Fractal dimension (FD), as an important parameter for the surface morphology of mechanical machining, can be used to analyze the friction characteristics of contacting surfaces. The accurate and rapid measurement of the FD is of significant importance. To this end, this paper presents a novel approach based on a convolutional neural network (3D-CNN) for the recognition of three-dimensional FDs on machined surfaces. We construct a dataset of anisotropic rough surfaces with different FDs using the Weierstrass-Mandelbrot (WM) fractal function and use a one-factor experimental design to analyze the influence of network parameters (network depth, filter size, filter quantity) on the accuracy of FD identification, finding the optimal combination of neural network parameters. By comparing our 3D-CNN method with three other methods (differential box-counting (DBC), triangular prism surface area (TPSA), and fractal Brownian motion (FBM)), we validated the effectiveness of our proposed method. The experimental results show that the average absolute percentage error of FD calculated by the 3D-CNN method can be controlled within 2%, and the method exhibits small errors throughout the full dynamic range of FDs. We also apply the proposed method to calculate the FD of the vertical milling surface and compare the results with the TPSA and FBM methods. The results show that the FD obtained by our method is close to the other two methods, and can be used to calculate the FD of three-dimensional surface profiles, thereby providing a new approach for the dynamic modeling and parameter identification of contact surfaces.
Nanoparticles have as characteristics super sliding, extreme pressure, self-healing, etc., which can improve the friction reduction and anti-wear performance of sliding components, when used as lubricating oil additives. Nano-copper particles have a good synergistic effect with other antifriction agents, anti-wear agents, antioxidants and grease additives because of their low shear strength and grain boundary slip effect, showing a better anti-friction and anti-wear effect. However, nanoparticles are prone to conglomerate, and this causes a bottleneck in the application of dispersant for nano-copper in a lubricating oil system. The regulation of nanosized effect and surface properties has great engineering significance in compensating for the precision in manufacturing accuracy. This paper comprehensively reviews the tribological research progress of nano-copper as a lubricant additive, which provides a reference to the application of nano-copper particles as lubricating oil additives on engineering tribology.
为探究内燃机中缸套-活塞环摩擦副在复杂工况下的摩擦因数变化规律,根据实际工况下的温度和压力,使用SRV高温摩擦试验机模拟内燃机系统缸套-活塞环之间的往复式摩擦运动,获得不同温度和压力下的摩擦因数,并测试不同温度下润滑油的黏度.以摩擦接触面温度、载荷和润滑油黏度为输入,摩擦因数为输出,构建BP神经网络预测模型.结果表明,BP神经网络具有较高的预测精度,测试集误差值稳定在1％以内,满足工程精度要求.
利用ABAQUS软件的Map Solution(MS)功能对2K型斯特封进行有限元仿真分析,该功能通过重启动分析和网格重构技术,解决了由网格畸变引起计算中断的问题,得到超高压工况下的收敛解.根据流体压力14、28、35、42、56 MPa下斯特封内、外行程的应力应变云图和密封面接触压力分布曲线,研究流体压力对密封件主应力、主应变和接触压力分布的影响规律;同时对比未使用MS功能的高压工况(35 MPa)下仿真结果,验证了 MS功能分析网格大变形问题的可靠性.结果表明:在超高压工况下,斯特封的最大主应力集中分布于空气侧PTFE阶梯形环与活塞沟槽、缸筒的接触区域,最大主应变出现在PTFE阶梯形密封环的卸荷角处;随着油液压力的增加,接触压力分布曲线趋势发生明显变化,空气侧的接触压力梯度减小;在相同流体压力下,外行程时密封面接触宽度大于内行程的接触宽度.
为改善摩擦组元SiO2颗粒与铜基体间界面结合性能,通过表面金属包覆处理的方式制备铜包覆SiO2.分别以铜包覆SiO2和普通SiO2颗粒作为摩擦组元之一,利用SPS烧结技术制备2种铜基粉末冶金摩擦材料.分析2种摩擦材料的微观组织、力学及物理性能,在MM1000-Ⅱ型惯性制动试验台上测试2种摩擦材料的制动摩擦磨损性能,并对2种摩擦材料的摩擦表面及其三维形貌特征、磨屑特征和摩擦表面物相进行微观分析,研究SiO2表面金属包覆处理对制动条件下铜基粉末冶金材料摩擦磨损性能的影响.结果表明:经铜包覆处理的SiO2与Cu基体间的界面结合性能明显改善,提高了材料的硬度、致密度及导热系数,特别是导热系数得到了显著提升;随着制动初速度的升高,2种摩擦材料的平均摩擦因数均呈现先上升后下降的趋势;在相同的制动条件下,与含普通SiO2材料相比,除了制动压力为0.8 MPa、制动初速度为100 km/h外,在其他各制动条件下含铜包覆SiO2材料具有较高的平均摩擦因数和较低的磨损率,且其摩擦表面更为平整;提高制动初速度均能够促进2种摩擦材料表面形成以氧化膜为主的摩擦膜,且含铜包覆SiO2材料的摩擦膜更均匀,因而保护作用更好,即磨损率低.
