Looseness Detection Of Flange Bolts Based On Electro-mechanical Impedance

Complex mechanical systems are assembled by various parts and components,of which bolt connection,as the most typical form of assembly,has the advantages of easy disassembly and reliable connection,and often plays an important role in connection,fastening and load transfer in complex structures.However,bolt connection is easy to self-loosening under the reciprocating cyclic load.If the bolt connection can not be detected in the early stage and the anti-loosening measures can not be taken,it may cause serious safety accidents.Therefore,it is of great significance to develop the detection technology of bolt loosening.Mechanical and electrical impedance technique using piezoelectric properties of piezoelectric material inspection,has the advantages of fast response speed and is sensitive to minor injuries,have been applied in the field of bolt looseness detection gradually,but mostly for lap plate such as simplified structure,practicality is not strong,and study of flange connection structure is commonly used in engineering such as common complex installation,detection accuracy is not high.Therefore,this paper takes the flange-bolt connection as the research object,and based on the research status of electromechanical impedance technology,adopts the method of combining theoretical analysis,finite element simulation and experimental verification to systematically study the detection technology of the loose state of flange bolt.The main research contents are as follows:To illustrate the mechanism of damage detection based on electrical impedance method,set up under the action of external force through the analysis of the mechanical characteristics of piezoelectric materials and matrix structure coupling model of one dimensional mechanical and electrical impedance of piezoelectric materials is derived-electrical impedance matrix of the structure of the coupling equation,based on the exploration to the impedance peak move as the theoretical foundations of the feature of bolt looseness damage detection.Because the coupling system between the flange structure and the piezoelectric plate is difficult to be expressed in an analytical form,a simulation model of the coupling between the mechanical and electrostatic fields is established based on the analysis software COMSOL.Firstly,the effects of bolt loosening degree and damage distance on electromechanical impedance were investigated,and the feasibility of using impedance peak movement as damage characteristic was verified.In addition,the limitations of using single band impedance for detection are analyzed,and the qualitative relationship between excitation frequency and effective recognition range of piezoelectric plate is further explored,which lays a foundation for the proposed multi-band fusion detection method.A detection platform for flange bolt looseness based on electromechanical impedance was established.The impedance analyzer is used to measure the impedance of the piezoelectric plate on the measuring flange,and the impedance signals in multiple frequency bands are collected for comparative analysis.The analysis results further verify the conclusions about the impact of bolt loosening on the impedance obtained in the simulation.In addition,based on the limitations of single-band impedance detection,the feasibility of multi-band impedance fusion for damage localization was analyzed based on the experimental data.In order to solve the problem that the single-band impedance could not accurately identify the bolt loosening state,a multi-band fusion bolt loosening detection method was proposed,which took the impedance peak movement as the damage feature.First through the damage characteristics of fusion under the multiband impedance of each piezoelectric intelligent classification model is established,and then by combining the piezoelectric patches of recognition results and the relationship between bolt and the position of the piezoelectric element distribution are introduced to determine the position of the loose bolts and loosen,eventually to the test the accuracy of the models were evaluated,the results show that: The detection model proposed in this paper can accurately identify the loosening state of bolts in the flange structure.