Ultrasonic Angle-Beam Technique as a Tool for Quantitative Characterization of Small Closed Cracks.

Abstract

An ultrasonic nondestructive evaluation method has been developed for the quantitative characterization of smaller closed cracks. The method is based on a novel ultrasonic angle-beam technique, where the use of an oblique longitudinal 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 closure by solving an inverse problem. The calibration equation for the open cracks, which is considered as the basis for the evaluation of closed cracks, is newly analyzed in the present paper, and a modified form of the calibration equation is proposed which can be extended to a number of practical applications. The accuracy and reliability of the calibration equation is demonstrated here by applying the method to a number of both closed and open cracks in stainless steel specimens. In addition, the possibility of evaluating the cracks in different materials of interest is studied here experimentally in the perspective of the present approach, and is compared with those of the usual methods of evaluation.