Imaging of Closed Cracks by Water-Coupled Sensor Array Based on Nonlinear Lamb Waves

Nonlinear waves have shown higher sensitivity to closed cracks in fatigue, corrosion, and thermal damage than linear waves. Using the frequency information, the existence of a closed crack can be detected along a 1D wave path. However, the extraction of nonlinear waves in the time domain is rarely reported. In this study, nonlinear Lamb waves at a closed crack formed by a thermal pulse are extracted in the time domain. Combining with the sensor array technique, an image is reconstructed to show the location of the closed crack on a 2D plate. The recognized crack is 1 mm wide, 2 cm long, and 1 mm deep. The distance between the transmitter and the crack is set to 100, 150, and 200 mm to demonstrate the reliability of the proposed method. The method reported facilitates the damage identification and predictive maintenance of plate-like structures.