Application Research And System Implementation Of Piezoelectric Impedance Method In Structural Health Monitoring

Large civil engineering structures are inevitably damaged under the action of longterm load effect,natural environment erosion,material aging and sudden natural disasters.If early structural damage is not detected in time,the damage will accumulate until sudden structural failure occurs.Therefore,it is of great social significance and economic value to study effective structural health monitoring methods and develop structural damage monitoring systems suitable for engineering practice,so as to identify early structural damage timely and accurately.In view of the problems faced by the application of piezoelectric impedance method in structural health monitoring,the following work has been carried out specifically:1.Based on the piezoelectric effect and characteristic parameters of piezoelectric ceramics,the impedance characteristics and coupling model of PZT are analyzed and discussed in detail.Combining with the background of structural health monitoring engineering,the quantitative structural damage index is defined,which provides a theoretical basis for the experimental study of bolt tightening monitoring by piezoelectric impedance method.2.In order to verify the feasibility of piezoelectric impedance method in bolt tightening monitoring,bolt tightening state detection at different positions and bolt loosening detection at different distances were carried out by impedance analyzer.The real and imaginary impedance curves of three bolts at different positions are analyzed respectively.The results show that the real and imaginary impedance curves deviate regularly with the change of bolt loosening conditions.The tightening factor was extracted from the collected data,and the relationship between the change degree of tightening factor and the bolt position was analyzed.At the same time,it is helpful to optimize the layout of piezoelectric sensors for practical monitoring by analyzing the changes of real and imaginary parts of bolt loosening impedance at different distances.3.The overall design scheme of wireless impedance measurement system is proposed.In this scheme,ZigBee wireless network is used to communicate with each other in order to realize multi-node network monitoring for structural health.The hardware circuit of impedance measurement based on AD5933 is designed and developed.The impedance measurement range of AD5933 is expanded by series connection with known impedance measured.At the same time,the data transmission between computer and impedance measurement node is realized by PC client developed on LabVIEW platform.4.The wireless impedance measurement system is tested and the bolt detection experiment is carried out with the system.The experimental results of bolt detection show that the impedance spectrum curve collected by the system can qualitatively judge the bolt damage state,and the trend of the impedance spectrum curve and the tightening factor is also consistent with the monitoring results of impedance analyzer.In summary,this paper has formed a monitoring method,technology and instrument for bolt tightening based on piezoelectric impedance method.The research results have a certain role in promoting the application of piezoelectric impedance method in the field of structural health monitoring.