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Adhesion in the wheel-rail contact under contaminated conditions
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi. (KTH Railway Group)
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 [en]
adhesion, wheel-rail contact, contaminants, rough surfaces
National Category
Tribology
Identifiers
URN: urn:nbn:se:kth:diva-48441ISBN: 978-91-7501-181-3 (print)OAI: oai:DiVA.org:kth-48441DiVA: diva2:457625
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
List of papers
1. Adhesion modeling in the wheel-rail contact under dry and lubricated conditions using measured 3D surfaces
Open this publication in new window or tab >>Adhesion modeling in the wheel-rail contact under dry and lubricated conditions using measured 3D surfaces
2013 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 61, 1-10 p.Article in journal (Refereed) Published
Abstract [en]

Adhesion between wheels and rails plays an essential role in the safe, efficient, and reliable operation of a railway network. Particularly under lubricated conditions, which can be a natural lubricant as water and an applied lubricant as rail oil, trains can experience adhesion loss. This paper presents an adhesion model constructed using the measured 3D wheel-rail surfaces. The numerical model comprises of three parts: a normally loaded contact model; an interfacial fluid model; and a rolling-sliding contact model. Simulation examples use the numerical model to investigate how water or oil contamination might affect wheel-rail adhesion in contacts with different surface roughness levels. Simulation indicates that adhesion peaks are almost at the same creep on different surfaces. The fluid load capacity is inversely proportional to the adhesion coefficient, both of which are clearly dependent on vehicle speed. Oil reduces adhesion coefficient more than water does. The adhesion coefficient on the low roughness surfaces is higher than that on the generated smooth surfaces under oil-lubricated conditions while it is the opposite for water-lubricated contact.

Keyword
wheel-rail contact, adhesion, numerical model, measured 3D surfaces
National Category
Tribology
Identifiers
urn:nbn:se:kth:diva-48770 (URN)10.1016/j.triboint.2012.11.022 (DOI)000317801400001 ()2-s2.0-84871800452 (Scopus ID)
Note

QC 20130212. Updated from submitted to published.

Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2017-12-08Bibliographically approved
2. Investigation of factors influencing wheel-rail adhesion using a mini-traction machine
Open this publication in new window or tab >>Investigation of factors influencing wheel-rail adhesion using a mini-traction machine
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.

Keyword
wheel rail, adhesion, surface roughness, rolling-sliding contact
National Category
Tribology
Identifiers
urn:nbn:se:kth:diva-48800 (URN)10.1016/j.wear.2012.05.006 (DOI)000308628400024 ()2-s2.0-84864324384 (Scopus ID)
Note

QC 20121031. Updated from submitted to published.

Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2017-12-08Bibliographically approved
3. A field test study of leaf contamination on railhead surfaces
Open this publication in new window or tab >>A field test study of leaf contamination on railhead surfaces
2014 (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. 228, no 1, 71-84 p.Article in journal (Refereed) Published
Abstract [en]

Leaves on railway tracks affect the level of adhesion between the wheel and rail, especially in autumn. When crushed by wheels, leaves form a tarnished, low level of adhesion layer that sticks to the railhead and often requires mechanical removal. A Stockholm local traffic track with a long history of adhesion problems was subjected to field tests on railhead contamination. On five occasions under different conditions, spaced over a year, the friction coefficient was measured using a tribometer and samples of the rail were taken. The techniques of electron spectroscopy for chemical analysis and glow discharge optical emission spectrometry were conducted to determine the composition of the top layer of rail contaminants and hardness was measured using the nano-indentation technique. The tarnished layer contains much higher contents of calcium, carbon and nitrogen than do leaf residue layers and uncontaminated samples. These high element contents are generated from the leaf material, which chemically reacts with the bulk material. The hardness of the tarnished layer is one-fifth that of the non-tarnished layer of the same running band. A chemical reaction occurs from the surface to a depth of several microns. The thickness of the friction-reducing oxide layer can be used to predict the friction coefficient and extent of leaf contamination.

Keyword
leaf, blackish layer, wheel/rail, field test, surface analysis
National Category
Tribology
Identifiers
urn:nbn:se:kth:diva-48804 (URN)10.1177/0954409712464860 (DOI)000328825400006 ()2-s2.0-84891056604 (Scopus ID)
Conference
The first International conference on Railway Technology: Research, Development and Maintenance, Las Palmas de Gran Canaria, Spain18-20 April 2012
Note

QC 20131202

Available from: 2011-11-23 Created: 2011-11-23 Last updated: 2017-12-08Bibliographically approved

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