Abstract
Brewster et al. have previously shown that the ultrasonic caustics can be applied for sizing the surface and the internal cracks in the circular rods by using the shear wave. However, the application technique by employing the longitudinal wave and the general evaluation procedure for the rods with an arbitrary diameter are not shown. Moreover, the accuracy of this technique has not been discussed in detail. In this study, we investigated about those points to improve the ultrasonic caustics technique. The crack is evaluated by employing the shear wave and the longitudinal wave, and the general relationship between an angle β0 of the receiver and a ratio a/D of the crack length a to the diameter D of rods is given for determining the crack length. The immersion method is employed to aluminum rods with a surface crack in the radial direction to verify that the minimum crack size of 2mm is evaluated by the ultrasonic caustics technique under present experimental conditions. It is also shown that the length of the surface crack in oblique direction and the length of the internal crack in radial direction can be evaluated by this technique.
