Theoretical And Experimental Studies Of PZT Impedance Method In 1-Dimensional Beams

The PZT-based electro-mechanical impedance (EMI) method is widely used in on-line structure monitoring as one of structural health monitoring technologies. The change of PZT coupling impedance, which is only involved by structure impedance when the PZT parameters are constant, can reflect the change of structure impedance which is coursed by the damages. The study of PZT coupling impedance model is one of the key problems in EMI methods. The previous model has two problems. One is to ignore bonding layer between PZT and structures, and the other is to use structure static impedance without taking the dynamic vibration into account. All of these will affect the accuracy of model and cause large errors between the calculated and experimental results.In the theoretical study, a modified electro-mechanical impedance model of 1-dimensional beam is presented. The presented model references the structure mechanical impedance analytical expression of one-dimensional beam. The effect of the adhesive layers on the dynamic interaction between PZT and host beam is also taken into account.For investigating the effects of the adhesive layer's bonding quality for testing the damage of 1-dimensional beam, the modified model is used for performing the numerical simulation of the PZT coupling impedance spectra in the 5-80 kHz range when the bonding coefficientξis 0.01,0.02 and 1.0, respectively. The adhesive strength of three kinds of adhesives, a-cyanoacrylate, epoxy resin and modified acrylate, are obtained by measurement and calculation, which is 0.882,7.621 and 10.198 MPa, respectively. Then the PZT coupling impedance spectra of the beams using the three different adhesives is measured in the range as the numerical simulation. Research showed that the coupling impedance spectrum of numerical simulation corresponded with experimental result well, and the relative error of frequency corresponding the peak between them is 0.25～6.06%. And the peaks of impedance spectrum shift to lower frequency as the bonding coefficient increasing. Then the coupling impedance spectra of the holes (diameterφ1mm) damage beams was measured, and the values of RMSD were calculated. The results reveal that the PZT coupling impedance increase 2.06～6.09% in the damage state. The RMSD increased as improving the quality of bonding layer.In order to investigate the effects of the testing frequency range and exciting voltage to test the damage of 1-dimensional beam, the experiment proceeded on aluminum beams. the impedance analyzer and high exciting voltage impedance measurement system (HEVIMS) were used in 90～110 kHz,190～210 kHz,790～810 kHz,890～910 kHz frequency ranges and 10,20,30 V respectively to measure the PZT coupling impedance spectra in the original and hole damage states. The results showed that the value of the coupling impedance increase 3.41～11.34% and 3.78～10.62% with the appearance of damage respectively. Then the values of Root Mean Square Deviation (RMSD) increased with the exciting voltage and testing frequency range increasing.