Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 30, 2017 - December 01, 2017
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, it has been confirmed that the magnitude of the difference frequency component excited changes depending on the instantaneous frequency, the difference frequency and the size of the damaged part by changing the input wave as two chirp waves whose frequency varies with time. In this paper, in order to clarify how the magnitude of the difference frequency component is determined, a model explaining the emergence of the difference frequency component was formulated assuming a quadratic nonlinearity at the contacting surfaces in the damage part. The derived solution using a perturbation method suggested a proportional dependence of the magnitude of the difference frequency component to the product of the amplitudes of the two input waves, which was then confirmed by an experiment in the case the input frequencies were time-invariant.
