线接触摩擦副织构化表面动压润滑性能

为研究线接触摩擦副织构化表面动压润滑性能,建立其理论模型,并运用多重网格法进行数值分析,探讨工况参数(载荷、转速)和微织构参数(面积占有率、深径比)对表面油膜压力的影响;在MMW-1A摩擦磨损试验机上研究微织构面积占有率与摩擦因数的关系。结果表明,线接触条件下微织构化表面的油膜平均压力随着载荷和转速的增大而增大,随着微织构面积占有率的增大而先增大后减小,随着深径比的增大而减小;而摩擦因数随着微织构面积占有率的增大而先减小后增大再减小;存在最优的微织构面积占有率,使得油膜平均压力最大和摩擦因数最小。试验结果较好地验证了数值模拟结果,表明线接触摩擦副织构化表面具有较好的减摩特性。     

Elastohydrodynamic Lubrication of Rough Surfaces under Oscillatory Line Contact with Non-Newtonian Lubricant

This paper presents the results of a transient analysis of elastohydrodynamic lubrication (EHL) of two parallel cylinders in line contact with a non-Newtonian lubricant under oscillatory motion. Effects of the transverse harmonic surface roughness are also investigated in the numerical simulation. The time-dependent Reynolds equation uses a power law model for viscosity. The simultaneous system of modified Reynolds equation and elasticity equation with initial conditions was solved using the multigrid, multilevel method with full approximation technique. The film thickness and the pressure profiles were determined for smooth and rough surfaces in the oscillatory EHL conjunctions, and the film thickness predictions were verified experimentally.

For an increase in the applied load on the cylinders or a decrease in the lubricant viscosity, there is a reduction in the minimum film thickness, as expected. The predicted film thickness for smooth surfaces is slightly higher than the film thickness obtained experimentally, owing primarily to cavitation that occurred in the experiments. The lubricant film under oscillatory motion becomes very thin near the ends of the contact when the velocity goes to zero as the motion direction changes, but a squeeze film effect keeps the fluid film thickness from decreasing to zero. This is especially true for surfaces of low elastic modulus. Harmonic surface roughness and the viscosity and power law index of the non-Newtonian lubricant all have significant effects on the film thickness and pressure profile between the cylinders under oscillatory motion.     

Investigation into the Normal Contact Stiffness of Rough Surface in Line Contact Mixed Elastohydrodynamic Lubrication

In this work, the statistical asperity microcontact models in combination with the acoustic spring model and the load sharing concept are utilized to study the interfacial normal contact stiffness for a rough surface in line contact elastohydrodynamic lubrication (EHL). Two different statistical microcontact models of Greenwood and Williamson (GW) and Kogut and Etsion (KE) are employed to derive the normal contact stiffness expressions for a dry rough line contact considering the purely elastic contact and the multiple regimes elastic–elastoplastic–fully plastic contact, respectively. The liquid film stiffness is calculated based on the relationship between film thickness and bulk modulus of the lubricant. The lubricant film thickness equations are employed in conjunction with the load sharing concept and the empirical formulas for the maximum contact pressure in a dry rough contact are fitted for the GW model and the KE model, to evaluate the relationship between film thickness and motion velocity for the purely elastic GW microcontact model and the multiregime KE microcontact model, respectively. The comparison with experimental results shows that the KE model predicts closer total contact stiffness results than the GW model. The stiffness contributions from the solid asperity contact and lubricant film are obtained and effects of surface roughness, applied load, motion velocity, and type of lubricant on the normal contact stiffness are analyzed.     

面接触润滑条件下表面形貌对动压润滑的影响

利用课题组自主研发的面接触光干涉油膜厚度测量系统,对表面凹槽滑块的流体动压润滑油膜厚度进行了试验测量.试验中以静止的微型凹槽滑块平面和旋转的光学透明圆盘平面构成润滑副,且两润滑平面始终保持平行;在载荷固定的条件下,对油膜厚度—速度曲线进行测量.结果表明凹槽的宽度、深度、方向和位置等因素对油膜厚度有着重要影响.     

