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

Sammanfattning: 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.