An application is developed with surface mounted lead zirconate titanate (PZT) patches for sensing damage in the form of a stress-induced crack in a concrete substrate. A localized crack is introduced in a controlled manner using a fracture test. Full-field displacements obtained using digital image correlation are used for crack penetration and crack width measurements. Electrical impedance (EI) measurements are obtained from the individual PZT patches, which are attached at different locations relative to the crack. Stress wave transmission measurements are performed using the PZT patches as actuator-receiver (AR) pairs. The EI measurements indicate that small, quantifiable changes in the mechanical impedance of the substrate are experienced by the PZT patch in the vicinity of the localized crack, which sensitively detect crack initiation. The stress wave-based measurements are very sensitive to the presence of physical discontinuity created by a localized crack in the stress wave path. A measure of stress wave attenuation, the attenuation factor is developed, to quantify the measured changes in the stress wave produced by the physical discontinuity in concrete upon unloading a stress-induced crack. The physical discontinuity due to a stress-induced crack opening on the order of 10 μm can be detected from the measured changes in the attenuation factor. The physical discontinuity in the concrete associated with a stress-induced crack opening on the order of 100 μm produces a complete attenuation of the stress wave of 120 kHz. The combined use of PZT patches in the EI and the AR modes can be used to detect local changes close to a PZT patch and it allows distributed sensing over the entire volume of a structural element.
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