Verification of the use of micro-CT scanning to assess the features of entire squat type defects

Squats and studs are defects in railheads that share features, but have different causes. This paper examined four squat and stud samples from three different traffic environments to compare features using μ-CT X-ray scans, surface and subsurface inspection. μ-CT scanning has been used before as a non-destructive method to investigate rail defects, but not the entire defect. The scans were verified and allowed the identification of areas of interest when sectioning the samples further. The scan volumes were also used to create 3D models of the crack networks for the 3 samples that were scanned. All defects contain similar superficial features but the depth and severity of the subsurface damage varies. This work provides a visualisation of the 3D nature of studs in a way not seen before, as a 3D model the crack network from an in-service defect. The models of two of the defects showed the influence of hollow wheels initiating defects, as the crack seemed to initiate on the field side, grow down and towards the gauge side, before resurfacing as the longitudinal crack noted in all four defect samples. One sample is believed to have initiated due to contamination of the weld and the only squat sample, which failed in track, was believed to be ingot cast steel containing many inclusions. Three samples were studs and one was a squat. Each defect developed for different reasons, although the two metro samples were similar. One of the studs shows branching of cracks that, based on its changing angle of growth, could continue to grow into transverse defects, breaking the rail. The three defects that were scanned would all be classed as studs, but their crack morphology varies, possibly because they are all from different traffic environments. They also show slight differences to other studs in literature

Field studies on sleeper deflection and ballast pressure in heavy haul track

Deflection of sleepers (vertical displacement) and ballast pressure (vertical stress) under traffic loads are two important performance indicators for determination of rail track quality. Excessive values of these parameters can adversely affect the track structural stability, accelerate the track deterioration and consequently affect the safety of running trains. This paper reports field tests on two heavy haul tracks in Australia with normal operating condition and similar traffic loads. In the first test site, the ballast pressure and sleeper deflection were measured. In the second site, only the sleeper deflections were recorded; however, in this site, the capping layer interface was modified using inserts of various design of geogrids. Analysis of results obtained from these field measurements provide valuable insights into the sleeper deflection and ballast pressure magnitudes and patterns under real life traffic in heavy haul tracks as well as the effects of geogrids on reducing the sleeper deflections