Various destructive and nondestructive testing techniques have been used for testing the joint quality in adhesive bonding. Ultrasonic testing has proven to be one the most efficient methods for this purpose. Among the many different ultrasonic testing techniques, C-scan imaging seems to be the most efficient for testing adhesive joints. In this paper, new testing schemes are proposed for extraction of the required information from the ultrasonic signals acquired in a C-scan imaging process. Three different indices, which are based on the amplitudes of the ultrasonic radio frequency signals, are introduced. Compared to the gating and peak detection approach used in conventional ultrasonic C-scan imaging, these indices provide much more information about the quality of the bonding in an adhesive joint. Moreover, while only one side of the adhesive layer can be tested in conventional C-scan imaging, the new technique makes the testing of both sides of the adhesive
possible with scanning performed on one side of the specimen. Furthermore, in the case of very thin samples, where the returned echoes are not separable and, hence, no C-scan images can be generated, the new technique works quite well. The capability of the proposed approach in providing C-scan images from a number of samples, some of which are considered not to be testable by conventional ultrasonic testing techniques, is demonstrated.
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