Nonlinear edge wave generation in aluminum plates with microstructural damage

Abstract

Free edges are omnipresent in engineering components, such as I-beam flanges and aircraft wings. These components are subject to different types of damage with various scales, which can reduce their designed service life span. Nonlinear ultrasonic guided waves have attracted substantial research attention in the field of structural health monitoring (SHM), for identifying and tracking micro-defects in the early stage. Guided waves propagating along free edges are called edge waves. A number of studies have demonstrated that edge waves have the potential to characterise the defects near the structural edges. However, these studies have extensively studied the linear features of edge waves, typified as group and phase velocity, attenuation, and mode conversion. The nonlinear interactions of the edge waves and structural defects have not been fully understood. This study presents numerical and experimental analyses of nonlinear edge waves on the edge of an aluminum plate with microstructural damage. The focus has been directed to the higher harmonic generation. A three-dimensional (3D) finite element model (FEM) was developed and the material nonlinearity was simulated by Murnaghan's strain energy equation. Subsequently, the accuracy of the numerical model was validated by comparing numerical results with the experimental data. After that, the experimentally validated FEM was employed to carry out a parametric study to investigate the propagation characteristics of the nonlinear edge waves on aluminum plates with different fatigue levels. The results demonstrate that it is promising to use edge waves for detecting micro-defects in the free edges of metallic structures.