Modelling of cyclic and viscous behaviour of thermomechanically loaded pearlitic steels; Application to tread braked railway wheels
Doctoral thesis, 2018
Finite element (FE) analyses are carried out of generic heavy haul wheel designs subjected to thermal loading from high power drag braking. In these analyses, the results from using a plasticity and a viscoplasticity model are compared. Both models are calibrated against results from cyclic strain controlled (low strain rate) experiments with hold-time of ER7 wheel steel at different elevated temperatures. The comparison shows an increasing influence of the choice of material model with power of the drag braking.
Also, a methodology to simulate full scale brake rig tests is developed. It includes an axisymmetric thermal analysis, a 3D structural wheel-rail contact analysis and a 3D structural analysis with a traversing contact load. The wheel material behaviour is modelled by a plasticity model calibrated against cyclic strain controlled (low strain rate) experiments of ER7 steel. In addition, the infuence of important operational parameters such as axle load, maximum vehicle speed and block material is investigated with respect to the ratchetting life of the wheel tread.
To improve the modelling of the behaviour of ER7 steel for a wider range of loading rates and multiaxial loading, a viscoplasticity model is adopted and calibrated against test data of ER7 steel at different temperatures for slow cyclic strain controlled tests with hold-time, ratchetting tests with rapid cycles and cyclic biaxial tests. A simulation of a brake rig experiment is used to highlight the importance of using the viscoplasticity model in the prediction of the ratchetting fatigue life.
Finally, a cyclic plasticity model incorporating phase transformations is developed to examine what phases and residual stresses that are obtained in a railway wheel after repeated short term local heating followed by rolling contact. This model can be used to study thermal damage mechanisms in rail and/or wheel steels that may lead to initiation of cracks (e.g. squats (studs) in rails and crack clusters in wheels).
finite element analyses
rolling contact fatigue
full-scale brake rig testing
Chalmers, Industrial and Materials Science, Material and Computational Mechanics
High Temperature Tread Braking Simulations Employing Advanced Modelling of Wheel Materials
IHHA 2015,Perth,Australia,; (2015)
Paper in proceedings
A methodology to predict thermomechanical cracking of railway wheel treads: From experiments to numerical predictions
International Journal of Fatigue,; Vol. 105(2017)p. 71-85
Ali Esmaeili, Johan Ahlström, Magnus Ekh, Dimitrios Nikas, Tore Vernersson. Modelling of temperature and strain rate dependent behaviour of pearlitic steel in block braked railway wheels
Ali Esmaeili, Johan Ahlström, Magnus Ekh. Modelling of cyclic plasticity and phase transformations during repeated local heating events in rail and wheel steels
Thermomechanical capacity of wheel treads at stop braking: A parametric study
International Journal of Fatigue,; Vol. 113(2018)p. 407-415
Due to the geometry of the railway rails and wheels, a typical wheel-rail contact surface is merely the size of a coin. The material in the vicinity of this contact is subjected to very high loads. These loads are generated due to axle loads that can be from 10 tonnes up to 40 tonnes (for heavy duty railways) and also frictional forces in the rail-wheel interface caused by train acceleration, braking, and curving. Add to that the frictional heat generated between brake block and wheel during braking or between wheel and rail during braking and acceleration which might result in elevated temperatures up to 500℃. In severe cases, such as malfunctioning traction systems, temperatures might even reach 800-1000℃. These complex loading conditions might result in damage and failure of the rail and wheel material causing major maintenance costs in the railway industry.
To be able to understand load limits (e.g. the maximum allowed train axle loads), to plan an efficient maintenance schedule and also to improve the components’ design for obtaining sufficiently long life of the components, we need to have a good understanding of the material behaviour in the components under operational conditions.
Due to high strength, high wear resistance and relatively low cost, pearlitic steels are widely used for railway rails and wheels. In this thesis, an effort has been made to develop material models that are able to numerically simulate the behaviour of the pearlitic steel in railway wheels when subjected to mechanical and thermal loads. These models are used to simulate different scenarios of railway operational conditions and for study of possible damage mechanisms that might result in failure of the wheel material.
Research into enhanced tracks, switches and structures (In2Track)
European Commission (Horizon 2020), 2016-12-01 -- 2020-12-31.
Swedish Transport Administration, 2016-09-01 -- 2019-06-30.
Areas of Advance
Other Materials Engineering
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4524
Chalmers University of Technology
Virtual Development Laboratory (VDL-room), Chalmers Tvärgata 4C, Chalmers University of Technology, Gothenburg, Sweden
Opponent: Dr. David Fletcher, Department of Mechanical Engineering, The University of Sheffield, UK