Enhancement of ultrasonic surface waves at wedge tips and angled defects

The behaviour of sound waves interacting with wedges has attracted interest from researchers in geophysics and non-destructive testing. We consider here the near-field behaviour of Rayleigh waves incident on wedges and surface-breaking defects which propagate at an angle to the surface, such as rolling contact fatigue on rails. It has been shown that, for a detection point on the edge of the crack tip, a very large signal enhancement is observed for shallow angles. We explain this behaviour through considering the effect of the defect geometry, with changes in the frequency·thickness product leading to mode-conversion of the incident Rayleigh wave.