Friction in wheel - rail contacts

Abstract

SummaryIn the autumn, railroad traffic is often interrupted due to the occurrence of slippery tracks. The Dutch main operator (NS) and the infrastructure manager (ProRail) struggle with repeated delays. The layer between wheel and rail causing this phenomenon has not yet been identified, but can be quantified by rheological properties determined by correlating the measured friction between wheel and rail and the developed friction model. To this end, the research described in this thesis is twofold: theoretical; in which the wheel -rail contact is modelled in terms of contact and friction, and experimental; in which the friction between wheel and rail is measured to validate the developed model. The contact model between wheel and rail is approximated to be elliptical, which is shown to be accurate for the described purpose. The low friction situation is assumed to be caused by an interfacial layer, which is acting like a lubricant. Combining the previous two assumptions, a mixed lubrication friction model is developed for the Hertzian elliptical contact situation in which the interfacial layer is acting as a lubricant governed by the Eyring model. The mixed lubrication friction model results in the so-called Stribeck curve and/or the traction curve, which both take frictional heating and starved conditions into consideration. In addition, the changes in attack angle are also taken into account and a general viscoelastic model is proposed for both interfacial and boundary layers. In this way, most of the situations occurring in the wheel -rail contacts are covered, with the recommendation that future research should include the effect of spin. The validation of the friction model was performed by conducting laboratory experiments on general elliptical contacts in the presence of a lubricant. Field experiments are conducted for extracting the rheological properties of the interfacial layer causing the low friction by using the presented model. For the field experiments, two pioneer devices were developed and successfully used on the real track. One is a sliding sensor which measures the coefficient of friction between a curved shaped specimen pressed against and sliding along the rail, i.e. simple sliding conditions. A second device is developed and mounted on a train for measuring traction curves between a measuring wheel and the head (top) of the rail, i.e. rolling/sliding conditions, at velocities of up to 100 km/h. The measuring campaign was scheduled over 20 nights during the autumn of 2008 on three tracks of the Dutch rail network (Hoekselijn, Zeeuwselijn and UtrechtArnhem -Zwolle). Five characteristic traction curves were identified by the use of a statistical approach and rheological properties were extracted for the layer causing the low friction situation. Most of the approximately 6000 measured traction curves showed good agreement with the friction model, in which the viii Summary interfacial layer is represented by the Eyring behaviour. However, for some of them, viscoelasticity had to be taken into ...

Measurement methods and analysis tools for rail irregularities: a case study for urban tram track

“…2). In addition, because the correlation is related to dynamics aspects, the occurrence of defects is related to the train speed [4][5][6][7][8].…”

“…High contact stresses and rolling resistance induce friction heating and consequently wear [4]. Thus, traction and braking may lead to wheel sliding, which results in rail burn, wheel flat, unfavorable material phase transformation, and thermal cracks [5]. In addition to wear, fatigue, crack formation, and other permanent deformations, there is a particular type of defect which affects the rail surface called ''Rail Corrugation''.…”

“…In the contact area between rail and wheel, dynamic forces are exchanged: it has been noted that if the dynamic contact forces are high, then the level of corrugation will be high (though with a phase lag of around 135°) [4][5][6][7][8][9].…”

Contact and friction in systems with fibre reinforced elastomers

“…Therefore the shear behaviour of the interfacial layer will be modelled using the shear model for lubricated contacts from Popovici [66]. This model considers that the viscoelastic behaviour of the interfacial layer follows a Maxwell model with two elements, and that the shear behaviour of the interfacial layer can be described by models describing the behaviour of boundary lubrication layers [67][68][69].…”

“…To facilitate a comparison, two dimensionless numbers are defined [66]: the dimensionless shear stress parameter in Eq. 5.4 and the dimensionless viscosity parameter in Eq.…”