Wheel Passages Research Articles

Study on the effects of material hardening on the development of high-speed rail corrugation

To investigate the effect of material hardening on corrugation development, a theoretical model for corrugation development is proposed, which incorporates the consideration of material properties’ variation. Experiments were conducted to reproduce the corrugation phenomenon, and the mechanical properties of the hardened layer in corrugated rail were obtained utilizing Nano-indentation experiment. The corrugation depth gradually increased and eventually stabilized with the increase of rolling cycles, and the corrugation troughs exhibit greater material hardening compared to the peaks. The numerical algorithm for the corrugation development model was developed and the processes of corrugation development under conditions with and without material hardening were simulated. The growth of corrugation calculated using the model without material hardening exhibits a continual exponential increase with the number of wheel passages, which does not agree with what was observed in experiments and in the field. However, when considering material hardening, the development process of corrugation could be accurately reproduced.

An integrated 3D dynamic FE vehicle-track model in elasto-plasticity to investigate short pitch corrugation under cyclic wheel loads

The mechanism of rail short pitch corrugation has remained elusive in the past. The damage mechanisms of the corrugation are reported to be differential wear or plastic deformation. The former has been extensively studied, while the plastic deformation, especially under multiple wheel passages has been seldom studied. To uncover the facts behind it, an integrated dynamic vehicle-track model with the rail material treated in elasto-plasticity is developed. Further, a novel method which can simulate the material deformation under cyclical axle loads is proposed. This method is used to study the rail material response at corrugation. Our research found that for the cases studied, the rail material undergoes cyclic plastic deformation at corrugation peaks only for a limited number of cycles (2–4 cycles) before reaching the elastic shakedown limit. After that, no further residual stresses and strains accumulate. The plastic deformation at corrugation peaks weakens the corrugation amplitude, serving as an early corrugation attenuation mechanism. Conversely, work-hardening at corrugation peaks increases wear resistance at those peaks, promoting corrugation in the long term. The explanation of the corrugation development process under the interplays of the plastic deformation and wear has been validated by field corrugation data. Additionally, we propose a wear coefficient in the wear model to account for the work-hardening and change in the wear resistance. Experimental results of the hardness distribution show the similar characteristics to the numerical results.

Evolution of thermally induced white etching layer at rail surface during multiple wheel/train passages

A thermo-mechanical-phase transformation FEM was developed to quantitatively predict the formation process of thermally-induced white etching layer (WEL) at rail surface. A practical scenario of multiple wheel passages with two locomotives was introduced for a single train, and the evolution of martensitic WEL and the residual stress during ten train passages was reported. The results indicate that an effective heating period during wheel passage is a critical factor to influence WEL formation. For the given model parameters, the maximum volume fraction of martensite increases from 1.8% to 19.78% during the passage of ten trains. The residual stress distribution on the rail top is changed after WEL formation.

Vibration source properties of cargo trains: free field vibration and trackside measurement analysis

Annoyance caused by railway operations has gained increasing attention in the Netherlands. This has led to a multimillion research project into different aspects of train passages as a source of vibration. The project is initiated by the Dutch railway operator ProRail. In advance of this project a study has been performed on vibration signals at free field caused by cargo train passages at four different sites. The signals have been compared to trackside measurements. The trackside measurements consist of fibre optic measurements of the rail deflection at pre-installed locations different from the free field vibration measurement sites. Different vibration level indicators have been studied like train speed, axle loads and wheel roughness indicators and their correlation with vibration levels. Vibration levels are defined in several ways, a frequency weighted running mean square value (so-called Veffmax), a 2-second RMS level (unweighted) and levels per frequency band. Special attention is given to the variation in time of the measured vibration signals during the train passage to see whether 'bad quality' wheel passages can be identified. The results give valuable input for a future case study in which wheel quality and its influence on vibration levels will be studied further.

Influence of white etching layer on rolling contact behavior at wheel-rail interface

The existence of narrow and brittle white etching layers (WELs) on the rail surface is often linked with the formation of rail defects such as squats and studs, which play the key roles in rail surface degradation and tribological performance. In the present study, a systematic investigation on stress/strain distribution and fatigue life of the WEL during wheel-rail rolling contact was conducted based on a numerical model considering the realistic wheel geometry. This is the first study considering the influence of rail materials, loading pressure, frictional condition, WEL geometry (a/b), and slip ratio (Sr) in the practical service conditions at the same time. The results revealed much higher residual stress in WEL than in rail matrix. Stress changes along the rail depth matched with the previously reported microstructure evolutions. The current work revealed that the maximum difference in contact stress between the wheel passages of rail matrix and the WEL region (noted as stress variation) rises with the increase of loading pressure, the value of a/b, and Sr; but drops with the friction coefficient (μ). In addition, a critical length-depth ratio of 5 for a/b has been found. The fatigue parameter, FP, of the WEL decreased quickly with the length-depth ratio when it was less than 5 and then increased slightly when it was larger than 5. This study also revealed that the fatigue life of the WEL was reduced for high strength head hardened (HH) rail compared with standard carbon (SC) rail.

