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...     

声时差法测定螺栓的预紧应力

本文利用超声波沿轴向传播时的波速同轴向应力以及三阶弹性常数的关系，推导了声时差与应力的关系，采的时差法多探头同时测量同一法兰上的各螺栓的预紧应力，整个过程中各探头位置不变，可以克服多次耦合误差并使测量过程简便，精度高，本文还应研究了温度变化对声时差的影响，提出并且从实验数据算出几个只与材料有关，与螺栓的夹紧距离，直径以及总长我关的常数，使测量和应力计算变得简单，实验结果表明应力低于２４０ＭＰａ，夹     

Determination of forces in bolted joints

We propose a new approach to the determination of forces applied to a bolt in a tightened joint taking into account the variations of its stiffness and present the results of experimental investigations of the stress-strain diagrams of bolts for different values of tightening forces applied to the joints. The proposed procedure for the determination of forces acting on the bolt in the joint subjected to the action of variable loads takes into account the behavior of the stiffness of the joint regarded as a function of the load and tightening forces. We analyze different methods aimed at the determination of forces applied to the bolt according to the results of fatigue tests of bolts in tightened simple joints and present preliminary initial data required for the analysis of variable forces acting on the bolts in tightened joints. By using a new approach, we propose basic principles of design of economically efficient joints.     

An experimental investigation of the bolt clamping force and friction effect on the fatigue behavior of aluminum alloy 2024-T3 double shear lap joint

In this article, the effect of bolt clamping force on the fatigue life of bolted double shear lap joints was investigated. To do so, fatigue tests were carried out on the bolt clamped double shear lap joint specimens made of aluminum alloy 2024-T3. These fatigue tests were conducted with applied torques of 0.25, 2 and 4 N m at different cyclic longitudinal load levels in un-lubricated and lubricated states. From these tests the stress–life (S–N) data for different clamping forces for un-lubricated and lubricated states were obtained. The results show that clamping force increases fatigue life compared to clearance fit specimens. In general, at higher tightening torque higher fatigue lives were achieved, however, below a certain load level the life improvement was discontinued because of fretting phenomenon. Also lubricating the parts of the specimens reduces the advantage of clamping force or torque tightening.     

Finite element investigations of bolt clamping force and friction coefficient effect on the fatigue behavior of aluminum alloy 2024-T3 in double shear lap joint

In this paper, the effect of bolt clamping force on the fatigue life of bolted double shear lap joints was investigated numerically. To do so, finite element simulation results were used to illustrate the trends occurred in experimental fatigue tests showing the effect of bolt clamping on improving the fatigue life of double shear lap joints. The results show that clamping force decreases the resultant longitudinal stress at the hole edge thus the fatigue life increases compared to clearance fit specimens. In general, at higher tightening torque longer fatigue lives were achieved, however, below a certain load level the life improvement was discontinued because of fretting occurrence. Also lubricating the specimens reduces the advantages of the clamping force.     

Determination of forces in bolted joints

We propose a new approach to the determination of forces applied to a bolt in a tightened joint taking into account the variations of its stiffness and present the results of experimental investigations of the stress-strain diagrams of bolts for different values of tightening forces applied to the joints. The proposed procedure for the determination of forces acting on the bolt in the joint subjected to the action of variable loads takes into account the behavior of the stiffness of the joint regarded as a function of the load and tightening forces. We analyze different methods aimed at the determination of forces applied to the bolt according to the results of fatigue tests of bolts in tightened simple joints and present preliminary initial data required for the analysis of variable forces acting on the bolts in tightened joints. By using a new approach, we propose basic principles of design of economically efficient joints. Translated from Problemy Prochnosti, No. 5, pp. 126–134, September–October, 1997.     

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。     

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.     

