Bolt Preload Detection Based On Electromechanical Resistance Method

Bolt connection-the most widely used connection form in mechanical equipment.Bolt connection has the advantages of simple structure,compact connection,and easy assembly and disassembly.However,the conventional bolt preload loading process often relies on torque or torque-rotation method to control the preload,which makes it difficult to effectively detect and control the preload.Bolt preload testing has always been one of the most popular research directions in the field of machinery and high-end assembly.At the test method level,there are ultrasonic method,structural dynamic detection method,machine learning-based method and piezoelectric impedance method.Generally speaking,it is difficult to accurately quantify the preload of a single bolt in the testing of bolt preload.This paper adopts a test method based on electromechanical impedance method to realize a set of bolt pre-tightening test system.Through the self-built bolt preload test bench,the bolt preload and the corresponding piezoelectric element conductivity peak frequency are collected,and the relationship curve is obtained by calibrating the relationship between the two,thereby realizing the bolt preload test(The error is less than 5%).The work of this article mainly includes the following aspects:First,based on the piezoelectric equation and the electromechanical coupling system model,the electrical impedance and conductivity equations of the piezoelectric element in the electromechanical coupling system are established,and the characteristic frequency change of the one-dimensional axially loaded member is theoretically analyzed and the bolt obtained by simulation The internal stress of the head combined gives a model explanation of the phenomenon that the peak frequency of the electrical admittance of the piezoelectric element moves with the preload.Secondly,due to the complexity of the bolt structure,the coupling system with the piezoelectric element is difficult to describe analytically,so the electromechanical impedancebolt pre-tightening force model simulation based on the piezoelectric-solid mechanics coupling field is realized in the finite element software COMSOL,And extract the conductance parameters of the piezoelectric element under different preloads for analysis.The structure preliminarily verifies the effectiveness of the aforementioned mechanism model,and plays a guiding role in the frequency selection and the selection of the parameters to be tested in subsequent experiments.Thirdly,since there is currently no complete set of test equipment for testing bolt pretightening force using electromechanical impedance method,based on the test ideas of this article,through the use of precision impedance analyzers,special converters,pressure sensors,PCs and other equipment,an independent establishment based on electromechanical impedance The bolt pre-tightening force test bench,and its driver software is written based on Lab VIEW.Finally,the electromechanical impedance-bolt pre-tightening force calibration and verification test were carried out on the bolt pre-tightening force test bench.The electrical admittance of the piezoelectric element under different bolt pre-tightening forces was tested,and the two values were obtained through fitting.The quantitative relationship verifies the validity of the mechanism model and finite element simulation results in this paper,establishes an effective bolt pre-tightening force detection method,and verifies its accuracy and repeatability.The above research content in this paper can provide theoretical reference and experimental conditions for the research of single bolt preload.It has theoretical and practical significance to improve the assembly quality of bolted structures.