液压缸活塞表面微织构动压润滑性能分析

以织构化间隙密封液压缸为研究背景,利用平均雷诺方程对缸筒与活塞的配合处微织构流场进行数学建模,采用有限差分法对平均雷诺方程进行离散,分别对织构形貌为球缺面、圆柱面、圆锥面、抛物面、六面体和正方体进行数值模拟,获得最优微织构形貌,同时探讨了表面粗糙度,表面方向参数和面积占有率对表面摩擦因数的影响。结果表明:六种不同形貌的微织构均能在活塞表面产生动压润滑效果,圆柱形微织构表面动压润滑性能最好;粗糙表面的粗糙峰在运动过程中能够形成动压承载力,圆柱形表面的摩擦因数随粗糙度的增加而增加,微织构的摩擦因数随表面方向参数的增加而减小,随着面积占有率的增加而减小。     

考虑软三体接触的粗糙界面混合润滑模型研究

软三体颗粒润滑是利用大量松散的固体软颗粒在界面中的承载和剪切行为实现特殊环境下界面的减摩,因此研究软颗粒介质摩擦界面在剪切过程中的受力情况,对软三体颗粒润滑机理的分析以及润滑装置的设计都具有重要意义。研究中将第三体颗粒类比为流体,基于雷诺方程、黏度方程、Greenwood和Williamson接触模型（G-W模型）等建立了含大颗粒粗糙界面的混合润滑模型。该模型中摩擦副的总载荷及总摩擦力由流体、微凸体和大颗粒三部分共同构成。通过采用有限差分法对上述物理模型进行求解分析,探究膜厚比、第三体大颗粒的质量浓度、粒径以及试件的表面形貌、弹性模量对三体接触界面的承载和摩擦力的影响情况,进而分析大颗粒粒径和接触表面粗糙度耦合时软三体接触界面的力学性能。基于对所构建的软三体接触界面混合润滑模型的研究可知：合理选择大颗粒质量浓度、粒径以及试件的表面形貌、弹性模量有助于提高承载、减小摩擦力,使得软三体颗粒流具有更好的减摩润滑性能。     

Non-Linear Transient Stability Analysis of a Rigid Rotor Supported on Hydrodynamic Journal Bearings with Rough Surfaces

Non-linear transient stability analysis has been performed to study the sub-synchronous whirl stability of a rigid rotor supported on two symmetric hydrodynamic bearings with rough surfaces subjected to a unidirectional constant load. A Reynolds type equation for finite hydrodynamic bearings, with different models of rough surfaces, has been solved using the stochastic finite element method. The trajectories of the journal center have been obtained by solving the equations of motion of the journal center by the fourth-order Runge-Kutta method. Results show an increase in the stability with transverse roughness and a decrease in the stability with isotropic roughness. A small improvement in stability is obtained with longitudinal roughness.     

圆柱与刚体平面弹性接触的静摩擦系数

库仑-阿蒙顿定律表明摩擦系数只取决于材料性质。现有研究表明,摩擦系数不仅与温度、相对运动速度、表面光洁度等有关,还与正压力有关。文章以圆柱与刚体平面接触为研究状况,使用分析软件,计算出摩擦系数解析式与物体的材料特性无关,适用性广。     

薄膜粗糙表面有摩擦接触问题的数值计算研究

采用ANSYS的APDL语言编程通过参数化变量方式实现了薄膜粗糙表面有摩擦接触问题的整个建模与分析过程,其中包括参数化生成满足高斯分布的随机粗糙表面与计及摩擦因数和薄膜/基体弹性模量比变化情况下的自动有限元分析过程。计算结果表明:当摩擦因数一定时,随着薄膜/基体弹性模量比的增大,应力分布逐渐向基体深处扩展,粗糙表面上各点接触压力一致减小,接触压力峰值减小的最大幅度为9.0%;当弹性模量比一定时,摩擦因数的变化对基体部分应力分布的影响不大,然而随着摩擦因数的增加,粗糙表面上各点接触压力增大,接触压力峰值增加的最大幅度为13.2%,可见摩擦因数和弹性模量比对薄膜粗糙表面的接触应力有明显影响。     

基于高斯粗糙表面的角接触球轴承微弹流润滑研究

基于二维数字滤波法模拟高斯粗糙表面,建立考虑高斯粗糙表面形貌及热效应的角接触球轴承微弹流润滑模型,采用多重网格积分法求解弹性变形,采用Gauss-Seidel及Jacobi迭代法迭代求解压力,采用逐步扫描法求解油膜能量方程,采用渐进网格加密法求解强耦合非线性微弹流润滑方程组。结果表明:当x、y方向自相关长度相同时,随着粗糙表面均方根值的增加,油膜压力及温度明显增加,膜厚显著减小;反之,油膜压力及膜厚在自相关长度较小的方向出现明显的纹理特性,且当纹理特性与润滑油流动方向相同时,油膜温度显著减小。     

