Parametric studies on the effect of defect characteristics on their detection and sizing by ultrasound

Abstract

This paper describes the experimental results of the characterisation of the ultrasonic response produced by planar ‘diffusion welded’ defects, inspected with the pulse-echo technique with probes at angles of inclination of 45°, 60° and 70°. In particular, the amplitude and time locus curves for orthogonal scanning lines at the defect plane and passing through its middle have been determined. In general, a diffuse presence of effects linked to mode conversion phenomena of the ultrasonic wave incident on the defect was observed, which in many cases made interpretation of the results more complicated. For the embedded vertical defects (tilt angle equal to zero) it was possible to determine the curves giving the echo maximum amplitude as a function of the defect depth; these curves have a regular behaviour which follows the line of the DAC curve quite well. Even for surface defects which can be detected by the corner effect, one finds quite regular behaviour as a function of the various parameters (defect height, probe angle, tilt angle), while it is more complicated to interpret the results for the embedded inclined defects (tilt angle different from zero), probably because of the different contributions of the mode conversion phenomena in the individual cases.