Detection of Contact-type Failure Based on Nonlinear Wave Modulation Using Self-excited Ultrasonic Vibration

Abstract

This paper presents the new detection method of contact-type failure based on nonlinear wave modulation utilizing ultrasonic vibration driven by self-excitation. It is difficult to detect contact-type failure such as fatigue cracks and peeling in the structure. The constructional element of infrastructure is excited by environmental disturbance or forced excitation. In this situation, the contact condition of the failure fluctuates in synchronization with vibration. Amplitude and phase of ultrasonic fluctuate in the vicinity of contact-type failure. This phenomenon is called non-linear wave modulation. Detection method of contact-type failure based on nonlinear wave modulation was proposed. In this paper, the new detection method utilizing ultrasonic vibration driven by self-excitation. Firstly, nonlinear wave modulation can be expressed by linear time-varying system caused by fluctuation of natural frequency. We have developed a self-excitation method that oscillates at the natural frequency and changes the excitation frequency following the natural frequency fluctuation. Frequency modulation occurs in nonlinear wave modulation using self-excited ultrasonic vibration. This frequency modulation is considered to be an evaluation index of the level of failure. The detection experiment of contact type failure using a beam structure was performed. It oscillated at the natural frequency, and it was confirmed that the frequency modulation occurred according to the natural frequency fluctuation by the nonlinear wave modulation. Furthermore, the influence that the amplitude of the subsonic vibration gave to a frequency change and confirmed that it became the damage index is investigated.