Measurement And Analysis Of Vibration Characteristics Of Bolt Bonded Sheets

Bolt connection is widely used in various industrial fields,which is a common mechanical structure of the connection.Many factors affect the bolt connection.Under the working environment of vibration,impact and cyclic load,the bolt connection will become loose and broken,which will affect the reliability and connection quality of the whole structure.Therefore,the research of bolting is of great significance.At present,the research on bolted joints mainly focuses on the research of joining and joining surfaces,including the modeling of joint surfaces and the identification of the contact stiffness of joints.Among them,the identification of the dynamic characteristics of bolted joints is a difficult point to study.At present,the modeling and simulation analysis of bolted composite and bolted composite structures are mostly based on statics,and has less research on the dynamic characteristics of the bolt in vibration condition.Based on the above problems,this paper focuses on the analysis of the vibration characteristics of bolted thin plates based on the mechanical modeling of the single bolt joints,taking a single bolt joint as an example;this includes the following four parts:(1)The vibration test system of vibration table,LMS signal acquisition system and the BK4517 sensor were used to test the vibration test of bolted joint thin-plates structure.First,modal hammering experiments were carried out to obtain the natural frequencies values of each order of the structure.Under different pre-tightening for more groups of experiment and fixed frequency sweep test,obtained the connecting sheet accurate natural frequencies and vibration response.Through the analysis of experimental data,it was found that the natural frequency and vibration response of the bolted plates are increased with the increasing of the pretension force,and the combination structure of the bolt shows the nonlinear vibration characteristics.(2)The finite element modeling method of single bolt joint joint is studied,and the modeling of solid modeling,virtual material modeling and spring damping element is used.The relationship between pre-tightening torque and pre-tightening force is discussed,and the expression of the relation between pre-tightening torque and pre-tightening force is established.The fractal contact model is used to identify the characteristic parameters of the virtual material.Fuzzy inference system is applied to establish the relationship between input force and output volume of preload and bolt joint stiffness,and the stiffness of bolt connection joint is finally obtained through fuzzy reasoning.By using the three finite element modeling methods,the rationality of the modeling method is determined by comparing the static analysis results.(3)On the basis of static analysis,the inherent characteristics of the bolt joint plate structure are analyzed by the finite element solid modeling method.Different pretightening methods are set up,and the natural frequency is obtained by modal analysis of the thin plate structure.The rationality of the analysis result is proved by comparison with experimental value The results show that the intrinsic frequency increases with the increase of pretension.When the preloading sequence is different,the natural frequency of the bolt is changed,but the change law between the pretightening sequence and the natural frequency is not linear.By calculating the standard variance of residual pretightening force in different pretightening sequences,a better pretightening sequence were obtained.At the same time,the change trend of natural frequency of the structure with different pretightening methods is also studied.(4)The finite element solid modeling method is used to analyze the vibration response of bolted thin plates.The variation of vibration response of structural members under different preload conditions is studied.The results show that the vibration response value of the structure increases gradually when the pretension force increases gradually.This is due to preload becomes larger,the stiffness of the overall structure becomes larger,the damping effect of the joint between the smaller,then the vibration response will be larger.When changing the pretensioning sequence,the vibration response value of the structure also shows a nonlinear relationship with the pretensioning sequence.The results of the above analysis and experimental observations of the vibration response changes are basically the same.The modeling of bolted joints and joint structures,especially the vibration modeling,is a difficult problem to be solved urgently in the field of structural mechanics.The research in this paper can be used to identify the parameters of bolted joints and to further study the vibration characteristics of bolted composite structures modeling for reference.