Numerical investigations of rolling contact fatigue crack growth in a rail head
Doctoral thesis, 2024
Rolling Contact Fatigue (RCF) cracks in railway rails are critical due to their impact on safety and maintenance costs. A rail break can be the ultimate consequence of progressive crack growth. Understanding influential mechanisms involved in RCF initiation and propagation is essential for developing effective inspection, maintenance, and replacement strategies. Despite extensive research on understanding mechanisms, and predicting RCF crack growth, there are still open questions, particularly regarding the direction and rate of RCF crack growth. This is due to the complex non-proportional and compressive loading from wheel‒rail contact in combination with rail bending and thermal loads.
This thesis aims to develop and employ a numerical framework for predicting directions and rates for RCF crack growth in railway rails under operational loading. A numerical procedure for simulating a propagating crack in 2D is developed. The finite element model features an inclined surface-breaking crack subjected to wheel‒rail contact load, rail bending, and temperature drop as isolated scenarios and in combinations. The effective crack propagation direction is predicted based on an accumulative vector crack tip displacement criterion. The influence of crack face friction and crack growth rate predictions are added to the numerical framework. It is observed that frictional cracks tend to go deeper into the rail under a pure contact load and under a combination of bending and contact loads, while friction has a moderate influence on crack paths under combined tensile thermal and contact loads. Furthermore, friction reduces crack growth rates.
The numerical framework for a frictionless stationary crack is extended to the 3D case of a semi-circular gauge corner crack embedded in a 60E1 rail. Results are evaluated at points along the crack front. The influence of crack size and inclination, magnitude and position of the contact load, wheel‒rail tractive forces, rail bending with different track support conditions, and varying thermal loads is studied. Rail bending and tensile thermal loads are found to promote downward growth compared to pure contact load cases. The location of the contact load significantly influences predicted growth rates while the influence of a tractive force decreases (rapidly) with depth. Rail lives computed from the integration of predicted growth rates are comparable to growth rates found in field investigations.
This thesis aims to develop and employ a numerical framework for predicting directions and rates for RCF crack growth in railway rails under operational loading. A numerical procedure for simulating a propagating crack in 2D is developed. The finite element model features an inclined surface-breaking crack subjected to wheel‒rail contact load, rail bending, and temperature drop as isolated scenarios and in combinations. The effective crack propagation direction is predicted based on an accumulative vector crack tip displacement criterion. The influence of crack face friction and crack growth rate predictions are added to the numerical framework. It is observed that frictional cracks tend to go deeper into the rail under a pure contact load and under a combination of bending and contact loads, while friction has a moderate influence on crack paths under combined tensile thermal and contact loads. Furthermore, friction reduces crack growth rates.
The numerical framework for a frictionless stationary crack is extended to the 3D case of a semi-circular gauge corner crack embedded in a 60E1 rail. Results are evaluated at points along the crack front. The influence of crack size and inclination, magnitude and position of the contact load, wheel‒rail tractive forces, rail bending with different track support conditions, and varying thermal loads is studied. Rail bending and tensile thermal loads are found to promote downward growth compared to pure contact load cases. The location of the contact load significantly influences predicted growth rates while the influence of a tractive force decreases (rapidly) with depth. Rail lives computed from the integration of predicted growth rates are comparable to growth rates found in field investigations.
Finite element analysis
Crack growth rate
Crack growth direction
Paris law
Rolling contact fatigue
Crack face friction
Rail deterioration
Vector crack tip displacement
Virtual Development Laboratory (VDL), Chalmers Tvärgata 4C, Gothenburg
Opponent: Professor Roger Lewis, Department of Mechanical Engineering, The University of Sheffield, United Kingdom
Author
Mohammad Salahi Nezhad
Chalmers, Industrial and Materials Science, Material and Computational Mechanics
Numerical predictions of crack growth direction in a railhead under contact, bending and thermal loads
Engineering Fracture Mechanics,;Vol. 261(2022)
Journal article
Numerical prediction of railhead rolling contact fatigue crack growth
Wear,;Vol. 530-531(2023)
Journal article
M. Salahi Nezhad, F. Larsson, E. Kabo, A. Ekberg. Finite element analyses of rail head cracks: Predicting direction and rate of rolling contact fatigue crack growth
M. Salahi Nezhad, E. Kabo, A. Ekberg, F. Larsson. Rolling contact fatigue crack propagation in rails ‒ numerical investigation on consequences of operational load variations
Railways provide a safe and efficient mode of transport with a low carbon footprint and high capacity. These features promote sustainability and reduce global warming. As a result, demand for rail transportation has increased in recent decades and is expected to significantly increase in the future. This imposes high demands on the expensive and sensitive railway infrastructure.
The steel-to-steel contact between the wheel and rail results in a contact area the size of a coin. The wheel load including frictional forces due to acceleration, braking and/or curve negotiation is transferred through this small contact patch. As a result of these loads, Rolling Contact Fatigue (RCF) cracks are formed. In addition, bending and tensile thermal forces due to restricted thermal contraction are acting in the rail.
To fulfil the increased demands, efficient maintenance is essential. This can be carried out as corrective and/or preventive maintenance. The former is typically more costly and disruptive to traffic. Shift to preventive maintenance requires a deeper understanding and predictive abilities regarding how RCF cracks form and grow. It is particularly of importance to know how fast and in which direction cracks grow to avoid deep cracking that is difficult to mitigate and may pose a safety risk.
This study aims to improve predictions of surface initiated RCF crack growth in rails under operational loading using numerical simulations. For this, a numerical framework is developed to investigate crack growth direction and rate under a wheel‒rail contact load in combination with rail bending and tensile forces due to restricted thermal contraction. The influence of operational conditions is investigated with the aim of improving maintenance planning and thereby promoting a more sustainable railway network.
The steel-to-steel contact between the wheel and rail results in a contact area the size of a coin. The wheel load including frictional forces due to acceleration, braking and/or curve negotiation is transferred through this small contact patch. As a result of these loads, Rolling Contact Fatigue (RCF) cracks are formed. In addition, bending and tensile thermal forces due to restricted thermal contraction are acting in the rail.
To fulfil the increased demands, efficient maintenance is essential. This can be carried out as corrective and/or preventive maintenance. The former is typically more costly and disruptive to traffic. Shift to preventive maintenance requires a deeper understanding and predictive abilities regarding how RCF cracks form and grow. It is particularly of importance to know how fast and in which direction cracks grow to avoid deep cracking that is difficult to mitigate and may pose a safety risk.
This study aims to improve predictions of surface initiated RCF crack growth in rails under operational loading using numerical simulations. For this, a numerical framework is developed to investigate crack growth direction and rate under a wheel‒rail contact load in combination with rail bending and tensile forces due to restricted thermal contraction. The influence of operational conditions is investigated with the aim of improving maintenance planning and thereby promoting a more sustainable railway network.
Growth of rolling contact fatigue cracks (CHARMEC MU38)
Chalmers Railway Mechanics (CHARMEC), 2019-09-01 -- 2024-08-31.
Driving Forces
Sustainable development
Areas of Advance
Transport
Subject Categories
Applied Mechanics
Other Materials Engineering
Infrastructure
C3SE (Chalmers Centre for Computational Science and Engineering)
Chalmers e-Commons
ISBN
978-91-8103-074-7
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5532
Publisher
Chalmers
Virtual Development Laboratory (VDL), Chalmers Tvärgata 4C, Gothenburg
Opponent: Professor Roger Lewis, Department of Mechanical Engineering, The University of Sheffield, United Kingdom