Ultrasonic Frequency-Mixing Nonlinear Detection of Microcracks in Metal Plates

Detection of early microcracks in metallic structures is critical for analyzing structural failure and life prediction, Conventional Non-Destructive Testing (NDT) methods are not sensitive to the identification of microcracks in structures. In this paper, nonlinear ultrasonic mixing detection method is utilized for the study of microcrack damage detection. Based on the nonlinear wave theory, an ultrasonic nonlinear mixing model containing microcracks is established. The nonlinear interaction between two rows of single-frequency lamb waves in the same direction and collinear with the microcrack interface after mixing was analyzed, and the influence of the change of microcrack depth and width on the mixing modulation effect was studied. At the same time, the influence of the distance between the two excitation points on the propagation characteristics of nonlinear mixing ultrasonic waves is considered. The results show that the nonlinear parameters of the sum frequency and the difference frequency sideband increase with the increase of microcrack depth and decrease with the increase of microcrack width. Within a certain range, the sum frequency and difference frequency nonlinear parameters decrease with the increase of the distance between the two excitation points. These works lay the foundation for the engineering application of nonlinear ultrasonic Lamb wave mixing detection.