Characterization of Progressive Fatigue Damage in Solid Plates by Laser Ultrasonic Monitoring of Zero-Group-Velocity Lamb Modes

We propose a method for nondestructive characterization of progressive fatigue damage in solid plates, using a zero-group-velocity (ZGV) Lamb mode generated and detected by lasers. Our experimental results depict a nonmonotonous change in the ZGV mode frequency with an increasing number of loading cycles, and more importantly its drastic decrease prior to the specimen failure. We report three experiments on three specimens made of aluminum, which fail after different numbers of loading cycles. Despite this difference, the three nonmonotonous variations of the ZGV mode frequency with an increasing number of loading cycles are superimposed when plotted as a function of the normalized fatigue lifetime. This feature stresses out the potential of the technique to locate fatigue damage, to predict the fatigue lifetime, and to qualitatively, and even quantitatively, assess the different stages of fatigue damage in micrometer- to potentially centimeters-thick solid plates.