Evaluation of contact-type failure development based on frequency modulation due to nonlinear wave modulation utilising self-excited ultrasonic natural vibration

This paper presents a novel evaluation method of contact-type failure development based on nonlinear wave modulation utilising self-excited ultrasonic vibration. The contact-type failure, e.g. fatigue crack, delamination of composite material and debonding, is difficult to detect by using linear ultrasonic waves or vibrations. When the contact condition of the contact-type failure is fluctuated caused by structural low-frequency vibration, the amplitude and phase of ultrasonic waves passing nearby the failure area is fluctuated in synchronization with low-frequency vibration (nonlinear wave modulation). The fluctuation of natural frequencies caused by fluctuation of local contact stiffness is the cause of this amplitude and phase fluctuation. Therefore, frequency of ultrasonic natural vibration excited by local feedback control changes, chasing the change of natural frequency automatically. Thus, the frequency fluctuation of ultrasonic natural vibration in synchronization with low-frequency vibration (frequency modulation) occurs caused by nonlinear wave modulation. In this paper, the experimental investigation of proposed evaluation method is performed. Especially, the dependence of the proposed evaluation index of contact-type failure on the viscous damping is clarified. Firstly, the design of an analogue circuit of local feedback control is explained. Secondly, it is confirmed that the self-excitation of ultrasonic natural vibrations can be implemented. Finally, it is clarified that the variation width of the frequency fluctuation is a novel evaluation index of contact-type failure level, which is independent from the variation of the viscous damping. © 2022 COMADEM International. All rights reserved.