Year

2015

Degree Name

Doctor of Philosophy

Department

Faculty of Engineering and Information Sciences, School of Mechanical, Materials and Mechatronic

Abstract

In wheel-rail contact, the locomotive adhesion characterises the capability of the locomotive to convert available friction into traction at the interface. Recently developed AC (Alternating Current) drive induces a higher adhesion level compared to DC (Direct Current) drive. This significantly affects the wheel-rail contact conditions such as damage initiation, high contact temperature due to frictional rolling, and wear of the rails.

Three-dimensional (3D) elasto-plastic finite element model (FEM) was used in this thesis to examine the wheel-rail contact on a straight track. Some sub-components of the track such as railpads, sleepers and ballast were also included in the model. Rolling contact stress states and material response of wheel/ rail under three contact situations (high adhesion, low adhesion and full slip) were investigated. Canted and non-canted rails were considered to determine the effect of the cant angle on the contact stress levels. Furthermore, the effects of contact curvature on the contact zone and contact pressure were also observed, and the response of material was predicted by a shakedown diagram.

The more complicated rolling phenomenon of the wheel on a curved track was also investigated numerically in this thesis. Due to the influences of super-elevation (also called track cant), angle of attack (AOA) and rail cant, stress states on the high rail are significantly different from that on the low rail. The new and worn profiles were considered in the simulation to examine different contact situations: new wheel/new rail, new wheel/worn rail, and worn wheel/worn rail contacts. Material responses, the formation of rail corrugation and fatigue defects on both low and high rails were anticipated based on the results from simulations.

In order to compare stress states AC and DC locomotives, two locomotive models of AC (C44ACi) and DC (Cv40-9i) currently run in Australia were evaluated under diverse operational situations (wheel loads, angle of attack and adhesion level). The software LS-DYNA was employed to build up a comprehensive wheel/rail contact model. The numerical model was constructed based on Australian wheel/rail profiles. Moreover the analytical method was also applied to evaluate the temperature rise on the rail, respectively. Calculation of wear volume on rail was eventually performed using the Archard’s wear model.

Finally a 3D coupled thermal-mechanical FE model was developed to examine the temperature rise due to high adhesion contact and the thermal influence on residual stress-strain, wear and rail life. The numerical model employed the moving heat source code developed by Goldak. The mechanical and thermal properties of the rail material were governed by temperature. The influence of repeated multi-passes from multiple wheels on one point of the rail was also taken into account. Moreover the formation of white etching layer (WEL) on the rail surface combined with rolling cycles can potentially lead to rail damage. A sub-2D FE model of WEL was also carried out to examine the stress state on the WEL if formed on the rail surface.

The current thesis focuses on modelling wheel-rail contact under high adhesion condition, and explanation of the subsequent damage formation on the rail. The model provides a better understanding of the influences of high adhesion condition on contact stress states, damage initiation and also temperature rise on the rail. To the best of the author’s knowledge, the simulation of wheel-rail contact under high adhesion condition has not been studied elsewhere, and is presented in this study for the first time.

FoR codes (2008)

0912 MATERIALS ENGINEERING, 0913 MECHANICAL ENGINEERING

Download

Share

COinS
 

Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.