Influence of railway wheel tread damage and track properties on wheelset durability – Field tests and numerical simulations

Wheel tread damage leading to high magnitudes of vertical wheel–rail contact forces is a major cause of train delays in the Swedish railway network, particularly during the coldest months of the year. According to regulations, vehicles generating wheel–rail impact loads exceeding the limit values must be taken out of service for wheel maintenance. This may lead to severe traffic disruptions and associated high costs. On the other hand, increased wheel‒rail impact loads cause elevated stress levels in wheels, axles and bearings and may shorten the life of track components, resulting in higher costs for vehicle and track maintenance. Thus, alarm limits should provide a balance between preventing operational failures and minimising the number of stopped trains. The aim of this thesis is to enhance the understanding of the consequences of wheel tread damage and to identify better means of addressing them. To achieve this aim, the ability of numerical simulations to investigate different operational scenarios is crucial. A versatile and cost-efficient method to simulate the vertical dynamic interaction between a wheelset and a railway track, accounting for generic distributions and shapes of wheel tread damage, has therefore been extended and improved. The dynamic coupling between the two contact points (one on each wheel) via the wheelset axle and via the rails and sleepers is accounted for. Post-processing steps to evaluate fatigue impact at critical positions in the wheelset have been developed. The applied simulation models have been calibrated and verified by extensive field tests. Measurement campaigns with two different Swedish passenger trains have been carried out. In the first field test, impact loads generated by a wheelset with severe tread damage were measured. Measurements and simulations have been used to illustrate how wheel–rail loads and fatigue impact depend on the three-dimensional shape of the tread damage. The effects of speed and travelling direction of the vehicle, position in the sleeper bay where the defect strikes the rail, lateral position of the wheelset, and track stiffness on wheel–rail contact forces and wheelset durability have been investigated.In the second long-term field test, axle stresses have been monitored using an instrumented wheelset on a passenger train in revenue traffic. By post-processing of test results, statistical models of stress spectra for different stretches of the Swedish rail network were obtained. Moreover, the parameters describing such models have been related to track characteristics in terms of the presence of curves, switches & crossings and irregularities in track geometry. This allowed to develop numerical routines to evaluate wheelset durability depending on operational parameters. These studies are used to initiate a discussion on improved wheelset maintenance procedures

A comprehensive model of the railway wheelset-track interaction in curves

Train-track interaction has been extensively studied in the last 40 years at least, leading to modelling approaches that can deal satisfactorily with many dynamic problems arising at the wheel/rail interface. However, the available models are usually not considering specifically the running dynamics of the vehicle in a curve, whereas a number of train-track interaction phenomena are specific to curve negotiation. The aim of this paper is to define a model for a flexible wheelset running on a flexible curved track. The main novelty of this work is to combine a trajectory coordinate set with Eulerian modal coordinates; the former permits to consider curved tracks, and the latter models the small relative displacements between the trajectory frame and the solid. In order to reduce the computational complexity of the problem, one single flexible wheelset is considered instead of one complete bogie, and suitable forces are prescribed at the primary suspension seats so that the mean values of the creepages and contact forces are consistent with the low frequency curving dynamics of the complete vehicle. The wheelset model is coupled to a cyclic track model having constant curvature by means of a wheel/rail contact model which accounts for the actual geometry of the contacting profiles and for the non-linear relationship between creepages and creep forces. The proposed model can be used to analyse a variety of dynamic problems for railway vehicles, including rail corrugation and wheel polygonalisation, squeal noise, numerical estimation of the wheelset service loads. In this paper, simulation results are presented for some selected running conditions to exemplify the application of the model to the study of realistic train-track interaction cases and to point out the importance of curve negotiation effects specifically addressed in the work.The authors acknowledge the financial contribution of the Spanish Ministry of Economy and Competitiveness through the project TRA2013-45596-C2-1-R.Martínez Casas, J.; Di Gialleonardo, E.; Bruni, S.; Baeza González, LM. (2014). A comprehensive model of the railway wheelset-track interaction in curves. Journal of Sound and Vibration. 333(18):4152-4169. https://doi.org/10.1016/j.jsv.2014.03.032S415241693331

Railway-induced ground vibrations – a review of vehicle effects

This paper is a review of the effect of vehicle characteristics on ground- and track borne-vibrations from railways. It combines traditional theory with modern thinking and uses a range of numerical analysis and experimental results to provide a broad analysis of the subject area. First, the effect of different train types on vibration propagation is investigated. Then, despite not being the focus of this work, numerical approaches to vibration propagation modelling within the track and soil are briefly touched upon. Next an in-depth discussion is presented related to the evolution of numerical models, with analysis of the suitability of various modelling approaches for analysing vehicle effects. The differences between quasi-static and dynamic characteristics are also discussed with insights into defects such as wheel/rail irregularities. Additionally, as an appendix, a modest database of train types are presented along with detailed information related to their physical attributes. It is hoped that this information may provide assistance to future researchers attempting to simulate railway vehicle vibrations. It is concluded that train type and the contact conditions at the wheel/rail interface can be influential in the generation of vibration. Therefore, where possible, when using numerical approach, the vehicle should be modelled in detail. Additionally, it was found that there are a wide variety of modelling approaches capable of simulating train types effects. If non-linear behaviour needs to be included in the model, then time domain simulations are preferable, however if the system can be assumed linear then frequency domain simulations are suitable due to their reduced computational demand

