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Investigation of factors influencing wheel-rail adhesion using a mini-traction machine
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi. (KTH Railway group)
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.ORCID iD: 0000-0003-2489-0688
Institute for Surface Chemistry, Life Science and Chemical Industries Section, Stockholm, Sweden.
2012 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 292/293, 218-231 p.Article in journal (Refereed) Published
Abstract [en]

Adhesion in the wheel-rail contact is a key factor determining stable running conditions and safety during train driving and braking. This paper presents an experiment performed in a mini-traction machine to simulate the problems of low adhesion in the wheel-rail contact. Tests were conducted under dry conditions and using water or oil as lubricants to study the influence of surface roughness on the adhesion coefficient. The results indicate that the adhesion coefficient can be reduced to as low as 0.02 for smooth surfaces lubricated with water. For rougher contact surfaces, the water-lubricated tests indicate a higher adhesion coefficient than do oil-lubricated ones, but also a clear dependence on water temperature. The oil-lubricated tests indicate a very slight dependence of the adhesion coefficient on variation in rolling speed, temperature, and surface roughness.

Place, publisher, year, edition, pages
2012. Vol. 292/293, 218-231 p.
Keyword [en]
wheel rail, adhesion, surface roughness, rolling-sliding contact
National Category
Tribology
Identifiers
URN: urn:nbn:se:kth:diva-48800DOI: 10.1016/j.wear.2012.05.006ISI: 000308628400024Scopus ID: 2-s2.0-84864324384OAI: oai:DiVA.org:kth-48800DiVA: diva2:458565
Note

QC 20121031. Updated from submitted to published.

Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Adhesion in the wheel-rail contact under contaminated conditions
Open this publication in new window or tab >>Adhesion in the wheel-rail contact under contaminated conditions
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Railway vehicles require a certain level of adhesion between wheel and rail to operate efficiently, reliably, and economically. Different levels of adhesion are needed depending on the vehicle running conditions. In the wheel tread–railhead contact, the dominant problem is low adhesion, as low adhesion on the railhead negatively affects railway operation: on one hand, the vehicle will lose traction resulting in delay when driving on low-adhesion tracks; on the other hand, low adhesion during deceleration will extend the braking distance, which is a safety issue.

This thesis examines the influence of several contaminants, i.e., water, oil, and leaves, on the adhesion in the wheel tread–railhead contact. This study will improve our knowledge of the low-adhesion mechanism and of how various contaminants influence adhesion. The thesis consists of a summary overview of the topic and three appended papers (AC).

Papers A and B focus mainly on water and oil contamination examined using two methods, numerical simulation and lab testing. In paper A, real measured wheel and rail surfaces, low- and high-roughness surfaces, along with generated smooth surfaces are used as input to the numerical model for predicting the adhesion coefficient. Water-lubricated, oil-lubricated, and dry contacts are simulated in the model. In the research reported in paper B, scaled testing using a mini traction machine (MTM) was carried out to simulate the wheel–rail contact under lubricated conditions. Two types of disc surfaces of different roughnesses were run at different contact pressures and temperatures. A stylus machine and atomic force microscopy (AFM) were used to measure the surface topography. A study of leaf contamination on the railhead surface, based on field testing, is presented in paper C. Railhead surface samples were cut and the friction coefficient was measured on five occasions over the course of a year. Electron spectroscopy for chemical analysis (ESCA) and glow discharge optical emission spectrometry (GD-OES) were used to detect the chemical composition of the leaf-contamination layer on the railhead surface.

The main conclusion of the thesis is that different contaminants reduce the adhesion coefficient in different ways. Oil reduces the adhesion coefficient by carrying the normal force due to its high viscosity. Water can reduce the adhesion coefficient to different degrees depending on the surface topography and water temperature. The mixture of an oxide layer and water contamination may have an essential impact. A leaf-formed blackish layer causes low adhesion by means of a chemical reaction between the leaves and bulk material. The thickness of the friction-reducing oxide layer predicts the friction coefficient and the extent of leaf contamination.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. 27 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2011:15
Keyword
adhesion, wheel-rail contact, contaminants, rough surfaces
National Category
Tribology
Identifiers
urn:nbn:se:kth:diva-48441 (URN)978-91-7501-181-3 (ISBN)
Presentation
2011-12-01, B242, KTH, Brinellvägen, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20111123Available from: 2011-11-23 Created: 2011-11-18 Last updated: 2012-01-27Bibliographically approved
2. 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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