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.     

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。     

普通螺母及自锁螺母对螺栓标定特征曲线的影响

采用纵波法并使用自制的内螺纹夹具,分别选择普通螺母和自锁螺母来标定螺栓,通过不同的拧紧策略和标定方法,分析普通螺母和自锁螺母标定螺栓特征曲线的差异.结果表明:采用普通螺母和自锁螺母标定螺栓因方法不同会获得不同的标定特征曲线,自锁螺母的锁紧扭矩使螺栓温度升高导致超声波声时差增加,因此获得的标定特征曲线会平行右移.     

室温下C/C复合材料紧固件拧紧特性

本文研究了C/C复合材料紧固件在不涂防松胶（简称不涂胶）和涂防松胶（简称涂胶）两种状态下的拧紧特性。试验测试了两种状态下C/C复合材料紧固件拧紧力矩与预紧力的关系,并对两种状态下紧固件摩擦系数和拧紧力矩分配关系进行了深入分析。结果表明:涂胶与不涂胶相比,相同拧紧力矩作用下,螺栓预紧力增大20%~82%,且不涂胶状态下预紧力与拧紧力矩线形关系较好;不涂胶和涂胶两种状态下,螺纹副摩擦系数分别为0.41、0.35,端面摩擦系数分别为0.59、0.41,涂胶后两对摩擦副摩擦系数均降低;另外,涂胶和不涂胶两种状态下施加拧紧力矩在端面摩擦副、螺纹摩擦副和附加力矩中比例分配规则略有不同。      

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.     

Three-dimensional finite element analysis of threaded fastener loosening due to dynamic shear load

The two most widespread causes of failure of threaded fasteners subjected to dynamic loads are fatigue and vibration induced loosening. This paper presents results of a study on failure of threaded fasteners by vibration induced loosening caused due to dynamic shear loads. Previous experimental work has revealed that fastener loosening occurs as a result of complete or localized slip at the thread and head contact surfaces. A three-dimensional finite element (FE) model is used to study details of four different loosening processes that are characterized by either complete or localized slip at the head and thread contacts. The FE model is found to be capable of adequately modeling factors that influence slip and predicting the different loosening processes. Primary factors that influence slip at fastener contacts are discussed. The results show that loosening can occur at relatively low shear loads due to the process of localized slip.     

高压转子拧紧扳手传动系统卡滞原因

某高压转子拧紧扳手的传动系统在拧紧螺母过程中发生卡滞,通过宏观观察、断口分析、金相检验及硬度测试等方法,对传动系统的卡滞原因进行了分析.结果表明:1号传动齿轮轴承单侧锁紧的浪式带扣保持架在装配或工作过程中受到冲击载荷,造成搭扣错位、变形、脱扣,致使滚珠偏离预定的运行轨道.当滚珠偏离预定轨道时,形成应力集中,导致局部应力...     

Investigation into the loosening mechanism of bolt in curvic coupling subjected to transverse loading

It has been widely observed that fasteners turn loose when subjected to dynamic loads in the form of shock, vibration or transverse cyclic loading. This reduces the preload force of bolt and leads to joint failure. Such failures can be catastrophic in safety critical applications. In this paper, the self-loosening of bolts in curvic coupling is analyzed based on the self-rotation of nut in the cases of cyclic torque loads on discs after the preload of bolts. The three-dimensional finite element model for curvic coupling and threads is established in commercial finite element software ANSYS to study the details of the self-loosening process of bolt. Such processes are characterized by microslip at the curvic, the bolt head and the thread contact surfaces. It is found that due to the application of the cyclic transverse load, the nut rotation can occur for only localized slip without complete slip at the bolt head contact surface and the thread surface. However, the curvic surface always shows complete slip under all external loads. The microslip on all contact surfaces are identified to be the major mechanisms responsible for the self-loosening of a curvic coupling. The results obtained agree quantitatively with the experimental observations.     

调速型鼠笼式异步磁力联轴器的轴向力研究

调速型鼠笼式异步磁力联轴器即永磁调速器,它的力学参数、磁场分布对其传递能力及整个系统的稳定性与可靠性具有很大的影响,因此有必要对其工作时的轴向力进行深入研究.基于等效面电流法,推导出联轴器在低转差率下的螺旋进给/退出轴向力计算表达式;同时采用电磁场分析软件Magnet对其进行模拟分析,得到了不同啮合长度、不同转差率下的螺旋进给/退出轴向力值,并进行了对比分析.调速型鼠笼式异步磁力联轴器轴向力由完全啮合状态至脱离状态呈现先增大后减小的趋势;在相同输入转速情况下,转差率越大,轴向力越小,在脱离状态时趋于稳定值.这对于调速型鼠笼式异步磁力联轴器以及其它类型磁力联轴器的理论研究、参数设计与优化及其应用都有着一定的理论意义及实际应用价值.     

