Dual use of PZT patches as sensors in global dynamic and local electromechanical impedance techniques for structural health monitoring

In this article, a new approach is proposed to effectively detect the initiation and progression of structural damage by combining the global dynamic and the local electromechanical impedance (EMI) techniques, using the same set of surface-bonded piezoelectric ceramic (PZT) patches as sensors. The PZT patches are used to determine the natural frequencies and the strain mode shapes of the structure (for use in the global dynamic technique) as well as to acquire the electromechanical admittance signature (for use in the EMI technique) to facilitate an improved damage assessment. Occurrence and location of the incipient damage are determined using the EMI technique, whereas for moderate to severe damages, the location and the severity are arrived at through the global dynamic technique. Finally, damage severity is determined in terms of the original stiffness of structure using the strain mode shapes directly determined using the PZT patches. The proposed technique is illustrated using two specimens—a 4-m long steel beam and a mild steel plate 1260 mm × 630 mm × 6.5 mm in size. The integrated approach provides greater information about damage, is simple to apply, does not involve any numerical/analytical modeling a priori, and is at the same time very cost effective.