Academic literature on the topic 'STRESS ANALYSIS OF RAIL WHEEL'

Railway is one of the most important, reliable and widely used means of transportation, carrying freight, passengers, minerals, grains, etc. Thus, research on railway tracks is extremely important for the development of railway engineering and technologies. The safe operation of a railway track is based on the railway track structure that includes rails, fasteners, pads, sleepers, ballast, subballast and formation. Sleepers are very important components of the entire structure and may be made of timber, concrete, steel or synthetic materials. Concrete sleepers were first installed around the middle of last century and currently are installed in great numbers around the world. Consequently, the design of concrete sleepers has a direct impact on the safe operation of railways. The "permissible stress" method is currently most commonly used to design sleepers. However, the permissible stress principle does not consider the ultimate strength of materials, probabilities of actual loads, and the risks associated with failure, all of which could lead to the conclusion of cost-ineffectiveness and over design of current prestressed concrete sleepers. Recently the limit states design method, which appeared in the last century and has been already applied in the design of buildings, bridges, etc, is proposed as a better method for the design of prestressed concrete sleepers. The limit states design has significant advantages compared to the permissible stress design, such as the utilisation of the full strength of the member, and a rational analysis of the probabilities related to sleeper strength and applied loads. This research aims to apply the ultimate limit states design to the prestressed concrete sleeper, namely to obtain the load factors of both static and dynamic loads for the ultimate limit states design equations. However, the sleepers in rail tracks require different safety levels for different types of tracks, which mean the different types of tracks have different load factors of limit states design equations. Therefore, the core tasks of this research are to find the load factors of the static component and dynamic component of loads on track and the strength reduction factor of the sleeper bending strength for the ultimate limit states design equations for four main types of tracks, i.e., heavy haul, freight, medium speed passenger and high speed passenger tracks. To find those factors, the multiple samples of static loads, dynamic loads and their distributions are needed. In the four types of tracks, the heavy haul track has the measured data from Braeside Line (A heavy haul line in Central Queensland), and the distributions of both static and dynamic loads can be found from these data. The other three types of tracks have no measured data from sites and the experimental data are hardly available. In order to generate the data samples and obtain their distributions, the computer based simulations were employed and assumed the wheel-track impacts as induced by different sizes of wheel flats. A valid simulation package named DTrack was firstly employed to generate the dynamic loads for the freight and medium speed passenger tracks. However, DTrack is only valid for the tracks which carry low or medium speed vehicles. Therefore, a 3-D finite element (FE) model was then established for the wheel-track impact analysis of the high speed track. This FE model has been validated by comparing its simulation results with the DTrack simulation results, and with the results from traditional theoretical calculations based on the case of heavy haul track. Furthermore, the dynamic load data of the high speed track were obtained from the FE model and the distributions of both static and dynamic loads were extracted accordingly. All derived distributions of loads were fitted by appropriate functions. Through extrapolating those distributions, the important parameters of distributions for the static load induced sleeper bending moment and the extreme wheel-rail impact force induced sleeper dynamic bending moments and finally, the load factors, were obtained. Eventually, the load factors were obtained by the limit states design calibration based on reliability analyses with the derived distributions. After that, a sensitivity analysis was performed and the reliability of the achieved limit states design equations was confirmed. It has been found that the limit states design can be effectively applied to railway concrete sleepers. This research significantly contributes to railway engineering and the track safety area. It helps to decrease the failure and risks of track structure and accidents; better determines the load range for existing sleepers in track; better rates the strength of concrete sleepers to support bigger impact and loads on railway track; increases the reliability of the concrete sleepers and hugely saves investments on railway industries. Based on this research, many other bodies of research can be promoted in the future. Firstly, it has been found that the 3-D FE model is suitable for the study of track loadings and track structure vibrations. Secondly, the equations for serviceability and damageability limit states can be developed based on the concepts of limit states design equations of concrete sleepers obtained in this research, which are for the ultimate limit states.

