Rail break research is the focus of the project. A comprehensive study of past rail-break failures shows that more than 70% of the failures occurred at the thermite weld sections.
A failure analysis worksheet consisting of a diagnostic and prognostic section was introduced for systematic analysis and documentation. The prognosis portion includes the information of failure location, track geometry, train speed and the information of service history, such as dates of installation and service duration and so on, while the diagnostic portion includes the calculated fracture toughness, crack growth rate and total number of cycles to failure. Once digitalized and computerized, this worksheet will provide capability for easy failure data collection and post-analysis of thermite weld failures in the future.
This project has developed a systematic diagnosis and prognosis approach to assess the root cause of rail-weld track breaks and provide vital knowledge on the failure mode and failure analysis mechanisms:
- Analyse the past failure reports to identify the failure modes and root cause of thermite weld failures
- Conduct mechanical test to quantify the fracture toughness and fatigue behaviour of thermite weld materials
- Apply fracture assessment to evaluate the thermite weld specimen performance
Fractographic analysis study of the fracture surfaces was developed to correlate failure appearance with failure cause. Traditional Scanning electron microscopy (SEM) is a powerful magnification tool but is limited in its use for large rail specimens. The use of Laser Scanning Microscopy (LSM) for fractographic analysis allows study of surface features and cracks without having to cut out the fracture surface.
Fracture and fatigue tests have been conducted to study the fracture performance and fatigue resistance of thermite weld specimens. Three-point slow bend tests, three-point fatigue test and Charpy test, conducted with respect to BS EN standards, show the brittle fracture properties of thermite weld failures.