Thermomechanics of tread braking: Braking capacity of railway wheels
Doctoral thesis, 2024
Tread brakes are the most common type of railway braking system, wherein a block of friction material is pushed onto the rolling surface, or 'tread', of a railway wheel. Although simple, inexpensive, and maintenance-efficient, a complex thermomechanical loading situation occurs, in which the elevated temperatures from the frictionally dissipated energy interact with wheel-rail rolling contact loads. This may cause damage to the wheels and other components, resulting in disruptive and costly maintenance procedures. In severe cases, it could lead to wheel failure and derailment.
The aim of this thesis is to determine thermomechanical limits of the tread braking system and to find in which situations the wheel and brake experience damage which exceeds safe or economical limits or fail entirely. In addition, it aims at presenting models capable of accurately simulating the dimensioning or critical loading cases. To achieve this, knowledge building based upon experimental campaigns and numerical simulations has been made.
The temperature field around the wheel has been studied in full-scale experiments and in-field conditions. Results from these studies show that the temperature field has the potential to form severe long-wavelength non-uniformities, which have the potential to induce increased levels of residual stresses in the wheel. The thermal degradation experienced by the pearlitic steel is shown to significantly affect the mechanical strength of the material, causing plastification in the rolling surface.
The numerical work has focused on both calibrating a finite element material model to accurately and stably model the behaviour seen in experiments and then employing it to study the braking scenarios envisioned. Both simulations of tread braking at high brake loads and rolling contact at elevated temperatures are studied in the thesis.
The aim of this thesis is to determine thermomechanical limits of the tread braking system and to find in which situations the wheel and brake experience damage which exceeds safe or economical limits or fail entirely. In addition, it aims at presenting models capable of accurately simulating the dimensioning or critical loading cases. To achieve this, knowledge building based upon experimental campaigns and numerical simulations has been made.
The temperature field around the wheel has been studied in full-scale experiments and in-field conditions. Results from these studies show that the temperature field has the potential to form severe long-wavelength non-uniformities, which have the potential to induce increased levels of residual stresses in the wheel. The thermal degradation experienced by the pearlitic steel is shown to significantly affect the mechanical strength of the material, causing plastification in the rolling surface.
The numerical work has focused on both calibrating a finite element material model to accurately and stably model the behaviour seen in experiments and then employing it to study the braking scenarios envisioned. Both simulations of tread braking at high brake loads and rolling contact at elevated temperatures are studied in the thesis.
Finite element modelling
Railways
Pearlitic Steel
Experimental Studies
Thermomechanics
Rolling Contact
Author
Eric Landström Voortman
Chalmers, Mechanics and Maritime Sciences (M2), Dynamics
Thermomechanical testing and modelling of railway wheel steel
International Journal of Fatigue,;Vol. 168(2023)
Journal article
Improved modelling of tread braked wheels using an advanced material model
FISITA Library,;Vol. EB2022(2022)
Paper in proceeding
Analysis and testing of tread braked railway wheel — Effects of hot spots on wheel performance
International Journal of Fatigue,;Vol. 180(2024)
Journal article
Voortman Landström, E., Vernersson, T. Lundén, R. Characterisation and Evaluation of Global Uneven Heating during Railway Tread Braking – Brake Rig Testing and Field Study
Voortman Landström, E. de Lara Todt, M. Vernersson, T., Lundén, R. Non-uniform temperature and residual stress effects during railway tread braking
Voortman Landström, E., Ozaki, R., Handa, K., Vernersson, T. Thermomechanical Contact Behaviour of Tread Braked Wheels
Voortman Landström, E., Vernersson, T. Numerical study of rolling contact fatigue at tread braking conditions
Stopping trains remains as vital a task as running them, and the former of these is the purpose of the braking system. Although most modern passenger trains one might have come across primarily rely on regenerative braking, more or less every train is also equipped with mechanical friction brakes. For freight trains, most of the braking effort may come from a system which has barely been changed since its inception in the latter half of the 19th century: the tread brake. This is where modern train braking began, and for the topic of this work, also partially where it continues. It is a simple, inexpensive and maintenance-efficient system capable of assisting more modern regenerative alternatives or carrying the full brake load by itself. The drawback is that the wheel is used as a friction-heated component, transforming the kinetic energy of the train to heat, which can cause damage at high braking loads. Future requirements of increased speeds, higher axle loads, lower noise emissions and the ever-present desire to minimise costs have however made the following question relevant:
What are the actual limits of the tread braking system?
The primary aim of this thesis is to determine safe and efficient usage limits of the tread braking system via a combination of numerical simulations, laboratory experiments and field tests. Temperature behaviour, thermomechanical effects, material damage and wheel-rail rolling contact as well as the combinations of them are all considered. A custom-made brake roller rig developed during the course of this project is used in combination with modern measurement techniques such as high-speed radiometry to study the behaviour and thermomechanical effects of elevated and non-uniform temperatures. Modelling and simulation of the experimental and other cases are then investigated to both improve current finite element models and to attempt to accurately provide computational results that can gauge the limits of the tread braking system and its components.
What are the actual limits of the tread braking system?
The primary aim of this thesis is to determine safe and efficient usage limits of the tread braking system via a combination of numerical simulations, laboratory experiments and field tests. Temperature behaviour, thermomechanical effects, material damage and wheel-rail rolling contact as well as the combinations of them are all considered. A custom-made brake roller rig developed during the course of this project is used in combination with modern measurement techniques such as high-speed radiometry to study the behaviour and thermomechanical effects of elevated and non-uniform temperatures. Modelling and simulation of the experimental and other cases are then investigated to both improve current finite element models and to attempt to accurately provide computational results that can gauge the limits of the tread braking system and its components.
A holistic model of wheel tread life
Swedish Transport Administration (TRV), 2024-07-01 -- 2029-12-31.
Tread braking – capacity, wear and life (CHARMEC SD11)
Chalmers Railway Mechanics (CHARMEC), -- .
Subject Categories (SSIF 2011)
Mechanical Engineering
Areas of Advance
Transport
Infrastructure
C3SE (Chalmers Centre for Computational Science and Engineering)
ISBN
978-91-8103-150-8
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5608
Publisher
Chalmers