The ratcheting phenomenon remains a persistent concern in modern railways due to its close association with head checks, a typical type of rolling contact fatigue. This study presents experimental research focussing on elucidating the mechanical, hardening, and material ratcheting properties of one bainitic (B320) and two pearlitic (R220 and R260MN) rail steels. The experiment consisted of monotonic tension, uniaxial cyclic strain range, and uniaxial cyclic stress range tests. Two load cases representing the equivalent stresses experienced by rails under real-life wheel-rail contacts were used in the cyclic stress range tests to assess the rail ratcheting behaviour in railway operating conditions. The test results highlighted that the two pearlitic steels showed similar mechanical strength and ratcheting behaviour; and by contrast, the bainitic steel exhibited superior mechanical strengths and yielded significantly weaker ratcheting responses for both load cases. The study then characterised the three rail steels by calibrating for them the hardening parameters of two classical constitutive models: Chaboche and Ohno-Wang II (OWII) based on the monotonic and cyclic strain range tests. The hardening parameters of the constitutive models were then optimied based on the cyclic stress range tests to represent the material ratcheting behaviours of rail steels for each load case. Notably, the OWII model demonstrated higher precision in reproducing ratcheting strains and rates than the Chaboche model, which faced limitations in simulating relatively low ratcheting rates. This study enhanced the understanding of the mechanical and ratcheting properties of the investigated rail steels and provided insights into the applicability of constitutive models for predicting and mitigating rail ratcheting effects.

Friction behaviour at the wheel–rail interface is of critical importance for railway operations and maintenance and is generally characterised by creep curves. The V-Track test rig was used in this study to measure both the lateral and longitudinal creep curves with uncontaminated dry interface conditions, utilising contact pressures representative of operational railway wheel–rail systems. The novelties of this study are threefold. 1. With proper representations of train/track components, the V-Track tests revealed the effects of structural dynamics on measuring wheel–rail creep curves in real life. 2. Pure lateral and longitudinal creepage conditions were produced with two distinct experimental principles—displacement- and force-controlled—on the V-Track, i.e., by carefully controlling the angle of attack and the traction/braking torque, respectively, and thus the coefficient of friction from lateral and longitudinal creep curves measured on the same platform could be cross-checked. 3. The uncertainties in the measured creep curves were analysed, which was rarely addressed in previous studies on creep curve measurements. In addition, the measured creep curves were compared against the theoretical creep curves obtained from Kalker’s CONTACT. The influence of wheel rolling speed and torque direction on the creep curve characteristics was then investigated. The measurement results and findings demonstrate the reliability of the V-Track to measure wheel–rail creep curves and study the wheel–rail frictional rolling contact.

Frictional heat is generated at the wheel-rail interface during train operations, particularly under high slip ratios during acceleration and braking. Thermal effects can accelerate wear, induce plastic deformation, and contribute to thermal fatigue. Reliable modelling of wheel-rail contact that considers friction-induced thermal effects is desirable for the accurate prediction of wheel-rail interface deterioration. Several analytical and numerical models have been proposed to simulate thermal or thermomechanical wheel-rail loads but have rarely been validated, especially in high slip ratio scenarios where flash temperatures exceed 200 °C. This study develops and experimentally validates a three-dimensional thermomechanical finite element (FE) wheel-rail contact model for high slip ratio conditions, with contact temperatures reaching 360 °C. The model incorporates key mechanical parameters, including wheel loads, coefficients of friction, and slip ratios. Simulated rail surface temperatures across various slip ratios (5 %, 10 %, and 15 %) are compared with the flash temperatures measured with an onboard infrared thermal camera, showing good agreement with a maximum deviation of 9.9 %. This confirms the reliability of the model for simulating wheel-rail contact under thermal effects.

