ICRI Project: Quantify Surface Damage
Quantify Surface Damage
Quantify Surface Damage
Participants: Alok Jahagirdar (NRC), Sylvie Chenier (NRC)
The objective of this project is to advance techniques for assessing the surface condition of rail that have relevance and application to remediation (e.g. through rail grinding) and risk assessment (by relating surface condition to inspection reliability and rail failure).
The project approach consists of two stages:
- A destructive metallurgical analysis of RCF damage on the rail in both freight and transit systems, and
- A non-destructive eddy current (EC) evaluation of the RCF surface damage in these same rails.
Each part consists of the following:
- Development of an “RCF matrix” quantifying rail running surface fatigue damage as a function of rail type and position in track, tonnage accumulation, traffic condition, as well as other environmental and maintenance conditions the rails are subjected to during their life-cycle.
- Inspection of the RCF surface damage through non-destructive EC technology in an effort to build a link between surface damage observed through destructive metallography and non-destructive EC inspection techniques.
A methodology for metallurgical analysis of RCF crack planes has been developed for implementation into the RCF matrix.
To date 33 rail samples have been analyzed and included in the RCF matrix. RCF metrics include crack position on the railhead, angle to surface, as well as crack length and depth. EC measurements are taken for each sample and Vickers micro-hardness traces collected on representative samples. Two bins in the RCF matrix have enough hi-rails samples analyzed to allow a direct comparison of RCF crack depths and crack angles; 4.0-4.9 degree curves with 500-599 MGT, and 5.0-5.9 degree curves with 600-699 MGT and the following main observations were made:
- Results comparison for each of the selected bins indicates an increasing crack angle with increasing lateral position (i.e. distance from the gauge face). Cracks are shallow (i.e. small angle to the surface) at the gage-face (GF), but their angle increases as the position shifts toward TOR, becoming orthogonal to the running surface at TOR. This trend can also be seen across the entire population of hi-rails found within the 33 rails that were analyzed.
- Comparing the crack angles from the two bins indicates that in sharper curves the transition from GF to TOR crack angles occurred more rapidly, i.e. cracks approached the 90-degree orthogonal orientation sooner than they did in shallower curves.
- For most samples analyzed, there is a good correlation between metallography and transverse EC scans. Longitudinal scans do not always provide a good correlation.