Crack identification using sensing sheets

Reliable early-stage damage detection requires continuous monitoring over large areas of structure, with high spatial resolution of sensors. Technologies based on Large Area Electronics (LAE) can enable direct sensing and can be scaled to the level required for Structural Health Monitoring (SHM), in which thin-film strain sensors and control circuits are integrated on the flexible electronics and deposited on a polyimide sheet that can cover large areas of structures. This paper presents the development stage of a prototype strain sensing sheet based on LAE for crack detection and localization. Two types of sensing-sheet interconnects with size 6x6 inch were designed and manufactured, and dense arrays of strain sensors were laminated onto the interconnects. The sensing sheets were bonded to steel plates, which had a notch on the boundary so that fatigue cracks could be generated under cyclic loading. The sensors within the sheet that were close to the notch tip successfully detected the initialization of fatigue crack and localized the damage on the plate. The sensors that were away from the crack successfully detected the propagation of fatigue crack based on the time history of measured strain. Thus, the results of the tests validated general principles of the sensing sheets for crack detection.