Lamb wave damage detection using time reversal DORT method

Abstract

Among structural health monitoring methods, Lamb waves are frequently used as a diagnostic tool to detect damage in plate-like structures. The decomposition of the time reversal operator (DORT) method is a selective detection and focusing technique using an array of transmit–receive transducers. Unlike body waves, the propagation of Lamb waves is complicated due to their dispersive and multimode characteristics. So it is hard to locate different scatterers on the plate directly using the DORT method because of the asymmetry of the time reversal transfer matrix. In the present paper a damage detection technique to make the transfer matrix symmetric for the Lamb wave DORT method is proposed. It is found that the number of significant eigenvalues is not exactly equal to the number of damage targets and two significant eigenvalues are associated with one damage target. An experiment is carried out to distinguish and locate two simulated points of damage on an aluminum plate. The behavior of reflected multimode waves is analyzed by studying the eigenvalues and eigenvectors of the time reversal operator matrix. This method, which uses a PZT array and operates under multimode pulse-echo mode, can estimate the position of the damage zone in the 2D image by numerically backpropagating a selective eigenvector using the A0 and/or S0 Lamb wave propagation analytical solution. The experimental results illustrate the proposed method.