Electro-mechanical Impedance Model For Damaged Structures And Its Applications

Electro-mechanical impedance (EMI) method utilizes the electro-mechanical coupling effectof piezoelectric patches, in which the EMI signatures changes with damages appearing in thestructures. The wavelength of the elastic wave is very short due to the adopted high-frequencyexcitation, and thus the EMI signals are sensitive enough to detect minor incipient damages in thestructures. EMI technique can exactly diagnose and identify the types of damage, damage severity,damage propagation and even the damage position. Firstly based on the Timoshenko beam theory,the high-frequency vibration of the coupled structural system consisting of PZT-adhesive-hostcracked beam is investigated using the improved MRRM via the recursive formulae (IMRRM).The given numerical results validate the feasibility and validity of the established EMI model ofdamaged structures by comparing with MRRM and3D FEM.Because of limitation of the simplified beam theory employed by IMRRM and MRRM aswell as the drawbacks of the model itself, it may result in certain secondary mode shapes not beingexcited, and thus the inaccurate results will be obtained. Furthermore, IMRRM and MRRM canonly apply on1D structures, such as rods,beams and frame structures, and cannot apply on2D and3D structures. This may lead to some limitations in practical applications.Many researches havedemonstrated that3D FEM is an effective method to establish accurate EMI model for the morecomplex engineering structures and can also satisfy the analysis of high-frequency vibration aswell as multi-coupled problems, and the obtained results are reliable and accurate comparing withthe experimental results. Thus, this paper will adopt software ANSYS to establish3D FEM EMImodel in order to achieve a more in-depth research. Then, the damage detection of the damagedbeams, plate,3D solid and frame structures will be conducted through the proposed model.Based on the shear lag stress model and the peel stress law, parameters study including theeffects of vibration modes, interface properties of bonding layer,and the damage parameters etc. onEMI signatures are conducted using the present3D FEM method. The root-mean-square deviation(RMSD) damage index is then introduced in the paper to evaluate damages. The EMI analysis ofthe damaged2D plate and3D solid structures are also implemented by the proposed model, thenumerical results testify the practicability and validity of EMI technique in the field of damage detection. Finally, the method of reverberation-ray matrix (MRRM) and3D FEM are employed toestablish the EMI model for the cracked frame. Parameters study about the depth and location ofthe flaw as well as the characteristics of bonding layer on EMI signatures are also carried out. Thecomparison study between the MRRM and the3D FEM shows that the present EMI model isavailable for detecting the cracks in the frame structures.