针对航空发动机轴承腔气液两相环境非接触式机械密封启动过程的磨损问题,提出高压侧具有引流槽、可实现零泄漏的润滑密封端面结构.基于雷诺方程建立润滑膜流场分析模型,求解计算具有动压-润滑组合槽的机械密封性能,并与普通螺旋槽机械密封进行了性能对比,讨论高压侧引入润滑槽对液膜厚度、液膜刚度、泄漏率以及摩擦性能的影响规律,通过高速性能试验及摩擦磨损试验验证计算的准确性和端面的减磨效果.端面结构在低速阶段的接触摩擦试验显示,具有组合槽的密封端面在相同的启停工况下端面摩擦因数可以有效降低50％-75％,高速性能试验结果显示,具有组合槽和仅有动压槽的机械密封在工况范围内均能保持理想的负泄漏率,说明气液两相润滑机械密封能够在工作环境中处于理想的泵送状态,实现了对润滑油的绝对密封效果.外侧深槽与动压浅槽组合的机械密封端面结构可以显著改善端面摩擦磨损状况,可为高速和超高速轴承腔气液两相机械密封端面减磨优化设计提供参考.
磁性液体是一种功能材料,既具有液体的流动性,又具有固体磁性材料的磁性,在密封中的应用是其最成功的应用之一.磁性液体密封作为高新密封技术,被广泛应用在军工、化工、航空航天等领域.目前,磁性液体密封技术在密封气体介质和真空中的研究已经趋于成熟,相比之下,对液体介质的密封还存在很大局限性.从磁性液体与被密封液体介质的界面稳定性、界面破坏过程以及用于液体介质的密封装置结构设计三方面,对磁性液体旋转密封技术的研究进展进行阐述,总结三类用于液体介质密封的磁性液体密封结构设计方法的技术特点和缺点,最后对磁性液体在液体介质密封中的前景作出展望.
Aimed at the crack problem in the tungsten carbide（WC） coating on the friction pair of the hydraulic cylinder, a key component of the control rod hydraulic drive mechanism for nuclear reactor, the research on grinding process optimization and stress relief treatment of WC coating was carried out.The basic properties and friction and wear performance of the WC coating prepared by the optimized process, and the cold state performance of hydraulic cylinder were tested.The results show that the improved preparation process solves the crack problem of WC coating.The basic performance and friction and wear performance, the cold state motion resistance, and leakage rate of the hydraulic cylinder coating processed by this process can meet the operating requirements of the control rod water pressure drive mechanism.The research results lay a foundation for the overall performance research of the control rod hydraulic drive mechanism, as well as the further development and engineering application of the control rod hydraulic drive technology.
The wear resistance of plastic ring plays an important role in composite seal.In order to select suitable anti-friction materials, this paper studied the micro-friction and wear of QT500 with five kinds of high molecular weight polyethylene（UHMWPE）,PTFE+40% copper powder, PTFE+7% carbon fiber, PTFE+7% carbon fiber +5%MoS 2 ,polyether ether ketone（PEEK）.Two materials, PTFE+7% carbon fiber and UHMWPE,were screened out for comparative experiments under different fretting stroke and lubrication conditions.The results show that the average friction coefficient of UHMWPE material increases with the increase of fretting stroke under both dry friction and oil lubrication conditions, and the friction coefficient of PTFE+7% carbon fiber material has little fluctuation with the number of cycles when it reaches a stable state.According to the test results, PTFE+7% carbon fiber is recommended when the fretting stroke is less than or equal to 0.2 mm, and UHMWPE is recommended when the fretting stroke is greater than 0.2 mm.
盾构机主驱动唇形密封性能直接影响整台盾构机的施工效率.盾构机主驱动唇封密封介质为润滑脂,工作时唇口温度可达50-60℃,为更好地预测唇封的密封性能,考虑润滑脂流变特性、唇口温度对流场分析、密封材料的影响,建立盾构机唇形密封流固热耦合仿真模型.利用流速分离法推导润滑脂二维雷诺方程,采用赫兹接触模型计算粗糙峰接触压力,结合有限元软件开展热力耦合分析,实现唇封温度场及摩擦力矩、泄漏率等关键性能参数的定量预测.结果表明:考虑温度场后唇封最大接触压力减小,接触宽度增大,摩擦力矩减小.温度对唇封应力应变状态及密封性能产生较大影响,这对盾构机主驱动唇形密封设计具有一定指导作用.