Thermo-mechanical coupled finite element analysis of rolling contact fatigue and wear properties of a rail steel under different slip ratios

Abstract A multi-step FE modeling strategy has been proposed to predict the temperature evolution, thermo-mechanical response, surface fatigue life and wear behaviors in railway rail for multi wheel passages. Equivalent contact pressure and heat source were coupled and moved simultaneously on rail surface to achieve a balanced advantage of low computational cost and high accuracy. Wheel configuration at locomotive plays a significant role on rail temperature. The highest temperature of 776.05 °C was developed with a slip ratio of 9.43% after 9 wheel passages. Rolling contact fatigue life of rail material decreased quickly with slip ratio due to significant thermal softening effect. Transition from mild to severe wear was found at slip ratio of 2.38% according to the corresponding rail flash temperatures.

Rolling contact fatigue assessment of repair rail welds

A repair welding procedure is numerically simulated. To validate the numerical model, analyses of the temperature evolution in a repaired rail are compared to existing full-scale test results. Thermomechanical simulations are carried out to evaluate the residual stress formation during welding and how the residual stress field is influenced by subsequent wheel passages during operations. The risk of rolling contact fatigue (RCF) is analysed and results discussed. It is found that tensile stress magnitudes resulting from welding decrease substantially during rolling contact loading. The influence of the residual stresses on RCF is found to be minor on the surface and somewhat more severe in a layer at the bottom of the repair weld. In addition to residual stresses, there is also a risk that welding introduces material defects and alters material properties. The influence of these factors on the risk of RCF is discussed.

Experimental Analysis of Rail Contact Fatigue Damage on Frog Rail of Fixed Common Crossing 1:12

Assembled fixed common crossings of the steel grade R350HT with high switch angles are subjected to quick rail contact fatigue (RCF) deterioration. The crossings are a significant cost driver in railway maintenance and have an important influence on reliability and availability in railway transportation. The present paper is devoted to the experimental study of the deterioration causes that is based on inertial and geometrical measurements on one crossing during its full lifecycle. The causes are classified into primary technical ones and secondary ones, which depend on the operational work and maintenance of track and rolling stock. The primary causes are studied using analyses of the impact position and inertial measurements on the frog nose during the crossing lifecycle, the end of which is marked by RCF defects. An application of the machine learning technique t-distributed stochastic neighbor embedding (t-SNE) allowed to determine a small cluster of high-impact loadings that correspond to the future damage zone location. The appearance of the high-impact loadings group on a certain location is explained by the secondary causes: rail and wheel wear and wheel lateral position. A multivariate kinematic modeling of wheel passages from wing to frog rail provided the wheel trajectories, impact position, and trajectory kink angle in the impact point. The distribution of the calculated impact angles along the frog rail demonstrated the presence of a small cluster of high-impact angles outside of the zone subjected to the highest number of impacts. The results of the geometrical measurements correspond to those obtained by the acceleration measurements.

Numerical investigation of crack initiation in rails and wheels affected by martensite spots

White etching layers (WELs) in the form of thermally induced martensite spots are often associated to so-called stud defects on rail surfaces and so-called rolling contact fatigue clusters on wheel treads. These defects might promote further material deterioration of rails and wheels and it is thus of importance to deepen the knowledge regarding their initiation mechanisms. The aim of this study is to gain insight into the problem by making qualitative assessments of different operational scenarios, involving various axle loads and amount of friction. To this end, this paper considers crack initiation, quantified through the Jiang–Sehitoglu low cycle fatigue criterion, in the vicinity of pre-existing WELs (in the form of martensite spots) subjected to varying contact load conditions. Three-dimensional finite element analyses are conducted to model phase transformations as well as the resulting residual stresses. It is seen that the contact pressure magnitude and WEL thickness affect the results only moderately, while the traction coefficient has a significant detrimental influence. It is furthermore seen that occasional wheel passages that are off-set in the lateral direction with respect to the WEL spot’s centre might be responsible for crack initiation on the gauge corner side of the rail surface.

