217 Integrity Diagnosis of Bolted Joint Based on Reflectivity Fluctuation Caused by Nonlinear Vibro-acoustic Modulation

This study concerns integrity diagnosis method of bolted joint based on nonlinear vibro-acoustic modulation. When the structure that has the contact-type failure is vibrating at low-frequency, the pair of the contactsurfaces of two components is tapping and clapping owing to low-frequency vibration. In this condition, the scatter characteristics, such as wave transmissivity and reflectivity, of high-frequency waves in vicinity of the contact-type failure are fluctuated in synchronization with low-frequency vibration. The time fluctuation of reflection intensity, which eχpresses the scatter characteristics in the specific location, of high-frequency waves at the contact-type failure is given as the reflection intensity map which plots time-spatial map. It is possible to show in the modulation index, which is the time fluctuation of the reflection intensity, at each contact-type surface locations . The modulation index of reflection intensity at the contact-type surface location is increasing with the developement of the damage level. Especialy, in this paper,the theory of contact-type failures detection on the reflection intensity fluctuation caused by nonlinear vibro-acoustic modulation is applied to structure which has single bolted joint and the evaluation index of intensity of the bolt loosening which controled by tightening torque is proposed. The trend that the modulation index of reflection intensity at the bolted joint is increasing with the developement of the bolt loosening is verified.