螺旋桨重力会导致船舶推进轴系发生挠曲,造成艉轴承边缘润滑状态恶劣.采用一种磁水复合支撑形式的艉轴承,通过引入永磁体磁力作用,改善桨重因素对艉轴承边缘润滑状态的不利影响;构建永磁体三维磁力特性分析方法,探究不同永磁体材料磁性质和布置形式对磁力承载性能的影响规律;基于艉轴承弹性流体动压润滑分析方法,获取永磁体形性特征对润滑特性的影响规律.结果表明:磁承载力受永磁体材料剩磁的影响明显,材料剩磁越大,永磁体承载力越大,轴承润滑状态相对越好;沿周向增加磁块数目或增加永磁块轴向长度可以增大永磁体的承载力,但永磁体承载效率可能下降,设计时需综合考虑;磁体的布置形式也对磁力承载性能和润滑性能影响显著,在永磁体体积相同的情况下,更为合理的布置形式可使永磁体承载力与艉轴承最小水膜厚度明显增大.
为了改善水润滑轴承材料热塑性聚氨酯(TPU)的减振降噪性能,以TPU为基体、聚四氟乙烯(PTFE)为添加剂,通过物理共混的方式制备PTFE/TPU改性复合材料.在RTEC摩擦磨损实验机上模拟泥沙工况,对复合材料进行不同速度和载荷下的摩擦学试验,通过分析复合材料的力学性能、摩擦因数、表面形貌以及振动噪声行为,探讨其摩擦磨损规律与减振降噪性能.结果表明:复合材料的拉伸强度和邵氏硬度均随着PTFE含量的增加而先增加后降低,质量分数8％PTFE改性TPU复合材料表现出最好的力学性能;随着速度与载荷的增大,复合材料的摩擦因数逐渐增大,材料表面损伤、变形、剥落等严重损伤逐渐增多;与纯TPU相比,改性复合材料的摩擦磨损剧烈程度更低,摩擦因数的变化幅度较小且摩擦因数曲线相对光滑,材料微观表面的损伤更少;随着速度与载荷的增大,复合材料的振动响应与辐射噪声现象增大,振动与噪声信号的平均强度增大,频域上的频率分量增多,幅值分量增大,主频向高频转移;PTFE能够改善TPU的摩擦学性能,降低摩擦因数,同时赋予复合材料一定的减振降噪性能,并且效果在高速、高载荷下更为明显.
低速重载等极端工况下摩擦诱导异常振动会极大地影响舰船推进轴系中水润滑轴承的稳定运转.针对水润滑轴承开展考虑横向振动的摩擦动力学性能研究,建立受横向振动效应影响的水润滑轴承混合润滑和流体动压润滑模型,分析2种状态下轴承的振动特性;通过将轴颈平衡位置下的坐标代人轴承横向振动模型中,得到轴颈的扰动量,研究不同激励幅值对轴承摩擦力的影响规律,探明弹性变形条件下水润滑轴承的摩擦诱导振动机制.结果表明:当轴承出现接触,横向振动对轴承的摩擦力影响较显著,将导致轴承摩擦力呈现非线性变化.研究结果为评估横向振动对摩擦力的影响程度、揭示轴承摩擦振动机制提供支撑.
为获取摩擦过程中产生的多源信息,基于环境设计理论分析摩擦学试验研究的现状和需求,构建摩擦过程多源信息采集系统的递归对象模型,通过识别关键冲突并寻求解决方案,实现系统的整体方案设计.通过多传感器部署和LabVIEW软件开发,研制一种基于通用摩擦磨损试验机的摩擦过程多源信息采集系统,实现摩擦过程中的振动、声音、声压等多源信息的实时采集、存储和展示.将系统进一步集成化并基于Unity 3D构建摩擦磨损试验机的数字孪生虚拟实体,同时为便于多源信息的后续利用,提出相应的信号预处理方法.通过试验验证该系统满足摩擦试验中多源信息的采集需求,能够为后续开展多源信息融合、多学科信息关联映射提供数据基础,也为实现基于摩擦学衍生量的摩擦学状态监测提供数据基础.
