AN EXAMINATION OF TRAILING ECHOES IN TAPERED RODS

Abstract

Ultrasonic evaluation of complex structures is frequently challenging because of limited physical access to locations of interest. Cylindrical waveguides are an attractive solution for accessing complex structures, particularly at high temperatures, although trailing echoes resulting from mode conversions along the waveguide boundaries often interfere with the ultrasonic measurements. Tapered rod usage has already demonstrated an ability to reduce the impact of trailing echoes, but a clear relationship between taper angle and amplitude of trailing echoes has not been established. The research presented here considers the effect of the taper angle on trailing echoes in a through transmission configuration. Experiments confirm that attenuation of trailing echoes increases with the taper angle, but they also show that above a certain angle, the attenuation tends to be constant. The trailing echoes also spread out in time as the taper angle increases. Thus, a preferred angle may exist that gives the best signal for a particular rod length, diameter and inspection application. Finite difference and ray tracing methods were used to model the effect of the taper angle on trailing echoes using 2D simulations. Comparisons to experiments indicate that a full 3D model may be required to provide a reasonable match to the measurements and allow determination of an optimal taper angle.