Influence of wheel tread damage on wheelset and track loading – Field tests and numerical simulations

Licentiate thesis, 2020

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, in particular during the coldest months of the year. According to regulations, vehicles generating contact forces exceeding the limit value for allowed wheel–rail impact loads must be taken out of service for wheel maintenance. This may lead to severe traffic disruptions and higher costs. Increased wheel‒rail impact loads also 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. Wheel tread irregularities also lead to increased levels of rolling noise, impact noise and ground-borne vibration.

The aim of the thesis is to enhance the understanding of wheel tread damage and its consequences and to identify better means of addressing them. To achieve this aim, the ability for 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 wheelset (comprising two wheels, axle and any attached equipment for braking and power transmission) and track with two discretely supported rails are described by three-dimensional finite element (FE) models. The dynamic coupling between the two wheel‒rail contacts (one on each wheel) via the wheelset axle and via the sleepers and ballast is considered. The simulation of dynamic vehicle–track interaction is carried out in the time domain using a convolution integral approach, while the non-linear wheel–rail normal contact is solved using Kalker’s variational method. Non-symmetric wheelset and track designs, as well as non-symmetric distributions of wheel tread damage or rail irregularities can be studied. Based on Green’s functions, a post-processing step has been developed to compute time-variant stresses at locations in the wheelset axle which are prone to fatigue. In an extensive parameter study, wheel–rail impact loads and axle stresses have been computed for different shapes and sizes of wheel tread damage.

The simulations need to be calibrated and validated by tests. To this end, field tests with two different Swedish passenger trains with severe wheel tread damage have been carried out. Time histories of numerically evaluated axle stresses have been compared to measured data from an instrumented wheelset. Simulations have been used to demonstrate that variations in rail roughness level, and the angular position of a strain gauge with respect to that of a discrete wheel tread defect, may lead to a significant influence on predicted axle stresses.

Developed numerical routines to predict stresses at critical locations in the wheelset from condition monitoring data will improve understanding and possibilities to handle wheel tread deteriorations. A discussion on future applications in terms of improved wheelset maintenance procedures is initiated.