研究碳纤维/聚四氟乙烯(CF/PTFE)、玻璃纤维/聚四氟乙烯(GF/PTFE)复合材料与氮化硅陶瓷配副在海水环境下的摩擦学性能与润滑机制,分析滑动速度对摩擦副海水润滑性能的影响规律.结果表明:在海水润滑条件下,随着滑动速度的增加,PTFE、CF/PTFE、GF/PTFE材料与Si3N4陶瓷配副时的摩擦学性能均有明显改善,摩擦因数与磨损率均呈显著降低的趋势,其中CF/PTFE复合材料表现出更为优异的摩擦学性能,在1 000 r/min滑动速度下摩擦因数低至0.026.磨损表面表征结果表明,在海水润滑条件下,PTFE基复合材料在摩擦过程中由于摩擦化学反应生成了润滑膜,可为摩擦副提供良好的润滑和减磨作用,从而减少摩擦磨损行为的发生.
Water-filled impedance tube is an important testing facility for underwater sound absorption materials. However， most water-filled impedances can only meet the requirements under normal hydrostatic pressure， and it still challenging for testing under high hydrostatic pressure. Especially， the sealing problem is the key. In this paper， the seal of the water-filled impedance tube is designed， including the seal for hydrophones， the top flange with the sample holder and the bottom flange with the underwater transducer. They are sealed by the mounting tube and O-ring， respectively. This design can not only improve the sealing performance， but also guarantee the fast and convenient installation of the hydrophone and the sample. The hydrostatic pressure test shows that the designed water-filled impedance tube can meet the sealing requirements under 3.15 MPa without obviously pressure dropping or water leaking. The underwater acoustic test indicates that the water-filled impedance tube can achieve good measurement at high hydrostatic pressure up to 1.5 MPa. This provides a reliable test basis for the design and improvement of the seal of water-filled impedance tube．
人字闸门底枢作为半球面摩擦副,在水下长时间以低速、重载工况运行,易因磨损导致故障.传统的油脂润滑容易造成环境污染,而固体镶嵌润滑是更为适宜的润滑方式.为了研究不同材料和轴瓦镶嵌结构对底枢摩擦副摩擦学性能的影响,通过试验得到石墨填充润滑材料的力学性能以及不同条件下的摩擦因数;以三峡大坝人字闸门底枢为研究对象,从工程实际与理论分析角度设计了相同孔径和渐变孔径2种不同轴瓦镶嵌结构,利用有限元软件分析了球面静态接触和旋转运行状态下的接触应力,对比了光滑轴瓦、相同孔轴瓦和渐变孔轴瓦的理论摩擦因数.结果表明:从应力角度,相同镶嵌结构下石墨润滑优于高分子赛龙材料润滑;在相同填充面积条件下,3种结构中最大等效应力从大到小依次为渐变孔结构、相同孔结构和光滑结构,而从润滑以及理论摩擦因数角度看,渐变孔结构性能最好,然后依次为相同孔结构和光滑结构;相比镶嵌孔路径,无镶嵌孔路径上的轴瓦等效应力较小.因此,在实际应用中,应确保力学偏置方向与轴瓦的无镶嵌孔区域相符,以减小应力集中并提高润滑性能.
橡塑双层复合材料水润滑轴承综合了橡胶阻尼性好和塑料摩擦性能好的特点,是一种极具发展潜力的新型水润滑轴承,然而其润滑承载机制尚不明确.采用流固耦合仿真方法研究该种轴承在不同载荷、轴瓦厚度和弹性模量下的轴瓦变形分布特点和规律.结果表明:轴瓦变形主要发生在橡胶层,橡胶层轴瓦变形影响塑料层轴瓦的形状,并使其整体发生移动;随载荷增大,轴瓦变形量增大,轴瓦刚度系数减小;随塑料层轴瓦厚度增大,轴瓦总变形量近似线性减小,轴瓦刚度系数增大;而塑料层轴瓦弹性模量的变化对轴瓦总变形和刚度系数影响相对较小.
针对水下法兰连接器密封面的泄漏问题,利用各向同性粗糙表面的流量因子修正平行圆板泄漏模型,建立膜厚比与泄漏率的关系;运用MATLAB和COMSOL软件联合生成接触密封面实体,并对4种作业温度下的3种均方根粗糙度密封面进行有限元分析,得到粗糙表面平均接触压力与膜厚比的关系;通过数学推导和曲线拟合的方法建立了4种作业温度下3种粗糙表面平均接触压力与泄漏率的关系.结果表明:作业温度对透镜垫表面质量要求有很大影响,在作业温度为20～100 ℃时,均方根粗糙度为0.4 μm的透镜垫可满足泄漏率指标要求,而在100～150 ℃高温采油作业时,只有均方根粗糙度为0.2 μm时才能满足泄漏率指标要求.
