THE ROLE OF THERMAL INPUT ON SQUAT TYPE DEFECTS IN RAILS

The recently discovered squat type defect which is understood as a thermal defect has renewed interest in rolling contact fatigue damage in railway studies. These defects were reported to appear in several locations across the globe where the cost incurred for their removal leads to a major increase of track maintenance cost. While the growth mechanism for classical rolling contact fatigue squat is well understood, limited research has so far been undertaken for squat type defects leaving them poorly understood, especially in their initiation and propagation mechanism. The presence of white etching layer in all locations where these defects have been found strongly suggests that thermal input is responsible for their development rather than fluid assisted growth that is responsible for the development of classical rolling contact fatigue squats. In this thesis, research is reported that combines morphological analysis data with a boundary element model to understand the direct influence of these thermally transformed layers on the initiation and propagation of squat type defects in rail. Furthermore, the work has been extended to explore the possibilities for defect detection in rails reaching a positive proof of concept outcome. It is expected that this approach could serve as a basis for maintenance schedules in order to avoid rail failure due to inadequate understanding of this type of defect.