NUMERICAL SIMULATION FOR THE EFFECT OF SOUND VELOCITY ANISOTROPY ON SHIFT OF PROBE INDEX AND BEAM ANGLE OF ULTRASONIC ANGLE PROBES

Abstract The probe index and beam angle of angle probes are very important characteristics in ultrasonic angle beam examination, which are recommended to be measured by using a standard specimen, STB-A1 (IIW-l/ISO-2400). However, it has not been made clear how sound velocity anisotropy, if it exists, affects those characteristics in the STBs or in similar specimens. In order to clarify the problem, an analytical study was carried out by the numerical simulation method for ultrasonic angle beam examination, which had been developed by the author. In consequence, the following results were obtained. (1) Large negative shifts of the probe position, which mean positive shift of the probe index, are observed for the beam angles of angle probe larger than 45 degrees when the maximum sound velocity is at 45 degrees to the scanning surface of STBs. There exist negative shifts of probe index at the beam angles smaller than 45 degrees. The reverse phenomena take place if the maximum sound velocity occur at 0 and 90 degrees to the scanning surface. (2) The opposite side shift of probe position is observed in the case of the measuring beam angle probes because the reflecter is a convex cylinder rather than a concave one. Therefore, the decided beam angles of angle probe by the STBs are largely shifted ones due to the summation of both the shift effects.