旋滑条件下弹流润滑数值分析

建立旋滑条件下椭圆接触弹流润滑的数学模型,用多重网格法求得该条件下的完全数值解,研究速度、载荷、偏心距和椭圆比对油膜厚度、形状和压力的影响。结果表明,偏心距较小时,油膜厚度和形状都与普通弹流有明显的不同;速度、载荷和椭圆比增加及偏心距减小,均会导致接触区两侧最小膜厚的差值增大,油膜形状的非对称性增强;速度、椭圆比增加,油膜厚度增加,接触区压力减小,载荷增加或偏心距减小,油膜厚度减小,接触区压力增加。     

双重润滑条件下的刀具切削特性研究

为实现清洁切削技术,将Al2 O3包覆CaF2复合粉体作为添加相,采用真空热压烧结工艺制备了一种Ti(C,N)基自润滑金属陶瓷刀具(TMC刀具),研究了Ti(C,N)基金属陶瓷刀具在微量润滑作用下切削300M钢的切削性能,结果表明:双重润滑与干切削方式相比,其三向切削力FX、FY、FZ分别减小了36.8％、13.1％和...     

Experimental Study on the Tribological Properties of Powder Lubrication under Plane Contact

Powder lubrication has been studied using a plane contact tribometer. Four kinds of powders—polytetrafluoroethylene (PTFE), graphite, MoS₂, and ball-like copper—were used during the experiments. The results show that powder can be introduced into frictional clearance without any special treatment. The powder's physical properties significantly influence the tribological characteristics in the powder lubrication. The friction coefficient and wear are obviously decreased when the powders are PTFE, graphite, and MoS₂, which are excellent solid lubricants. At lower load capacity, powder lubrication using ball-like copper had certain antifriction effects, but it rapidly became worse with increasing load capacity. Observation with optical microscopy showed that the lubricant film is dynamically formed on the rubbing surfaces in most experiments.     

供油条件对线接触热混合润滑性能的影响

为提高齿轮、圆柱滚子轴承等线接触副零件的润滑性能,有必要研究供油条件对其混合润滑特性的影响。基于平均流量模型,建立考虑供油条件的线接触非牛顿热混合润滑模型。将入口供油量作为控制乏油程度的参数,同时考虑膜厚比(最小膜厚与粗糙度的比值)与粗糙峰接触载荷比(粗糙峰接触载荷与总载荷的比值)来判断润滑状态,研究供油量、速度、接触副材料和环境黏度对混合润滑性能的影响。结果表明：随着供油量的增加,膜厚比增加,粗糙峰接触载荷比减小,最小膜厚与中心膜厚逐渐增大,平均摩擦因数逐渐减小,油膜最高温度逐渐增加,但最终都趋于稳定值;对于3种不同接触副(钢-钢、钢-Si₃N₄和Si₃N₄-Si₃N₄),钢-钢接触副的总压力与油膜温度最低,Si₃N₄-Si₃N₄接触副的总压力与油膜温度最高;在充分供油时,Si₃N₄-Si₃N_...     

PMMA-玻璃面接触流体润滑特性研究

以静止的PMMA平面滑块和旋转的光学透明玻璃盘为润滑副,利用基于光干涉原理的微型面接触润滑油膜测量系统,对PMMA-玻璃形成的润滑油膜厚度及形状进行测量。结果表明,由于润滑面的低弹性,在润滑油膜压力作用下固体表面发生明显的弹性变形,该变形随速度、载荷和PMMA滑块倾角的变化而变化;油膜厚度随速度的增加而明显增加,随载荷增加明显降低,滑块倾角对油膜形状也有明显影响。     

