Thermo-Mechanical-Metallurgical Modelling of Pearlitic Steels and Railhead Repair Welding
Doctoral thesis, 2024
The efficiency of rail transport is attributed to low rolling resistance, which comes at the cost of high contact pressures between rail and wheel. Consequently, both the rail and wheel can be susceptible to fatigue crack initiation and propagation due to the resulting high stresses and large number of load cycles in service. Therefore, the mechanical performance of the rail and wheel material is critical for safe operation. Thermal loading, such as that caused by wheel locking or railhead repair welding, can cause gradual or drastic changes in local material behaviour, resulting in significant detrimental effects to the rail and wheel. This thesis presents a phenomenological modelling framework for numerical simulations of the thermo-metallurgical-mechanical behaviour of pearlitic railway steels during and after high-temperature thermal loading.
The framework consists of a material model that incorporates cyclic hardening plasticity, phase transformation kinetics, transformation-induced plasticity, multi-phase homogenisation, and recovery of the virgin material state after cyclic melting and solidification. The ability of the model to simulate intricate thermo-metallurgical-mechanical behaviour is demonstrated in quasi-static material point simulations. The material model is implemented in a finite element framework to obtain a simulation-based tool that balances computational efficiency, simulation fidelity, and engineering applicability. Several simulations demonstrate the effectiveness of this tool, including simulations of a wheel flat, laser-induced martensitic patches on the rail surface, and railhead repair welding processes. The simulation-tool is also validated against experimental data, in terms of residual material states after high-temperature processes.
The thesis provides insights into the evolution of material phases and stresses under thermal loading in high-temperature railway processes, as well as the redistribution of residual stresses during subsequent operational loading conditions. For instance, simulations of the railhead repair welding process indicate that pre-heating has a minor impact on the quality of the repair, while the welding build-up paths have a significant impact. The simulations also highlight the critical region for fatigue crack initiation by showing how residual tensile stresses are reduced near the surface of the rail or wheel and increased at some distance below during operation for the repaired rail.
The framework consists of a material model that incorporates cyclic hardening plasticity, phase transformation kinetics, transformation-induced plasticity, multi-phase homogenisation, and recovery of the virgin material state after cyclic melting and solidification. The ability of the model to simulate intricate thermo-metallurgical-mechanical behaviour is demonstrated in quasi-static material point simulations. The material model is implemented in a finite element framework to obtain a simulation-based tool that balances computational efficiency, simulation fidelity, and engineering applicability. Several simulations demonstrate the effectiveness of this tool, including simulations of a wheel flat, laser-induced martensitic patches on the rail surface, and railhead repair welding processes. The simulation-tool is also validated against experimental data, in terms of residual material states after high-temperature processes.
The thesis provides insights into the evolution of material phases and stresses under thermal loading in high-temperature railway processes, as well as the redistribution of residual stresses during subsequent operational loading conditions. For instance, simulations of the railhead repair welding process indicate that pre-heating has a minor impact on the quality of the repair, while the welding build-up paths have a significant impact. The simulations also highlight the critical region for fatigue crack initiation by showing how residual tensile stresses are reduced near the surface of the rail or wheel and increased at some distance below during operation for the repaired rail.
Pearlitic steels
Railhead repair
Welding simulations
Phase transformations
Cyclic plasticity
Finite element analysis
Homogenisation
Virtual Development Laboratory and online (password: 821697)
Opponent: Professor Håkan Hallberg, Solid Mechanics, Lund University, Sweden
Author
Björn Andersson
Chalmers, Industrial and Materials Science, Material and Computational Mechanics
Have you ever wondered how trains can travel long distances with such ease and efficiency? The answer lies in the fascinating world of mechanics and materials science, where the steel used in railway tracks and train wheels faces incredible challenges. Thermal loads are especially challenging. Imagine a train barrelling down the tracks, and a brake locks as the train is about to stop. The friction between the wheel and rail generates intense heat, causing sparks to fly like from a blacksmith's forge. An incident like this causes significant local changes in the wheel material, which may be detrimental to its mechanical performance. The rail is subjected to even more severe thermal shock loads during welding, whether it is when rail sections are joined during construction or when new material is added to the rail surface during repairs.
This thesis presents the development of a simulation-based assessment tool that incorporates thermo-mechanical-metallurgical modelling of how railway steel behaves when subjected to repeated intense heat and mechanical load. This tool is used to simulate various scenarios such as train wheel brake lockups and railhead repair welding. By testing these simulations against real-world data, it is shown that the approach works and that it can actually help to identify where problems might occur and how they can be prevented. Put simply, the research presented in this thesis aims to make train travel smoother, more sustainable and safer for everyone.
This thesis presents the development of a simulation-based assessment tool that incorporates thermo-mechanical-metallurgical modelling of how railway steel behaves when subjected to repeated intense heat and mechanical load. This tool is used to simulate various scenarios such as train wheel brake lockups and railhead repair welding. By testing these simulations against real-world data, it is shown that the approach works and that it can actually help to identify where problems might occur and how they can be prevented. Put simply, the research presented in this thesis aims to make train travel smoother, more sustainable and safer for everyone.
Numerical simulations of welding and other high temperature processes (CHARMEC MU37)
Chalmers Railway Mechanics (CHARMEC) (MU37), 2019-03-18 -- 2024-03-15.
European Commission (EC), 2019-03-18 -- 2024-03-15.
Driving Forces
Sustainable development
Subject Categories
Applied Mechanics
Other Materials Engineering
Vehicle Engineering
Metallurgy and Metallic Materials
Roots
Basic sciences
Areas of Advance
Materials Science
Infrastructure
Chalmers e-Commons
ISBN
978-91-8103-017-4
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5475
Publisher
Chalmers
Virtual Development Laboratory and online (password: 821697)
Opponent: Professor Håkan Hallberg, Solid Mechanics, Lund University, Sweden