由振动引起的螺栓连接预紧力松脱的数学模型

引入一种数学模型以研究螺纹连接在横向振动作用下引起的松脱.此横向振动激励会引起螺纹接触面间的滑动以及螺栓头与支撑表面之间的滑动.式中包括剪切力、支撑力以及螺纹摩擦阻力矩,它们均与振动速度相关,当所施加横向振动激励足够大时,螺纹连接会出现松脱现象.本文研究了螺栓预紧力、支撑力及螺纹摩擦系数、横向振动激励以及螺栓头下部弯矩...     

复合材料螺接力学行为精细化有限元分析方法

针对航空用纤维增强树脂基复合材料螺栓连接的力学行为研究难题,采用有限元软件二次开发的方法,提出了涵盖层合板高效建模、扭矩与预紧力关系、钉孔配合间隙与滑移过渡段、渐进损伤判断与性能退化等方面的精细化有限元分析模型。提出了基于应变等效原理的紧固件预紧力-扭矩试验测试方法,降低了紧固件预紧力-扭矩转换精度对数值模拟精度的影响。提出了基于修改螺栓头与层合板接触平面摩擦因数的方法以实现对含钉孔配合间隙的复合材料螺接接头的力-位移响应在滑移过渡段的较好模拟。复合材料单搭接螺接接头单剪试验和有限元预测的力-位移曲线对比结果显示极限载荷最大预测误差为17.2%,证明了所提方法能有效地预测复合材料单钉/多钉螺接结构的力学性能演变规律,且所提方法提高了预测结果与试验结果的匹配度,提升了有限元分析的效率,为航空先进复合材料连接结构的力学行为分析奠定了建模技术基础。     

Influence of tightening procedures and lubrication conditions on titanium screw joints for lightweight applications

In recent years, the need for lighter vehicles led to the widespread of lightweight alloys, such as titanium, also in the field of threaded fasteners. Unluckily, the replacement of steel bolts with titanium ones, usually suggested because of their favourable ratio between strength and weight, is not quite straightforward. The coefficient of friction, a key parameter in bolted joints design, changes drastically when switching from steel to titanium. Some results concerning the frictional behaviour of bolted joints involving titanium screws are here presented: friction and torque coefficients were calculated, according to ISO 16047, for joints made up of a hexagon socket head screw made of titanium alloy (Ti–6Al–4V), a bush made of aluminium alloy (EN AW 7075 T6) and a steel nut (ISO 4032). Data were collected by performing several tightening tests on ad-hoc designed specimens, which allowed the evaluation of the different tribological behaviour of the same joint under three different conditions of lubrication (dry, Teflon^® added oil, and ceramic paste). 20 repeated tightenings (re-tightenings) have been analysed in order to simulate some maintenance operations. The DOE method was applied to manage the tests, while the results were analysed by the ANOVA and P-value methods. Out of the two lubricants examined, the ceramic paste showed the best results in terms of friction coefficients constancy throughout the re-tightening operations, as well as the best protection of the thread and underhead surfaces against wear.     

螺纹联接件的微动损伤研究

从试验和数值分析两个方面研究了螺栓预紧力矩对ＬＹ１２ＣＺ铝合金双盖板对接螺纹联接件微动损伤的影响。在高频疲劳试验机上进行了微动试验,对接触表面间的微动损伤状况进行了观察分析。     

Frictional changes during repeated tightening of zinc plated threaded fasteners

Tightening a bolt to a torque value is the most popular means of controlling the preload provided by a threaded fastener. However, repeated tightening and loosening of a threaded fastener, can have a dramatic effect on the friction coefficient. These changes will, in turn, will affect the preload and can, therefore, have an adverse effect on the structural integrity of an assembly. This study investigates the effect of repeated tightening on electro-zinc plated (EZP) nuts, bolts and washers. It is found that significant wear of the contact surfaces of the bolt/nut thread and nut face occurs upon repeated tightening.     

Performance and Durability of High Temperature Foil Air Bearings for Oil-Free Turbomachinery

The performance and durability of advanced, high temperature foil air bearings are evaluated under a wide range (10 to 50 kPa) of loads at temperatures from 25° to 650 °C. The bearings are made from uncoated nickel based superalloy foils. The foil surface experiences sliding contact with the shaft during initial start/stop operation. To reduce friction and wear, the solid lubricant coating, PS304, is applied to the shaft by plasma spraying. PS304 is a NiCr based Cr₂O₃ coating with silver and barium fluoride/calcium fluoride solid lubricant additions.

The results show that the bearings provide lives well in excess of 30,000 cycles under all of the conditions tested. Several bearings exhibited lives in excess of 100,000 cycles. Wear is a linear function of the bearing load. The excellent performance measured in this study suggests that these bearings and the PS304 coating are well suited for advanced high temperature, oil-free turbomachinery applications.     