Various models for simulating rail ratcheting behaviour were developed to study rolling contact fatigue (RCF) damage in rails. However, limitations remain in terms of the accuracy of wheel–rail contact modelling and computational efficiency of the cyclic loading simulation. This study developed an efficient 3D finite element (FE) procedure to simulate ratcheting in rails subjected to numerous load cycles. The procedure simulates a wheel rolling repeatedly over a rail section with updated stress–strain states, enabling automatically executed cyclic loading simulation given a predefined number of cycles. To ensure the accuracy of the contact modelling, the effect of meshing schemes on subsurface stress distribution was examined. In addition, the FE contact model with the selected meshing scheme, which balances accuracy and computational efficiency, was verified against the widely accepted CONTACT program. Subsequently, a non-linear kinematic hardening (NLKH) steel material was used in the FE model for ratcheting simulations with up to 100 wheel-loading cycles. The rail surface and subsurface stress states were replicated under partial-slip wheel–rail rolling contact conditions with traction coefficients of 0.10, 0.20 and 0.35, respectively. The ratcheting behaviour was extensively analysed in terms of plastic deformation, contact patch evolution, and ratcheting rates. The simulated plastic deformation was found to alter the contact geometry and thus contact stresses, which in turn affect further accumulation of plastic deformation and subsequent ratcheting strains. These findings highlighted the importance of considering the interplay between the rail ratcheting behaviour of the rail and evolving contact conditions for predicting ratcheting and RCF damage in rails.

A review of prediction methods for wheel-rail rolling contact was first prcsented. It is found that thc 3-D transient rolling contact model dcveloped using the explicit finite elemcnt method seems to be the most suitable approach for analyses of transient wheel-rail rolling-sliding-jumping contact at 400 km/h, or at higher speeds, and in the presence of short/medium-wave irregularities. Therefore, a transient rolling contact model was developed to simulate the dynamic curving of a wheelset on a typical curved track in the time domain. Harmonie or ideal rail corrugation was taken as the typical short/medium-wave irregularity to study its influences on transient rolling-sliding-jumping contact, with a wave-length ränge of 30-210 mm considered on the basis of field observations of high-speed wheels and rails in Operation. Be-sides corrugation geometry, corrugation oecurring on the high and/or the low rails was also taken into aecount properly, with the speed up to 500 km/h. Considering dynamic unloading caused by dynamics of low and medium frequency, the critical sizes of short/medium-wave irregularities were determined, at which the wheel-rail contact loss just oecurred. Fi-nally, proposals for management of wheel-rail short/medium-wave irregularities were discussed from the aspects of impor-tance, rationality and application limitations, and compared with the corrugation limit recommended for rail grinding Operations in Management Measures of High-speed Railway Rail Grinding.

Polygonal wear is a type of damage commonly observed on the railway wheel tread. It induces wheel-rail impacts and consequent train/track components failure. This study presents a finite element (FE) thermomechanical wheel-rail contact model, which is able to cope with the three possible generation and development mechanisms of polygonal wear: initial defects, thermal effect, and structural dynamics. The polygonal wear-induced impact contact and further development of wear are simulated. The simulated elastic contact solutions are verified against the program CONTACT. Different material properties (elastic, elasto-plastic and elasto-plastic-thermo, i.e. with thermal softening) and initial polygonal profiles are then applied to the FE model to investigate the influence of wheel/rail material and wear amplitude on wheel-rail contact stress and wear development. The simulations indicate that the wheel-rail impact-induced temperature may reach up to 362 ℃ at the contact interface, and the high temperature at the contact area influences wheel-rail contact stress and wear depth.

A time-domain finite element model is developed to study the transient rolling contact of a driving wheelset over a curved track with Low Adhesion Zones (LAZs) shorter than 1.0 m. LAZs on one rail, i.e., unilateral LAZs occurring more likely, is treated for a speed up to 500 km/h. Structural vibrations of wheelset are analyzed to explain the transient contact forces, creepages and the resulting irregular wear. LAZs on high rails are found more detrimental than those on low rails. The results explain the occurrence of flats and rolling contact fatigue in bad weather, although significant wheel idling is absent.

A better understanding of wheel-rail dynamic interaction is necessary for the capacity increase of railway transportation. This chapter briefly introduces the consequences, modeling and detection methods of wheel-rail dynamic interaction, and maintenance of the weak track spots where wheel-rail dynamic interaction often occurs. Wheel-rail dynamic interaction causes high-amplitude vibration and noise and accelerate structural degradation. Owing to the capabilities of handling nonlinear material properties and arbitrary contact geometries and considering dynamic effects, the explicit finite element approach is proposed to model wheel-rail dynamic interaction. Three numerical examples are presented to simulate wheel-rail impacts, frictional instability, and flange contact, respectively; and Rayleigh waves are observed in the simulation results. Wheel-rail dynamic interaction-related problems can be detected with the measurements of wheel-rail contact force, axle box acceleration, and track vibration. The weak track spots can be maintained by stiffness, geometric controls, and friction management.

