防松胶对螺纹连接预紧力影响试验研究

鉴于螺纹在涂胶前后或涂不同种类防松胶、施加相同拧紧力矩时产生的螺栓预紧力差别较大,对空间光学遥感器装配中常用防松胶对螺纹连接预紧力影响进行定量试验研究,结果表明,在螺纹上涂硅橡胶D04(L)与不涂胶相比,相同拧紧力矩时螺栓预紧力减小50%~70%;涂厌氧胶乐泰243、相同拧紧力矩时螺栓预紧力增大46%~98%。某类防松胶使用前需对其对螺纹连接预紧力影响进行定量测试,据测试结果调整螺栓的拧紧力矩达到预期预紧力;在对预紧力精确控制的连接区域,力矩扳手紧固方式不再适用。     

室温下C/SiC复合材料螺纹紧固件的拧紧特性

探讨了C/SiC陶瓷基复合材料螺纹紧固件在室温下的拧紧特性。试验测试了紧固件在拧紧和拧松过程中, 力矩与预紧力两者的对应关系, 记录了预紧力在短时、 长时内的减小比率, 并用显微镜观察了螺纹面的磨损情况。另外, 分析了材料非线性拉伸行为对拧紧状态所造成的影响。结果表明: 拧紧、 拧松力矩与预紧力之间近似呈线性关系, 螺纹面和支承面的平均摩擦系数分别为0.52和0.46; 随拧紧力矩增大, 螺纹面产生一定程度磨损, 螺纹之间的相互嵌入作用减弱, 因此预紧力在拧紧后的降幅减小, 稳定性提高; 对螺栓进行适当的预拉伸处理, 提高材料的弹性极限后, 可提高紧固件的抗松弛能力。     

螺栓拧紧过程中工况对复合材料连接结构夹紧力的影响

针对复合材料结构螺栓连接,拧紧工况的不同会改变端面和螺纹间的摩擦系数,从而影响到扭矩系数,使夹紧力随拧紧力矩变化的趋势十分复杂.首先对螺栓连接过程进行理论分析,得到了夹紧力和复合应力状态下螺栓屈服夹紧力的表达式.然后以某型号螺栓为对象进行试验研究,在规定的目标预紧力下,分别测得了不同润滑条件、垫圈条件和拧紧速度下的拧紧...     

C/SiC陶瓷基复合材料螺栓连接件的振动响应特性及防松性能

通过对C/SiC陶瓷基复合材料螺栓连接件的模态进行计算和试验分析,确定了其模态参数和振动响应特性;然后通过对C/SiC陶瓷基复合材料螺栓连接件进行正弦扫频振动试验,研究了拧紧力矩对螺栓连接件振动性能的影响规律;最后研究了液态聚硼硅氮烷（L-PBSZ）对C/SiC陶瓷基复合材料螺栓连接件防松性能的影响。研究结果表明：一阶和三阶固有计算模态频率与试验模态频率一致,因此可以采用有限元分析方法对C/SiC陶瓷基复合材料螺栓连接件进行振动响应特性分析;采用正弦扫频振动频谱信号差值曲线分析方法可以检测螺栓连接件是否松动;SEM观察表明,L-PBSZ改性的C/SiC陶瓷基复合材料螺栓连接件的螺纹副间形成陶瓷填充体,使得螺纹与螺母间有效摩擦系数和有效摩擦面积增加,因此螺母松脱退出的力矩增大,提高了C/SiC陶瓷基复合材料螺栓连接件的防松可靠性能。     

C/C复合材料与石墨材料干态摩擦磨损行为

在M-2000型摩擦磨损实验机上,以GCr15钢为配副,对石墨材料和C/C复合材料在干态条件下的滑动摩擦进行研究。结果表明:C/C复合材料的摩擦系数和体积磨损均比石墨材料的低。具有光滑层炭结构 (SL) 的C/C复合材料的摩擦系数和体积磨损量比具有粗糙层结构 (RL) 的C/C复合材料低;低密度石墨的摩擦系数和体积磨损量比高密度石墨材料高。随时间延长,RL结构的C/C复合材料摩擦系数在60、80、200 N时有小幅度的增长,另三种则下降; SL结构的C/C复合材料摩擦系数除60 N外基本保持平稳;石墨材料的摩擦系数随时间延长表现出增长趋势。SEM观察表明: RL结构的C/C复合材料摩擦表面随载荷增加而趋向完整,SL结构的C/C复合材料的摩擦表面随载荷增加变化不大。而高密度石墨摩擦表面比密度低的石墨完整。C/C复合材料比石墨更适宜用作航空发动机轴间密封材料。      

碳/碳复合飞机刹车材料低能摩擦性能研究

研究了碳/碳(简称C/C)复合飞机刹车材料在低能载条件下的摩擦磨损性能,分析了刹车力矩与刹车速度之间关系曲线,探讨了C/C复合材料因能载变化出现摩擦系数最大值的根本原因.结果表明:随着刹车比压增加,摩擦系数最大值下降;低能条件下C/C复合材料摩擦面较粗糙,磨损率约为正常能载下的两倍.     

