Research On Active Structural Health Monitoring Method For Bolt Looseness

Bolt connection is widely used in large mechanical structures due to its advantages of convenient operation,dismantling and easy maintenance.However,during the service of structure,bolt connection is easy to loose due to external load or bad environment,which will undermining its structural integrity.Therefore,it is of great importance to detect structural bolts looseness.Distinguish from the traditional nondestructive testing method,the structure health monitoring technology does not need the structure to stop running and can detect the structural state in real time,so that it can find the bolt loosening in time and prevent the development of damage.Based on active structural health monitoring technology,the detection of bolt looseness in metal structures is studied by using the two major damage detection methods based on ultrasonic guided waves and electromechanical impedance.Firstly,we analyzed and discussed the effects of environmental temperature change on the structure of Lamb wave propagation.Based on that,Independent Component Analysis method is proposed to eliminate the effects of temperature change in damage detection,and which is verified by the simulation and experiment of the aluminum plate structure.Secondly,based on the principle of damage detection based on electromechanical impedance,a set of self-made impedance measurement system is designed and developed,and the system is used to detect the bolt looseness on the steel plate.The main content of this paper is as follows:Firstly,the research background of structural health monitoring technology and the present situation of two active structural health monitoring technologies were summarized,and the main work of this paper was also presented.Secondly,the piezoelectric materials and their piezoelectric effects was briefly introduced.Based on the wave equation of elastic thin plate,the basic theory of Lamb wave and dispersion characteristics of Lamb wave were deduced and analyzed.Based on the one-dimensional single degree of freedom spring mass damping model coupled with piezoelectric patches,the theory of electromechanical impedance method for structural damage detection is discussed.Thirdly,three damage index and corresponding imaging methods in Lamb wave damage detection methods were summarized.And four damage indexes representing the damage degree in electromechanical impedance method were introduced.Fourthly,the influence of temperature change on the propagation of Lamb wave in the structure was discussed in the form of formula deduction.Based on that,Independent Component Analysis method to eliminate the interference of temperature change in the detection of Lamb wave bolted loosening was proposed,and the specific mechanism of the method was analyzed theoretically.The feasibility of this method was verified by numerical simulation and experiment.Fifthly,based on the principle of damage detection using electromechanical impedance,a self-made system for measuring impedance was developed.By comparing the signal from the traditional impedance instrument and establishing the error index,the accuracy of the impedance measured by this system was demonstrated.With the help of this system,the bolted loosening test was carried out,and the damage degree was quantitatively characterized by using damage index.Sixthly,based on NI data acquisition platform and with the help of Lab VIEW programming,a set of structural health monitoring system including two active damage detection techniques of ultrasonic guided wave and electromechanical impedance was developed,By designing experiments,the feasibility of this system was tested.Finally,conclusions of the whole work was summarized.The shortcomings of this study and the direction of further work were presented.