Effect of skin hydration on the dynamics of fingertip gripping contact

The dynamics of fingertip contact manifest themselves in the complex skin movements observed during the transition from a stuck state to a fully developed slip. While investigating this transition, we found that it depended on skin hydration. To quantify this dependency, we asked subjects to slide their index fingertip on a glass surface while keeping the normal component of the interaction force constant with the help of visual feedback. Skin deformation inside the contact region was imaged with an optical apparatus that allowed us to quantify the relative sizes of the slipping and sticking regions. The ratio of the stuck skin area to the total contact area decreased linearly from 1 to 0 when the tangential force component increased from 0 to a maximum. The slope of this relationship was inversely correlated to the normal force component. The skin hydration level dramatically affected the dynamics of the contact encapsulated in the course of evolution from sticking to slipping. The specific effect was to reduce the tendency of a contact to slip, regardless of the variations of the coefficient of friction. Since grips were more unstable under dry skin conditions, our results suggest that the nervous system responds to dry skin by exaggerated grip forces that cannot be simply explained by a change in the coefficient of friction.     

航天器结构用不同材质的侧面销钉和螺母组件的耐蚀性能研究

目的 针对航天器结构用不同材质的侧面销钉和螺母组件在实际的使用工况下极易出现腐蚀与咬死的问题,对不同材质的侧面销钉和螺母组件的耐蚀性能进行研究。方法 分别在高量级腐蚀条件和低量级腐蚀条件下,采用重复拧紧试验方法,对侧面销钉和螺母开展耐腐蚀性能、防咬死性能研究。结果 在高量级腐蚀条件下,无表面处理的30CrMnSiA侧面销钉+TC4螺母组件在经历12 h腐蚀试验后,其表面发生了100%的腐蚀;经历过重复拧紧试验的30CrMnSiA（表面镀镍）侧面销钉+TC4螺母组件,在经历12h腐蚀试验后,其表面腐蚀面积>50%;未经历重复拧紧试验的30CrMnSiA（表面镀镍）侧面销钉+TC4螺母组件,在经历12 h腐蚀试验后,其腐蚀面积约为25%～50%。在低量级腐蚀条件下,经历重复拧紧试验和未经历重复拧紧试验的30CrMnSiA（表面镀镍）侧面销钉+TC4螺母组件均未发生表面腐蚀,而30CrMnSiA（无镀镍）侧面销钉+TC4螺母组件的腐蚀面积为25%～50%。镀镍处理可以显著提高30CrMnSiA侧面销钉的耐腐蚀性能。结论 经过镀镍表面处理的30CrMnSiA侧面销钉比经过表面钝化处理的1...     

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.     

Berechnung der drehwinkelgesteuerten Montage von Schraubenverbindungen

Calculation of tightening with angular control for bolted connections For high utilization of bolted connections, tightening beyond yield point of the screw is recommended – the keyword is tightening with angular control or „turn‐of‐the‐nut‐method”︁. Up to now calculations for technical design of bolted connections are due to assembly only with elastic stressing of the bolt. Therefore, assembly specifications of angular controlled tightening are formulated from experience or experiment. This paper proposes a handable method for calculation of snug torque and tightening angle and shows dependencies of most important parameters. Besides this a verification of the calculated results with experimental tests is done. Considered are most significant influences, which are bolt materials behaviour, geometry, length of plastification and friction.     

一种精确的医学细胞图像边缘检测法

细胞边缘检测是进行细胞形态分析的基础,其检测结果直接影响病情分析和诊断的结果。传统的边缘检测算子由于受噪声影响比较大,无法检测细胞可靠的边缘位置,因而不宜应用于细胞形态分析。提出一种用迭代算法求图像分割最佳阈值和运用数学形态学的腐蚀算法实现轮廓提取相结合的细胞图像边缘精确检测算法,并给出仿真实例。与传统的边缘检测算子Laplacian-Gauss算子、Sobel算子相比较,该算法具有检测精度高和抗干扰能力强的优点。     

Experimental results and finite-element predictions of the effect of nut geometry, washer and Teflon tape on the fatigue life of bolts

