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.
Twin disc tests were carried out to evaluate the wear resistance and Rolling Contact Fatigue (RCF) of premium R400HT rail samples in contact with E8 wheel samples. The wear rate and friction coefficient were correlated with the frictional work expended at the contact interface (the Tgamma approach). Accelerated RCF tests were also carried out on the premium R400HT rail and the results were compared to those obtained for standard R260 rail. The wear rates of rail samples were consistently lower than those reported in the literature for other contacting pairs in which the rail material studied is softer than R400HT. Also, the energy needed for the transition from the moderate to severe wear regime significantly increased for the hardened rail. Fatigue cracks were shallower for R400HT when compared with standard rail material. Hardened rails also showed lower mean spacing between fatigue cracks. This new information can be used to improve wear simulations of wheels and rails by using more realistic wear equations.
Some railway managers and practitioners fear that introducing premium rail materials will have a detrimental effect on the wheels of trains that use the line. A review of relevant investigations across all scales in the laboratory, and in the field has been carried out. This showed that, as rail hardness increases, its wear, and overall system wear reduces. Wheel wear does increase with increasing rail hardness, but only for wheels running on rails that are softer than them. Similar trends were observed in all studies, so it seems that the fears were unfounded.While the wear trends appear well characterised some issues have been identified. One relates to the varying work hardening capability of wheel and rail materials. Often only bulk hardness is quoted, but work hardening can increase material surface hardness by up to 2.5 times and make materials that were initially softer, harder than the opposing material. Another related issue is test length. It is essential that enough cycles are applied such that the materials reach steady state wear, i.e., the point at which work hardening has reached its limit. In previous work it is not always clear that steady state wear has been reached. Some gaps have been identified in the current knowledge base, the largest of which is the failure to determine which mechanisms lead to the wear trends seen.Analysis of recent work on different clad layers on rail discs and premium rail materials allowed some of these gaps to be addressed. Results indicated that opposing wheel material hardened to the same level independent of rail hardness. Wheel wear is therefore stress driven under the conditions used, and dictated by the wheel material properties only. At higher slip levels relationships become less clear, but here temperature and therefore hot hardness is most influential and is as yet uncharacterised.
This paper presents details of a new model of railway overhead electric power line dynamics for prediction of contact wire-pantograph contact forces and wire uplift. It is validated against data from EN50318:2002, and against data from track tests conducted at Network RailÕs Melton Rail Innovation and Development Centre using a class 395 high speed electric multiple unit. Its advantage over previous approaches is its implantation in a commercial nonlinear finite element package allowing application for a wide range of overhead line geometry.Overhead electric lines and their support structures are highly stressed components largely without redundancy, and their integrity (both mechanical and electrical) is crucial to the functioning of railway infrastructure. Their failure can be understood in terms of component wear, fatigue and corrosion, in addition to electrical equipment life expiry. These processes are driven by a combination of factors including cable tension, dynamic load from current collection pantographs, the frequency of support, and environmental loading (e.g. sparking and sidewinds). The model described here is able to support decision making and cost effectiveness regarding these aspects for new installations (e.g. designing for compliance with EN50119:2009) and for maintenance of existing systems. The route for further extending its capabilities is outlined.
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