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

Experimental and theoretical studies of the wear of heat exchanger tubes

A study of heat exchanger tube wear has been completed. A simple theoretical model of elastic/plastic deformation has been developed and used in a new model of wear. Experimental results were used to corroborate the theoretical developments. A literature survey of wear mechanisms and wear models was conducted to provide the author with an opportunity to familiarize himself with current knowledge of the field of tribology. Experiments were conducted to simulate a heat exchanger tube/support wear system. For the first series of experiments, a simple impacting rig was used, while a second set was conducted using a much more accurate rig and facilities of the National Research Council of Canada's Tribology Laboratory. Modifications to the NRC rig were designed by the author to incorporate the specific specimen geometries. The main operating parameters of the test apparatus were varied in an effort to determine their effect on wear rates. Force and displacement data were collected and the normal and shear forces calculated, as was the work input. Comparison between the frictional work input and the measured wear showed that there was an approximately linear correlation between work and wear rates. Inspection of the surfaces of the worn specimens showed that a number of wear mechanisms operate in this wear system but that wear is primarily due to delamination and shear fracture. Also, it was noticed that the micro-surface geometry of the worn specimens has a consistent texture, regardless of magnitude and angle of impact between the tube and ring. A model of plastic contact deformation was developed to allow calculation of the contact parameters between two surfaces, given that the softer surface is repeatedly plastically deformed. This model says that repeated stress cycles lead to the introduction of residual stresses, which combined with work hardening of the material, lead the softer material to an elastic shakedown state. Once the typical asperity contact state is known, the typical stress distribution is calculated using Hertzian line contact stress formulae. A series of computer programs were developed to calculate the stress distribution beneath a sliding contact. The depth of maximum shear stress can then be found. This depth corresponds to the expected wear particle thickness. A wear sheet was assumed to form when the frictional work input is equal to the energy required to cause failure in ductile shear. A wear equation was then developed to predict the wear rate between a heat exchanger tube and its support. The final wear model has seen limited comparison with experimental results. The theoretical work input was found to be about 25% of the correlated bulk work. This indicates that the geometry assumptions of the model are quite reasonable. Unfortunately, the predicted wear rate was found to exceed the measured values by a factor of about 5000. If this empirical value is factored into the the wear model, then the predicted results are found to correspond well with the experimental values.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat

Stochastic Modeling Applied to Vehicle-Track Performance and Safety

The application of a Monte-Carlo stochastic modeling technique to simulate a loaded coal car fleet running over a sharp curve has successfully reproduced the distributions of wheel/rail forces measured in the field. In the case of lateral force, wheel/rail friction and contact conditions are found to have the highest impact among the many parameters evaluated. For vertical force, the unevenly loaded condition is identified as one of the key factors. To better diagnose truck performance based on wheel/rail force measurements collected by the Truck Performance Detector (TPD), normalization methods to reduce \u201cfalse alarms\u201d due to non-truck factors such as wheel/rail friction and contact conditions are required.Peer reviewed: YesNRC publication: Ye

Rolling contact fatigue, wear and broken rail derailments

Rolling contact fatigue (RCF) and wear are inevitable in the wheel/rail system, but resulting failures and derailments need not also be inevitable. Understanding why and under which conditions broken rails and derailments are likely to occur will focus research, inspection and maintenance efforts to minimize their probability. RCF leads to many broken rails, and rails with severe RCF damage are difficult to inspect. Wear on the other hand reduces the extent of crack growth and hence can be beneficial in some cases. On the other hand, wear changes wheel and rail profiles, may expose virgin material to contact stresses, and reduces the section strength, which may lead to higher stress from bending and torsion. These influences are explored together with case studies of operational derailments. Based on this information and the current state of the art – both theoretical and practical – a number of issues are raised which need to be addressed through further developments in understanding and mitigating strategies to reduce the risk of failures from RCF and wear

Rolling contact fatigue, wear and broken rail derailments

Rolling contact fatigue (RCF) and wear are inevitable in the wheel/rail system, but resulting failures and derailments need not also be inevitable. Understanding why and under which conditions broken rails and derailments are likely to occur will focus research, inspection and maintenance efforts to minimize their probability. RCF leads to many broken rails, and rails with severe RCF damage are difficult to inspect. Yet wear reduces the extent of crack growth and hence can be beneficial in some cases. On the other hand, wear changes wheel and rail profiles, may expose virgin material to contact stresses, and reduces the section strength, which may lead to higher stress from bending and torsion. These influences are explored together with case studies of operational derailments. Based on this information and the current state of the art – both theoretical and practical – a number of issues are raised which need to be addressed through further developments in understanding and mitigating strategies to reduce the risk of failures from RCF and wear