Laser-based structural training algorithm for acoustic emission localization and damage accumulation visualization in a bolt joint structure

Acoustic emission caused by structural damage encompasses important information about structural integrity. In particular, acoustic emission can detect phenomena that are difficult to determine, such as microcracks and internal cracks. However, conventional acoustic emission has shown limitations in complex structure applications for years. In this article, we propose a Q-switched laser scan–based structural training technique to achieve accurate acoustic emission localization and visualize accumulated damage in complex structures with a single PZT sensor (acoustic emission sensor). The proposed method compensates for the difference in characteristics between the actual acoustic emission wave and the laser-induced elastic wave using laser-based structural training algorithm. Acoustic emission localization in complex structures is accomplished by cross-correlation in the time domain. Pencil-lead break method is used as the source for acoustic emission to simulate the real damage-induced acoustic emission event. The proposed laser-based structural training algorithm with a laser scanning interval of 2 mm achieved an average localization error of 1.84 mm in two Al-alloy layers with fastener structure. Finally, the accumulated damages were visualized by appending the damage index of the acoustic emission waves at accurately localized points.