Grinding of rails is a technique widely used within the railway industry to balance the degradation of the condition of the rail with the required performance of the rail. The principal focus of this research is the impact of wear and rolling contact fatigue (RCF) cracks on structural integrity of rails, and how rail grinding affects this relationship. A numerical model which predicts growth of RCF-initiated cracks in rails has been adapted to take into account periodic grinding of the surface of the rail. The suitability of some of the simplifying assumptions of the adapted model, referred to as the Grinding Model, has been examined with a physical test program, using full scale rail vehicles and track. This test program studied the persistence of the characteristic surface roughness of the rail generated by grinding, and was carried out to determine whether the effect of this roughness on crack growth can be neglected in the Grinding Model. The Grinding Model has been used to predict crack size, in order to investigate the effect of different grinding strategies, consisting of a depth of grinding applied at a certain interval during a representative pattern of rail vehicle traffic over the rail. The use of the Grinding Model to find grinding strategies which match an optimum criterion has been demonstrated. The applicability of this optimisation technique and the model in its current state of development, to the specification of rail grinding operations, in the context of maximising safe rail life and minimising rail life cycle cost, is discussed.

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This thesis presents the results of an investigation into the effect of surface metallurgy on the rolling contact fatigue behaviour of rail. The investigation has used laboratory based rolling/sliding twin disc testing of samples with a surface metallurgical feature simulated on them. The samples used in laboratory testing have been compared with samples of rail removed from track. Two surface metallurgical features have been investigated: decarburisation and white etching layer. Decarburisation is the loss of carbon from the surface of the rail due to oxidation at high temperatures, resulting in a softer layer at the surface (180HV compared to 250HV bulk). The decarburised layer has been simulated in this research by heat treating discs in a laboratory furnace with an air atmosphere. The results show that by increasing the depth of decarburisation the growth rate of cracks within the sample, along with the wear rate, increases. At the maximum depth of decarburisation allowed on rail by the standard (O.5mm) there was little difference in the wear or rolling contact fatigue behaviour with or without decarburisation. White etching layer (WEL) forms on the surface of rail due to the action of the wheels and is a very hard layer (>850HV) up to 250mm deep. White etching layer has been simulated in two ways: spot welding and gross sliding of the discs. The results have shown that cracks initiate preferentially at weak spots at the surface, such as the interface between the WEL and pearlite or along proeutectoid ferrite boundaries. It has been found that the growth of cracks below the surface depends on the strain history of the subsurface pearlite. The results indicate that white etching layer is detrimental to rail life through either the promotion of rolling contact fatigue and/or wear.

A series of rail image inspection algorithms have been developed for Tata Steels Scunthorpe rail production line. The following thesis describes the contributions made by the author in the design and application of these algorithms. A fully automated rail inspection system that has never been implemented before in any such company or setup has been developed. An industrial computer vision system (JLI) already exists for the image acquisition of rails during production at a rail manufacturing plant in Scunthorpe. An automated inspection system using the same JLI vision system has been developed for the detection of rail‟s surface defects during manufacturing process. This is to complement the human factor by developing a fully automated image processing based system to recognize the faults with an improved efficiency and to allow an exhaustive detection on the entire rail in production. A set of bespoke algorithms has been developed from a plethora of available image processing techniques to extract and identify components in an image of rail in order to detect abnormalities. This has been achieved through offline processing of the rail images using the blended use of different object recognition and image processing techniques, in particular, variation of standard image processing techniques. Several edge detection methods as well as adapted well known Artificial Neural Network and Principal Component Analysis techniques for fault detection on rail have been developed. A combination of customised existing image algorithms and newly developed algorithms have been put together to perform the efficient defect detection. The developed system is fast, reliable and efficient for detection of unique artefacts occurring on the rail surface during production followed by fault classification on the rail imaging system. Extensive testing shows that the defect detection techniques developed for automated rail inspection is capable of detecting more than 90% of the defects present in the available data set of rail images, which has more than 100,000 images under investigation. This demonstrates the efficiency and accuracy of the algorithms developed in this work.

Le présent travail vise à élaborer des soudures aluminothermiques de Hautes Performances tout en réduisant leur temps de réalisation. Un procédé de soudage visant à optimiser la soudure (refroidissement accéléré et meilleure tenue en service) est proposé. Les soudures classiques et améliorées sont comparées. La caractérisation métallurgique et thermique des soudures par aluminothermie est réalisée. Un modèle numérique en couplage thermomécanique est développé afin de déterminer l’effet de l’histoire thermique sur les performances des rails soudés. La simulation est validée avec les résultats expérimentaux. Ce travail aborde l’étude de l’influence des contraintes résiduelles sur la tenue en service des rails soudés par aluminothermie. Les contraintes résiduelles sont déterminées sur des soudures classiques, refroidies rapidement, meulées et martelées. Les résultats des contraintes résiduelles sont analysés et comparés avec ceux obtenus numériquement par éléments finis. Des essais de fatigue sont menés sur les différentes configurations pour évaluer l’influence de ces paramètres sur la durée de vie.On montre dans ce travail que les contraintes résiduelles de traction en présence de défauts jouent un rôle important dans les initiations de rupture dans les soudures aluminothermiques. Le refroidissement accéléré des soudures proposé dans cette étude génère des contraintes résiduelles de compression en peau relativement élevées et améliore la tenue en service. De même, le martelage des cordons des soudures améliore la durée de vie par l’atténuation de l’effet d’entaille. / The aim of this study is to develop a “high performance” aluminothermic weld while reducing its execution time. A welding optimised process (rapid cooling and improved performance) is proposed. The standard and improved welds are compared. The thermal and metallurgical characterization of aluminothermic welds is performed. In order to determine the influence of thermal history on the weld’s performance, a thermomechanical finite element model is developed and validated with experimental results. This study addresses the influence of residual stresses on service performance of aluminothermic welded rails. Residual stresses are determined on standard, quickly cooled, ground and peened welds. The measuring results of residual stresses are analyzed and compared with those obtained numerically by finite elements model. Fatigue tests are carried out on these configurations in order to evaluate the influence of these parameters on the lifetime. The experiments show that tensile residual stresses are detrimental and may lead to failures in the presence of weld defects. The rapid cooling process proposed in this study generates compressive residual stresses and improves service life. Besides, the weld’s fillet peening enhances the fatigue performance by reducing the notch effect.