航天器驱动机构轴系摩擦力矩建模与分析研究

基于接触力学、摩擦学及角接触轴承拟静力学理论,建立了固体润滑角接触轴承摩擦力矩理论计算模型,并在航天器驱动机构的边界条件下,研究了航天器驱动机构轴系摩擦力矩与预紧力之间的关系,从理论上分析了轴系预紧力对轴系摩擦力矩的影响并进行了试验验证。研究表明,固体润滑角接触轴承摩擦力矩随着轴向载荷的增大而增大,当轴系拧紧力矩达到临界值后,摩擦力矩随着拧紧力矩的增大而增大;且理论分析值和试验值的趋势一致,数值接近;说明基于拟静力学建立的摩擦力矩计算模型能较好地实现低速下的固体润滑轴承和轴系摩擦力矩预测。     

微造型阀芯摩擦副的动压承载及润滑特性

以水液压滑阀的阀芯摩擦副为研究对象,通过在阀芯表面设计微造型结构以改善其动压承载和润滑性能。采用基于N-S方程的CFD方法分析微造型阀芯摩擦副的流场,得到微造型阀芯表面的压力分布曲线、承载力曲线以及摩擦力曲线,研究阀芯叠合量大于2.5 mm时,叠合量的大小对微造型阀芯摩擦副动压承载及润滑性能的影响。研究结果表明:光滑阀芯的表面无动压润滑效果,而微造型阀芯的表面可产生油膜动压支撑;且随着阀芯叠合量的减小,微造型阀芯表面的承载力值呈上升趋势,从而使阀芯和阀套间摩擦副的接触摩擦力减小。     

弹性材料表面织构对摩擦副润滑性能的影响

为了研究弹性材料表面微织构对摩擦副空化现象和润滑特性的影响,建立考虑空化效应的二维弹性织构计算模型,采用流固耦合方法计算润滑流场与材料变形之间的相互作用。对比刚性材料表面微织构,从弹性模量、滑动速度、微织构深度以及织构间距等方面分析弹性材料表面织构对摩擦副润滑性能的影响,通过实验验证模拟结果的准确性。结果表明：弹性织构摩擦副比刚性织构摩擦副摩擦因数更小,润滑性能更好;存在最优织构深度,使得弹性织构摩擦副的摩擦力最小且承载力最大;适当增大滑动速度以及织构间距可以提高弹性摩擦副的润滑性能;随着弹性模量的降低,弹性变形和油膜厚度增加,空化现象更为显著,摩擦副的润滑性能得到提升。     

考虑热弹流润滑作用的滚珠丝杠副摩擦力矩建模与分析

针对以往研究中滚珠丝杠副摩擦力矩计算方法中未考虑润滑作用对其影响,或未考虑接触弹性滞后效应以及滑移摩擦效应对其影响的情况。首先基于单个滚珠接触效应建立其热弹流润滑方程;然后在考虑润滑效应的基础上建立其黏性摩擦力、弹性滞后摩擦力及滑移摩擦力方程;最后提出一种基于全滚珠载荷分布与热弹流润滑耦合的滚珠丝杠副摩擦力矩计算模型,建立了预紧力、转速与摩擦力矩之间的耦合关系。试验结果表明,当预紧力从1 kN变化到6 kN,在滚珠丝杠低转速(100 r/min)时,摩擦因数变化范围为0.005 6～0.006 5。随转速的提髙摩擦因数升高且变化量逐渐增大,说明国际标准DIN ISO3408-3:2006中将滚珠丝杠副空载摩擦力矩测量速度定为100 r/min具有合理性,验证了所提出的摩擦力矩计算方法的准确性。     

不同真空度气体对粗糙表面接触摩擦的影响

在大气压作用下,通过对不同真空度下接触物体表面摩擦力的测量,研究气体对粗糙接触物体表面摩擦的影响,该实验采用的摩擦副材料是铝合金/有机玻璃、45钢/有机玻璃。实验结果显示:随着真空度的增大,2种摩擦副的摩擦力近似呈现线性变化,静摩擦因数则先减小而后趋于稳定,再有回增的趋势;45钢/有机玻璃摩擦副静摩擦因数取得最小值所对应的真空度比铝合金/有机玻璃摩擦副的更大。通过分析得出静摩擦因数变化的原因:随着真空度的增大,摩擦副接触间隙间的气体密度减小,当固体刚开始运动时,产生摩擦的气体分子与固体表面的分子减少;随着真空度的增大,正压力增大,材料的变形程度增大。     