Railway track geometry degradation due to differential settlement of ballast/subgrade – Numerical prediction by an iterative procedure

An iterative procedure for numerical prediction of long-term degradation of railway track geometry (longitudinal level) due to accumulated differential settlement of ballast/subgrade is presented. The procedure is based on a time-domain model of dynamic vehicle–track interaction to calculate the contact loads between sleepers and ballast in the short-term, which are then used in an empirical model to determine the settlement of ballast/subgrade below each sleeper in the long-term. The number of load cycles (wheel passages) accounted for in each iteration step is determined by an adaptive step length given by a maximum settlement increment. To reduce the computational effort for the simulations of dynamic vehicle–track interaction, complex-valued modal synthesis with a truncated modal set is applied for the linear subset of the discretely supported track model with non-proportional spatial distribution of viscous damping. Gravity loads and state-dependent vehicle, track and wheel–rail contact conditions are accounted for as external loads on the modal model, including situations involving loss of (and recovered) wheel–rail contact, impact between hanging sleeper and ballast, and/or a prescribed variation of non-linear track support stiffness properties along the track model. The procedure is demonstrated by calculating the degradation of longitudinal level over time as initiated by a prescribed initial local rail irregularity (dipped welded rail joint).

An efficient approach to the analysis of rail surface irregularities accounting for dynamic train–track interaction and inelastic deformations

A two-dimensional computational model for assessment of rolling contact fatigue induced by discrete rail surface irregularities, especially in the context of so-called squats, is presented. Dynamic excitation in a wide frequency range is considered in computationally efficient time-domain simulations of high-frequency dynamic vehicle–track interaction accounting for transient non-Hertzian wheel–rail contact. Results from dynamic simulations are mapped onto a finite element model to resolve the cyclic, elastoplastic stress response in the rail. Ratcheting under multiple wheel passages is quantified. In addition, low cycle fatigue impact is quantified using the Jiang–Sehitoglu fatigue parameter. The functionality of the model is demonstrated by numerical examples.

Terrain physical properties derived from orbital data and the first 360 sols of Mars Science Laboratory Curiosity rover observations in Gale Crater

AbstractPhysical properties of terrains encountered by the Curiosity rover during the first 360 sols of operations have been inferred from analysis of the scour zones produced by Sky Crane Landing System engine plumes, wheel touch down dynamics, pits produced by Chemical Camera (ChemCam) laser shots, rover wheel traverses over rocks, the extent of sinkage into soils, and the magnitude and sign of rover‐based slippage during drives. Results have been integrated with morphologic, mineralogic, and thermophysical properties derived from orbital data, and Curiosity‐based measurements, to understand the nature and origin of physical properties of traversed terrains. The hummocky plains (HP) landing site and traverse locations consist of moderately to well‐consolidated bedrock of alluvial origin variably covered by slightly cohesive, hard‐packed basaltic sand and dust, with both embedded and surface‐strewn rock clasts. Rock clasts have been added through local bedrock weathering and impact ejecta emplacement and form a pavement‐like surface in which only small clasts (<5 to 10 cm wide) have been pressed into the soil during wheel passages. The bedded fractured (BF) unit, site of Curiosity's first drilling activity, exposes several alluvial‐lacustrine bedrock units with little to no soil cover and varying degrees of lithification. Small wheel sinkage values (<1 cm) for both HP and BF surfaces demonstrate that compaction resistance countering driven‐wheel thrust has been minimal and that rover slippage while traversing across horizontal surfaces or going uphill, and skid going downhill, have been dominated by terrain tilts and wheel‐surface material shear modulus values.

Rail squats: progress in understanding the Australian experience

Rail squats or studs, being a sub-surface crack in a track below a depression of the rail surface, have been studied in the Australian CRC for Rail Innovation project R3.105, from a number of perspectives. Examination of squats on track by the Rail Corporation of NSW has revealed statistics about their distribution. Examination with optical and scanning electron microscopy at the University of Queensland has shown the frequent presence of a brittle white etching layer (WEL) on the rail surface. This has led to successful adaptation of eddy currents to detect WEL rather than cracks. Tests at the University of Queensland have investigated whether the WEL can form below the normal 720℃ needed to form austenite. Examination of crack surfaces shows beach marks indicative of growth in modes II and III. Neutron diffraction testing of Australian rail has shown residual stresses in a railhead with a WEL, similar to those reported elsewhere, but with a broad surface layer in compression, not a narrow running band. Elasto-plastic finite element simulation has shown residual compression transforms into residual shear at a crack tip, which increases that due to plastic deformation from successive wheel passages, tending to encourage the crack to continue in a direction of sub-surface growth. The rate of growth of squats measured on-track in Sydney shows crack growth that corresponds to a power law with a low exponent, implying that the stress intensity at the crack tip is not a strong function of crack length. This is partly due to the localised nature of contact stresses, which allows the crack to grow beyond the region loaded. However, accounting for this effect leads to the prediction of a smaller reduction in growth rate than that observed. It is likely the low exponent reflects a smaller effect of water on crack growth, as the crack enlarges. There is also a redistribution of contact loading that occurs as a crack grows.

