Damage Area Evaluation Using a New and Simple Signal-Processing Algorithm in the Ultrasonic Wave Propagation Visualization Technique

概要

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The research purpose of this study is to overcome some technical weak points of the conventional non-destructive inspection technique based on the ultrasonic wave propagation visualization. It is well-known that, in thin-walled structures, propagating ultrasonic waves become Lamb waves. We focus on thin plates, where Lamb waves excited by a pulse laser are employed. When ultrasonic Lamb waves propagate in the thin plates, the particles along the through-thickness direction of the whole plate vibrate. The present experimentation employs a pulse laser scanning method in an inspection region. A remote non-contact scanning by the pulse laser with a fixed sensor enables us to inspect an arbitrarily shaped object, such as curved structures. In this study, we have put forward an improved method based on the conventional wave propagation visualization technique, which can not only estimate the existence and location of a damage, but also evaluate the damage area. In this method, more than three fixed sensors are employed and a new signal index with the corresponding processing technique is proposed based on the normalized strain energy distribution in the inspection region during a specified time period when Lamb waves propagate from the source point to the inspection region. The proposed method has been validated by using the results of both experiment and numerical analysis.