Boundary element analysis of surface waves interaction with finite-size, surface-breaking cracks in the railhead

The interaction of surface acoustic waves with finite-size, surface-breaking, semi-circular cracks in the railhead is studied numerically, and experimentally. We focus on the behavior of the reflection coefficient of the Rayleigh wave from such cracks in the far field of the crack, when the depth of the crack is comparable to the wavelength of the interrogating surface wave. The theoretical, boundary element, and experimental results presented are in very good agreement over the range were the crack depth is much smaller or much larger compared to the wavelength of the incident Rayleigh wave. In the transition regime, between these two limiting cases, only the boundary element and experimental data show good agreement since the theoretical predictions are no longer applicable. In the high crack depth to wavelength ratio regime, the boundary element and experimental results close to the crack approach the limiting value of the reflection coefficient from a 90-degree corner. The results of this study is very useful to the design of the wheel probe for rail ultrasonic inspection and the signals analysis to detect gauge corner cracking in railhead.