality is the presence of particles. Pin-on-disc tribometers are used to study airborne wear particles originating from different sliding contacts in a controlled laboratory environment. One important aspect when measuring airborne particles is to ensure isokinetic sampling conditions. Another important aspect is that the concentration and the particles distribution entering the sampling probe are representative for the emissions generated. It is therefore important to have an estimation of the sampling efficiency of the test system. The aim of this paper is to investigate the particle sampling efficiency of a pin-on-disc tribometer setup. In addition, a modified sampling setup that allows isokinetic sampling is investigated. CFD simulations to investigate air and particle motion were performed for both the existing and the modified configuration. The results show that the velocity field at the outlet does not allow isokinetic sampling for the existing configuration. In the modified configuration a sampling pipe is used to make isokinetic sampling possible. A comparison between the two configurations show that the modified configuration increases the sampling efficiency with almost 40% for ultrafine particles and about 20% for fine and coarse particles. It remains to validate the CFD simulations with experiments.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Design
Identifiers
urn:nbn:se:kth:diva-223386 (URN)
Conference
ECOTRIB 2017, 6th European COnference on TRIBology 7–9 June 2017, Ljubljana, Slovenia
Note

QC 20180221

Available from: 2018-02-20 Created: 2018-02-20 Last updated: 2018-02-21Bibliographically approved
Li, X. & Olofsson, U. (2017). A study on friction and wear reduction due to porosity in powder metallurgic gear materials. Tribology International, 110, 86-95
Open this publication in new window or tab >>A study on friction and wear reduction due to porosity in powder metallurgic gear materials
2017 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 110, p. 86-95Article in journal (Refereed) Published
Abstract [en]

It has been widely acknowledged that controlled texturing on a surface can contribute to friction and wear reduction at lubricated sliding contact interfaces. This paper investigates the influence on friction and wear of different pore size distributions of powder metallurgy gear materials. The pore sizes are controlled by different densities of the powder metallurgic materials. Two different kinds of powder metallurgy (PM) gear materials were applied and a standard gear material are used as a reference. The friction and wear coefficients of PM materials sliding on PM materials increase with increasing pore size. The friction and wear coefficients of regular steel sliding on PM materials decrease with increasing pore size. No matter what the material of the disc, peeling is one of the main damage mechanisms of powder metallurgy pins with the biggest porosity.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Powder metallurgy gear material, Pore size, Friction, Wear
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-206671 (URN)10.1016/j.triboint.2017.02.008 (DOI)000398871700010 ()2-s2.0-85013213277 (Scopus ID)
Note

QC 20170510

Available from: 2017-05-10 Created: 2017-05-10 Last updated: 2017-05-10Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2489-0688

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