Time reversibility of a Lamb wave for damage detection in a metallic plate

In this paper, an experimental study has been carried out to develop a baseline-free damage detection technique using the time reversibility of a Lamb wave. The experiments have been carried out on a metallic plate. Time reversibility is the process in which a response signal recorded at a receiver location is reversed in time and transmitted back through the receiver to the original transmitter location. In the absence of any defect or damage in the path between the transmitter-receiver locations, theoretically the signal received back at the original transmitter location (reconstructed signal) is identical to the original input signal. The initial part of the present work is aimed at understanding the time reversibility of a Lamb wave in an undamaged metallic plate. This involves a thorough study of different parameters such as frequency, pulse frequency band width, transducer size and the effects of tuning these parameters on the quality of a reconstructed input signal. This paper also suggests a method to mitigate the effects of the frequency dependent attenuation of Lamb wave modes (amplitude dispersion) and thus achieve better reconstruction for an undamaged plate. Finally, the time reversal process (TRP) is used to detect damage in an aluminium plate without using any information from the undamaged structure. A block mass, a notch and an area of surface erosion are considered as representative of different types of damage. The results obtained show that the effect of damage on TRP is significant, contrary to the results reported earlier