Evaluation of Contact-Type Failure Using Frequency Fluctuation Caused by Nonlinear Wave Modulation Utilizing Self-excited Ultrasonic Vibration

This study concerns the evaluation method of contact-type failure, which is difficult to detect by linear ultrasonic because of transmission of ultrasonic at the contact surfaces utilizing frequency fluctuation caused by nonlinear wave modulation. When the contact-failure is vibrated by low-frequency vibration, the amplitude and phase of ultrasonic in the vicinity of the failure area is fluctuated in synchronization with low-frequency vibration (nonlinear wave modulation). This amplitude of amplitude fluctuation and phase fluctuation is the evaluation index of contact-type failure. However, the change in this index depends on the viscous damping of the structure. In the nonlinear wave modulation utilizing self-excited ultrasonic vibration, the frequency of ultrasonic vibration is fluctuated by low-frequency vibration. The frequency fluctuation may be the evaluation index of contact-type failure independent of the viscous damping of the structure. In this paper, the experimental verification using beam structure is done. Firstly, the self-excitation technique of ultrasonic natural vibration using feedback control is introduced. Secondarily, it is shown that the amplitude of frequency fluctuation is the evaluation index of contact-type failure by experiment. The uniform beam structure with simulated failure, which is simulated the contact-type failure is used. The vibration characteristics of this structure and the self-excited ultrasonic vibration excited by feedback control can measure easily. Finally, the viscous damping dependency of the frequency fluctuation is investigated. As the result, it is shown that the amplitude of frequency fluctuation is the evaluation index independent of viscous damping.