Damage Identification of Metallic Structures Using A0 Mode of Lamb Waves

A Lamb wave-based technique was developed for detecting damages in metallic structures, such as cracks and holes in metallic beams and plates. For metallic structures with transverse cracks and holes, A(0) mode of Lamb waves was employed due to its shorter wave length compared with S-0 mode, which leads to high sensitivity to small damages. Two kinds of excitation techniques for generating comparatively pure A(0) mode using piezoelectric lead zirconate titanate (PZT) actuators were realized experimentally. In one technique, two PZT actuators with applied out-of-phase voltages were attached on both sides of the structures. While in the other technique, a kind of grease lubricant was used between the bottom surface of one PZT actuator and the surface of the specimens. Both techniques were able to enhance the component of A(0) mode and reduce the component of S-0 mode effectively. Secondly, in terms of the arrival time of the A(0) wave mode reflected from damages obtained using the wavelet analysis, the positions of damages were identified accurately. The above two techniques were then validated by identifying the transverse cracks and holes in aluminum beams and plates, respectively. Numerical simulations using the finite element method (FEM) for the wave propagation in these structures with damages were carried out. The obtained experimental and numerical results demonstrate that it is possible to identify damage position very accurately by using only sensor data of defective structures without referring benchmark signals (sensor data of intact structures).