固体润滑滚子轴承的接触表面应力分析研究

为获得固体润滑滚动轴承滚动体与滚道处的接触应力,通过固体润滑滚子轴承拟动力学分析并考虑涂层的影响,获得了滚子轴承稳定运行过程中滚动体的力载分布。通过建立带涂层接触的平面应变问题的力学模型,将涂层与基底两种材料的特性等效为一种材料来求解滚子与接滚道触应力分布情况,并与轴承的拟动力学分析相结合,获得了滚子轴承中滚动体与固体润滑膜接触表面的接触变形、接触半径与外加载荷之间的关系,讨论了不同涂层的弹性模量以及不同涂层厚度对接触界面应力分布的影响。当涂层弹性模量比基底大时,涂层的存在使得接触半宽减少,最大名义接触应力增加;涂层弹性模量比基底小时,则与之相反。当涂层的厚度<0.01mm时,涂层的存在对固体润滑滚子轴承的接触表面应力分布影响较小;在一定范围内,当涂层的厚度逐渐增大时,涂层对轴承接触表面应力分布的影响增大。     

等温密封环摩擦状态演变预测与试验研究

结合浮动密封环的工作特点,提出一种基于载荷分配概念的密封摩擦状态演变预测模型。设定载荷分配系数,对粗糙表面微凸体接触和流体润滑接触两个部分摩擦力进行建模计算,根据微凸体承载力和总承载力等参数信息获得总摩擦因数值。模拟计算获得反映密封接触特性的摩擦因数与转速、压力以及表面粗糙度的关系曲线,仿真曲线历经完整的摩擦与润滑区,能够对不同摩擦状态下的接触特性进行预测。利用密封系统试验台对模型进行分析和验证,结果表明两者变化趋势保持一致,具有共同特征,说明密封摩擦预测模型能够真实反映密封摩擦副的接触规律及其变化情况,是预测密封摩擦状态的有效方法。     

高速滑滚接触条件下摩擦副的热分析

高速旋转摩擦副生热加剧会引起零部件的工作温度异常升高,严重时会导致摩擦副表面润滑失效、摩擦副胶合甚至咬死,严重威胁系统的正常运行。针对摩擦生热问题,建立高速滑滚摩擦副的表面温升计算模型:分别利用接触理论和传热学分析两滚子摩擦副的接触特性和摩擦生热,将结果作为边界条件施加到接触摩擦副的有限元模型中,得到摩擦副的表面温升及沿深度方向温度变化情况。通过与高速台架试验中获得的摩擦副表面温度进行比较,表明了高速滑滚摩擦生热模型正确,为分析摩擦副表面热失效行为提供了理论基础。     

润滑接触摩擦力的往复式实验研究

在往复式试验机上研究实际加工表面球-盘式接触混合润滑摩擦特性,比较采用不同黏度润滑油光滑接触摩擦力的大小。针对表面粗糙度幅值和纹理对摩擦行为的影响进行研究,结果表明,混合润滑时较高黏度润滑油的摩擦力较小;表面粗糙度幅值在混合润滑时对摩擦力影响较大,且随速度增加而增强,边界润滑时影响很小。与纵向纹理相比,横向纹理表面的摩擦力较小且稳定,低速时这种差别更加明显。     

青铜-石墨热喷涂层在干摩擦和水润滑条件下的摩擦磨损性能

在MM-200摩擦磨损试验机上研究了青铜-石墨热喷涂层在干摩擦和水润滑条件下的摩擦磨损性能,采用扫描电镜(SEM)对磨损表面形貌进行了观测和采用X射线能谱分析(XPS)分析了涂层成分。结果表明,在水润滑条件下涂层摩擦因数和磨损率均低于干摩擦条件下;在水润滑条件下磨损机制为轻微磨粒磨损和犁削磨损,在干摩擦下主要是较为严重的粘着磨损和犁削。这是由于水润滑降低了摩擦副界面温度,提高了石墨润滑膜的韧性,改善了润滑效果,从而阻止了粘着磨损的发生,水还促进了钢偶件表面致密氧化膜的形成,从而减轻磨损。因此水润滑对涂层磨损性能有较大影响。     