<p>A general approach to numerically simulating wear in rollingand sliding contacts is presented in this thesis. A simulationscheme is developed that calculates the wear at a detailedlevel. The removal of material follows Archard’s wear law,which states that the reduction of volume is linearlyproportional to the sliding distance, the normal load and thewear coefficient. The target application is the wheel-railcontact.</p><p>Careful attention is paid to stress properties in the normaldirection of the contact. A Winkler method is used to calculatethe normal pressure. The model is calibrated either withresults from Finite Element simulations (which can include aplastic material model) or a linear-elastic contact model. Thetangential tractions and the sliding distances are calculatedusing a method that incorporates the effect of rigid bodymotion and tangential deformations in the contact zone.Kalker’s Fastsim code is used to validate the tangentialcalculation method. Results of three different sorts ofexperiments (full-scale, pin-on-disc and disc-on-disc) wereused to establish the wear and friction coefficients underdifferent operating conditions.</p><p>The experimental results show that the sliding velocity andcontact pressure in the contact situation strongly influencethe wear coefficient. For the disc-on-disc simulation, therewas good agreement between experimental results and thesimulation in terms of wear and rolling friction underdifferent operating conditions. Good agreement was alsoobtained in regard to form change of the rollers. In thefull-scale simulations, a two-point contact was analysed wherethe differences between the contacts on rail-head to wheeltread and rail edge to wheel flange can be attributed primarilyto the relative velocity differences in regard to bothmagnitude and direction. Good qualitative agreement was foundbetween the simulated wear rate and the full-scale test resultsat different contact conditions.</p><p><b>Keywords:</b>railway rail, disc-on-disc, pin-on-disc,Archard, wear simulation, Winkler, rolling, sliding</p>

La presente tesi descrive l’analisi dinamica condotta su un sistema ferroviario quale una sala , un carrello e un vagone. La posizione dei punti di contatto tra la ruota e la rotaia è determinata tramite lo studio delle posizioni di equilibrio della sala poggiata su una coppia di rotaie. L’analisi permette anche di determinare la normale e le curvature principali delle superfici della ruota e della rotaia nei punti di contatto. Al fine di ridurre i tempi di calcolo, i risultati dello studio sono stati memorizzati in una tabella di calcolo usata per l’analisi dinamica della sala, del carrello e del vagone. E’ stata condotta l’analisi dinamica di un carrello formato da due sale e dal telaio. Il telaio è collegato alle sale per mezzo del sistema di sospensione primario che agisce lungo le tre direzioni principali: longitudinale, trasversale e verticale. Il carrello può muoversi lungo un tracciato rettilineo o curvilineo con o senza angolo di sopralzo e in presenza o assenza di una perturbazione trasversale iniziale. Le caratteristiche di contatto sono determinate per mezzo della tabella di calcolo. Per ridurre di tempi di calcolo è stato sviluppato un nuovo metodo per l’interpolazione delle tabella di calcolo. Per l’integrazione delle equazioni differenziali del moto sono stati testati due metodi che sono stati confrontati con i risultati forniti dal software multibody Simpack. E’ stato condotto uno studio in prossimità delle condizioni critiche del carrello sia su un tracciato rettilineo che curvilineo. La velocità critica è stata determinata attraverso l’analisi del moto di serpeggio usando due metodi. La velocità critica, le forze di contatto e i limiti di deragliamento sono stati determinati in diverse condizioni di carico e di tracciato. E’ stata inoltre analizzata l’influenza della rigidezza longitudinale del sistema di sospensione primario e secondario sulle condizioni critiche del carrello e del vagone sia su un tracciato rettilineo che curvilineo.<br>The present thesis describes an investigation on the railway system motion like a wheel-set, a bogie or a wagon. Through the search of equilibrium configurations, the positions of contact points between rails and wheels are first located. The detection methods allow also the definition of the normal vectors to rail and wheel surfaces and the principal curvatures at contact points. To reduce computing time the results are stored in a lookup table that can be used for dynamic analysis of wheel-sets, bogie or wagon. A dynamic analysis has been performed on a bogie composed of two wheel-sets and a frame. The bogie frame is joined to the wheel-sets by means of a primary suspension system, acting on the three principal directions, i.e. longitudinal, transverse and vertical. The bogie moves along rails following its variable path. In particular, the dynamic analysis investigates the bogie behaviour in both straight and curved paths, with or without an initial perturbation and a super-elevation angle. Imposing an initial transverse disturbance, the hunting motion is observed and the critical speed value estimated. The contact characteristics have been determined by means of the lookup table. In order to minimize cpu-time, a new method for the interpolation of the lookup table entries has been developed. Finally, two different methods for the integration of the differential equations have been tested and comparisons with the results obtained by Simpack-rail multibody software are discussed. The railway systems have been analyzed in proximity of their critical conditions both in straight and curved tracks. The critical speed is estimated through the rise up of hunting motion. The critical speed, the contact forces in the critical conditions and the derailment limits are determined under different load conditions and track paths; two methods are used for its determination. The influence of the longitudinal suspension stiffness of the primary and secondary suspension systems on the critical conditions of the bogie and wagon are deduced for straight and curved track type.

