Long-term rail damage evolution in railway crossings

Doktorsavhandling, 2020

To accommodate the passage of wheels in intersecting traffic routes, fixed railway crossings have discontinuous rails leading to an intense load environment due to repeated wheel-rail impacts. This gives rise to high costs associated with repair and maintenance of the rails in the crossing. For given traffic conditions, several approaches to crossing design can be undertaken to mitigate the material degradation and hence reduce the life cycle cost. In the present thesis, the option of selecting a more suitable crossing material is explored.

To obtain a guideline for material selection, the in-track performance of different materials during the life of a crossing needs to be predicted. In this work, an existing simulation methodology is extended by improving its robustness and computational efficiency. The methodology is able to account for the dynamic vehicle-track interaction, resolve the elasto-plastic wheel-rail contact, and consider the main damage mechanisms related to the running surface of a crossing rail. In this thesis, the methodology is updated by including a metamodel of plastic wheel-rail normal contact, which is introduced to meet the computational challenge of performing a large number of finite element simulations. The metamodel is based on the contact theory of Hertz. It is shown that the metamodel yields accurate results while accounting for the inelastic material behaviour.

The simulation methodology is applied to several test cases. In the first study, it is employed to compare the short-term performance of two rail steel grades that are commonly used in crossings: the fine-pearlitic steel R350HT and the austenitic manganese steel Mn13. A representative load sequence generated by means of Latin hypercube sampling, taking into account variations in worn wheel profile, vehicle speed and wheel-rail friction coefficient, is considered. After 0.8 million gross tonnes (MGT) of traffic, it is predicted that the use of rolled Mn13 will result in approximately two times larger ratchetting strain as compared to the R350HT. In the second study, the methodology is used to simulate approximately 12 MGT of traffic in a crossing. The results of the simulations are compared with data measured in the field. It is shown that the simulations are in good qualitative agreement with the measurements. Finally, the methodology is used to quantify the difference in long-term damage between crossings with different crossing angles. As expected, the crossing with the largest crossing angle is subjected to the highest impact loads and exhibits the most damage after 52 MGT of simulated traffic.