Defects Evaluation in Lamb Wave Testing of Thin Plates

In the present study, dispersion and displacement curves of ultrasonic lamb wave, propagated in Aluminum thin plates, were drawn. Two ultrasonic lamb wave techniques, pulse-echo (a1 mode as emitter) and emission (s1 mode as emitter), were used for interpretation of notch defects with depths of 10%, 30% and 60% of plate thickness. Thickness of plate was 2 mm and the nominal centre frequency of transducers was 2 MHz. It was observed that these techniques are sensitive to evaluate defects, especially in short probe to defect distances. Also, it was found that amplitude analysis can give some qualitative and quantitative information about defects depth. But evaluation results were not sometime repeatable. The basic of evaluation was using a special DAC curve which was easy for applying by operators. In this respect, pulse echo method resulted in better sensitivity of amplitude to defects depth and distance variations as compared to emission method.