Ultrasonic angle-beam technique as a tool for quantitative characterization of small closed cracks

An ultrasonic nondestructive evaluation method has been developed for the q uantitative characterization of smaller closed cracks. The method is based on a novel ultrasonic angle-beam technique, where the use of an oblique lon gitudinal wave with a small angle of incidence upon the specimen surface is emphasized. Using the present method, size of the small closed cracks can be evaluated nondestructively together with the information of crack closur e by solving an inverse problem. The calibration equation for the open crac ks, which is considered as the basis for the evaluation of closed cracks, i s newly analyzed in the present paper, and a modified form of the calibrati on equation is proposed which can be extended to a number of practical appl ications. The accuracy and reliability of the calibration equation is demon strated here by applying the method to a number of both closed and open cra cks in stainless steel specimens. In addition, the possibility of evaluatin g the cracks in different materials of interest is studied here experimenta lly in the perspective of the present approach, and is compared with those of the usual methods of evaluation.