Damage Detection of an Aluminum Plate by Using Nonlinear Ultrasound with a Frequency-swept Excitation

Abstract

In the traditional nonlinear ultrasound methods, one or dual excitation pulses with fixed center frequencies are usually simultaneously sent to the structures to generate nonlinear interaction near the damage, and some nonlinear parameters are applied to identify the structural damages in early age. However, when the damage evolves, the nonlinear effect due to damages usually changes, and the best matching frequency also shifts. Therefore, a new method based on nonlinear ultrasound with a frequency-swept excitation is proposed. In this new method, a frequency-swept signal is proposed to take place of the pulse with a fixed frequency, the wavelet packet decomposition is introduced to process the nonlinear response signal, and a nonlinear damage index is used for damage size estimation. To validate the method, some experiments are conducted on an aluminum plate. The experimental results of three specimens show that the nonlinear damage index is influenced by both the frequency band of the excitation signal and the diameter of the simulated damage. Moreover, when the best frequency band (260 kHz~280 kHz) is selected, the proposed damage index is linearly increases as the size of the simulated damage changes from 0 mm to 0.7 mm, which indicates that this index can be applied to identify damages with a small size on plates. This study puts forward a new avenue to detect structural damages with a small size in an early age on plate-like structures.