基于变粘度条件的流体静压支承摩擦转矩的研究

在研究圆形静压支承中,如果考虑到粘度随温度变化的特性,则与油膜厚度相关的摩擦转矩关系曲线不再是粘度为常数时的双曲线,这时曲线的形状发生了明显的变化。本文对油膜厚度和摩擦转矩的关系进行了深入的理论分析,从而揭示了其本质规律,为设计出结构合理、性能优良的静压支承提供了理论依据。     

螺栓联接件的微动损伤及其涂胶防护试验研究

通过试验分析 ,提出了螺栓联接件的两种不同类型的疲劳破坏形式 ,即孔口应力集中破坏和微动疲劳破坏 ,并研究了不同的螺栓预紧力矩对螺栓联接件微动损伤的影响情况。试验结果表明 ,螺栓预紧力矩大小的改变会引起螺栓联接件不同程度的微动损伤 ,而在联接板面间进行涂胶防护是防止其产生微动损伤的一种较好的方法。最后对涂胶和未涂胶两种螺栓联接件的微动振幅、板面应力、以及由于微动摩擦而产生的板面温升等参数进行了对比测试 ,得出了初步的结论。     

Development of an Apparatus to Investigate Friction Characteristics of Constant-Velocity Joints

Constant-velocity (CV) joints have become standard design and an integral part of modern vehicles, primarily due to their superiority in terms of CV torque transfer. Despite widespread usage of constant velocity joints there are certain aspects of their friction, wear, and contact characteristics that are not well understood. In this article, the need to directly measure CV joint internal contact and friction forces is addressed by designing and constructing an instrumented advanced CV joint friction apparatus using actual tripod-type joint assemblies. The apparatus is capable of measuring key performance parameters such as friction and wear under different realistic operating conditions of oscillatory speeds and CV joint articulation angles. The apparatus incorporates a custom-installed triaxial force sensor inside of the CV joint to measure in situ internal CV joint forces (including friction). The CV joint apparatus is under full computer control and is communicating with all measurement components via a master Labview control program. Experiments under different articulation angles and lubrication conditions were performed and the measurements were correlated with published data.     

压水堆堆内构件异种材料螺纹联接件在热循环载荷下的疲劳试验分析研究

压水堆电厂的反应堆堆内构件中的螺纹联接件与一般联接件不同,在高温、辐照环境中工作,除承受机械载荷外,还承受由于水流以及地震等引起的动态载荷。而在寿命期内反复的冷-热-冷循环,会使异种材料联接件产生交变循环热应力,甚至会使预紧力松弛,因此预紧力合适与否将直接影响联接件联接的可靠性。对通过模拟实际联接结构的联接件进行热循环试验和分析,研究热循环载荷对预紧力和联接结构的影响。     

异面斜置滚子滑动离合器极限力矩特性研究

在考虑摩擦接触与滚子动力学平衡条件下研究了滚子修形参数与Von Mises应力间的关系,给出了不同工况条件下的最优修形参数.同时,在最优修形条件下,研究了异面斜置滚子滑动离合器的极限力矩特性.     

Stability Analysis of Floating Ball Bearing

Conventional disk drive motors supported on ball bearings (BBs) cause nonrepeatable runout (NRRO) due to the surface imperfections on balls and raceways. NRRO is a source of track misregistration between head and disk that inhibits high track density in a hard disk drive. Fluid dynamic bearings with herringbone grooves either on the rotating or stationary surfaces are a suitable replacement for conventional ball bearings. Herringbone grooved bearings have considerably lower noise level than ball bearings and have better stability compared to plain journal bearings at concentric operating position. However, herringbone-grooved patterns are difficult to manufacture because groove depth is of the order of bearing clearance. The major limitation of the BBs is the direct contact between the rotating and stationary parts and also lack of damping effects. This present work attempts to overcome these drawbacks in BBs by eliminating the metal-to-metal contact using a layer of fluid film, and a theoretical analysis of stability characteristics of a floating BB is presented. Results indicate that there is an improvement in the stability of floating BB rotor systems with increase in outer to inner film clearance ratio (β) from 0.7 to 1.3, and with decrease in ratio of outer race radius to inner race radius (δ) from 3.0 to 1.2.     

Friction torque in grease lubricated thrust ball bearings

Thrust ball bearings lubricated with several different greases were tested on a modified Four-Ball Machine, where the Four-Ball arrangement was replaced by a bearing assembly. The friction torque and operating temperatures in a thrust ball bearing were measured during the tests. At the end of each test a grease sample was analyzed through ferrographic techniques in order to quantify and evaluate bearing wear.A rolling bearing friction torque model was used and the coefficient of friction in full film lubrication was determined for each grease, depending on the operating conditions.The experimental results obtained showed that grease formulation had a very significant influence on friction torque and operating temperature. The friction torque depends on the viscosity of the grease base oil, on its nature (mineral, ester, PAO, etc.), on the coefficient of friction in full film conditions, but also on the interaction between grease thickener and base oil, which affected contact replenishment and contact starvation, and thus influenced the friction torque.     

