轴向激励下螺栓连接结构的松动机理研究

发布时间：2018-06-23 13:44

本文选题：螺栓连接 + 轴向激励　；参考：《西南交通大学》2016年博士论文

【摘要】：由于结构简单、拆卸方便和成本低等优点,螺栓连接结构广泛应用于各类工程结构中。作为重要的连接部件,其性能对整个结构的安全性和可靠性具有重要影响。在振动环境下,松动是螺栓连接结构失效的主要形式之一。鉴于螺栓松动机制的重要性和复杂性,国内外对其进行了广泛的研究。但是由于加工精度和表面粗糙度不同等原因,螺栓松动试验结果重复性差、分散性大,难以发现松动的规律,对于螺栓的松动机制至今尚未形成统一的认识。开展螺栓松动试验的研究,具有重要的科学意义,不仅可以深化对螺栓松动机理的认识,而且为工业实际螺栓防松提供重要的理论指导。本论文基于自主研制的螺栓松动试验装置,成功再现了轴向激励下螺栓连接结构的松动过程,并在在不同预紧力矩/预紧力和交变载荷幅值等试验参数下,系统开展了轴向激励下螺栓/铝制件连接结构和螺栓/钢制螺母连接结构的松动试验；对螺栓进行表面处理,研究聚四氟乙烯涂层(PTFE涂层)、二硫化钼涂层(MoS2涂层)和氮化钛涂层(TiN涂层)对螺栓连接结构防松性能的影响；基于MoS2涂层螺栓,通过理论计算获取合理的预紧力,并研究其防松性能。在动力学分析的基础上,运用光学显微镜(OM)、扫描电子显微镜(SEM)和电子能谱仪(EDX)进行微观分析,并结合有限元计算,系统揭示了螺栓连接结构的松动机理。完成的主要研究内容和获得的主要结论如下：(一)轴向激励下螺栓连接结构松动机理基于动力学响应以及螺纹表面损伤形貌分析,结合有限元计算,发现螺栓连接结构的松动机理是结构的塑性变形和接触界面的微动磨损。(1)螺栓连接结构的松动过程可分为两个阶段：第一阶段,由于螺栓连接结构的塑性变形以及接触表面粗糙峰被去除,螺栓轴向力迅速下降；第二阶段,随着循环次数的增加,由于材料的棘轮效应,塑性变形趋于稳定,微动磨损是螺栓轴向力下降的主要原因。(2)研究表明预紧力矩/预紧力、交变载荷幅值、循环次数等试验参数对螺栓连接结构的松动行为具有强烈的影响：随着预紧力矩/预紧力的增大,螺栓残余轴向力与预紧力之比增大,螺纹表面的磨损程度逐渐降低,主要的磨损机制由疲劳磨损、粘着磨损向磨粒磨损转变；随着交变载荷幅值的增大,螺栓残余轴向力与预紧力之比减小,螺纹表面的磨损程度加剧,主要的磨损机制由磨粒磨损向疲劳磨损转变；由于磨屑的塞积、排出,螺栓轴向力在试验过程中出现先增大后减小的现象,但总体呈减小趋势；在MoS2润滑剂润滑条件下,螺栓/铝制件连接结构的残余轴向力与预紧力之比相对于无润滑条件下较大,螺纹表面的损伤程度相对较轻,主要的磨损机制为磨粒磨损。(二)轴向激励下不同涂层螺栓连接结构的松动机理(1)在螺栓松动过程的第一阶段,由于界面摩擦系数低,PTFE涂层和MoS2涂层螺栓表面粗糙峰少,螺栓轴向力在此阶段变化小；反之,TiN涂层螺栓轴向力在此阶段下降相对明显。(2)在螺栓松动过程的第二阶段,由于PTFE涂层的结合强度低,螺纹表面的PTFE涂层磨损严重,螺栓轴向力在此阶段变化大；MoS2涂层摩擦系数小,螺纹表面摩擦应力小,且该涂层结合强度高,接触界面的磨损轻微,螺栓轴向力在此阶段变化小；由于TiN涂层的耐磨性能好,接触界面的磨损轻微,螺栓轴向力在此阶段变化也小。(3)在螺栓表面涂覆MoS2涂层后,在与未经过表面处理的螺栓螺纹根部相同的应力状态下,预紧力可以提高近20%。此时螺纹接触界面的摩擦应力和单位面积的摩擦耗散能减小,说明螺纹表面的损伤轻微；接触面积增大,螺纹根部由交变载荷引起的累积塑性应变减小。螺栓的防松性能得到大幅度的提高。(三)螺栓连接结构的精确建模及数值分析运用Matlab软件和ABAQUS软件建立了螺栓连接结构的精确模型,并通过理论计算验证了有限元模型的有效性,研究结果表明：(1)第一圈工作螺纹约承受全部轴向力的30%,前三圈工作螺纹约承受全部轴向力的70%。螺栓第一圈工作螺纹牙底的应力集中系数最大,随着圈次的增加,应力集中系数首先迅速降低,然后缓慢下降。此外,螺母螺纹牙底的应力集中系数相对较低。(2)沿螺栓径向方向,靠近螺纹牙顶区域单位面积的摩擦耗散能最大,说明此区域损伤较为严重；靠近螺纹牙底区域由于没有发生相对滑动,因此该区域损伤轻微。沿螺栓周向方向,单位面积的摩擦耗散能总体呈现减小趋势,说明随着工作螺纹圈次的增加,磨损总体呈减轻趋势；但是单位面积的摩擦耗散能不是单调减小的,导致螺纹表面的磨损不均匀。(3)随着预紧力的增大,螺纹接触界面的摩擦应力略微增大,但相对滑移量明显减小,表面单位面积的摩擦耗散能减小,说明螺纹表面的损伤减轻；同时,螺纹接触面积增大,螺纹根部由交变载荷引起的累积塑性应变减小。因此,残余轴向力与预紧力之比增大。随着交变载荷幅值的增大,螺纹接触界面的摩擦应力和相对滑移量均增大,表面单位面积的摩擦耗散能增大,说明螺纹表面的磨损加剧；同时,螺纹根部由交变载荷引起的累积塑性应变增大。因此,残余轴向力与预紧力之比减小。(4)降低螺栓头部／被连接件和螺纹接触界面的摩擦系数,并适当提高预紧力,可降低由交变载荷引起的塑性变形和螺纹表面单位面积的摩擦耗散能,从而有效提高螺栓的防松性能。
[Abstract]:Due to the advantages of simple structure , convenient disassembly and low cost , the bolt connection structure is widely used in various engineering structures . As an important connecting part , the performance of the bolt has an important influence on the safety and reliability of the whole structure .
The effect of PTFE coating ( PTFE coating ) , molybdenum disulfide coating and TiN coating on the anti - loosing performance of bolted connection structure was studied by surface treatment of bolts .
Based on the analysis of dynamic analysis , the loose mechanism of bolt connection structure is analyzed by means of OM , SEM and EDX .
In the second stage , with the increase of the number of cycles , the plastic deformation tends to be stable due to the ratchet effect of the material , and the fretting wear is the main reason for the decrease of the axial force of the bolt .
With the increase of the amplitude of the alternating load , the ratio of the residual axial force of the bolt to the pre - tightening force is reduced , the wear degree of the thread surface is increased , and the main wear mechanism is changed from the wear of the abrasive particles to the fatigue wear ;
