Pulse-Echo and Pitch-Catch: Ultrasonic C-Scan of Adhesively Bonded Single Lap-joints

The non-destructive testing of adhesively bonded single lap joints can be conducted using either low-frequency Lamb waves in a pitch-catch mode or high-frequency bulk waves in a pulse-echo mode. Each method has its advantages and disadvantages over the other one. This paper presents a comparison between both techniques for damage imaging of adhesively bonded lap joints. The measurement method of high-frequency ultrasound is conducted in a pulse-echo approach using a delay line transducer. On the other hand, the low-frequency ultrasound measurement method is carried out in a pitch-catch configuration by using a PZT disk moved by a positioning system over the scan area. In both methods, the signals are acquired in a C-scan manner over the adhesive joint area. Applying signal processing techniques, including frequency-wavenumber filtering, bandpass filtering, and root-mean-square, images of the scan area are obtained. Finally, discussions on the results of using the two methods are presented.