Performance of ballasted track under impact loading and applications of recycled rubber inclusion

© 2018 Chinese Academy of Sciences. All rights reserved. In this paper a review of the sources of impact loads and their effect on the performance of ballasted track is presented. The typical characteristics and implications of impact loading on track deterioration, particularly ballast degradation, are discussed. None of the procedures so far developed to design rail track incorporate the impact that dynamic loading has on the breakage of ballast and therefore it can be said to be incomplete. An intensive study on the impact of induced ballast breakage is needed in order to understand this phenomenon and then use the knowledge gained to further advance the design methodology. A stiff track structure can create severe dynamic loading under operating conditions which causes large scale component failure and increases maintenance requirements. Installing resilient mats such as rubber pads (ballast mat, soffit pad) in rail tracks can attenuate the dynamic force and improve overall performance. The efficacy of ballast mats to reduce structural noise and ground vibration has been studied extensively, but a few recent studies has reported how ballast mats and soffit pads reduce ballast degradation, thus obviating the necessity of a comprehensive study in this direction

Condition Monitoring of Railway Crossing Geometry via Measured and Simulated Track Responses

This paper presents methods for continuous condition monitoring of railway switches and crossings (S&C, turnout) via sleeper-mounted accelerometers at the crossing transition. The methods are developed from concurrently measured sleeper accelerations and scanned crossing geometries from six in situ crossing panels. These measurements combined with a multi-body simulation (MBS) model with a structural track model and implemented scanned crossing geometries are used to derive the link between the crossing geometry condition and the resulting track excitation. From this analysis, a crossing condition indicator Cλ1-λ2,γ is proposed. The indicator is defined as the root mean square (RMS) of a track response signal γ that has been band-passed between frequencies corresponding to track deformation wavelength bounds of λ1 and λ2 for the vehicle passing speed (f = v/ λ). In this way, the indicator ignores the quasi-static track response with wavelengths pre-dominantly above λ1 and targets the dynamic track response caused by the kinematic wheel-cross-ing interaction governed by the crossing geometry. For the studied crossing panels, the indicator C1-0.2 m,γ (λ1 = 1 and λ2 = 0.2) was evaluated for γ = u, v, or a as in displacements, velocities, and accelerations, respectively. It is shown that this condition indicator has a strong correlation with vertical wheel–rail contact forces that is sustained for various track conditions. Further, model calibrations were performed to measured sleeper displacements for the six investigated crossing panels. The calibrated models show (1) a good agreement between measured and simulated sleeper displacements for the lower frequency quasi-static track response and (2) improved agreement for the dynamic track response at higher frequencies. The calibration also improved the agreement between measurements and simulation for the crossing condition indicator demonstrating the value of model calibration for condition monitoring purposes

Time-domain modelling of high-frequency wheel/rail interaction

The interaction between wheel and rail is the predominant source of noise emission from railway operations in a wide range of conventional speeds. On the one hand, this wheel/rail noise concerns rolling noise and impact noise caused by the vertical interaction excited by roughness and discrete irregularities of the wheel/rail running surfaces, respectively. On the other hand, it concerns squeal noise generated by the tangential interaction due to frictional instability. The aim of this thesis is to develop a model for the combined vertical and tangential wheel/rail interaction induced by roughness, discrete irregularities or frictional instability. This is the main step in the formulation of a combined prediction model for the three different types of wheel/rail noise, which can be used as a design tool for noise reduction. In order to include the non-linearities in the contact zone, the interaction model presented in this thesis is formulated in the time domain. Wheel and track models are represented by Green’s functions, which leads to a computationally efficient formulation and allows the inclusion of detailed contact models. A two-dimensional (2D) vertical contact model consisting of a bedding of independent springs, and a three-dimensional (3D) vertical and tangential model based on an influence-function method for the elastic half-space, are considered. Non-Hertzian and transient effects are taken into account. In the thesis, the vertical interaction model has been applied for excitation by wheel/rail roughness and by wheel flats. In the former case, the model has been validated against existing established models. In the latter case, encouraging agreement with field measurements has been found. Results from simulations carried out with both the 2D and the 3D contact models for excitation by detailed measured roughness data indicate that significant errors may occur in the calculated contact forces, when the 3D roughness distribution is represented by the roughness on only one longitudinal line. The errors increase with a decrease in roughness correlation across the width of the contact. Frictional instabilities during curve negotiation have been investigated with the combined vertical/tangential interaction model. For both a constant friction law and a friction curve falling with the sliding velocity, stick/slip oscillations were observed. While the model is not yet considered completely reliable in the case of a falling friction curve due to the possibility of multiple solutions, the results in the case of constant friction are in good qualitative agreement with previouslypublished findings on curve squeal

Towards a Standard Approach for Wear Testing of Wheel and Rail Materials

Examination of the literature for wear testing methodologies for wheel and rail material reveals that while only a few different techniques have been used there is a wide variety in exactly how the tests have been conducted and the resulting data reported. This makes comparison of the data very difficult. This work, carried out as part of the International Collaborative Research Initiative (ICRI) which is aiming to bring together wheel/rail interface researchers from across the world to collate data and knowledge to try to solve some of the common problems that are faced, has examined the different approaches used and attempted to pull together all the good practice used into a test specification for future twin disc testing for wheel and rail materials. Adoption of the method will allow data to be compared reliably and eventually enable data to be compiled into wear maps to use as input, for example, to multi-body dynamics simulation wear prediction tools