Damage detection with high-frequency electric impedance signals

High-frequency electric impedance signals (HFEIS) were used for structural health monitoring, and are very sensitive to the early-stage damages of structures. A coupled system of piezoelectric patch-adhesive-main structure was considered. The main structure was modelled as a one-dimensional bar that vibrated longitudinally. A shear lag model was used to describe the shear transmission between piezoelectric patch and main structure. The model accounts for different bonding properties. The equations of dynamic system of the coupled system were derived by using transfer matrix method. The analytical expression for the electric impedance of the piezoelectric patch was obtained. The correctness and effectiveness of the proposed analysis method was verified numerically. Results showed that the interfacial properties have an important effect on the electric impedance signals, and that HFEIS can be feasibly used to detect small and local damages.