Towards simulation-based optimisation of materials in railway crossings

Licentiate thesis, 2018

Railway crossings are subjected to an intense load environment caused by the rail discontinuities needed to accommodate the passage of wheel flanges in intersecting traffic directions. This gives rise to high costs associated with repair and maintenance. For given traffic conditions, several approaches 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 to improve robustness and computational efficiency. The methodology is able to account for the dynamic vehicle-track interaction, resolve the elasto-plastic wheel-rail contact, and account for the main damage mechanisms related to the running surface of a crossing.

In this thesis, the methodology is updated with a metamodel for plastic wheel-rail normal contact that is introduced to meet the computational challenge of a large number of finite element simulations. The metamodel is inspired by the contact theory of Hertz, and for a given material it computes the size of the contact patch and the maximum contact pressure as a function of the normal force and the local curvatures of the bodies in contact. The model is calibrated based on finite element simulations with an elasto-plastic material model. It is shown that the metamodel can yield accurate results while accounting for the inelastic material behaviour.

Furthermore, the simulation methodology is employed to compare the performance of two rail steel grades that are used in crossings: the fine-pearlitic steel R350HT and the austenitic rolled 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 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.