La meccanica del contatto fra ruota ferroviaria e rotaia, è una delle più importanti aree di studio nell’Ingegneria Ferroviaria. Ad oggi, un vasto numero di formulazioni analitiche sono state proposte dai ricercatori, con lo scopo di valutare i parametri di contatto tra ruota e rotaia ed arrivare ad una descrizione affidabile delle forze che agiscono nell’area di contatto. Comunque, solo alcuni dei metodi disponibili permettono di considerare, nelle loro elaborazioni, la reale geometria di contatto tra ruota e rotaia o la non linearità delle proprietà dei materiali impiegati. Un’alternativa ai metodi analitici per descrivere la fisica del contatto tra ruota e rotaia e di fare uso di tecniche computazionali numeriche quale l’Analisi agli Elementi Finiti (FEA – Finite Element Analysis). Il vantaggio di questo metodo è dato dalla possibilità di poter modellare complesse geometrie che permettono di simulare più accuratamente il contatto tra ruota e rotaia e determinare l’ampiezza degli stress e la loro distribuzione, oltre alla dimensione e forma dell’area di contatto. Per questa ragione, un modello agli Elementi Finiti tridimensionale della ruota ferroviaria e della rotaia è stato creato utilizzando Ansys Parametric Design Language di ANSYS per studiare il problema di contatto normale. Per verificare l’accuratezza dei risultati forniti dal modello, questo è stato validato in confronto alla teoria di Hertz sul contatto elastico. Questa teoria rappresenta la base sulla quale la maggior parte dei modelli computazionali vengono sviluppati. Il principali scopi di questa tesi sono quindi di studiare i problemi del contatto tra ruota e rotaia e di valutare l’influenza dei parametri operativi quali il coefficiente di frizione, lo spostamento laterale della sala montata e l’inclinazione della rotaia sul piano orizzontale, sulla fisica del contatto.

Low adhesion between wheel and rail is a recurrent problem for the rail industry. Low adhesion can lead to wheel slides and slips during acceleration and deceleration, which can cause large amounts of damage to the wheel and rail as well as causing safety issues and delays if a train cannot accelerate or decelerate when necessary. Adhesion in the wheel-rail contact is affected by the third body layer which is present in the contact patch between wheel and rail. It is composed naturally from steel wear debris and iron oxides, but often contains other contaminants such as organic matter, ballast dust, soil and grease. Different environmental conditions such as temperature, precipitation and humidity change the properties of this third body layer and therefore change adhesion conditions on the railway. Low adhesion has been well documented throughout the autumn season due to organic contamination, but also takes place throughout the year when no visible contamination is seen on the railhead, known as the “wet-rail” phenomenon. It is thought to occur when there are low levels of water on the railhead, formed by dew, mist or light rain, rather than heavy rain. The conditions and mechanisms that cause the phenomenon are not fully understood. Low adhesion does not occur very often and under what is likely to be a narrow window of conditions, which means that it can be difficult to simulate and study. The aim of this work was to use a combination of tribology and chemistry to better understand the cause of low adhesion throughout the year, known as the wet-rail phenomenon. It investigated low adhesion conditions that occur all year round, initially focusing on the role of iron oxide in low adhesion as it has previously been hypothesised that oxides could play a major role in the wet-rail phenomenon. Testing was carried out over a range of conditions on three different tribological test rigs to attempt to simulate low adhesion due to the wet-rail phenomenon, which produced valuable information about the causes of low adhesion. It was found that, under certain conditions, a combination of iron oxides and water could cause low adhesion in a simulated wheel-rail contact. Test methods were designed to simulate the wet-rail phenomenon, which can be used as a platform to better understand the causes of low adhesion and to test future mitigation methods.

This thesis developed an alternative laboratory element testing method to evaluate the response of the unsaturated soils of rail track foundations under repeated moving wheel loadings. The novel laboratory testing method is more capable of producing the realistic strength-deformation characteristics of the unsaturated soils with the effects of principal stress axis rotation (PSAR), which can be used to redesign the conservative rail track guidelines.

