Crack Depth Evaluation and Imaging Using Lamb Wavefield Measurements by a Movable PZT Sensor

In this article, nondestructive testing (NDT) using ultrasonic Lamb waves with a movable contact piezoelectric transducer (PZT) receiver is introduced for crack depth evaluation and damage imaging. An angle beam transducer (ABT) was used to excite a predominant S0 mode in an aluminum plate containing cracks with different depths, and a movable PZT disk was used to measure the wavefield in the plate. From the wavefield data collected by the measurement system, the transmitted and reflected waves caused by the presence of cracks were analyzed in the space-time and frequency–wavenumber domains. Frequency–wavenumber filters were employed to separate the incident and transmitted waves from reflected waves. The root mean square (RMS) of recorded signals was computed as a feature to provide information about the damage characteristics. The frequency and wavenumber variations of each mode were analyzed before and after the crack position to evaluate different crack depths. The filtered data obtained in the frequency–wavenumber domain were transformed back to the space-time domain using the inverse 2-D FFT, and an image fusion of reflected and transmitted RMS maps was implemented for damage imaging. This investigation has demonstrated the potential of using movable PZT sensors for collecting wavefield measurements for damage detection, visualization, and characterization.