Achieving robust acoustic emission-based damage characterization of scaled laminated composites under indentation

This paper presents a novel investigation on the robustness of Acoustic Emission (AE) technique on the characterization of indentation-induced Damage Mechanisms (DMs) in scaled laminated composites. AE is used to monitor a comprehensive series of scaled Quasi-Static Indentation (QSI) tests performed on Quasi-Isotropic (QI) S-glass/8552 epoxy composite plates, with in-plane and intra-plane scaling. A detailed assessment of the damage evolution is carried out through clustering of the monitored AE signals. The AE results indicated the existence of different DMs such as delamination, matrix cracking and fiber breakage. Ultrasonic C-scan and visual observations were also used to verify the AE based results. It was observed that both in-plane and intra-plane scaling alter the induced DMs, and the AE analysis was able to accurately identify and quantify the DMs in each case. However, the AE features (frequency, energy and count) were found to be dependent on different variables such as size, geometry and stacking sequence of the investigated samples. This research highlights the potential and challenges to develop AE as a reliable structural health monitoring system for impact/indentation damage monitoring of composite plates over a range of sizes and complexities.