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...     

考虑预紧力与阀杆力的电动截止阀体应力分析

建立了有预紧力的截止阀有限元计算模型，阐述了预紧力单元的原理及分析方法，利用ANSYS程序对截止阀在考虑和不考虑螺栓预紧力及阀杆闭合力作用下的应力进行了计算。结果表明，法兰螺栓预紧力及阀杆闭合力对阀体应力的影响不可忽略。     

螺栓连接对结构模态及传递特性影响研究

针对螺栓刚度及预紧力对装配体模态、传递函数影响较大而在设备装配中因处理困难常被忽略问题,利用有限元计算、试验结合对比方法分析、研究。用ANSYS软件预应力模态分析及谐响应分析对装配体进行仿真计算;对三种刚度螺栓分别施加相同预紧力,对钢制螺栓施加六组不同预紧力进行试验;分析对比计算值与试验值误差。结果表明,忽略接触阻尼的计算值与试验值存在最大误差约15%;同一预紧力时,随螺栓刚度的提高固有频率呈增大趋势,各阶频率的最大变形量随之增大;随预紧力的增大,结构传递函数趋于明朗化。     

基于8.8级螺栓疲劳性能的预紧力优化

测量了8.8级螺栓的拉伸性能,根据螺栓材料的强度极限和屈强比研究了预紧力分别为强度的10%、30%和50%的极限条件下材料的疲劳性能。结果表明,当8.8级螺栓的预紧应力从10%强度极限提高到50%强度极限时,其疲劳极限由370 MPa降低到263 MPa。根据有效应力(σˉσˉ)参数法处理预紧应力对8.8级螺栓疲劳曲线的影响,得到了疲劳极限处的有效应力(σˉ10^7=562.75MPaσˉ10^7=562.75MPa)。当有效应力σˉ<σˉ10^7σˉ<σˉ107时预紧的8.8级螺栓不会发生疲劳失效,由此得到了8.8级M6和M27两种螺栓在不同应力比下所对应的最大预紧力和预紧扭矩曲线。     

基于特征参数的栓接结合部螺栓预紧力评估

为了解决频响函数法在栓接结合部特征参数辨识中的不适定性问题及期望通过定量评估螺栓预紧力以评估栓接结合部损伤程度,采用正问题求解思路,提出依据动力方程定义参数辨识的目标函数并利用特征参数定量计算螺栓预紧力的评估方法。建立栓接结合部等效线性模型,通过模态试验测量不同预紧力下的结构频响函数;构建目标函数,采用粒子群优化算法获取不同预紧力下的特征参数,并通过多项式拟合特征参数与预紧力之间的关系曲线,从而评估螺栓预紧力;通过数值仿真和试验验证方法的有效性和适用性。研究结果表明:所提方法能够准确辨识结合部参数,利用拟合的关系曲线可以准确地定量评估螺栓预紧力。     

法兰连结结构的振动测试试验分析

利用虚拟仪器LabVIEW软件,针对法兰连接结构振动测试试验,开发具有信号发生(频率可调的伪随机和正弦)、数据采集、谱分析等数据处理功能的分析系统,完成了法兰螺栓连接结构在不同预紧力下的振动试验。通过对试验数据的谱分析、差量分析表明:法兰螺栓连接结构的非线性特性对结构动态响应影响是显著的,各种非线性振动现象明显,信号不对称性表现的尤其突出,且与螺栓的预紧状态密切相关。借助于频谱信息,可判定螺栓松紧的程度,为结构连接状态的诊断提供依据。     

旋转型超声电机在冲击环境下的失效模式研究

随着超声电机在武器系统中的应用,研究分析冲击环境下电机的失效模型,为超声电机应用在武器系统等高过载环境中提供意见与建议变得十分具有意义。分析了电机中关键部件在冲击载荷下可能存在的失效模式:压电陶瓷的断裂与脱胶;定子的塑性变形引起工作频率的漂移;定转子的塑性变形和预紧力机构中紧固螺栓的松动引起预压力的减少甚至消失。通过动力学仿真对超声电机各个部件的受力情况与应力波传递过程进行分析,分析结果显示预紧力机构是整个结构中最容易被损坏的部分。通过空气炮对超声电机进行冲击过载实验,当冲击过载达到26 546g时,超声电机中用于施加预紧力的螺栓松动,预紧力结构失效,其它结构部件没有发生明显损坏或变形。研究结果为超声电机应用于武器系统等高过载环境中提供理论依据与改进意见。     

