Active detection of block mass and notch-type damages in metallic plates using a refined time-reversed Lamb wave technique

Abstract

A recently proposed refined time-reversed Lamb wave method for baseline-free damage detection is tested experimentally for detecting block mass and notch-type damages in isotropic plates. The experimental results were compared with finite element simulations. The frequency of best reconstruction has been determined experimentally for the actuator–plate–sensor system by performing the time reversal process for a range of frequency, which is found to be very different from the sweet spot frequency exciting a single mode, hitherto recommended for improving the performance of the time reversal process-based techniques. It is shown that the damage indices (DIs) computed by using the conventional main wave packet of the reconstructed signal are less sensitive to the presence of damage, which is consistent with some recently reported experimental results by other groups. The present method with extended wave packet shows excellent sensitivity to damage for both block mass and notch-type damages and also ensures a low threshold for the undamaged case when used at the best reconstruction frequency. The refined DIs reflect the true severity of damage. It was observed that a putty on the plate has no significant change in the DIs in the present method, whereas a baseline method would identify it as a damage due to very significant scattering by the putty.