Structural Damage Identification Using Electro-Impedance Monitoring Approaches

With the rapid development in economy and society of our country and the improvement demands of society, various kinds of large and complex engineering structures have constantly appeared. With the development of civil engineering structures into large scale, complicated and intelligent technology, the problems concerning health monitoring and damage identification of many important engineering structures have received considerable attentions in academic and engineering field. The successful application for piezoelectric smart material provides a new method for structural damage identification technology of significant engineering structures and infrastructures. The advantages of EMI-based approaches include, but are not limited to, a lightweight and inexpensive sensor, high sensitivity to incipient damage for high-frequency actuating, and immunity to ambient or far-field loads. In recent year, the EMI technique has been gradually used in various types of structures, such as aerospace, mechanical engineering and civil engineering. However, there are still a lot of challenges in impedance model, data analysis and damage identification. This paper studies the interaction between structure and sensor impedance model of embedded type and surface paste type electro-mechanical impedance sensor (EMIS). And the structural damage identification methods based on the impedance information are established. The research works and innovations in the thesis concerning theoretical analysis and experimental research are as follows: (1) By the three-dimensional coupled vibration principle of EMIS, the mechanical properties of embedded EMIS are analysed, and the three-dimensional effective electromechanical impedance model is established. By the new electromechanical impedance model, the electrical admittance equation of the interaction between EMIS and the host structure is derived. (2) A modified methodology for monitoring structure changes using an electromechanical impedance technique is proposed. In the proposed method, the changes in the host structure are monitored by using the "active" part associated with the effective structural mechanical impedance, which is extracted from the measured raw admittance signatures. Then, the effective structural mechanical impedance is considered as a new damage sensitive feature factor. By introducing the damage index RMSD and CC, the change of the structure inherent attributes is reflected. Through the experimental results, the advantage of the modified methodology is discovered. (3) Based on the interaction between EMIS and the host structure, the electromechanical impedance model of pipeline structure considered the influence of bonding layer is established and the coupled electromechanical admittance equation was derived. Based on the electromechanical admittance equation, the effective mechanical impedance of the pipeline is extracted with the measurement of the coupled electromechanical admittance. The establishment of this new electromechanical impedance model provides a theoretical basis for the application of pipeline structural damage identification by the electromechanical impedance methods.(4) Based on the extracted effective mechanical impedance, the traditional electromechanical impedance technique is improved by a proposed damage sensitive feature factor. The model experiments of straight pipeline and K type pipe joint is conducted. The effective structural mechanical impedance and damage sensitive feature factor are derived from the measured electrical admittance, and the damage index RMSD is proposed. By discussing the change regularity of damage index RMSD, the development process and degree of the local damage in pipeline structure is quantitatively described. In the experiments, the reasonable layout of EMIS network provides a basis for the quantitative identification of the crack damage in the monitored structures. Based on the experimental analysis, the extraction method of the damage sensitive feature factor is proposed. And the quantitative damage identification technology by the information fusion of multiple EMIS is developed to study the dependency relationships between the damage sensitive feature and the damage position and damage degree.