界面滑移对圆柱形凹坑织构滑动轴承摩擦力的影响

为研究不同的滑移情况对圆柱形凹坑织构滑动轴承摩擦力的影响,建立含有圆柱形凹坑织构的滑动轴承在不同界面滑移状态下的摩擦力计算模型,探究影响织构化滑动轴承摩擦力的参数,并借助ANSYS分析不同滑移情况下界面滑移对圆柱形凹坑织构滑动轴承摩擦力的影响规律。结果表明:织构化滑动轴承的摩擦力主要是由轴颈线速度、油膜滑移比、轴承的进出油口压力、织构处油膜压力、织构深度、油膜厚度和承载力决定;不同滑移情况下织构模型的摩擦力均小于无织构模型;且在上下表面均滑移时,圆柱形凹坑织构在出口位置时表现出最优的承载和减摩效果;适当地增加圆柱形凹坑织构的深度可以改善模型的摩擦性能,但是过深的凹坑织构并不能发挥出其性能。     

The numerical analysis of the radial sleeve bearing with combined surface slip

In order to improve the carrying capacity and reduce the temperature rise in high speed and precise spindle systems, a combined surface radial sleeve bearing using the interfacial slip technique was discussed. An extended Reynolds equation was derived based on the modified slip length model considering the limiting shear stress. By means of the finite differential methods, the characteristic analysis and optimization of the slip region of the combined surface sleeve bearing were carried out, and it has been proved that there is still a considerable large load support in a parallel sliding gap. Comparing with the general journal bearing, the load capacity and end leakage rate of the combined surface sleeve bearing can be increased greatly and the load capacity can be increased by 1.75 times. The attitude angle, friction drag, temperature rise of the combined bearing can be decreased distinctly and the temperature rise can be decreased by 92.4%.     

An analytical approach on the tribological behaviour of pocketed slider bearings with boundary slip including cavitation

Slider bearing performance depends on the boundary conditions at the interface between the solid surfaces and the fluid. This paper presents the combined effect of pockets and boundary slip on the load support and friction of parallel sliding systems using analytical solutions for a simple pocketed bearing. The effect of cavitation was of particular interest with respect to the inlet suction mechanism. It was demonstrated that applying boundary slip in a pocketed slider bearing gives a reduction in load support compared with the textured bearing without wall slip. Adding slip over the whole surface could retard the presence of cavitation. The influence of boundary slip is explored, and was found to significantly affect the frictional behaviour. Copyright © 2016 John Wiley & Sons, Ltd.     

Analysis of Micropolar and Power Law Fluid–Lubricated Slider and Journal Bearing with Partial Slip–Partial Slip Texture Configuration

An analysis of micropolar and power law fluid–lubricated partial slip–partial slip texture slider and journal bearings is presented. The nondimensional pressure and shear stress expressions for a partial slip texture configuration are analyzed using narrow groove theory. The parameters used in the analysis are nondimensional partial slip length, nondimensional partial slip–partial slip texture length, nondimensional depth of recess, ratio of land with slip to recess, nondimensional slip coefficient, coupling number; ratio of characteristic length to film gap, and power law index. A partial slip configuration with a higher slip coefficient yields an improvement in load capacity and reduction in coefficient of friction compared to a partial slip texture configuration for micropolar and power law shear thinning (pseudoplastic) fluid-lubricated slider and journal bearings.     

Numerical Analysis of a Slider Bearing with a Heterogeneous Slip/No-Slip Surface

The behavior of a fluid-film bearing depends on the boundary conditions at the interfaces between the liquid and the solid bearing surfaces. For almost all solid surfaces, the no-slip boundary condition applies. However, a number of researchers have recently found that slip can occur with specially engineered surfaces. These include molecularly smooth surfaces and surfaces with micron-scale patterns. By constructing an engineered heterogeneous surface on which slip occurs in certain regions and is absent in others, the flow in the liquid film of a bearing can be altered, and such characteristics as load support and friction can be improved. In the present study, a numerical analysis of a slider bearing with such an engineered slip/no-slip surface is analyzed. Slip is assumed to occur when a critical shear stress is exceeded and follows the Navier relation. The results show that with a critical shear stress of zero, a significant increase in load support and decrease in friction can be achieved with an appropriate surface pattern. With nonzero values of critical shear stress, an instability occurs over a range of speeds. At speeds above this range, the bearing behaves similar to the case with zero critical shear stress, while below this range it behaves like a conventional bearing.     

