Experimental results obtained during fatigue testing of a spot-welded lap-shear structural-joint specimen are presented. In these experiments, the electro-mechanical (E/M) impedance technique was used for structural health monitoring, damage detection, and NDE. The test specimens were instrumented with piezo-electric wafer transducers, and the base E/M impedance signature was recorded over the relevant frequency range. Fatigue testing was applied to initiate and propagate crack damage of controlled magnitude. Preliminary tests were performed to correlate stiffness decrease with damage progression and remaining life. Then, during the health monitoring tests, the specimens were continuously monitored for stiffness decrease indicative of damage. E/M impedance signatures were periodically recorded, as the damaged progressed. Signature data was processed, and the damage index was calculated. The initiation and propagation of damage, i.e., structural crack, was successfully correlated with the E/M impedance measurements. Damage index values were observed to increase as crack damage increases. Sensing and the localization principles of E/M impedance NDE method were confirmed. Rejection of spurious information was also confirmed. Through these experiments, the E/M impedance technique has been, once again, proved to be a powerful tool with good potential for damage detection, health monitoring, and NDE.

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