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This study presents the results of modelling the rolling contact of the elastic sphere and the elastic half-space in the presence of a thin intermediate viscoelastic layer which properties are described by an elastic nonlinear Winkler body in the normal direction and a viscoelastic Maxwell body in the tangential direction. The analytical–numerical approach for the estimation of contact fatigue damage, accumulated in the elastic half-space under rolling friction conditions, is developed. The proposed model can be used, in particular, to study the effect of mechanical properties of the friction modifiers (elastic moduli and relaxation times) and its thickness as well as the relative slippage on the formation of the surface and under surface contact fatigue cracks in rails. The results of the analysis can also be applied for the estimation of efficiency of solid lubricants in rolling contacts under given operating conditions. [ABSTRACT FROM AUTHOR]

Based on the measured spectra of rail roughness and track structures longitudinal roughness, the rail grinding limit is studied with the help of an established coupled dynamic metro vehicle–track model and a rolling contact fatigue model. The results indicate that metro rail grinding control should be regulated according to corrugation wavelength range and operating speed. Based on the rolling contact fatigue model, longer wavelength of rail corrugation has less influence on the wheel rolling contact fatigue. For the metro lines with a maximum operating speed of 80 km/h, the average levels of rail corrugation in the wavelength ranges of 30–65 mm, 65–125 mm, and 125–250 mm should be less than 5.4, 24.8, and 33.8 dB re 1 μm, respectively; for the ones with the operating speed of 80–120 km/h, the corresponding average corrugation levels in the three wavelength ranges should be less than 4.4, 9.8, and 29.8 dB re 1 μm, respectively. [ABSTRACT FROM AUTHOR]

A finite element-based simulation was carried out to investigate the effects of friction-induced thermal load on rail under varied wheel slip conditions. The surface temperature rise from six different percentage slips (1%, 1.5%, 2%, 5%, 8.5%, and 10%) at the contact interface was examined for eight-wheel pass. The residual stresses and accumulated plastic strains evolved by the effect of localized temperature rise are estimated. Analytical formulation for conduction mode of heat transfer at the contact patch is used to estimate the temperature distribution. The interaction of thermal-elastic-plastic field conditions is obtained by a proposed simulation model. This is implemented in commercial finite element software ANSYS 14.0. In order to capture the steep thermal gradient beneath the contact surface, refined mesh is used in the upper layers up to a depth of 2 mm of the simulation domain. For better manifestation of thermally affected material layers, a temperature dependent bilinear-kinematic hardening material condition is applied. Results indicate the maximum temperature rise at about 0.6a from the trailing end in the contact ellipse of semi-major axis a. At higher slippage conditions the initial pearlitic rail steel gets converted to martensite which is often observed on rail surface as white etching layer known to be associated with rolling contact fatigue. The study reveals the mechanisms of thermally induced defects observable on rail surface. The outcomes, in addition, can provide useful information for the development of thermo-mechanically superior rail steels. [ABSTRACT FROM AUTHOR]

In this study, experimental tests to assess rolling contact fatigue in uncoated and coated steel substrates with TiN and CrN coatings are presented. A thrust bearing tester was used. The tests were carried out in lubricated conditions at 1560 r/min, using a contact pressure of 2.09 GPa. The surface damage was analyzed by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. The substrates coated with CrN showed a fatigue life above 100 million cycles. On the other hand, with TiN, the time for crack nucleation was much shorter, approximately 60 × 104 cycles. [ABSTRACT FROM AUTHOR]

Polymer nanocomposite has received great research interest in design of engineering components owing to its remarkable improvement in tribological characteristics. Rolling contact fatigue is a predominant failure mode of the many functional components like gears, bearings, cams, ball screw rods and rail wheels. Nanosize clay fillers were dispersed into the polymer using melt intercalation method to produce polymer nanocomposite material. Injection-molded disc-type specimens were made to run against each other on twin-disc test rig designed in-house. To understand the behaviour of the materials, rolling contact fatigue behaviour against different contact loads under constant speed were studied. Rolling contact fatigue testing of polymer nanocomposite has revealed significant difference from the pristine PA6 behaviour in failure modality and temperature rise. Addition of nanoclay to polymer although improved the modulus and strength of the nanocomposite, deteriorated the rolling contact behaviour. Rolling contact fatigue performance of PA6 was better than that of the clay-reinforced polymer nanocomposite under all tested conditions. Polymer nanocomposite materials have shown poor wear resistance as the specific wear rate was calculated to be higher for PNC materials under rolling contact fatigue conditions. Difference in surface temperature rise in PA6 and polymer nanocomposite has led to the different failure mechanism and reduction in rolling contact fatigue life of polymer nanocomposite materials. [ABSTRACT FROM AUTHOR]