Critical Load Analysis for a Layered Half-Space under Sliding Indentation

Analyses are presented for cracking or delaminating problems of thin coatings on dissimilar thick substrate materials under a normal and a tangential force. Based on the energy principle associated with the consideration of substrate deformation, an analytical expression has been proposed to predict the critical load of an adherent stiff thin coating on a compliant substrate. The critical load has been shown to depend on the hardness, the coating thickness, the surface energy of adhesion, the coefficient of friction, contact areas of a scratch track, and elastic moduli of coatings and substrates. Experimental observations of microscratch testing on a CrN coating deposited on a soft coating, labeled as SC-I, over a Cu/Zn alloy substrate have shown that buckling and cracking in a semicircular arc ahead of an indenter are the predominant failure modes, thereby confirming the assumption of the theoretical calculation. Using Beuth's solution, a simple fracture model describing the cracking of thin coatings has been developed over a range of practical elastic mismatches and applied to solve cracking problems of compliant coatings in this work. Microscratch results from another soft coating, labeled as SC-II, on a Cu/Zn alloy substrate have revealed that cracks first occur along the edge of the circular contact area in the rear of the indenter due to the tensile stress. The stress formulae of Hamilton and Bower and Fleck are therefore introduced into this model to compute the critical load required to initiate a crack in the coating and the stress intensity factor of the coating.

     

动压滑动轴承润滑状态与磨损分析

运用物理分析与理论计算的方法对动压滑动轴承的不同润滑状态进行分析,说明轴承在不同润滑状态下运行时的磨损情况及其对轴承运行性能的影响。文中结合具体实例进行计算并对引起轴承损伤的原因进行分析,说明轴承所处的润滑状态对其磨损和寿命有着直接的关系。     

Hydrodynamic Behavior of Viscoelastic Liquids in a Simulated Journal Bearing

The hydrodynamic effect of viscoelasticity in bearing performance was investigated experimentally by measuring the pressure distribution of viscoelastic liquids and Newtonian liquids in a simulated plain journal bearing. The pressure distribution of the viscoelastic liquids was somewhat different from that of the Newtonian liquids, showing a flattening of the pressure profile and a shift of the circumferential position of the peak pressure. Such a difference contributes to a small recovery of the loss of the load-carrying capacity due to the non-Newtonian viscosity for viscoelastic liquids. It may also contribute to a further reduction of friction beyond the effect of shear thinning. The difference of cavitation on the divergent region of the bearing for these two different kinds of liquid was evident. The viscoelastic liquids showed less extent of cavitation. The experimental conditions conform closely to those used in the classical hydrodynamic lubrication theory. The experimental data indicate that the full fluid film occupies half a bearing starting at 0° and ending at 180°, and the subatmospheric pressure in the divergent region is leveled off at a certain negative pressure. Based on this boundary condition, a computer solution in solving the Reynolds equation for a finite bearing gives very good agreement with experiment.     

单缸熄火工况下船舶柴油机主轴承润滑分析

多缸大功率船舶主机在一缸熄火后继续工作,将偏离设计工况,工作性能参数将发生较大变化。通过构建多体动力学计算模型,对比分析船舶主机在额定工况与一缸熄火工况下的主轴承润滑状况。在4#缸熄火状况下,其两侧主轴承MB4与MB5在其正常发火时刻,即曲轴转角188°附近载荷变化较大,由下瓦受力变成了上瓦受力;此时两轴承油膜压力分布也随之发生变化,高油压区分布于上瓦;轴承间隙高度与油膜压力相对应地变化;两轴承轴心运动轨迹出现明显改变,皆有剧烈的离心和向心运动,若长时间运行,轴承有发生穴蚀破坏的危险。     

Simulation of the Lubrication of Isotropically Rough Surfaces

The lubrication of area-distributed isotropic rough surfaces is studied by a Monte Carlo method. Small square elements of isotropically rough bearing surfaces are considered. Inside such an element, the film height values have a prescribed probability density distribution, but are generated in a random sequence. Mean unit flow and friction in the elements are determined by applying Reynolds' and solving it numerically by a finite-difference technique.

The boundary conditions are provided by generating typical pressures along the elements edges.

Accuracy in the computations is ensured by describing each basic valley-ridge trace by a minimum of 16 point values.

The results demonstrate that isotropic roughness enhances pressure flow (compared with smooth bearings of the same nominal profile). A rough moving surface enhances shear flow while stationary roughness reduces it. However, quantitatively the results deviate from all current theories, including the one previously put forward by the author. The findings of the present analysis are readily expressible in a modified Reynolds' equation.