Field investigations into the adhesion recovery in leaf-contaminated wheel–rail contacts with locomotive sanders

Locomotives of railways worldwide have been using sand since 1838 to improve the wheel–rail adhesion during traction and braking operations. In more recent years, sanders have also been fitted to electrical and diesel multiple units in some railways to fight (often in combination with traction control or wheel slide protection systems) the low-adhesion conditions, especially encountered in autumn due to leaf contamination. In spite of the worldwide broad use of sand, different standards on sanding practice appear to be used by different railways, while there is a lack of fundamental understanding on the influence of sanding parameters, such as particle size distribution, feed rate, and number of sanding axles (among others), on the adhesion recovery, wear, and train detection. In order to gain a better understanding of these interrelationships, the authors have carried out laboratory investigations in recent years. As a continuation of that work, the influence of the sand particle size on the adhesion recovery in leaf-contaminated contacts is investigated in this article by means of traction tests of an electrical locomotive in a stabling yard. Three differently sized silica sands are used in the testing. In addition to the particle size investigations, the standard sand currently used in the Dutch railways is also tested to quantify its effectiveness against leaf contamination. Besides the immediate adhesion improvement upon sanding, the remaining friction level left for subsequent tractive wheel passages is also investigated for all sands tested. Furthermore, baseline tests (i.e. without application of sand) are also performed to obtain some quantitative insight into the impact of leaf contamination on the wheel–rail adhesion in the field.

Field investigations into the performance of magnetic track brakes of an electrical multiple unit against slippery tracks. Part 1: Adhesion improvement

Some rolling stock designed for conventional and high-speed railway operation has magnetic track brakes (MTBs) to have an additional brake independent of the wheel–rail adhesion to be mostly activated in emergency situations. In recent years, interest has grown in some railways towards the possible use of MTB against slippery tracks. However, there seems to be a lack of knowledge on the major benefits and possible side effects of using MTB to overcome low-adhesion conditions. This hinders the realization of a cost-benefit analysis to look at possible implementation. In order to contribute to a better understanding, field tests have been performed with the permanent MTB of an electrical multiple unit in a stabling yard. Low-adhesion conditions have been created by three types of contamination representative of slippery tracks, i.e. leaves, water, and grease. The entire work has been divided in two parts. In this Part I, emphasis is put on the adhesion recovery, in particular the benefit for subsequent wheel (or train) passages. Baseline tests (i.e. no use of MTB) have also been performed with water and leaves. Additionally, an adhesion improver widely used in the Dutch and British railways has also been tested with leaves to allow for a comparison in effectiveness with MTB under similar operating conditions. In each test, the wheel–rail adhesion conditions along the initially contaminated track have been measured to evaluate the adhesion improvement under the different testing conditions.

Effects of Machine-Induced Soil Compaction on Growth and Yield of Sugarcane

Problem statement: Sugarcane is one of the main economic crops in Thailand. After planting, it can be harvested annually for several successive ratoon crops. Recently, soil compaction due to mechanization has been recognized as a serious problem in sugarcane production. Therefore, this study aimed to clarify the effects of soil compaction on the growth and yield of sugarcane. Approach: The field experiments were conducted in loamy soil using a Randomized Complete Block Design (RCBD) with four treatments of soil compaction prepared by 0, 5, 15 and 20 numbers of wheel passages of a tractor. Results: The results showed that soil compaction had significant effects on both the growth and yield of sugarcane, with the exceptions of tillering and Brix. The greatest reduction in yield compared with the control field was 22.9%, which resulted from compacting with 15 tractor passages. The influence of block or furrow irrigation was indicated by the positive effect that higher watering had on minimizing the impact of soil compaction on the growth of sugarcane. Conclusion: Effects of soil compaction on growth and yield of sugarcane were clarified to some extent.