Investigation the effect of tightening torque on the fatigue strength of double lap simple bolted and hybrid (bolted–bonded) joints using volumetric method

In this research, the effect of the tightening torque on the fatigue strength of 2024-T3 double lap simple bolted and hybrid (bolted–bonded) joints have been investigated experimentally by conducting fatigue tests and numerically by implementing finite element analysis. To do so, three sets of specimens were prepared and each of them subjected to tightening torque of 1, 2.5 and 5 Nm and then fatigue tests were carried out under different cyclic longitudinal load levels. In the numerical method, the effect of the tightening torque on the fatigue strength of the considered joints has been studied by means of volumetric method. To obtain stress distribution around the notch (bolt hole) which is required for the volumetric method, nonlinear finite element simulations were carried out. In order to estimate the fatigue life, the available smooth S–N curve of Al2024-T3 and the fatigue notch factors obtained from the volumetric method were used. The estimated fatigue life was compared with the available experimental test results. The investigation shows that there is a good agreement between the life predicted by the volumetric method and the experimental results for different specimens with a various amount of tightening torques. The results obtained from the experimental analysis showed that the hybrid joints have a better fatigue strength compared to the simple bolted joints. In addition, the volumetric method and experimental results revealed that the fatigue life of both kinds of the joints were improved by increasing the clamping force resulting from the torque tightening due to compressive stresses which appeared around the bolt hole.     

Fatigue in engine connecting rod bolt due to forming laps

An analysis was performed to asses the failure root cause of an automotive diesel engine which experienced collapse only 6 month after revision. The connecting rod bolts torque disassembly was monitored and fractured parts were selected to laboratory fracture analysis. It was verified with fatigue rupture of one of the fourth connecting rod bolt. Tensile tests were performed in four of the remaining connecting rod bolts. During this procedure, it was verified another bolt with fatigue crack propagation an indication that the first fatigued bolt did not have suffer torque relaxation. A finite element analysis was performed in connection with an analytical fracture mechanics approach aiming to evaluate the relation between tightening force and fatigue crack propagation in connecting rod bolts. The engine collapse occurred due to forming laps in the grooves of the bolt shank. Finally, some design improvements were suggested for avoid future failures: a gap in the groove length at the connecting rod cap interface, enough to avoid combination of forming laps and higher stress amplitude; increase of the bolt torque assembly to reduce stress amplitude.     

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。      

The effect of bolt length in the fatigue strength of M24×3 bolt studs

In this study we evaluated the effect of bolt length on the fatigue behavior of joints with bolt studs used in the flange/housing assembly of a gas compressor for polyethylene polymerization. The bolt stud used is the M24×3 class 8.8. Two different bolt lengths were evaluated. A slim spread sleeve was used in the case of the longer bolts. The torque control was used to achieve the tightening preload. However, the preload and cyclic strains were monitored. The fatigue strength increases with increasing bolt stud length, even with the use of the slim spread sleeve. The study showed a difference between the theoretical and the experimental load factor for the case of short joints.     

八角垫高压密封结构预紧力分析和试验研究

石油、化工、核电行业法兰螺柱预紧过程中, 螺柱预紧应力计算与保证垫片应力均匀分布的预紧方法是工程实际中值得研究的问题. 该文通过对螺柱垫片系统进行物理结构分析, 受力过程分析, 提出了一种基于垫片线性变形的螺柱应力分布数学模型及预紧方法. 研究表明模型计算结果与试验结果相符合, 满足实际规律. 因此, 该数学模型能用于分析预紧过程中螺柱应力变化情况;计算出螺柱具有相同密封应力的初始载荷及只需一次加载就可以达到理论密封应力的预紧优化方法. 这使得在预紧过程中不必采用边预紧边测试应变的方法来进行指导, 更有效保证密封性能.     

