Defect characterization in Al welded joints by non-contact Lamb wave technique

The use of air-coupled sensors to detect flaws in Al welded joints and the advantage of Lamb wave for their characterization has been proved. Ultrasonic waves were generated by a pulsed laser and by contact angle-beam transducer, and received by an air-coupled capacitive transducer. Laser-based configuration was used to quickly locate the defect, whereas the angle-beam contact probe configuration to characterize it thanks to the dispersive behavior of Lamb waves. Guided waves allow inspection of the complete thickness with only one scan, permitting to detect and to size both internal and surface defects; their high flexibility in the measurement is due to the various parameters characterizing their behavior when compared to the bulk waves. Moreover, L-scan configuration can be used to inspect single-side access structures, and compared to the conventional A, B, C and P-scan allows to reduce inspection time, and therefore the related costs.