Optimisation of railway track maintenance requires knowledge of how a deteriorated track geometry will affect subsequent loading and damage of the track. This is the scope of the current study where, in particular, the influence on track shift forces and rolling contact fatigue is investigated through numerical simulations. To this end, track geometries are obtained from field measurements. Lateral irregularities are extracted and scaled to represent different levels of geometry deterioration. Multibody simulations of dynamic train–track interaction featuring two freight wagon types are performed under different operational conditions. Track shift forces and rolling contact fatigue damage are further evaluated from simulation results. It is found that track shift forces tend to follow a normal distribution for moderate levels of lateral track geometry irregularities, and that an approximate linear relationship between standard deviations of lateral irregularities and track shift forces can be established. The relation between lateral track irregularity magnitude and rolling contact fatigue is more complex. Increasing levels of lateral irregularities will decrease the fraction of curve length affected by rolling contact fatigue for sharp curves, whereas for shallow curves it increases. As detailed in the article, this is caused by the lateral movement of the contact point as imposed by the track irregularities. Furthermore, the influence of wheel/rail friction and wear is investigated. [ABSTRACT FROM AUTHOR]

Highly localized stresses generated at the gauge corner of the outer rail cause fatigue cracking. The longitudinal bending stresses in the rail underhead radius position are of special interest, as tension spikes have been identified at this location during in-track measurements under high axle load conditions. The tension spike is a result of vertical and lateral head bending on the web. This effect is highly localized and is additional to the stresses generated due to vertical and lateral bending of the whole rail profile (the so-called global bending). This study examined contact and bending stresses by modelling the rail on a discrete foundation using finite elements and by considering the loading to be a fully slipping elliptical Hertzian contact patch. The analysis revealed that the tensile longitudinal stress was highly dependent on several service conditions: the contact patch offset from the rail centreline, the ratio of lateral (L) to vertical (V) loads, the direction of lateral traction, foundation stiffness and seasonal temperature variations. The tension spike increases, and the depth below the contact surface at which the stresses become tensile reduces, as the contact patch offset and/or the L/V ratio increases. Both these enhance the tendency for rolling contact fatigue cracks to turn downwards and become transverse defects. This is because an increase in tensile bending stresses together with both residual and thermally induced stresses can facilitate cracks to turn perpendicular to the tensile stresses once they reach a critical length. Shear traction towards the gauge corner was found to be the most damaging phenomenon. [ABSTRACT FROM AUTHOR]

In the 1970s, a rolling contact fatigue defect that was christened a squat was identified on the British railway network, primarily at first on the West Coast Main Line. Two productive decades of international research on squats followed, which later contributed to a rapid understanding of gauge corner cracking, which differs in detail but is similar in many important respects to a classic squat. In the last 10–15 years, a rail defect that is superficially similar to the classic squat has appeared on several railways. This has been investigated in some detail, initially in Australia and more recently also in Europe as part of the Innotrack project. These investigations have both assumed that the investigated defect is a classic squat. This paper reviews research on the squat and on its younger cousin. It forms the basis for a companion paper that presents original observations from track and detailed metallurgical examinations of specimens of the more recent squat-type defect. The review in this paper is used in the companion paper to identify features of the two types of defects that are similar and those that are significantly different. [ABSTRACT FROM AUTHOR]

