Damage detection in a woven-fabric composite laminate using time-reversed Lamb wave

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 and the receiver locations, theoretically, the signal received back at the original transmitter location (reconstructed signal) is identical to the original input signal. Therefore, differences in the transmitted and reconstructed signals are an indication of the possibility of a defect being present. An experimental study of a baseline-free damage detection technique using time reversibility of Lamb wave for a woven-fabric composite laminate is presented in this article. The initial part of the study is aimed towards obtaining the best possible reconstruction of the input signal by tuning various parameters of interest, including an experimental study of the frequency-dependent attenuation of Lamb wave modes (amplitude tuning). A finite element simulation has also been carried out to study the effect of amplitude tuning. Finally, the time-reversal concept is used to detect damage in woven composite laminates without using any information from the undamaged structure. In this study, a small block mass bonded to the surface, surface erosion and local impact are considered as representative of different types of damage. The results obtained show that the Lamb wave technique using time-reversal concept identifies correctly the presence of damage in woven-fabric composite laminates, thus providing a basis for baseline-free damage detection in composite structures.