The effect of nut geometry, curved spring washer and a sealing material (Teflon tape) on the fatigue life of M12 and M16 ISO bolts was investigated. This was accompanied by the study of the axial and bending stress distribution in threads by numerical simulation of bolt and nut connections using the finite‐element method. The experimental results showed that the highest fatigue life is achieved for a slotted tapered nut. The presence of a spring washer also increases the fatigue life, providing that the correct tightening torque is applied to produce a pretension in the bolt. The use of Teflon tape as a filling material between engaging threads of the bolt and nut is shown to significantly increase the fatigue life. On the whole, the highest fatigue life is obtained for a slotted tapered nut using washer. Four fracture mechanisms were observed for bolt–nut connections during the fatigue tests.     

Q460高强钢柱在近爆荷载作用下的动力响应研究EI北大核心CSCD

采用有限元软件ANSYS/LS-DYNA,建立钢柱有限元模型,运用流固耦合计算方法,模拟Q460高强钢柱在爆炸荷载作用下的动力响应,在此基础上提出了分段等效三角波计算方法对结构/构件施加爆炸荷载,并对影响钢柱动力响应的主要因素进行数值分析。结果表明:分段等效三角波计算方法和流固耦合方法计算吻合较好,验证了分段等效三角波计算方法的可行性;爆炸冲击波速度快,荷载峰值大,持续时间短,对钢柱的破坏力极强;钢材强度等级越大,钢柱抵抗变形的能力越强;炸药位置越低,柱脚越容易发生剪切破坏;翼缘作为迎爆面更能抵抗爆炸冲击的作用;适当减小翼缘和腹板的宽厚比能增强钢柱抵抗动力荷载的能力。提出的分段等效三角波计算方法为研究抗爆提供进一步参考。     

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.     

Influence of contact configuration on fretting fatigue behavior of Ti–6Al–4V under independent pad displacement condition

Fretting fatigue tests were conducted, using cylindrical pad and flat pad with rounded edges, at various applied pad displacements and at two normal forces on the pad under a constant bulk stress amplitude condition. The evolution of tangential force was independent of the contact configuration at a given normal force. The ratio of the tangential force to normal force increased and stabilized to a certain value with increasing applied pad displacement. The minimum fretting fatigue life was observed at the relative slip range between 50 and 60 μm and it was independent of both contact configuration and applied normal force. With increase in the applied pad displacement the response of the tangential force (Q) and the relative slip (δ) showed different fretting conditions, i.e. stick, stick-slip and gross slip. The gross slip condition was characterized by rectangular shape of the Q–δ curve with or without monotonically increasing value of Q with increasing fretting fatigue cycles. Surface profile on the fretting scar was affected by the contact configurations. For cylinder-on-flat contact, the profile showed surface damage (e.g. material loss or wear) along the entire contact area. However, the fretting damage in flat-on-flat (with rounded edges) contact was concentrated on the edge, not affecting much of the flat portion of the fretting scar.     

基于滑移线场的闭挤式精冲主冲力计算及实验验证

目的研究基于滑移线场的闭挤式精冲主冲力计算,为后续的仿真模拟提供理论基础。方法根据闭挤式精冲的成形特点,建立闭挤式精冲坯料变形区的力学模型,通过处理刚塑性体平面应变问题的方法,利用滑移线理论建立闭挤式精冲的滑移线场,通过该滑移线场的建立计算冲裁过程中的主冲裁力。结果滑移线法计算出的结果,并通过精冲实验进行了验证,实验得到冲裁力的大小与滑移线法所计算出的冲裁力相差0.8%,经过分析,认为误差的存在主要由摩擦力的忽略及材料被视为刚塑性材料所致。结论滑移线法计算冲裁力是比较适用的,为闭挤式精冲的工艺参数提供了较为精确的计算方法。     

Evaluation of the Clamping Force of Bolted Joints Using Local Mode Characteristics of a Bolt Head

It is important to determine and control the clamping force of a bolted joint. Due to its simple setup, the torque control method is typically used to control the clamping force when tightening bolts. After tightening, hammer tests, ultrasonic techniques and methods employing sheet materials as sensors are often used. Many methods have been proposed, but using them to determine and control the clamping force during or after tightening bolts is labor intensive or expensive. Here we conduct impact tests with an impulse hammer combined with experimental modal analysis to determine the clamping force by interpreting the change in the local mode frequency of a bolt head in the high frequency region as a function of the clamping force. To demonstrate the applicability of our method, we also investigate its limits with regard to bolt sizes.