Fundamental Study on Detectability of Subsurface Defects by Ultrasonic Testing

Abstract Ultrasonic testing is commonly used for detecting inner defects. Recently, new methods are trying to apply for detecting subsurface defects. In this paper, several ultrasonic testing methods were applied both for detecting the subsurface defects in the testblocks, which were produced using diffusion bonding, and for estimating their sizes and locations. When using a broad-band type probe, an edge of a defect located at 1 mm or deeper from the surface can be detected by tip echo method. Surface wave method can be effectively used to determine the upper edge of a defect. Mode conversion method can be used to estimate the lower edge of a defect. Using creeping wave method, echo amplitude is approximately proportional to defect height in the case of small defects. Conventional angle beam method (frequency: 2 MHz, refraction angle: 70 deg.) is not effective for estimating defect size and location but available for detecting subsurface defects.