Dynamic wheel-rail interaction over rail squat defects

The dynamic interaction between wheel and rail generates the vibration and acoustic radiation transmitted through other media such as structural track systems, air pressure, and rolling stocks. Noteworthy, both wheel and rail irregularities often induce additional impact vibration and noise along the rail corridor. Rail squats and studs are typically classified as the development of any cracks that have grown longitudinally and laterally through the subsurface and become a laminated crack resulting in a depression of the rail surface. The rail defects are commonly referred to as ‘squats’ when they are initiated from rolling contact fatigue cracks, and as ‘studs’ when they are associated with a white etching layer due to wheel slips or excessive tractive effort. Interestingly, recent research shows that rail squats can be found almost everywhere, and every type of track structures, gradients and geometries in either light passenger or heavy freight traffics and for low, medium or high speed trains all over the world. A more pronounced issue appears when the crack grows and finally flakes off the rail. This paper highlights the monitoring of wheel-rail interaction over rail squat defects. Using the axle box acceleration data obtained from the calibrated track recording vehicle, the frequency spectra can be analysed. The results demonstrate an apparent influence of squats on the wheel-rail interaction over the defective section and increased acoustic radiation at the high frequency range.