Crack Depth Measurements with the Aid of SAW NDE

This report presents results of measurements of crack depth with the aid of acoustic bulk and surface waves. Both simulated and real fatigue cracks were examined. Two techniques were employed, one took advantage of the very efficient mode conversion between acoustic surface waves and shear waves at the crack tip; the other technique used the diffraction of shear waves at the crack tip. Both techniques were used on a number of simulated {spark eroded) and real cracks in Al 2024. In one fatigue specimen which contained an elliptical crack 4.5 mm in length and 1.25 mm in depth, crack closure studies were carried out. The precision of crack depth determination was judged to be better than 10%