A refined Lamb wave time-reversal method with enhanced sensitivity for damage detection in isotropic plates

In this work, we critically examine the effectiveness of the time-reversed Lamb wave based baseline-free damage detection technique for notch-type damage in isotropic plates, through finite element (FE) simulation of an integrated actuator–plate–sensor system. The FE simulation has been verified with experiments. We show that the single-mode tuning, hitherto recommended for improving performance of the time-reversal process (TRP) based technique, does not generally lead to the best reconstruction of the original input signal. The results of the TRP in the presence of notch-type damage show that the damage indices (DIs) computed using the conventional main wave packet of the reconstructed signal do not show any significant change with an increase in damage size, which is consistent with some recently reported experimental results by other groups. A new method of computing the DIs with extended signal length is proposed, which shows excellent sensitivity to damage, and also ensures a low threshold for the undamaged case, when used at the best reconstruction frequency. The same refined DIs, however, are not effective, when used at the so called sweet spot frequency exciting a single mode. Refined DIs based on correlation and similarity of the reconstructed signal reflect the true severity of damage.