Research On Key Technology Of Piezoelectric Intelligent Bolt

Bolt is an important connecting element of modern machinery and is widely used in various mechanical connecting structures for national defense and people’s livelihood industry.The bolts in service,under the influence of load,will loosen or break due to the change of pretightening force,forming potential safety hazards and causing accidents.Therefore,it is of great significance to monitor the bolt pretightening force.In this paper,the detection of development status of bolt pretightening force is systematically introduced,and a new bolt pretightening force monitoring method is proposed,in which a piezoelectric film is deposited on the bolt surface.The new method achieves higher integration for axial force detection,overcomes the disadvantage of uncertain thickness of traditional acoustic coupling layer,and reduces the monitoring interference factors.The feasibility of real-time monitoring of axial force by p-wave s-wave ratio method is improved.The method breaks through the limitations of surface geometry and size of bolts.The main research contents include:The first chapter systematically introduces the development status of bolt preload detection.The principles,advantages and limitations of several mainstream bolt preload testing methods are introduced.The chapter 2 describes the basic knowledge of piezoelectric effect and acoustic elastic effect,and the principle of ultrasonic time-of-flight method and ultrasonic wave velocity ratio method to test bolt axial force based on acoustic elastic effect.In chapter 3,ZnO piezoelectric thin films were fabricated on Si,Ti,Ti/Si and Au/Ti/Si substrates by pulse laser deposition(PLD).The surface morphology,thickness,microstructure,composition and piezoelectric properties of ZnO thin films were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),Raman spectroscopy,atomic force microscopy(AFM),and piezoresponse force microscopy(PFM).The influence of different substrates and bottom electrodes on ZnO piezoelectric thin film prepared by PLD was studied.In chapter 4,the simulation of ultrasonic flight time in bolt is created by using the discontinuous Galerkin algorithm using explicit module of COMSOL multi-physical field coupling numerical analysis software.The terminal voltage waveform is processed by shorttime Fourier transform(STFT)based on Matlab platform to distinguish p-wave and s-wave in frequency domain.In chapter 5,the ultrasonic monitoring experimental platform was built and the experimental scheme was designed.The ultrasonic p-wave time-of-flight method was used to test the axial force of bolt.By contrast,ultrasonic probe was used to measure the axial force of bolts based on ultrasonic p-wave time-of-flight method.The linear regression curves of the piezoelectric integrated bolt and the ultrasonic probe were drawn by using Lab VIEW software to process the experimental data.The linear relationship between the axial stress of the bolt and the ultrasonic propagation time was verified by error and relative error analysis.The stability and accuracy of the piezoelectric integrated bolt were verified by experiments.Chapter 6 summarizes the research work of this thesis and prospects the future research direction.