Structural Health Monitoring Technology Based On Electromechanical Impedance Coupling Model Of Circular Piezoelectric Transducer

With the rapid development of modern industries,various large-scale facilities and complex structures are constantly emerging.Although the strength of materials has been greatly improved,the performance degradation and damage of the structure during service are still unavoidable.Both service and maintenance of vital structures face new challenges.Therefore,it is of great engineering and social significance to monitor,diagnose,evaluate and predict its service status in real time to avoid catastrophic consequences based on structural health monitoring(SHM)technology.Electromechanical impedance(EMI)technology,as one of the typical active structural health monitoring methods,has been widely used in aerospace,civil engineering,and mechanical engineering fields.This technology has the advantages of strong resistance to external interference,isolation of remote effects,and high sensitivity of damage detection.Existing EMI monitoring methods are mainly based on the processing method of directly acquiring impedance signals and calculating their corresponding damage indicators,while there are few related researches on the monitoring methods and damage localization methods based on the EMI theoretical model between a piezoelectric sensor(PZT)and the monitored structure due to the complexity.Given the above problems,this thesis has conducted in-depth research on SHM methods based on piezoelectric sensors and EMI theoretical models and has developed an EMI model for surface-mounted circular piezoelectric sensors and the corresponding characteristic signals.The work mentioned in this thesis has promoted further development of EMI technology.The main research contents and innovative work of this article are summarized as follows:(1)On the research of theoretical model of EMI,a new EMI model suitable for surface-mounted "circular PZT-structure" is proposed.Aiming at the limitations of the existing piezoelectric sensor's EMI model,a new theoretical model suitable for circular piezoelectric ceramics was developed.The model has the advantages of simple formulation,clear mechanical impedance coupling relationship between the piezoelectric sensor and host structure,and high accuracy.The proposed model further perfects the theoretical system of EMI-related studies.(2)On the research of EMI characteristic signal extraction,a new method suitable for EMI signal processing of "circular PZT-structure" is proposed.Based on the new EMI coupling model proposed in this thesis,a characteristic signal processing method suitable for surface-mounted circular PZT was developed,named DCMI(Directly Coupled Mechanical Impedance)signal extraction method.This method divides the EMI theoretical model of circular PZT into two parts:"damage-sensitive component"and "damage-insensitive component".Through theoretical derivation,a DCMI signal that is more sensitive to initial damage and its growth can be obtained.Better results can be obtained by calculating damage indicators or location imaging based on the extracted signals.(3)On the research of localization algorithms,an improved probability-weighted damage localization algorithm suitable for EMI technology is proposed.One of the currently applied visualization methods in the field of SHM is the probability-weighted damage imaging(PDI)algorithm.However,the PDI algorithm has not been found in the field of EMI,and the classic PDI algorithm has a poor effect on near-boundary damage locations.Therefore,this thesis makes great modification on the classic PDI algorithm and then proposes an algorithm,named MPDI(Modified Probabilityweighted Damage Imaging)algorithm.Besides,this thesis conducts a detailed comparison and analysis between MPDI and classic PDI algorithm.The investigation results show that MPDI algorithm can effectively reduce the limitations of the classic PDI algorithm and sufficiently improve the imaging effect.(4)On the research of structural damage location,a new method for structural damage localization based on "DCMI-MPDI" is proposed.To improve the accuracy of structural damage localization and imaging based on EMI signals,a comprehensive damage imaging method is originally proposed.The extracted DCMI signal and the improved MPDI algorithm are integrated to form a "DCMI-MPDI" damage imaging method.The method is then applied to damage localizing and imaging of plate-like metallic structure and composite structure to study its effectiveness when used for locating damages near the boundary and other locations.The experimental verification results show that the "DCMI-MPDI" method proposed in this thesis can accurately identify and locate structural damage,and has a good engineering application prospect.