Quantitative Analysis For Structural Health Monitoring Based On EMI Technique

In the last decade, a new structural health monitoring (SHM) technique called electro-mechanical impedance (EMI) method using high frequency electrical impedance signatures obtained from the piezoelectric patches bonded on the monitored structures was developed in the field of real-time on-line structural damage detection. Because the wavelength of the excitation is very small at high frequencies, the EMI signatures are sensitive enough to detect minor damages in the structures. However, due to the complexity of the damaged structures and the difficulties in the high-frequency analysis, this technique fails to exactly correlate changes in the signatures to physical and geometrical parameters of the structures. Thus, we can not obtain further information about damages including damage severity, damage propagation and damage location.In order to establish a more accurate EMI model, a shear lag model is employed to describe the behavior of the bonding layer, i.e. connection between PZT patches and the host structure is realized by the transfer of shear stress. Furthermore, the inertia effect of the piezoelectric patches is taken into account.The transfer matrix method (TMM) is first employed to study a damaged rod based on classical rod theory, in which only axial vibration is considered and an analytical expression for the electro-mechanical impedance (or admittance) is derived. Numerical results indicate that the structural damages can be theoretically identified by EMI technique. However, for Mindlin-Herrmann rods, Euler-Bernoulli beams and Timoshenko beams, TMM may become invalid at high frequencies due to the instability during numerical computations. Thus, the reverberation matrix method...