Damage Detection Using Electro-Mechanical Impedance Technique For Beam And Plate-like Structures

With the development of large-scaled exploitation of ocean resources, more and more attentions have been paid to the structural safety of the platform. A large number of accidents show that the destruction of ocean platform is often caused by the fatigue damage of tubular joints which are constantly subjected to the wave-induced loads. However, it is difficult for the existing health monitoring technology to identify the damage in the ocean platform at the early stage, which misses the right time of the damage repair and the safety warning. The electromechanical impedance technology (EMI), which integrates the sensing and exciting functions in one element, can be achieved with spontaneously (actively) high frequency excitation and the local damage-sensitive features. Thus the EMI can meet the requirements for crack identification in oil platform. As a basis for this application, EMI was used to detect the damage in beam and plate-like structures in the dissertation. Theoretical analysis and numerical simulations were carried out to study the interactions between the structure and the PZT element. The main contents of the dissertation include the followings:Firstly, the state of the art of the EMI were summarized and reviewed. The theoretical developments of the EMI were presented, and the relationship between the structurally mechanical impedance and the electricity conductance of the PZT. The modeling method of the interactions between the structure and the PZT was briefly introduced.Secondly, the interaction model of beam/plate-like structure-PZT was built by using of the impedance analysis method as well as the coupling finite element method, respectively. Then the impedance characteristics of beam and plate were studied with the analysis and the model test. It is shown that the frequencies corresponding to the peaks of the impedance curve obtained by the impedance analysis agree well with those by the coupling finite element analysis. However, the amplitudes of the peaks for two methods are different for the plate.Thirdly, the scale models of beam and plate are designed, and the feasibility of the damage detection with EMI was presented. The effects of the damage severity, damage location, frequency band-width, voltage amplitude and the glue on the admittance spectrum are considered experimentally. Accordingly, the relationship between admittance signal and the occurrence of the structural damage as well as the damage type, the degree and the distance are obtained. Then the reasonable frequency range and frequency sampling interval are proposed. Based on the results of the analysis and experiments, the conclusions of the study were made and the prospect for the further research are presented...