Defect detection in thin plates by ultrasonic lamb wave techniques

In the present study, the ability of ultrasonic lamb wave testing for defect detection and sizing in a thin aluminium plate (2mm in thickness) was investigated. The numerical methods were applied for drawing the dispersion and displacement curves of lamb waves in order to adopt mode selection. Two ultrasonic lamb wave techniques, pulse-echo (a1 mode as emitter) and emission (s1 mode as emitter), were applied for interpretation of notch defects with depths of 10, 30 and 60% of plate thickness. It was observed that these techniques are sensitive enough to evaluate notch defects, especially in short probe to defect distances. Defect location and defect length were proposed to be determined in the manner similar to common ultrasonic testing methods. Also, a Distance-Amplitude-Correction (DAC) curve was proposed for defect sizing which showed that amplitude analysis can give some qualitative information about defect depth but results were not always repeatable. The pulse-echo method showed better sensitivity for defect detection and sizing.