Tests in a full-scale roller rig, a full-scale linear test rig, and a twin-disc machine are numerically evaluated and compared in terms of rolling contact fatigue loading. From previously evaluated contact patch sizes, a Wöhler curve relationship is established and matched towards experimentally established fatigue lives. In addition, non-linear finite-element simulations are carried out. Key data needed for the numerical evaluations, as well as difficulties in translating experimental data to numerical models are highlighted. A key parameter here is the interfacial wheel—rail friction. Additional simulations were carried out to establish the latter. However, the conformal contact in the linear test rig makes such simulations very uncertain. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate geometric and material parameters that affect the interaction of multiple pre-existing (initiated) cracks due to rolling contact fatigue (RCF) loading conditions. In particular, the behaviour of short cracks (head checks) in railway rail is studied. Parameters of interest are initial crack angle and spacing, distribution of initial crack lengths, width of the load/contact zone, and the material properties (in particular, the friction coefficient). Furthermore, the sensitivity of the finite element (FE)-mesh density is investigated. An open question of particular interest is the effect of crack interaction, e.g. shielding, on the prevailing crack spacing. In view of all uncertainties of the material model as well as the three-dimensional geometric complexity of the RCF problem, it is important to obtain a good understanding of the sensitivity of parameter changes. This is achieved in the presented investigation, although it is carried out using simplifying assumptions such as plane strain, linear elasticity, and Hertzian pressure distribution. [ABSTRACT FROM AUTHOR]

Sub-surface-initiated spalling, which is the classical mode of failure in rolling element bearings is significantly influenced by the inhomogeneous and stochastic nature of the material microstructure. This microstructural disorder is one of the primary reasons for scatter in fatigue lives for a seemingly identical batch of bearings. In this study, a stochastic fatigue model that takes the material microstructure explicitly into account is used to investigate dispersion in spalling lives for rolling element bearings. Material microstructures are generated stochastically using the process of Voronoi tessellation. Input parameters to the fatigue model are obtained from torsional fatigue tests. Spalling lives are found to follow a three-parameter Weibull distribution more closely compared with the conventionally used two-parameter Weibull distribution. The stress-life results generated using the model are found to correlate well with the Lundberg- Palmgren theory. Based on parametric studies, a new statistical life equation for bearing life is proposed which is similar in structure to the Lundberg-Palmgren equation with a modification term. Parameters in the life equation are functions of torsional fatigue parameters for the material. [ABSTRACT FROM AUTHOR]

Bainitic steel grades generally have superior rolling contact and thermal fatigue resistances, but poorer wear characteristics when compared with 'conventional' pearlitic steel wheels. To improve the wear characteristics, the manufacturing process of bainitic materials needs to be carefully controlled. In this article, the manufacturing process of the 'MICRALOS' bainitic steel grade has been described. The main focus is on metallurgical testing activities performed in order to compare the new steel grade with standard pearlitic steels and to predict the service behaviour of the solid bainitic wheels. Further, on-going field tests on the iron ore line between Luleå and Narvik have been reported, with details about measurement methods and results. The performance of the wheels is reviewed and compared with the current scientific knowledge of bainitic steel grades and the deterioration of heavy haul wheels. Finally, benefits of and challenges for bainitic wheels in general and for the MICRALOS grade wheels in particular will be discussed. [ABSTRACT FROM AUTHOR]

The steering forces between the rail and wheels of freight vehicles can cause rolling contact fatigue (RCF) of the rail under normal curving conditions. A parametric study has been performed to quantify the effects of various freight vehicle parameters on the generation of RCF. The parameters that vary include primary clearances and stiffnesses, bogie and axle spacing, side bearing clearances, track geometry, unsprung mass, axle load, and wheelset conicity. Three different freight suspensions have been considered: an enhanced three-piece bogie, a rigid-frame bogie with primary suspension, and a two-axle vehicle with leaf springs. Simulations were performed for track curvature ranging from 400 to 10 000 m. The results show that some parameters have a significant effect on RCF, whereas others have no, or only a slight effect. The conclusions are intended to help analysts to focus their future studies on these important freight vehicle parameters. [ABSTRACT FROM AUTHOR]

Recent studies of the rail—wheel interface have shown that wear and rolling contact fatigue (RCF) are competitive phenomena. Wear, by removing the material from the contact surface, tends to limit the propagation of cracks formed by cyclic contact stresses. Several parameters influence these phenomena. This article studies the effects of various working conditions on the surface damage of railway steels. The competition between wear and RCF is particularly strong in dry rolling—sliding contacts, in which the damage severity of our test cases can be adequately predicted using the shakedown map. In wet contacts, RCF is prevalent: cracks rapidly propagate into the subsurface layer in response to hydraulic pressure penetration and then branch towards the surface causing severe damage (macroscopic pitting). The severity of this phenomenon depends strongly on the applied load and cannot be inhibited by wear due to the low friction. On the basis of these results, a general procedure is proposed to the structural integrity of rails. [ABSTRACT FROM AUTHOR]