Dynamic behaviours and fragility modelling of railway turnouts

Hamarat, Mehmet Zahid (2023). Dynamic behaviours and fragility modelling of railway turnouts. University of Birmingham. Ph.D.

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Abstract

In railways, turnouts, or also called switches and crossings, are widely reported as the origin of many problems owing to their involvement in many accidents and the major share on the budget of infrastructure managers. Turnouts have an asymmetrical and large geometry in order to enable diversion between railway tracks, leading to complex dynamic behaviour of the structure. The complex structure of turnouts and its dynamic effect catalyse the process of many failure types. One of common failures over a turnout structure is dynamic fragility. Particularly, high-frequency high-magnitude impact forces that are observed over turnout crossing noses cause many dynamic fragility problems including long terms defects such as fatigue.
This thesis aims at establishing a new numerical method to simulate dynamic fragility of turnout crossings from fracture mechanics’ point of view. In order to achieve this aim, first, it is targeted to improve the understanding of dynamic behaviours of turnouts under impact loadings varying from ideal environments to extreme events. A new numerical methodology is proposed to evaluate the complex behaviours of turnouts and its components. The new insights stemmed from this research has shown the importance of taking dynamic effects into account and the force spectra observed over the turnout structure. More importantly, the Multiphysics informed models helped to determine the critical section over a turnout structure and corresponding failure modes.
Following having a more comprehensive understanding of dynamic behaviours of railway turnouts, the fatigue behaviour of the critical section has been examined via Peridynamics. Peridynamics is a recent and promising numerical tool in the field of Fracture Mechanics. Prior to fatigue investigation, two new methodologies have been introduced into Peridynamics theory. Those methodologies have helped to track the formation of cracks, and reduce the simulation time significantly. It would not be possible to conduct fatigue simulations of complex geometries without those contributions. As is the final target, fatigue simulations have been carried over critical sections of a turnout as well as experimental geometries. It was found that the fatigue model in Peridynamics is promising in certain damage modes and confirms the general knowledge in most cases. Nonetheless, its efficiency has been found questionable in the case of fatigue over the crossing nose under a mixed mode compression loadings. The characteristics of Peridynamics have imposed certain limitations and it seems that those challenges must be addressed first in order to be able to increase the efficiency and to apply in railway applications.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):