Modelling the effect of rail dampers on wheel–rail interaction forces and rail roughness growth rates

Trains generate rolling noise because of the roughness of the wheel and rail running surfaces. Special acoustic grinding programmes have been introduced on some railways specifically to control rolling noise. Rail dampers are also used to reduce rolling noise; this paper studies rail damping as a possible mechanism to slow the rate of development of roughness on the surface of rails. This would reduce noise further over time or reduce the required frequency of grinding. High roughness growth on the rail occurs in situations with stiff vertical structural dynamics of the track. In particular the antiresonance above a sleeper at the pinned–pinned frequency has been identified as a wavelength fixing mechanism for short pitch corrugation. Rail dampers change the dynamic response of the rail, shifting the pinned–pinned frequency and smoothing the track receptance. Here, a simple time-stepping model is applied to calculate the interaction forces between wheel and rail for a track with and without rail dampers. The calculations show that rail dampers reduce dynamic interaction forces and shift the force spectrum to longer wavelengths. The interaction forces are used as input to an abrasive wear model to predict the roughness growth rate and the change in roughness after many wheel passages. Track without rail dampers is predicted to develop corrugation at the wavelength corresponding to the pinned–pinned frequency. With rail dampers the corrugation growth is reduced and shifted to a longer wavelength where its significance is diminished.

Effects of wheel passing frequency on wear-type corrugations

The growth behaviour of the vibrational wear phenomenon known as corrugation is investigated using predictive models. A feedback model for wear-type rail corrugation that includes a wheel pass time delay (inverse of wheel passing frequency) is investigated with an aim to determine what effects the value of frequency of successive wheel passages has on the growth of the amplitude of corrugations. A simplified feedback model [P.A. Meehan, W.J.T. Daniel, T. Campey, Wear-type rail corrugation prediction and prevention, in: Proceedings of the Sixth International Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2003) Gothenburg, Sweden, June 10–13, 2003, pp. 445–454] that encapsulates the most critical interactions occurring between the wheel–track structural dynamics, rolling contact mechanics and rail wear is investigated further to determine the growth of wear-type rail corrugations over multiple wheelset passages as a function of the passage time delay magnitude. Based on these results, numerical and analytical investigations are performed to identify conditions under which the wheel pass frequency has a significant effect on the growth of corrugations. A useful analytical prediction of maximum reduction in corrugation growth via speed or wheel base variation is developed, providing new insight into the prediction and possible control of wear-type corrugations.

Deformation and damage of a crossing nose due to wheel passages

The cyclic deformation of a crossing nose in a railway turnout due to repeated wheel passages is investigated by numerical simulations with the finite element code ABAQUS. An explicit finite element method is used to determine the dynamic response of the wheel–rail system. More detailed studies on stresses and strains in the crossing nose are performed on a quasi-static model calculated by the implicit finite element method. For both models nonlinear kinematic hardening is defined for the material behaviour in the finite element simulation. To predict the early evolution of damage, a damage indicator concept for ductile materials is integrated in the numerical calculations. A cast manganese crossing is compared to a crossing consisting of a steel composite. From the results obtained, an explanation for the good performance of manganese crossings observed in operated tracks is found. The study provides a method for the further research on fatigue and wear of crossings aiming at an improvement of crossings.

Rolling contact fatigue analysis of rails inculding numerical simulations of the rail manufacturing process and repeated wheel-rail contact loads

The present work is an investigation on how an initially introduced residual stress-state affects the service life of a rail, i.e. the time to fatigue crack initiation. The finite element (FE) method was used to make two-dimensional thermo-mechanical analyses of the rail cooling and roller straightening processes. The results became the initial conditions in a three-dimensional elastic-plastic rail model; the model is part of an FE tool developed for rolling contact fatigue (RCF) analysis of rails. The results from this tool were analysed for fatigue, for eight wheel passages, according to a method which incorporates a critical plane approach that evaluates fatigue damage on a cycle-by-cycle basis. A heavy-haul (30 tonne) train traffic situation on the Iron-ore Line in Sweden was studied with respect to subsurface fatigue crack initiation in straight track. Three examples using the rail model in the FE tool were assessed: (a) an initially stress-free rail, (b) a measured residual stress field in a newly manufactured rail, and (c) a calculated residual stress field from the cooling and roller straightening analyses. The results from the thermo-mechanical FE analyses of the rail manufacturing process showed tensile residual stresses in the longitudinal direction of the rail; this was validated with experimental measurements on newly manufactured rails. The FE tool and fatigue calculations revealed only small differences in results for the three examples. It was concluded that, because of the very high axle load in the present traffic situation, the local wheel-rail contact loads governed the fatigue life to crack initiation. Additional FE tool calculations were made to show the axle load at which rail manufacturing stresses reduce the fatigue life to crack initiation.