Nonlinear frequency mixing of Lamb wave for detecting randomly distributed microcracks in thin plates

Abstract

In engineering practice, the microcracks usually generate during the initial period of fatigue, and randomly distribute in the metallic structure. It is great challenge for linear non-destructive testing methods to detect those microscopic damages. In this work, the numerical simulations on nonlinear interaction between Lamb wave and microcracks are performed to investigate the behavior of frequency mixing in aluminum plates. From the simulation results, the nonlinear parameter based upon sum frequency shows a monotonically increase with the length of microcracks, and a monotonically decrease with the width of microcracks. The distribution area and density of the cracks also affect the nonlinear interactions between Lamb wave and microcracks. This work theoretically demonstrates that the nonlinear frequency mixing method is a robust strategy to detect microcracks at the initial fatigue stage in metal plates.