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

Abstract

In this paper, an experimental study has been carried out to develop a baseline-freedamage detection technique using the time reversibility of a Lamb wave. The experimentshave been carried out on a metallic plate. Time reversibility is the process in which aresponse signal recorded at a receiver location is reversed in time and transmitted backthrough the receiver to the original transmitter location. In the absence of any defect ordamage in the path between the transmitter–receiver locations, theoretically thesignal received back at the original transmitter location (reconstructed signal)is identical to the original input signal. The initial part of the present work isaimed at understanding the time reversibility of a Lamb wave in an undamagedmetallic plate. This involves a thorough study of different parameters such asfrequency, pulse frequency band width, transducer size and the effects of tuning theseparameters on the quality of a reconstructed input signal. This paper also suggests amethod to mitigate the effects of the frequency dependent attenuation of Lambwave modes (amplitude dispersion) and thus achieve better reconstruction foran undamaged plate. Finally, the time reversal process (TRP) is used to detectdamage in an aluminium plate without using any information from the undamagedstructure. A block mass, a notch and an area of surface erosion are considered asrepresentative of different types of damage. The results obtained show that theeffect of damage on TRP is significant, contrary to the results reported earlier.