螺纹紧固件工程应用研究

螺纹紧固件在工业生产中应用广泛,螺距、旋合长度、拧紧力矩是正确选用螺纹紧固件、提高螺纹紧固件连接可靠性的关键参数。对螺纹紧固件的螺距、旋合长度进行了介绍,对拧紧力矩进行了计算,并对扳手的选用进行了分析。     

角接触球轴承摩擦力矩波动性分析

针对低摩擦力矩角接触球轴承,利用能量守恒定律,研究角接触球轴承零件工作表面的波纹度对轴承摩擦力矩波动性的影响,从理论上对角接触球轴承零件工作接触表面的波纹度幅值、谐波阶次与轴承摩擦力矩波动性的关系进行分析,给出影响角接触球轴承摩擦力矩波动性的内、外滚道和钢球工作表面的主要波纹度谐波阶次和相应的激振频率,并试验验证.研究...     

球轴承摩擦力矩测量仪的设计与应用

为测量在不同载荷、转速等条件下球轴承的摩擦力矩特性,设计制造了球轴承摩擦力矩测量仪。介绍了测量仪的测量原理与技术方案。该测量仪模拟了轴承的载荷、转速、偏转力矩等工况,测量了轴承的摩擦力矩。对测量数据分析表明,该摩擦力矩测量仪能满足预定的设计要求,具有良好的稳定性,测量数据准确可靠,可为各种轴承摩擦力矩的测量提供准确的数据支持。     

机械结合部单元静态变形分析研究

整机是由许多通过结合部连接的构件组成的整体,而螺栓结合部是机床设计中的主要问题之一。螺栓结合部的结合状态比较复杂,研究过程和方法也相对复杂。结合面的研究首先从结合面的静态特性开始。该文首先简要介绍了影响结合部静态特性的主要因素及接触理论,并通过非线性接触表面层理论对螺栓结合部的接触变形进行了解析计算,为整机结合部的静态特性分析提供了边界条件。     

关节铰接双面接触摩擦对医用机械臂影响分析

以医用机械臂为研究对象,同时考虑关节旋转铰接圆柱面及端面２处的摩擦,提出端面接触系数,利用达朗伯定理对医用机械臂进行动静力学分析求得两接触面处的法向接触力,并基于库仑摩擦模型求得两接触面摩擦力矩,结合拉格朗日方程建立了不包含摩擦及包含摩擦的２种动力学模型,通过仿真求解分析得出对于所研究的医用机械臂及结构相类似的机械臂,铰接端面处的摩擦对机械臂关节输出扭矩及末端位置影响大于圆柱面处摩擦的影响,端面接触程度越高造成能量损失越大,机械臂末端位置轨迹越混乱。     

Simulation of friction and wear in the contact between the valve bridge and rocker arm pad in a cam mechanism

In this paper the surface velocities obtained from a rigid body model are used to simulate friction and wear in the contact between the rocker arm pad and valve bridge in the cam mechanism of a diesel engine. The friction is simulated with two different friction models, a 3D brush model capable of handling transient conditions such as an varying normal load and varying surface velocities and a Coulombian friction model. The wear simulations are based on a generalised form of Archard's wear model.The results presented here show that both the maximum wear depths and the wear distributions are influenced significantly by the combination of wear pad radius and the position of the wear pad radius centre relative to the rocker arm bearing centre. A combination with wear pad radius of 20 mm and centre position of 5 mm is found to give the least wear depths on both the wear pad and the valve bridge. It is also seen that the contact between the wear pad and the valve bridge is mainly a sliding contact and that the transitions from sliding in one direction to the opposite are very rapid. The change of the surface shapes due to wear has a negative effect on the contact situation causing very high contact pressures.     

考虑摩擦因素影响的结合面切向接触阻尼分形预估模型及其仿真

为准确计入结合面表面微观形貌对结合面的影响,提出结合面的“固-隙-固”接触模型。基于该接触模型和接触分形理论以及赫兹理论,建立考虑摩擦因素影响的结合面切向接触阻尼的分形预估模型,并通过数值仿真研究揭示有关参数对结合面切向接触阻尼的影响,为后续结合面动力学建模和动力学特性分析做准备。仿真分析结果表明：结合面的切向接触阻尼随结合面实际接触面积的增大而增大;随结合面法向载荷的增大而减小;随结合面间摩擦因数的增大而趋于恒定;实际接触面积影响cte*-μ曲线转折点(即临界摩擦因数μc)的位置,随着实际接触面积的增大,临界摩擦因数μc亦同时增大;不同的分形维数取值,尤其是分形维数取值在临界值(D=1.55)的两侧时,结合面间的接触行为存在较大差异。