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Friction Between Wheel and Rail: A Pin-On-Disc Study of Environmental Conditions and Iron Oxides
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.ORCID iD: 0000-0003-2489-0688
2013 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 52, no 2, 327-339 p.Article in journal (Refereed) Published
Abstract [en]

The coefficient of friction between railway wheels and rails is crucial to railway operation and maintenance. Since the wheel-rail system is an open system, environmental conditions, such as humidity and temperature, affect the friction coefficient. Pin-on-disc testing was conducted to study the influence of environmental conditions and iron oxides on the coefficient of friction between the wheel and rail. The iron oxides were pre-created in a climate chamber. The surfaces of the tested samples were analysed using X-ray diffraction, scanning electron/focused ion beam microscopy, and Raman spectroscopy. Results indicate that the coefficient of friction decreases with increasing relative humidity (RH) up to a saturation level. Above this level, the coefficient of friction remains low and stable even when the RH increases. In particular, when the temperature is low, a small increase in the amount of water (i.e., absolute humidity) in the air can significantly reduce the coefficient of friction. At high humidity levels, a water molecule film can keep the generated haematite on the surfaces, counterbalancing the effect of rising humidity.

Place, publisher, year, edition, pages
2013. Vol. 52, no 2, 327-339 p.
Keyword [en]
Friction, Wheel-rail contact, Iron oxide, Environmental conditions, Surface analysis
National Category
Tribology
Research subject
The KTH Railway Group - Tribology
Identifiers
URN: urn:nbn:se:kth:diva-133355DOI: 10.1007/s11249-013-0220-0ISI: 000326081700014Scopus ID: 2-s2.0-84890067519OAI: oai:DiVA.org:kth-133355DiVA: diva2:660970
Note

QC 20131031

Available from: 2013-10-31 Created: 2013-10-31 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Adhesion in the wheel-rail contact
Open this publication in new window or tab >>Adhesion in the wheel-rail contact
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

To attract more customers and compete with other modes of transportation, railway transport needs to ensure safety, punctuality, high comfort, and low cost; wheel–rail adhesion, i.e., the transmitted tangential force in the longitudinal direction during driving and braking, plays an important role in all these aspects. Adhesion needs to be kept at a certain level for railway operation and maintenance. However, wheel−rail contact is an open system contact. Different contaminants can present between the wheel and rail surfaces, forming a third-body layer that affects the adhesion. Prediction of wheel–rail adhesion is important for railway operations and research into vehicle dynamics; however, this prediction is difficult because of the presence of contaminants.

This thesis deals with wheel–rail adhesion from a tribological perspective. The five appended papers discuss wheel–rail adhesion in terms of dry conditions, lubricated conditions, leaf contamination, iron oxides, and environmental conditions. The research methodologies used are numerical modelling, scaled laboratory experiments, and field tests. The research objective is to understand the mechanisms of the adhesion loss phenomenon. 

A numerical model was developed to predict wheel–rail adhesion based on real measured 3D surfaces. Computer simulation indicates that surface topography has a larger impact on lubricated than on dry contacts. Plastic deformation in asperities is found to be very important in the model. Ball-on-disc tests indicate that water can give an extremely low adhesion coefficient on smooth surfaces, possibly due to surface oxidation. Investigation of lubricated contacts at low speed indicates that oil reduces the adhesion coefficient by carrying a normal load, while adhesion loss due to water depends on the surface topography, water temperature, and surface oxidation. A field investigation indicates that leaves reduce the friction coefficient because of the chemical reaction between leaves and bulk materials. The thickness of the surface oxide layer was found to be an essential factor determining adhesion reduction. Pin-on-disc experiments found a transition in the friction coefficient with regard to the relative humidity, due to a trade-off between the water molecule film and the hematite on the surface. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 31 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2013:15
Keyword
Adhesion, wheel-rail contact, contaminants, tribology
National Category
Tribology
Research subject
The KTH Railway Group - Tribology
Identifiers
urn:nbn:se:kth:diva-133342 (URN)978-91-7501-896-6 (ISBN)
Public defence
2013-11-22, F3, Lindstedtsvägen 26, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20131031

Available from: 2013-10-31 Created: 2013-10-30 Last updated: 2013-10-31Bibliographically approved

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