【作者】 杨雪；

【导师】 孙伟；

【作者基本信息】 东北大学 ， 机械工程（专业学位）， 2018， 硕士

【摘要】 螺栓联接广泛的应用在各个工业领域中,是机械结构件中常见的联接方式。影响螺栓联接的因素有很多,在振动、冲击、循环载荷等工作环境下,螺栓联接就会出现松动、折断等情况,从而影响整体结构的可靠性和联接质量。因此,对螺栓联接的研究有重要意义。目前,对螺栓联接的研究主要是对联接结合部的研究,包括结合部建模、结合部接触刚度识别等,其中,关于螺栓联接结合部动态特性参数辨识是研究的难点。目前对螺栓结合部或者螺栓组合结构的建模仿真分析研究大多是基于静力学,对其在振动条件下的动力学特性研究较少。基于以上问题,本文在研究单螺栓结合部力学建模的基础上,以一个螺栓联接薄板为例,重点研究了螺栓联接薄板振动特性的分析方法,具体包括以下4部分内容:(1)采用振动台、LMS信号采集系统以及BK4517传感器搭接的振动实验测试系统,对螺栓联接薄板结构件进行振动测试。首先,对研究对象进行模态锤击实验,获得结构件各阶固有频率。在不同预紧条件下,进行多组扫频实验和定频实验,获得了联接薄板精确固有频率和振动响应。通过分析实验数据发现随着预紧力的增加螺栓联接薄板固有频率及振动响应均增加,螺栓结合部使组合结构展示出非线性振动特性。(2)研究单个螺栓联接结合部有限元建模方法,采用实体建模、虚拟材料建模、弹簧-阻尼单元建模。讨论预紧力矩与预紧力之间关系,基于分形接触模型识别虚拟材料结合部特性参数。采用模糊推理系统建立预紧力与螺栓结合部刚度两者间输入量与输出量的关系,通过模糊推理,最终获得螺栓联接结合部刚度。以螺栓联接薄板为例分别利用上述3种有限元建模方法,对比静力学分析结果,确定建模方法的合理性。(3)采用有限元实体建模方式,在静力学分析基础上,对螺栓联接薄板结构进行固有特性分析。设置不同预紧方式,对薄板结构进行模态分析获得固有频率。通过与实验值比较证明了该分析结果的合理性。结果表明,随着预紧力逐渐增加,固有频率值也逐渐增加。预紧顺序不同时,螺栓联接薄板固有频率发生变化,但预紧顺序与固有频率之间变化规律并不是线性关系。通过计算不同预紧顺序的残余预紧力标准方差,可以获得较好的预紧顺序方式。同时还研究了预紧方式不同,结构的固有频率变化趋势。(4)采用有限元实体建模方式,对螺栓联接薄板进行振动响应分析。研究在不同预紧条件下,结构件振动响应的变化规律。结果表明,在预紧力逐渐增加时,结构件的振动响应值也逐渐增加。这是由于预紧力变大,整体结构件的刚度变大,结合部间阻尼影响变小,此时振动响应就会随之变大。当改变预紧顺序时,结构件的振动响应值与预紧顺序之间也呈现非线性关系。上述分析的结果与实验观测的振动响应变化规律基本一致。螺栓联接结合部及联接组合结构的建模,尤其是振动特性建模,是结构力学领域亟待解决的一个难点,本文的研究可为螺栓联接结合部参数辨识以及进一步深入研究含螺栓的组合结构振动特性建模提供参考。更多还原

【Abstract】 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.更多还原