低能载条件下C/C复合材料滑动摩擦磨损性能

采用MM-200型环-块摩擦磨损试验机测试了针刺碳毡增强C/C复合材料试样在不同载荷和转速条件下的摩擦磨损性能,借助数码显微镜和扫描电镜观察分析了摩擦表面形貌。结果表明:当转速较低时,摩擦系数比较稳定,磨损率随载荷提高而增大;当转速较高时,低载荷试样摩擦系数不大,磨损率有所增加,而高载荷试样的摩擦系数在5分钟左右时出现峰值然后回落并保持稳定,磨损率急剧增加,说明磨损机制发生变化;摩擦面平行于X-Y向的C/C复合材料磨损率较小,具有较好的摩擦磨损性能。     

C/C及C/C-Cu复合材料的摩擦磨损性能

通过化学气相渗透(CVI)、树脂浸渍/碳化(I/C)的工艺制成多孔的C/C预制件,采用气体压力浸渗方法向预制体中渗入铜,制备出C/C-Cu复合材料。以高密度C/C复合材料(1.9g/cm~3)作为对比样,在MM-200型磨损试验机上对其摩擦磨损性能进行测试,并对其微观结构和摩擦磨损机理进行分析。研究结果表明:C/C-Cu的摩擦系数比C/C复合材料的低,这主要与摩擦表面的摩擦膜有关,铜在摩擦力带动下填充摩擦表面的凹坑,并与碳材料共同形成摩擦膜,摩擦膜的碳含量越高,润滑效果越好。当C/C预制件密度为1.59g/cm~3时,C/C-Cu的摩擦系数和磨损量均小于C/C复合材料,摩擦磨损性能良好。     

轴向载荷对滚珠丝杠副摩擦力矩波动的影响及测试

根据赫兹接触理论分析预紧力及轴向作用力与丝杠接触刚度的关系,根据滚动丝杆摩擦力矩波动的滚珠进入滚道阻力影响法,分析在轴向载荷下滚动丝杆副摩擦力矩波动影响参数;通过对轴向力作用下的丝杠系统摩擦力矩实验测试,表明预紧力对摩擦力矩的波动起主导作用,轴向载荷下的丝杠系统以单向预紧力的方式加剧了摩擦力矩的波动量。     

C/ C坯体对 C/ C2Cu复合材料摩擦磨损行为的影响

采用无压熔渗方法制备炭纤维整体织物/炭2铜 (C/ C2Cu) 复合材料 , 在 MM22000型环2块摩擦磨损试验机上考察复合材料的摩擦磨损性能 , 利用扫描电子显微镜观察分析磨损表面形貌 , 研究 C/ C坯体对材料的摩擦磨损行为的影响及机制。结果表明 : 随着 C/ C坯体密度的增加 , 摩擦系数及 C/ C2Cu材料自身和对偶的磨损量均降低 ; 采用浸渍/炭化 ( I/ C) 坯体的 C/ C2Cu材料摩擦系数及自身和对偶件的磨损量均高于采用化学气相渗透(CVI) 坯体的试样; 摩擦面平行于纤维取向的试样摩擦系数低于垂直于纤维取向的试样 , 但磨损率较高。     

Development of an anti-loosening fastener and comparing its performance with different other threaded fasteners

Threaded fasteners are widely used for temporary joining of different components that require occasional disassembling. However, threaded fasteners may have the problem of loosening under vibrating conditions, which may lead to decreasing clamping force and, thereby, a system failure. In the present experimental investigation, anti-loosening ability of various fastening elements, such as conventional nut, nylock nut, flat washer, spring washer, inside and outside serrated washer, is tested with a conventional M16 high-tension steel bolt. A hybrid double nut is used to clamp the plates in which a conventional nut is used to tighten first, and one nylock nut is then placed at the outer side for further tightening. An adhesive-bonded nut is also tested, where an adhesive is placed between bolt and nut threads. All these fasteners are tested in terms of their loosening characteristics. Accelerated vibrating conditions are used for the test on an indigenously made test rig. A split bolt with taper pin is introduced for the first time to reduce loosening of fasteners. The split bolt with taper pin shows considerably good anti-loosening property compared with other threaded fasteners tested in this work.     

Threaded Fastener Secondary Locking Requirements

Secondary locking features in threaded fasteners are in widespread use in machinery, structures, and systems. In this paper, the mechanism for loosening of threaded fasteners is explained qualitatively and defined quantitatively in terms of the self-loosening moment inherent to threaded fasteners and external load-induced loosening moments. Equations for loosening moments are defined. This paper provides analysis which quantifies the locking action required to prevent loosening due to the inherent self-loosening moment and external load loosening moments in threaded fastener joints. This paper provides the basis and method for engineers to properly design or specify secondary locking features in threaded fasteners to provide sufficient locking and prevent loosening. Requirements for secondary locking feature moments are developed in terms of loosening moments and factor of safety. Test data and calculations are provided to substantiate the requirements. Examples are provided for common secondary locking features including prevailing torque and adhesive.     

