Time Reversal of Lamb Waves for Damage Detection in Thermoplastic Composites

The objective of this study is to evaluate the use of correlation methods as a damage detection criterion in the application of the Time Reversal of Lamb Waves (TRLW) approach. The dispersion and attenuation characteristics of the waves are used for determining the maximum area to be inspected in a two transducers configuration. The Finite Element (FE) Model and experimental data are compared for verification of the method. The experimental setup consisted of a pair of piezoelectric transducers, working both as actuator and sensors, separated by a predetermined distance. Different defect sizes and positions with respect to the transducers were introduced on both aluminum and thermoplastic composite plates. A waveform generator was used to excite the piezoelectric actuators. An oscilloscope was used for acquiring the signals from the transducers. Those signals were processed in Matlab TM for the application of time reversal and a correlation analysis. The damage consisted of a hole through the thickness varying its diameter and location. The FEM simulates the propagation of Lamb waves in aluminum plates in order to analyze TRLW for damage detection. Lamb waves were generated using a 5 cycle Hanning window at different frequencies. The FEM consisted of standard 3D elements (C3D8I) for the plates and PZT elements (C3D8E) for the transducers. In order to simplify the model the PZTs were assumed to be perfectly bonded to the plates. The FEM analysis was mainly focused on the S 0 -wave. The indication of the presence of damage is performed using the correlation between the original actuation and the time reversed signal.

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