波形齿夹具张拉CFRP 带的力学性能试验研究及夹具体系设计

对波形齿夹具在张拉CFRP 带时的受力状态的分析,理论上提出了CFRP 带理论伸长值的修正以及波形齿夹具配套螺杆的轴力、剪力验算。针对这3 个方面的问题,共设计了两大类试验来研究张拉CFRP 带时的波形齿夹具:一类是钢梁台座上仅张拉CFRP 带的试验;另一类是张拉CFRP 带加固钢筋混凝土T 形梁的试验。试验表明:以折减率来考虑波形齿夹具张拉CFRP 带的理论伸长值的修正;在张拉时螺杆轴力与CFRP 带的预拉力值呈定值比例,在工程实际中可以通过螺杆轴力值对CFRP 带预拉力值的监控。并提出了单个螺杆的轴力值与剪力值的计算公式。     

Effect of bolt clamping force on the fracture strength of mixed mode fracture in an edge crack with different sizes: Experimental and numerical investigations

To investigate the effect of bolt clamping force, resulting from torque tightening, on the mixed mode fracture (I and II) strength and effective geometry/loading factor of an edge crack with different lengths, experimental and numerical studies have been carried out. In the experimental part fracture tests were conducted on three batches of simple edge crack and bolt torque tightened with 3.5 and 7 N m edge crack at three different crack sizes of Poly methyl-methacrylate (PMMA) rectangular plate. The specimens’ fracture strength was obtained using a tensile test machine at different loading angles by employing a modified Arcan fixture. In numerical part, finite element simulations were employed to model the three test specimen batches at the three crack lengths to obtain their stress intensity geometry/loading factors. The results show that the bolt tightening torque significantly reduces the effective geometry/loading factor, and thus increases the joint fracture strength compared to bolt-less simple edge crack specimens. However, the bolt clamping effect on increasing the fracture strength was almost the same for different crack lengths.     

螺栓夹持填充孔复合材料层压板层间应力分析

为了研究含螺栓复合材料层压板连接接头的层间应力分布规律,提出了采用填充孔形式和虚拟界面层方法求解层间应力,并建立了三维有限元模型对受面内压缩载荷的螺栓夹持填充孔层压板进行分析。结果表明:层压板层间应力集中不仅发生在孔边,还会在螺栓头边缘附近出现,且夹持力越大螺栓头边缘附近的层间应力集中越严重;合理的螺栓夹持力能改善孔边应力状态,提高孔边抵抗分层的能力,但无法改善螺栓头边缘附近的层间剪切应力集中状态。因此,在进行含螺栓夹持的层压板机械连接结构孔边层间强度设计时,也要考虑螺栓头边缘的层间剪切应力集中问题,以提高复合材料结构的安全性。     

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.     

全长粘结式锚杆与隧道围岩相互作用研究

提出了一种新的锚杆计算模型,建立了对应的物理、几何和平衡方程,在此基础之上分析了接触面产生滑移时锚杆的内力分布。该模型体现了锚杆与均质围岩之间的力学作用本质,将锚杆内力描述为围岩位移的函数,与有限元法结合,可以求得复杂情况下的锚杆内力分布,而锚杆对围岩的作用等效于一组节点荷载施加到围岩节点上。实例计算表明,锚杆可以减少围岩位移和塑性区范围,其内力分布和中性点位置受锚杆长度、埋设位置、围岩状况、粘结强度等因素的影响。该模型为确定合理的锚杆支护参数提供了一种新途径。     

Tensile behaviors of friction bolt connection with bolt head corrosion damage: Experimental research B

In this study, the tensile characteristics of a friction connection using a high-strength bolt, based on the clamping force loss developed by sectional corrosion damage to the bolt head, was examined. Eighteen specimens with bolt connections were tested to evaluate the tensile strength. In these test specimens, artificial corrosion damage was introduced to the bolt head of the bolt connection, creating a clamping force loss. In the tensile strength tests, the tensile failures of connected steel plates were observed; the tensile strength was unaffected by the artificial sectional corrosion damage to the bolt head for this failure mode. However, the friction resistance of the specimens was affected by the clamping force of the bolt, and thus, their friction loads were slightly reduced depending on the sectional damage level of the bolt head. From the friction load–clamping force relationship, friction-resistance equations were used to approximate the friction resistance of the friction bolt connection.     

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.