螺纹摩擦对螺栓轴向力-伸长量特征曲线的影响

基于超声波技术,通过对螺栓进行拉伸试验,研究了不同外载下螺栓轴向力-伸长量特征曲线的差异,分析了螺纹摩擦对螺栓轴向力-伸长量特征曲线的影响.结果表明:螺栓的单向拉伸与扭转拉伸因受到的载荷方向不同而导致其屈服点不同;螺栓前期拧紧标定过程中螺纹摩擦对螺栓轴向力有很大影响,会影响后续子系统螺栓夹紧力的大小;不同的螺纹摩擦状态...     

Experimental analysis of the friction coefficient effect of the zinc‐lamella coated fasteners on bolt preload and tightening moment

Basic parameters of the bolt‐nut joints, which are ones of the most important elements of assembly processes, are the torque, bolt preload and friction coefficients between bolt and nut interfaces. In bolted joints tightened with torque and angle‐controlled method, friction coefficients of the fasteners are highly significant because they affect final torque and bolt preload values directly, creating a large uncertainty in regard to meet the minimum requirements on preloads considering the safety of joints and further systems, in case of this study, the vehicles being assembled. Also, the range of the lower and upper limits of friction coefficients of the coated fasteners affect process quality considerably in bolted joints tightened with torque and angle‐controlled technique. In this study, the effect of the friction coefficients on the bolt preload and final torque values in the vehicle chassis joints, which are created using torque and angle‐controlled tightening, were investigated experimentally. Therefore, bolt specimens which have both low and high friction coefficients, were tightened by the torque and angle‐controlled tightening method especially using high angle torque parameters on the vehicle chassis test bench. The torque and preload values obtained have been compared to each other and correlated in terms of the friction coefficients occurred.     

Tightening Tests and Friction Coefficients Definition in the Steering Shaft of Front Motorbike Suspension

Abstract: The steering shaft of front motorbike suspensions is, usually, tightened up the fork by means of a nut and a locknut. The aim of this study is to evaluate the actual relation between the bolt torque and the preloading force of the steering shaft by performing some tightening tests. The bolt torque is given by a torque wrench whereas the preloading force has been evaluated by means of a strain gauge located on the steering shaft. The steering shaft has a hollow section with an external thread so that the strain gauge has been applied on its internal surface. In relating the bolt torque to the bolt tension, the friction coefficients have been accurately calculated: the friction coefficient values increase notably after the first set of tightening tests mainly because of the spoiling of the contact surfaces.     

Direct Verification of Threaded Fastener Locking Compounds and Adhesives

This article explores the feasibility of a method to directly verify that thread lock compound or adhesive has cured sufficiently to provide secondary locking. The application of a torque after assembly and cure time was found to provide a viable verification test. Fastener material and coatings were found to significantly affect cure. For example, medium-strength anaerobic compound used with fasteners made of inactive material such as stainless steel had curing issues which prevented determination of a useful verification test torque. However, modifications such as higher-strength compound or primer can be introduced making this method viable even for fasteners made with inactive materials and coatings. This article outlines a process to implement this method in practice. This requires sample tests with representative product to determine a test verification torque. This process is particularly useful in identifying curing and locking performance issues, and provides guidance for modification so that the method can be successfully implemented in practice. Test results show that application of verification test torque with or without standard vibration test exposure does not degrade the locking performance.     

Experimental and numerical study of fatigue crack growth of aluminum alloy 2024-T3 single lap simple bolted and hybrid (adhesive/bolted) joints

In this paper, the effects of tightening torque (clamping force) on the fatigue crack growth rate and stress intensity factors in cracked single lap simple bolted and hybrid (adhesive/bolted) joints have been studied experimentally and numerically. To do so, series of fatigue crack growth tests for two different amounts of tightening torque in Aluminum alloy 2024-T3 pre-cracked joints have been carried out to record the fatigue crack growth and also the fatigue life of specimens. In the numerical part, finite element method was employed to obtain the stress intensity factors and also the effective stress intensity factor ranges for different crack lengths to explain the behavior of fatigue crack propagation. It was found that the hybrid joint has longer fatigue crack growth life compared to the simple bolted joint at a given bolt tightening torque. The results also showed that a higher bolt tightening torque provides improved fatigue crack growth life for both types of the joints.     

复合材料螺栓联接螺纹载荷分布规律研究

基于Abaqus有限元分析软件建立了复合材料螺栓联接的三维有限元模型,以预测复合材料螺栓联接的螺纹载荷分布,为使模型符合真实情况,将螺母支承在弹性地基上并通过Abaqus USDFLD子程序考虑了C基或SiC基复合材料拉压不对称特性。此外,本文对预测金属螺纹的载荷分布的Yamamoto方法进行了经验性的推广,使其可以反映C基或SiC基复合材料的各向异性和拉压不对称性。通过对比多组材料及几何参数下推广的Yamamoto方法（EYM）和有限元法（FEM）预测的螺纹载荷分布验证了推广的Yamamoto方法的有效性。研究结果表明：复合材料螺栓联接的载荷分布通常比金属联接的载荷分布更均匀;随着螺距与直径之比的增加,螺纹载荷分布不均程度有所增加;复合材料螺栓绕其轴线相对于螺母的转动对载荷分布几乎没有影响。