Wall slip and hydrodynamics of two-dimensional journal bearing

In the present paper, based on the limiting shear stress model, a multi-linearity finite element algorithm and quadratic programming technique are used to study the influence of wall slip on the hydrodynamic lubrication performance of a two-dimensional journal bearing (finite length journal bearing). It is found that if the lubricated surfaces are designed as homogeneous slip surfaces, the hydrodynamic force will be decreased. If the shaft surface (rotation) is a slippery surface with very low limiting shear stress, almost no fluid load support can be generated. If the sleeve surface is designed as the homogeneous slip surface, a low fluid load support together with a small friction drag can be obtained. However, if the sleeve surface is designed as an optimized slip surface with a slip zone in the inlet region, a high load support and low friction coefficient can be obtained. Optimization of the shape and the size of the slip zone can give the journal bearing many advanced properties.     

Boundary slip surface design for high speed water lubricated journal bearings

This paper presents the development of a numerical model for high speed and water lubricated journal bearings with different boundary slip arrangements. The effect of boundary slip and its possible mechanism are analyzed and discussed. The results suggest that a suitable combination of slip/no-slip surfaces on the sleeve of a journal bearing enables improvement of the tribological performance through (i) suppressing the occurrence of cavitation, (ii) enhancing the load bearing capacity, and (iii) reducing the interfacial friction between bearing sleeve and shaft. Such improvement becomes more significant for the bearings with smaller eccentricity ratio, smaller width and larger diameter.     

A Method for Measuring the Intensity of a Line Load Around a Shaft or Tube

The slip flow effect is considered to estimate the load capacity and the dynamic coefficients of an elastically-supported gas foil hearing when the local Knudsen number for the minimum film thickness is greater than 0.01. The compressible Reynolds equation with slip flow conditions is used to evaluate the load capacity. The linearized dynamic coefficient equations are obtained by the perturbation method. Numerical predictions compare the static and dynamic force performances considering slip flow at room-to-high temperate with the performance of elastically-supported foil bearing without slip flow for a range of bearing compliances and bearing numbers. It has been shown that the slip flow effect on the load capacity and the dynamic coefficients at high temperature is significant in the region of low bearing numbers.     

摩擦副表面沟槽型织构润滑性能的数值仿真

从目前的研究来看,织构的深度和载荷对油膜的润滑性能具有显著的影响,然而,在载荷变化的情况下,润滑膜的最小膜厚和黏性阻力是一个动态变化的过程。因此不同载荷下,最佳织构深度的选取还需系统地进行分析。通过建立沟槽型织构流体润滑模型,分析了织构的深度以及承载力对摩擦副的油膜厚度、压力、剪切力、以及摩擦因数的影响。结果表明：在承载力一定时,油膜厚度随织构深度的增加呈先增大后减小的趋势。在89 N载荷下时,存在最佳油膜厚度6.4184μm,此时织构深度为2.97μm,摩擦因数为0.0162。     

不对中径向滑动轴承微凹槽织构数值分析

为研究凹槽位置、深度、倾斜角和面积率等因素对不对中径向滑动轴承摩擦学性能的影响,基于Reynolds方程建立滑动轴承的摩擦润滑数学模型,采用有限差分法迭代求解不同凹槽微织构参数影响下的油膜压力,计算不同织构参数下轴承的承载力、摩擦力和端泄流量等。计算结果表明:凹槽微织构分布在升压区且轴向占比约50%时轴承承载力较高;相比于光滑轴承,微织构轴承的摩擦力更低,且凹槽的轴向占比和深度越大摩擦力越小;微织构对轴承的承载力具有削弱和增强的双重可能,存在最优的凹槽周向和轴向占比、深度和倾斜角使得轴承在较小摩擦力下具有更高的承载力;凹槽微织构的面积率与轴承承载力和摩擦力呈线性相关;轴承的不对中程度越小时,在光滑轴瓦表面加工合适参数的微织构时越有利于提高轴承的摩擦学性能。     