Accurate estimation of the coefficient of friction (CoF) is essential to accurately modeling railroad dynamics, reducing maintenance costs, and increasing safety factors in rail operations. The assumption of a constant CoF is popularly used in simulation studies for ease of implementation, however many evidences demonstrated that CoF depends on various dynamic parameters and instantaneous conditions. In the real world, accurately estimating the CoF is difficult due to effects of various uncertain parameters, such as wheel and rail materials, rail roughness, contact patch, and so on. In this study, the newly developed 3-D nonlinear CoF model for the dry rail condition is introduced and the CoF variation is tested using this model with dynamic parameters estimated from the wheel-rail simulation model. In order to account for uncertain parameters, a stochastic analysis using the polynomial chaos (poly-chaos) theory is performed using the CoF and wheel-rail dynamics models. The wheel-rail system at a right traction wheel is modeled as a mass-spring-damper system to simulate the basic wheel-rail dynamics and the CoF variation. The wheel-rail model accounts for wheel-rail contact, creepage effect, and creep force, among others. Simulations are performed at train speed of 20 m/s for 4 sec using rail roughness as a unique excitation source. The dynamic simulation has been performed for the deterministic model and for the stochastic model. The dynamics results of the deterministic model provide the starting point for the uncertainty analysis. Six uncertain parameters have been studied with an assumption of 50% uncertainty, intentionally imposed for testing extreme conditions. These parameters are: the maximum amplitude of rail roughness (MARR), the wheel lateral displacement, the track stiffness and damping coefficient, the sleeper distance, and semi-elliptical contact lengths. A symmetric beta distribution is assumed for these six uncertain parameters. The PDF of the CoF has been obtained for each uncertain parameter study, for combinations of two different uncertain parameters, and also for combinations of three different uncertain parameters. The results from the deterministic model show acceptable vibration results for the body, the wheel, and the rail. The introduced CoF model demonstrates the nonlinear variation of the total CoF, the stick component, and the slip component. In addition, it captures the maximum CoF value (initial peak) successfully. The stochastic analysis results show that the total CoF PDF before 1 sec is dominantly affected by the stick phenomenon, while the slip dominantly influences the total CoF PDF after 1 sec. Although a symmetric distribution has been used for the uncertain parameters considered, the uncertainty in the response obtained displayed a skewed distribution for some of the situations investigated. The CoF PDFs obtained from simulations with combinations of two and three uncertain parameters have wider PDF ranges than those obtained for only one uncertain parameter. FFT analysis using the rail displacement has been performed for the qualitative validation of the stochastic simulation result due to the absence of the experimental data. The FFT analysis of the deterministic rail displacement and of the stochastic rail displacement with uncertainties demonstrates consistent trends commensurate with loss of tractive efficiency, such as the bandwidth broadening, peak frequency shifts, and side band occurrence. Thus, the FFT analysis validates qualitatively that the stochastic modeling with various uncertainties is well executed and is reflecting observable, real-world results. In conclusions, the development of an effective model which helps to understand the nonlinear nature of wheel-rail friction is critical to the progress of railroad component technology and rail safety. In the real world, accurate estimation of the CoF at the wheel-rail interface is very difficult since it is influenced by several uncertain parameters as illustrated in this study. Using the deterministic CoF value can cause underestimation or overestimation of CoF values leading to inaccurate decisions in the design of the wheel-rail system. Thus, the possible PDF ranges of the CoF according to key uncertain parameters must be considered in the design of the wheel-rail system.<br>Ph. D.

