Abstract
This paper presents detection of contact-type failure based on frequency down-conversion of elastic vibration. The detection method using linear ultrasonic vibrations or waves can detect small failures. However, it is difficult to detect contact-type failure because of transmissivity of ultrasonic waves in the vicinity of a failure. When the test object with a contact-type failure is vibrating at two ultrasonic frequencies with different frequencies, the contact condition of the failure interface fluctuates by ultrasonic vibrations. In this situation, an elastic vibration of difference frequency component is generated (frequency down-conversion). Since difference frequency component is caused by local non-linearity. The contact-type failure can be regarded as the exciting point of the difference frequency component. In this paper, the localization method by using time reversal analysis of transient vibration caused by frequency down-conversion is proposed. First, the transient response characteristic of the difference frequency component is investigated using ultrasonic burst waves. It is confirmed that the excitation time by burst waves are related to the waveform of the transient waves in low-frequency range. Second, the localization experiment of contact-type failure in a uniform beam structure is performed.
