Lamb wave–based quantitative crack detection using a focusing array algorithm

Cracks are common defects in aluminum plate-like components that are in widespread use in aerospace, shipbuilding, and other industries. Ultrasonic detection using Lamb waves has proven to be an efficient method for crack detection and localization. However, quantitative information regarding crack size or orientation is of paramount importance for damage diagnosis and life prediction. In this article, employing a sparsely arranged piezoelectric sensor array, a quantitative crack detection and imaging approach using a Lamb wave–focusing array algorithm is developed and presented. Additionally, Lamb wave propagation on thin-wall plates and wave interaction with crack damage was studied using three-dimensional elastodynamic finite integration technique. The focusing array imaging algorithm was then developed and applied to both simulation and experimental data to generate intensity images of the structure under interrogation. Experimentally, wafer-type piezoelectric actuators/sensors are permanently installed on the testing structure to generate Lamb waves as well as to measure the waves propagating through the structures. Our results show that when applied to either experimental or simulated data, the focusing array algorithms yield images containing quantitative damage information. The results also demonstrate that three-dimensional elastodynamic finite integration technique can be used for future simulation-based investigations of sensing optimization for various damage scenarios.