Hybrid Passive/Active Impact Detection & Localization for Aerospace Structures

This paper presents finding from a recent set of formal performance assessments studies, quantifying the ability of a hybrid passive/active SHM system to detect impact damage. The SHM system itself is an integrated device including an array of PZT sensors with a central PZT actuator, analog-to-digital converter, memory and FPGA. In passive mode, the system uses the central PZT element for triggering and the array of PZT sensors to detect and localize acoustic emissions (AE) propagating from the impact source. Subsequently, an active mode is triggered to capture the guided wave (GW) response of the resulting impact damage to a narrowband excitation measured from the same PZT array. In both cases, a phase-coherent beamforming approach is used to process the data. A single node was mounted to a 0.6 x 0.6 m square 2 mm thick aluminum plate with a row of 20 fasteneres, which was then subjected to 36 impact events of ~20 J. In addition, 6 tests were conducted to further predict the presence of a loosened fastener on the assembly. Results of the study indicated that the AE mode was extremely sensitive to small impacts even at a great distance with localization errors on the order of 25 mm. Similarly, while the GW mode errors were closer to 50 mm for localization for ~0.5 mm dents, the error for detection of loosened fasteners was less than 5 mm.