Abstract

Wheel flats are the sources of high magnitude impact forces at the wheel-rail interface, which can induce high levels of local stresses leading to fatigue damage, and failure of various vehicle and track components. With demands for increased load and speed, the issue of wheel flats and a strategy for effective maintenance and in-time replacement of defective wheels has become an important concern for heavy haul operators. A comprehensive coupled vehicle-track model is thus required in order to predict the impact forces and the resulting component stresses in the presence of wheel flats.
This study presents the dynamic response of an Euler- Bernoulli beam supported on two-parameter Pasternak foundation subjected to moving load as well as moving mass. Dynamic responses of the beam in terms of normalized deflection and bending moment have been investigated for different velocity ratios under moving load and moving mass conditions. The effect of moving load velocity on dynamic deflection and bending moment responses of the beam have been investigated. The effect of foundation parameters such as, stiffness and shear modulus on dynamic deflection and bending moment responses have also been investigated for both moving load and moving mass at constant speeds.
This dissertation research concerns about modeling of a three-dimensional railway vehicle- track model that can accurately predict the wheel-rail interactions in the presence of wheel defects. This study presents a three-dimensional track system model using two Timoshenko beams supported on discrete elastic supports, where the sleepers are considered as rigid masses, and the rail pad and ballast as spring-damper elements. The vehicle system is modeled as a three-dimensional 17- DOF lumped mass model comprising a full car body, two bogies and four wheelsets. The railway track is modeled as a pair of three-dimensional flexible beams that considers two parallel Timoshenko beams periodically supported by lumped masses representing the sleepers.
The wheel-rail contact is modeled using nonlinear Hertzian contact theory. The developed model is validated with the existing measured data and analytical solutions available in literature. The nonlinear model is then employed to investigate the wheel-rail impact forces that arise in the wheel-rail interface due to the presence of single as well as multiple wheel flats.
The effects of single and multiple wheel flats on the responses of vehicle and track components in terms of displacements and acceleration responses are investigated for both defective wheel and the flat-free wheel. The characteristics of the bounce, pitch and roll motions of the bogie due to a single wheel flat are also investigated. The study shows that nonlinear railpad and ballast model gives better prediction of the wheel-rail impact force than that of the linear model when compared with the experimental data. The results clearly show that presence of wheel flat within the same wheelset has significant effect on the impact force, displacement and acceleration responses of that wheelset.
This study further presents the modeling of a MEMS based accelerometer in order to detect the presence of a wheel flat in the railway vehicle. The proposed accelerometer can survive in a dynamic shock environment with acceleration up to ±150g. Simulations of the accelerometer are performed under various operating conditions in order to determine the optimum configuration.