The axial force of the bolt is decreased after the increase of the axial force of the bolt in the course of the test , but there is a decrease trend .
Under the condition of lubricant lubrication , the ratio of residual axial force to pre - tightening force of bolt / aluminum part connecting structure is relatively light , the damage degree of thread surface is relatively light , the main wear mechanism is abrasive particle wear .
On the contrary , the axial force of the TiN coating bolt is relatively obvious at this stage . ( 2 ) In the second stage of the bolt loosening process , the PTFE coating on the thread surface is worn seriously due to the low bonding strength of the PTFE coating , and the axial force of the bolt is large in this stage ;
The friction coefficient is small , the friction stress of the thread surface is small , and the bonding strength of the coating is high , the wear of the contact interface is slight , and the axial force of the bolt is small in this stage ;
The wear resistance of TiN coating is good , the wear of the contact interface is slight , and the axial force of the bolt is small in this stage . ( 3 ) After the coating of the coating on the surface of the bolt , the pre - tightening force can be increased by nearly 20 % in the same stress state as the root of the bolt thread without surface treatment .
The results show that ( 1 ) the stress concentration coefficient of the first ring working thread is about 30 % of the total axial force , and the stress concentration coefficient of the first ring working thread is about 70 % . The results show that : ( 1 ) The stress concentration coefficient of the first ring working thread is relatively low .
Due to the absence of relative sliding in the area near the thread bottom , the area is slightly damaged . In the circumferential direction of the bolt , the friction dissipation in the unit area can generally reduce the trend , which indicates that with the increase of the number of working thread turns , the wear is generally decreasing .
However , the friction dissipation in the unit area is not monotonically decreasing , which leads to uneven wear of the thread surface . ( 3 ) As the pre - tightening force increases , the friction stress of the thread contact interface increases slightly , but the relative slip amount is obviously reduced , and the friction dissipation of the surface unit area can be reduced , so that the damage on the surface of the screw thread is reduced ;
Therefore , the ratio of the residual axial force to the pre - tightening force is increased . As the amplitude of the alternating load increases , the friction stress and relative slip amount of the thread contact interface are increased , and the friction dissipation of the surface unit area can be increased , so that the wear of the thread surface is increased ;
As a result , the ratio of residual axial force to pre - tightening force is reduced . ( 4 ) The friction coefficient of bolt head / screwed contact interface is reduced , and the pre - tightening force is increased properly . The frictional dissipation energy caused by alternating load and unit area of thread surface can be reduced , so that the anti - loosing performance of the bolt can be effectively improved .
【学位授予单位】：西南交通大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH131.3

【参考文献】