By modifying friction to the desired level, the application of friction modifiers (FMs) has been considered as a promising emerging tool in the railway engineering for increasing braking/traction force in poor adhesion conditions and mitigating wheel/rail interface deterioration, energy consumption, vibration and noise. Understanding the effectiveness of FMs in wheel–rail dynamic interactions is crucial to their proper applications in practice, which has, however, not been well explained. This study experimentally investigates the effects of two types of top-of-rail FM, i.e. FM-A and FM-B, and their application dosages on wheel–rail dynamic interactions with a range of angles of attack (AoAs) using an innovative well-controlled V-track test rig. The tested FMs have been used to provide intermediate friction for wear and noise reduction. The effectiveness of the FMs is assessed in terms of the wheel–rail adhesion characteristics and friction rolling induced axle box acceleration (ABA). This study provides the following new insights into the study of FM: the applications of the tested FMs can both reduce the wheel–rail adhesion level and change the negative friction characteristic to positive; stick–slip can be generated in the V-Track and eliminated by FM-A but intensified by FM-B, depending on the dosage of the FMs applied; the negative friction characteristic is not a must for stick–slip; the increase in ABA with AoA is insignificant until stick–slip occurs and the ABA can thus be influenced by the applications of FM.

Polygonal wear is a common type of damage on the railway wheel tread, which could induce wheel-rail impacts and further components failure. This study presents a finite element (FE) thermomechanical model to investigate the causes of wheel polygonal wear. The FE model is able to cope with three possible causes of polygonal wear: thermal effect, initial defects, and structural dynamics. To analyse the influences of the three causes on wheel-rail contact stress and wear depth, different material properties (i.e., elastic, elasto-plastic, thermo-elasto-plastic with thermal softening), and wheel profiles (i.e., round and polygonal) were used in the FE model. The simulation indicates that a high temperature up to 264.20 ℃ could be induced by full-slip wheel-rail rolling contact when the polygonal profile is used. The thermal effect, similar to that induced by tread brake, may then have a significant influence on wheel-rail contact stress and wear depth. In addition, the involvement of initial defects, i.e., polygonal profile, causes wheel-rail impact contact and remarkably increases the contact stress and wear. By reliably considering all the three possible causes, the proposed FE model is believed promising for further explaining the generation mechanisms of wheel polygonal wear.

Rolling contact fatigue (RCF) has been a persistent type of damage in rails. To guarantee the safety of railway operation and reduce the maintenance cost, various tests have been conducted to study the RCF damage. In this research, a state-of-the-art downscaled V-Track test rig at TU Delft was used to investigate the initiation of the head check (HC), a typical type of RCF damage. The V-Track test was designed to simulate the wheel-rail contact conditions with the stress state and spin creepage as similar as that in the field. The test rig ran up to 60, 000 load cycles, after which significant surface damage in the form of surface irregularity and cracks was observed in two different zones on the rails. The test results demonstrated that the V-Track is capable of maintaining steady-state loading conditions after a high number of load cycles. Using the same loading condition, a contact stress analysis was subsequently performed to identify the surface stress distribution and predict the pattern of plastic flow inside the contact patch. The plastic flow prediction was then confirmed by a microscopic analysis of the samples cut from the V-Track rails. Furthermore, the microscopic analysis indicated an opposite orientation of the plastic flow in the zone outside contact patch, which will be investigated in further studies.

The modeling of dynamic frictional rolling contact is crucial for accurately predicting behavior and deterioration of structures under dynamic interactions such as wheel/rail, tire/road, bearings and gears. However, reliable modeling of dynamic frictional rolling contact is challenging, because it requires a careful treatment of friction and a proper consideration of the dynamic effects of the structures on the contact. This study takes the wheel-rail dynamic interaction as an example to systematically explore the core algorithms for the modeling of dynamic frictional rolling contact by way of explicit finite element analyses. The study also theoretically demonstrates that the explicit finite element method handles nonlinearities in friction, material properties, arbitrary contact geometries and boundary conditions, and fully couples the calculation of frictional rolling contact with the calculation of high-frequency structural dynamics. An indirect validation method for dynamic contact solutions is proposed. To promote the broad use of the method, this paper proposes a detailed procedure for establishing robust wheel-rail dynamic interact tion models and obtaining dynamic contact responses. The proposed procedure can also be applied to the modeling of dynamic interactions occurring to tire-road, bearings and gears.