Scattering of ultrasonic-guided waves for health monitoring of fuel weep holes

A novel and effective approach for nondestructive in situ structural health monitoring of a hard-to-inspect location is presented in this article. Laser vibrometry is used to confirm that Lamb waves, generated by low-profile surface bonded piezoceramic transducers, are able to create circumferential creeping waves on the free surface of cylindrical cavities. The behavior of the propagating ultrasonic stress waves around the cavity and their interaction with simulated fatigue damage emanating from the top of the cavity is visualized. The transformation to a cylindrical co-ordinate system is found to be useful in visualizing wave scattering due to the presence of an open notch. Nondestructive evaluation of the structure is shown to be viable with the strength of the scattered spiralling creeping wave field maintaining its form and growing in amplitude as the notch length in increased. An informed selection of the excitation frequency is recommended as the A0 Lamb mode is found to be more efficient than the S0 Lamb mode in generating creeping waves around the cavity. Results from a receiving low-profile piezoceramic transducer are used to substantiate the laser vibrometry measurements and further establish the potential of the technique.

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