Detection of cracks in plates using piezo-actuated Lamb waves

Abstract

In this paper, a comprehensive methodology for locating and determining the extent oflinear cracks in homogeneous plates based on the time-of-flight analysis of Lamb wavepropagation is proposed. Piezoelectric sensors and actuators (PZTs) placed on a squaregrid configuration are used to excite and receive direct and reflected waves. Theactuation frequency, spacing of PZTs and length of the signal to analyze are firstdetermined. The grid is used to sweep across the plate to identify the location of acrack, if there is one. Elliptical loci of possible crack positions are constructedbased on the flight time of crack-reflected waves estimated using energy spectrafrom the Hilbert–Huang transform of the sensor signals. A detailed procedure forobtaining the ellipses is described, including the blind zones. After identifying thecrack position, the crack orientation is determined by varying the positions of thePZTs and observing the strength of the energy peaks in the Hilbert spectra.This provides the basis for moving the PZTs to estimate the extent of the crack.Experimental results obtained using aluminum plates with through, half-throughand concealed cracks showed that the proposed method is feasible and accurate.