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。     

预紧力对螺栓联接机匣模态频率的影响研究

为研究预紧力对螺栓联接机匣模态频率的影响,首先,从理论上建立预紧力作用下螺栓联接结构模态方程;其次,以螺栓联接板试件为例,基于有限元分析和试验相结合的方法,验证螺栓联接接触面处理方法的准确性;然后,建立较为精细的机匣有限元模型,进行不同预紧力作用下的机匣模态分析;最后,分析刚性机匣和预紧力作用条件下的实体机匣各阶固有频率相对差异,重点研究预紧力变化对各阶模态频率影响程度。研究表明,随着预紧力增大,机匣各阶固有频率总体上有所增大,并且预紧力对各阶固有频率的影响程度各不相同,结合振型图发现,对于连接面处相对变形较大的振型,其模态频率受预紧力影响较大;而对于连接面处相对变形较小的振型,其模态频率受预紧力影响较小。     

基于SMA连接的装配式梁柱钢节点滞回性能数值研究

采用形状记忆合金(SMA)作为节点连接材料,可限制装配式钢结构在强震作用下的塑性变形,提升结构抗震韧性。该文以一种采用SMA连接的韧性抗震装配式钢节点为研究对象,建立精细化实体有限元模型,并通过试验验证模型的有效性,进而分析SMA螺栓预紧力和SMA束初始拉应力对装配式钢节点受力状态和滞回性能的影响。研究结果表明：建立的有限元模型可以较好地模拟装配式梁柱钢节点的滞回行为;SMA束连接的装配式梁柱钢节点具有极好的抗震韧性,在低周循环往复荷载作用下梁柱钢构件及其连接件基本维持在弹性范围内,且残余位移近似为零;提高螺栓预紧力可增大螺栓与钢板的摩擦力,进而提高梁柱节点的承载能力和耗能能力,但增大SMA束初始拉应力对梁柱节点的受力状态和滞回性能影响不显著。     

力矩扳手在螺杆压缩机装配中的应用

介绍了螺杆压缩机装配过程中连接螺栓的受力情况，并对螺栓所受预紧力和扭矩进行了初步分析。     

力矩扳手在螺杆压缩机装配中的应用

本文介绍了螺杆压缩机装配过程中连接螺栓的受力情况，并对螺栓所受预紧力和扭矩进行了初步的分析。     

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.     

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.     

304不锈钢密封垫片开裂原因分析

采用化学成分分析、拉伸试验和断口分析等方法对304不锈钢裂解气压缩机出口法兰密封垫片的开裂原因进行了分析。结果表明：裂纹起源于螺栓槽处,氯离子的应力腐蚀开裂是造成垫片开裂的主要原因。含氯离子的沿海潮湿大气是导致垫片产生应力腐蚀的介质因素,装配不当造成螺栓槽处垫片过大的应力和应变是导致垫片出现应力腐蚀开裂的力学因素。     

Investigations on core basket bolts from a VVER 440 power plant

Non-destructive examinations using ultrasonic inspections were performed on core basket bolts at a VVER 440 unit. The four M12 bolts, manufactured from solution annealed Ti-stabilized stainless steel, had been replaced due to NDE indications. Destructive investigations were performed on three of these bolts. One bolt had suffered from intergranular stress corrosion cracking, enhanced by irradiation. Irradiation induced grain boundary segregation was observed in the material. The washer of the bolt with cracking had been unintentionally spot welded to the shielding plate, restricting the free movement of the components to adapt to the differences in thermal expansion during e.g. start-up. The stress situation is modeled using finite element computation, and the location and magnitude of high stresses due to spot welding is clearly shown. The reason for the NDE indications in the other bolts were incomplete filling of the flat slot of the bolt head when the bolt was welded to the washer to prevent unscrewing of the bolt during operation.     