涂层材料热特性参数对点接触弹流润滑的影响

为探究涂层材料热特性参数对点接触弹流润滑的影响,选择3种不同方法制备的类金刚石（DLC）涂层和氧化锆陶瓷涂层,构建考虑涂层热特性的点接触弹流润滑模型,分析涂层材料、涂层厚度和润滑剂的流变性对接触区润滑性能的影响。结果表明：在弹流润滑状态下具有不同热特性的4种表面涂层导致了膜厚的差异,固体表面温度及润滑区温度场会随涂层热惯性变化;热惯性最小的DLC涂层加在快速运动表面能获得更高的膜厚;随着涂层厚度的增加,会引起固体表面的温度升高,使摩擦因数降低;非牛顿流体对压力、膜厚的影响很小,但与牛顿流体相比,能获得相对较低的温度。在弹流润滑状态下,涂层覆在快表面对于减小摩擦、提高膜厚是有益的。     

特殊螺纹套管接头纳米铜干式涂层的制备及性能研究

以添加少量PTFE纳米颗粒的纳米铜为基体,以环氧树脂为黏结剂,制备出一种纳米铜固体润滑涂料;采用摩擦试验机研究室温下不同环氧树脂添加量的纳米铜涂层的摩擦性能,并与常规螺纹脂进行对比;利用盐雾试验机对涂层进行耐盐雾腐蚀测试;将纳米铜固体润滑涂料涂覆于套管螺纹表面,进行上卸扣试验。结果表明：环氧树脂质量分数为40%的纳米铜固体润滑涂层减摩性能和耐盐雾腐蚀性能等综合性能最佳,且涂层的摩擦性能优于螺纹脂;纳米铜干式涂层接头进行10次上卸扣试验后未发生黏扣现象,因此纳米铜干式涂层具有代替现有螺纹脂的潜力。     

聚四氟乙烯基固体润滑剂摩擦表面的X-光光电子能谱研究

利用扫描电镜(SEM)对聚四氟乙烯基固体润滑剂摩擦表面及在45^#钢表面所形成的润滑转移膜形貌进行表征；采用X-光光电子能谱(XPS)仪测定了聚四氟乙烯基固体润滑剂烧结前后、在45^#钢表面摩擦试验前后，试样表面的元素组成及价态的变化。结果表明：摩擦过程中固体润滑剂在45^#钢表面形成了润滑转移膜，在烧结及摩擦过程中发生了化学反应，并产生磨粒磨损、腐蚀金属等现象。     

The effects of contact configuration and coating morphology on the tribological behaviour of tetrahedral amorphous diamond-like carbon (ta-C DLC) coatings under boundary lubrication

ABSTRACT

Tribological studies were carried out with tetrahedral amorphous diamond-like carbon (ta-C DLC) coatings, varying in thickness and roughness, using two different contact configurations lubricated with seven types of hydraulic oils. Tribopair of cast iron and ta-C coated steel were tested in both non-conformal and conformal, unidirectional sliding contacts. The friction and wear results were mainly affected by the thickness of the coating in the non-conformal contact and the surface roughness of the coating in the conformal contact. Tests done with mineral base oil containing rust inhibitor in the non-conformal contact and with Polyalphaolefins and synthetic ester base oils in the conformal contact resulted in the lowest friction while that with mineral base oil containing zinc resulted in high friction and counterface wear. The results highlight the interdependence of contact configuration, lubricant chemistry, coating’s surface morphology and coating’s thickness in determining the tribological behaviour of ta-C coatings under boundary lubrication.     

微织构光固化填充h-BN的巴氏合金表面摩擦学性能

为了提高巴氏合金在油润滑条件下的摩擦学性能,在巴氏合金表面加工凹坑微织构并利用光固化填充方法填充六方氮化硼(h-BN)固体润滑剂,制备出h-BN与表面微织构相结合的复合润滑结构。研究复合润滑结构在油润滑条件下的摩擦学性能及其减摩润滑机制。结果表明：复合润滑结构的摩擦学性能远高于未织构面和纯织构面;当凹坑微织构直径较小时,织构密度为10%～20%时,复合润滑结构摩擦因数较小,而凹坑直径较大时,随着织构密度的增加,复合润滑结构摩擦因数逐渐减小;当织构密度小于20%时,凹坑直径较小的复合润滑结构摩擦因数小,当织构密度达到30%时,随着凹坑直径的增加,复合润滑结构摩擦因数减小。复合润滑结构能够改善巴氏合金表面摩擦学性能,是因为h-BN固体润滑剂的释放在巴氏合金表面形成了固体润滑薄膜,避免了润滑油膜较薄处的巴氏合金表面直接与45钢表面接触,且释放h-BN固体润滑剂后的微织构凹坑可以起到收集磨粒,储存润滑油的作用。     

