Detection of contact-type failure based on nonlinear wave modulation utilising ultrasonic vibration driven by self-excitation

摘要

In this paper, a novel method is proposed for detecting contact-type failure based on nonlinear wave modulation utilising ultrasonic vibration driven by self-excitation. In particular, the purpose of this paper is to propose an evaluation index independent of the viscous damping of the contact-type failures. When the structural element of an infrastructure with contact-type failures vibrates at low frequency caused by environmental disturbance or forced excitation, the contact stiffness of failure fluctuates in synchronisation with low frequency. In this case, the transfer characteristic of ultrasonic vibration fluctuates due to the fluctuation of contact stiffness. As a result, the amplitude and phase of ultrasonic vibration were modulated in synchronisation with low frequency (nonlinear wave modulation). The essence ofnonlinear wave modulation is the fluctuation ofnatural frequency caused by the fluctuation of modal stiffness. Therefore, this phenomenon can be expressed as a time-varying system caused by the fluctuation of natural frequency. In this research, the concept of a novel method for detecting contact-type failures utilising ultrasonic vibration driven by self-excitation was investigated using time response analysis. The self-excitation method by feedback control (local feedback control) using collocated sensor and actuator is the excitation method of natural vibration automatically. Therefore, the frequency of the ultrasonic vibration excited by local feedback control fluctuated simultaneous with the fluctuation of natural frequency caused by nonlinear wave modulation. It is clarified that the fluctuation range of frequency of ultrasonic vibration corresponds to the evaluation index ofdevelopment of the contact-type failure independent of viscous damping.