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Localization of Crack Initiation in a Pipe Structure Using a Laser Based Acoustic Emission Technique



This study presents a new acoustic emission technique that can localize a crack initiation event using training data obtained by surface-mounted MFCs and a pulsed laser excitation. First, an impulse response function of a sensing MFC mounted on the surface of a target structure is obtained by simulating an acoustic emission (AE) signal generated by a crack initiation with a non-contact pulsed laser excitation. Then, training impulse response functions are assembled by scanning the pulsed laser excitation over the surface of the target structure. Once a crack is initiated in the target structure, the AE signal generated from the crack initiation is recorded and compared with the training impulse functions using a unique concept of time reversal. Finally, the training impulse response function, which gives the maximum correlation with the actual crack initiation AE signal, is chosen from the training data set, and the crack initiation location is identified. The advantages of the proposed technique are that: (1) it can be applied even to complex structure without any additional geometric and/or temperature compensation; (2) only simple correlation calculation is required, making it attractive for real-time continuous monitoring; and (3) training is conducted using a non-contact pulsed laser excitation, which simulates the crack initiation event, and the existing sensors, which may already be installed for other structural health monitoring purposes. The effectiveness of the technique is validated on a SUS (Steel Use Stainless) pipe by imitating the crack initiation with a pencil-lead break.

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