Electro-mechanical Impedance Analysis And Damage Identification For Piezoelectric Smart Structures

Nowadays, more and more engineering security problems have drawn much attention bypeople in the field of engineering. The high expectations are paid by the people for structural healthmonitoring and thus technologies are required a higher level. Electro-mechanical impedance (EMI)is one of the new and developing methods. The electro-mechanical impedance method hasoccupied important position in structure health monitoring. Electro-mechanical impedance methoduses the electro-mechanical coupling effect of piezoelectric patches. The changes of themechanical impedance can be reflected from the electrical impedance. The prominent advantage ofelectro-mechanical impedance method is that its signals are sensitive enough for structural minordamages. However, due to the degree of precision of the EMI model and the difficulties in the highfrequency analysis, it is still developing process from the qualitative detection technology to thequantitative detection technology. Thus, this study will focus on these two sides.To electro-mechanical impedance model is important, so establish a more accurate EMImodel which for the coupled structural system consisting of the host structure, bonding layer andthe piezoelectric patches, a three-dimensional finite element method is employed. Then, to verify itcorrect by damage rod and bean, a comparison study with the mode superposition method usuallyemployed in the conventional EMI model and experiment results is implemented to prove theaccuracy and reliable of the proposed EMI model for damaged rods and beams. In order to verifythe three-dimensional finite element EMI model is accurate and reliable, the numerical simulationis carried out for the various damage severities and locations. Finally, parameters study includingthe finite element size, vibration modes, crack depths, the thickness of the adhesive layer, and thehost structure size etc. on EMI signatures are conducted.Corresponding to the theoretical research, experimental investigations of damage detection ofa steel frame using electro-mechanical impedance signatures are also implemented. Theexperimental program includes two aspects: the damage severities identification and damagelocalization. Damages are introduced by completely loosening bolts on the structure. Theexperiments show that the electro-mechanical impedance technology can detect damage in theactual structure, and have a certain degree of reliability and validity. Experimental data are thenanalyzed by the damage index which based on statistical methods for damage identificationquantitatively. The result shows that the EMI technique integrated with RMSD (Root Mean Square Deviation) or MAPD (Mean Absolute Percentage Deviation) index can identify the damageseverity and location effectively.