抄録
This paper presents a concept of damage detection method using nonlinearity of contact-type damage. Nonlinear ultrasonic methods have been presented as an effective inspection method for contact-type damage such as cracks and delamination. In this research, we propose a method based on “frequency down-conversion” phenomenon in which two simultaneously applied ultrasonic waves with different frequency are mixed at the contact-type damage and the component with the differential frequency emerges. In the proposed method, two ultrasonic swept waves are used as the excitation whose frequency varies with time while keeping the frequency difference constant. As a result of the frequency down-conversion, the response of the difference frequency emerges and the magnitude of the component varies depending on the instantaneous frequency of the input, which may capture the feature of the damage geometry. Experimental results using an aluminum thin plate show that the difference frequency component appears when the thin plate has simulated damage, and the magnitude of the component varies depending the instantaneous input frequency as well as the damage extent.
