Ultrasonic Evaluation of Dissimilar Solid-State Bonds

This paper discusses two special ultrasonic NDE problems of particular interest to dissimilar solid-state bonds. The first problem is the so-called “cold weld” effect which is a lack-of-bond type defect, but as opposed to other common types of defects in this category, it is very difficult to detect by ultrasound. The other problem, to be addressed in the second part of this paper, is the “blinding” effect of the strong interface reflection caused by acoustical impedance mismatch between dissimilar materials. Ultrasonic characterization of such bonds is rendered very difficult by the fact that the relatively weak signals generated by possible boundary imperfections are often overshadowed by this inherent reflection. A novel technique based on the symmetric part of the interface reflections from the opposite sides of the bond will be introduced to obtain quantitative information even from very good, apparently flawless bonds