Influence of Polyfluo-Wax on the Friction and Wear Behavior of Polyimide/Epoxy Resin–Molybdenum Disulfide Bonded Solid Lubricant Coating

Polyimide/Epoxy resin–molybdenum disulfide bonded solid lubricant coatings (denoted as PI/EP-MoS₂) were prepared. The influence of polyfluo-wax (denoted as PFW) on the microhardness and friction and wear behavior of as-prepared PI/EP-MoS₂ lubricant coating was measured using a microhardness tester and a reciprocating ball-on-disc tribometer, respectively. The worn surfaces of the lubricant coatings were observed with a scanning electron microscope, and their wear rate was determined with a Micro XAM surface mapping microscope. Moreover, the transfer films formed on the counterpart steel ball surfaces were analyzed by X-ray photoelectron spectroscopy. Results indicate that the incorporation of a proper content of PFW filler is effective at improving the antifriction performance of the PI/EP-MoS₂ lubricant coating while maintaining better wear resistance. Moreover, the friction coefficient of the lubricant coating decreases with increasing content of PFW from 2 to 10%, and the one with a filler content over 6% PFW has a steady friction coefficient of 0.07. The improvement in the antifriction performance of the lubricant coating with the incorporation of the PFW filler is attributed to the excellent lubricity of homogeneously distributed PFW.     

石墨干膜润滑剂在碳钢表面摩擦磨损性能试验研究*

传统油或脂润滑剂在极端工况环境下无法满足碳钢类零件的减摩要求,采用干膜润滑剂是提高极端工况环境下碳钢表面摩擦磨损性能的可行性方法。采用超声波分散方法制备以石墨粉末为基体的干膜润滑剂,使用压力喷涂技术使其沉积在碳钢试件表面,在端面摩擦试验仪中开展干摩擦和石墨干膜润滑剂润滑下摩擦磨损性能对比性试验研究。试验结果表明：石墨干膜润滑剂在碳钢表面的沉积效果较好,沉积的石墨干膜润滑剂具有较好的润滑性能,可以有效地保护碳钢表面不被过度磨损;喷涂石墨干膜润滑剂的碳钢试件的工作寿命随着压力载荷和主轴转速的增大而缩短,负载和滑动速度的联合作用会加速涂层向稳定方向的过渡;磨损过程中形成的微观润滑剂颗粒会形成颗粒流润滑,适当添加石墨颗粒粉末可能会延长润滑剂正常发挥减摩作用的时间。制备的石墨干膜润滑剂为碳钢在极端工况环境下的减摩提供了支持。     

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.     

Investigation on MoS2 and graphite coatings and their effects on the tribological properties of the radial spherical plain bearings

With constant enlargement of the application areas of the spherical plain bearings, higher quality lubrication of the bearings is required. To solve the lubricating problems of spherical plain bearings under high temperature, high vacuum, high speed, heavy loads and strong oxidation conditions, it is urgent for us to develop more excellent self-lubricating technologies. In this paper, the bonded solid lubricant coatings, which use inorganic phosphate as the binder, the mixture of MoS2 and graphite with two different weight proportions as the solid lubricant, are prepared by spraying under three different spray gun pressures. The bonding strength tests on the coatings show that the best spraying pressure is 0.2 MPa and the better mixing proportion of MoS2 to Graphite is 3:1. Then for the radial spherical plain bearings with steel/steel friction pair, after the coatings are made on the inner ring outer surfaces, the friction coefficient, the wear loss and the friction temperature of the bearings under four oscillating frequencies are investigated by a self-made tribo-tester. The test results, SEM of the worn morphologies and EDS of worn areas show that tribological properties of the bearing are obviously improved by the bonded solid lubricant coatings. When sprayed under the spray gun pressure of 0.2 MPa, the bearings have better anti-friction and anti-wear properties than those sprayed under 0.1 MPa and 0.3 MPa. Further as proved from the XPS analysis, between the coating with 3:1 mixing ratio of MoS2 to Graphite and the coating with 1:1 ratio, the former has less oxidation occurred on the surface and therefore has better tribological characteristics than the latter. This paper provides a reference to developing a new product of the radial spherical plain bearings with high bonding strength, oxidation resistance and abrasion resistance.