Abstract
This paper concerns detection sensitivity of contact-type failure based on nonlinear wave modulation. Failure which has contact interfaces (contact-type failure), such as fatigue crack, delamination of composite material and bolt loosening, is difficult to detect by ultrasonic test because ultrasonic wave do not reflect at the contact interfaces. In the structure is excited by low-frequency vibration such as environmental disturbance, the contact condition of interfaces is fluctuated. In this condition fluctuation, the high-frequency wave which propagates through the failure may undergo amplitude and phase modulation at the failure location because the transmissivity and reflectivity of high-frequency waves in the vicinity of the failure may fluctuates. The degrees of amplitude and phase modulation may variates depending on the fluctuation of contact interfaces. So, low-frequency vibration which fluctuates contact condition is one of important parameters to detect contact-type failure based on nonlinear wave modulation. In this study, the sensitivity variation due to low-frequency is investigated by the experiment using the uniform beam specimen which both ends fixed and simulated failure. At first, it is confirmed linear relationship between the modulation degree and the amplitude of low frequency. Furthermore, the effect of the positional relation of failure location and natural vibration mode on the modulation degree.