Proper functioning of Insulated Rail Joints (IRJs) is essential for the safe operation of the railway signalling systems and broken rail identification circuitries. The Conventional IRJ (CIRJ) resembles structural butt joints consisting of two pieces of rails connected together through two joint bars on either side of their web and the assembly is held together through pre-tensioned bolts. As the IRJs should maintain electrical insulation between the two rails, a gap between the rail ends must be retained at all times and all metal contacting surfaces should be electrically isolated from each other using non-conductive material. At the gap, the rail ends lose longitudinal continuity and hence the vertical sections of the rail ends are often severely damaged, especially at the railhead, due to the passage of wheels compared to other continuously welded rail sections. Fundamentally, the reason for the severe damage can be related to the singularities of the wheel-rail contact pressure and the railhead stress. No new generation designs that have emerged in the market to date have focussed on this fundamental; they only have provided attention to either the higher strength materials or the thickness of the sections of various components of the IRJs. In this thesis a novel method of shape optimisation of the railhead is developed to eliminate the pressure and stress singularities through changes to the original sharp corner shaped railhead into an arc profile in the longitudinal direction. The optimal shape of the longitudinal railhead profile has been determined using three nongradient methods in search of accuracy and efficiency: (1) Grid Search Method; (2) Genetic Algorithm Method and (3) Hybrid Genetic Algorithm Method. All these methods have been coupled with a parametric finite element formulation for the evaluation of the objective function for each iteration or generation depending on the search algorithm employed. The optimal shape derived from these optimisation methods is termed as Stress Minimised Railhead (SMRH) in this thesis. This optimal SMRH design has exhibited significantly reduced stress concentration that remains well below the yield strength of the head hardened rail steels and has shifted the stress concentration location away from the critical zone of the railhead end. The reduction in the magnitude and the relocation of the stress concentration in the SMRH design has been validated through a full scale wheel – railhead interaction test rig; Railhead strains under the loaded wheels have been recorded using a non-contact digital image correlation method. Experimental study has confirmed the accuracy of the numerical predications. Although the SMRH shaped IRJs eliminate stress singularities, they can still fail due to joint bar or bolt hole cracking; therefore, another conceptual design, termed as Embedded IRJ (EIRJ) in this thesis, with no joint bars and pre-tensioned bolts has been developed using a multi-objective optimisation formulation based on the coupled genetic algorithm – parametric finite element method. To achieve the required structural stiffness for the safe passage of the loaded wheels, the rails were embedded into the concrete of the post tensioned sleepers; the optimal solutions for the design of the EIRJ is shown to simplify the design through the elimination of the complex interactions and failure modes of the various structural components of the CIRJ. The practical applicability of the optimal shapes SMRH and EIRJ is demonstrated through two illustrative examples, termed as improved designs (IMD1 & IMD2) in this thesis; IMD1 is a combination of the CIRJ and the SMRH designs, whilst IMD2 is a combination of the EIRJ and SMRH designs. These two improved designs have been simulated for two key operating (speed and wagon load) and design (wheel diameter) parameters that affect the wheel-rail contact; the effect of these parameters has been found to be negligible to the performance of the two improved designs and the improved designs are in turn found far superior to the current designs of the CIRJs in terms of stress singularities and deformation under the passage of the loaded wheels. Therefore, these improved designs are expected to provide longer service life in relation to the CIRJs.

Early detection of rail defects is necessary for preventing derailments and costly damage to the train and railway infrastructure. A rail surface flaw can quickly propagate from a small fracture to a broken rail after only a few train cars have passed over it. Rail defect detection is typically performed by using an instrumented car or a separate railway monitoring vehicle. Rail surface irregularities can be measured using accelerometers mounted to the bogie side frames or wheel axles. Typical signal processing algorithms for detecting defects within a vertical acceleration signal use a simple thresholding routine that considers only the amplitude of the signal. As a result, rail surface defects that produce low amplitude acceleration signatures may not be detected, and special track components that produce high amplitude acceleration signatures may be flagged as defects. The focus of this research is to develop an intelligent signal processing algorithm capable of detecting and classifying various rail surface irregularities, including defects and special track components. Three algorithms are proposed and validated using data collected from an instrumented freight car. For the first two algorithms, one uses a windowed Fourier Transform while the other uses the Wavelet Transform for feature extraction. Both of these algorithms use an artificial neural network for feature classification. The third algorithm uses the Wavelet Transform to perform a regularity analysis on the signal. The algorithms are validated with the collected data and shown to out-perform the threshold-based algorithm for the same data set. Proper training of the defect detection algorithm requires a large data set consisting of operating conditions and physical parameters. To generate this training data, a dynamic wheel-rail interaction model was developed that relates defect geometry to the side frame vertical acceleration signature. The model was generated by using combined systems dynamic modeling, and the system was solved with a developed combined lumped and distributed parameter system numerical approximation. The broken rail model was validated with real data collected from an instrumented freight car. The model was then used to train and validate the defect detection methodologies for various train and rail physical parameters and operating conditions.<br>Ph. D.