Breakage of Automotive Spring Washer During Twist Test: A Metallurgical Analysis

A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a screw or nut. The washer used in automotive engine component is of split or spring lock washer. A ring split at one point and bent into helical shape. The benefit of spring lock washers lies in the trapezoidal shape of the washer. When compressed to loads near proof strength of the bolt, it will twist and flatten. This reduces the spring rate of the bolted joint which allows it to maintain more force under the same vibration levels. This prevents from loosening. The steel washer is one of the critical safety components for automobile engine, and its failure may cause severe safety issue. Before subjecting to manufacturing, the washer undergoes different process lines (wire rod → drawing → annealing → pickling → flattening → spring washer → single spring washer). After manufacturing of washer, toughness test is done to find out the metallurgical soundness and surface quality of the washer. In this toughness test the washer in a vice with the split ends free and straight above the vice jaws, a 90° segment of the free end is gripped with a wrench and bent. Washers should withstand twist test through a 90° angle without signs of fracture. The present paper highlights premature failure of automotive washer which failed during twist test. From the analysis, it has been observed that the distribution of spheroidized carbide is more uniform in good samples than that of rejected samples. Hardness profile variation was observed between good and bad spring samples. Overall investigation does not indicate any problem related to supplied wire rod material quality as no wire breakage problem observed. Inhomogeneous annealed structure in flat wire seems to result into variation in washer performance during twist test.     

Load disc from Hytorc helps to achieve more consistent bolting

A washer that can make flange assembly much more convenient by preventing the bolt from turning with the nut has been introduced by Hytorc Corp. This disc also converts torque directly to axial bolt stretch, makes the nut friction and thus the bolt load more predictable, and improves speed, safety and tool weight.This is a short news story only. Visit www.worldpumps.com for the latest pump industry news     

Bearing failure of composite bolted joints with non-uniform bolt-to-washer clearance

This paper investigates the effect of the relative positions of the bolt and the washer on bearing failure behavior of bolted composite joints with various lateral constraints. Two extreme diametral fit positions, with a positive or negative bolt hole-to-washer clearance, were considered. Experimental results show that the relative location can affect the initial failure loads but not the ultimate failure loads. The measured failure loads were also used to validate an existing analytical model.     

Characterisation of Contact Pressure Distribution in Bolted Joints

Abstract: The quantification of contact area and pressure distribution in a bolted joint is essential information, as it determines the integrity of the coupling. Current bolted joint design standards are based on analytical solutions of the pressure distribution, which, because of the inherent assumptions, frequently do not accurately represent the real conditions in a joint. This study uses a non‐intrusive ultrasonic technique to quantify the contact pressure distribution in a bolted connection. The advantage of this experimental technique is that the effect of actual contact conditions can be determined. An ultrasonic wave is focused onto the clamped interface, and the reflected sound signal recorded. In areas where the contact pressure is high, most of the ultrasound is transmitted, and the reflected sound signal is weak. Whereas, when the contact pressure is low, the vast majority of the ultrasound is reflected back. A parallel experimental calibration is then used to find the relationship between the reflected sound signal and contact pressure. In this way, the pressure distribution in a clamped interface is determined for a series of different bolt torques. Two different interfaces were investigated: the first consisted of two ground surfaces clamped together, and the second a turned profile pressed against a ground surface. The effect of a washer underneath the bolt head was also considered. The turned profile was found to cause the contact to spread; there was also a certain degree of fragmentation leading to higher peak pressures than in the ground interface case. With a washer positioned under the bolt head for the turned case, the clamping performance of the bolt was improved. Good agreement was found when comparing the ultrasonic measurements with previous studies, with respect to the spread of the contact pressure distribution. However, in this study, the peak contact pressure was found to occur away from the edge of the bolt hole, and to be influenced by the edge of the bolt head.