Hydrodynamic lubrication of a porous slider bearing with slip velocity

An inclined porous slider bearing is analysed with slip velocity at the porous boundary considered. The expressions for dimensionless loadcarrying capacity, friction and the centre of pressure are obtained in the form of integrals. Minimization of the slip parameter is essential to increase the load capacity.     

多唇往复滑环式组合密封数值模拟与分析

构建一种适用于多唇往复滑环式组合密封的数值模型,数值模型中包含固体力学分析、流体力学分析、接触力学分析、流固耦合分析。以含有3段密封唇的PS封为例,基于数值模型求解得到密封面油膜厚度分布、油膜压力分布、粗糙峰接触压力分布,以及内外行程的流量和密封界面的摩擦力。该数值计算方法解决了多唇密封中边界条件难确定的问题,通过迭代计算可得到稳态运行时各密封唇的边界条件。明确多唇PS封的密封机制,分析不同往复速度对密封性能的影响。结果表明：多唇PS封内外行程中各唇边界条件差异较大,外行程中,两唇之间的空隙处存在一定压力,内行程中空隙压力为0;外行程的密封面接触压力要小于内行程;增大往复速度会使多唇PS封净泄漏增加,摩擦力减小。     

Effect of deformation in magnetic fluid based transversely rough short bearing

Abstract

This investigation aims to analyse the performance of a magnetic fluid based rough short bearing incorporating a deformation effect. The associated stochastically averaged Reynolds equation is solved with suitable boundary conditions to obtain the expression for pressure distribution, which results in the calculation of the load carrying capacity. The expression for the friction is obtained for both plates. It is seen that the load carrying capacity increases nominally as a result of the magnetic fluid lubricant. Furthermore, the film thickness ratio increases the load carrying capacity. It is found that the load carrying capacity increases as the ratio of the length/outlet film thickness increases, while this trend is reversed in the case of magnetisation. Moreover, it is noticed that friction remains unaltered because of the magnetic fluid lubricant. Furthermore, it is interesting to note that the deformation also unalters the friction. This article suggests that the negative effect of the standard deviation can be neutralised up to a certain extent by the combined positive effect of the magnetisation parameter, the film thickness ratio and the ratio of the length/outlet film thickness, especially when the deformation is relatively less. Therefore, this study offers some scopes for extending the bearing’s life. Finally, the bearing can support a load even in the absence of flow, unlike in the case of conventional lubricant.     

Theoretical Prediction of Journal Bearing Stability Characteristics Based on the Extent of the Slip Region on the Bearing Surface

Journal bearing performance depends on the boundary conditions at the interfaces between the fluid and the solid surfaces. In the derivation of the Reynolds equation used to predict the bearing performance, the no-slip boundary conditions of the fluid and the solid interfaces are used. Recent research has shown that a slip can occur on specially made surfaces, the conventional no-slip boundary conditions are not valid, and the Reynolds equation is no longer applicable. If the slip is allowed to occur in certain regions, the fluid flow in the bearing can be altered, and the bearing stability characteristics can be improved. In this article, the numerical stability analysis of a journal bearing based on the extent of the slip region on the bearing surface is analyzed. An extended Reynolds equation is derived based on the slip length model, using a no-slip boundary condition against the journal surface and the slip against the bearing surface. A linearized perturbation method is used to determine the stability limit of a rigid rotor supported on two symmetrical journal bearings. Using the linear stability analysis, the linearized stiffness and damping coefficients, the threshold speed, and the critical whirl ratio are evaluated. The effects of the slip parameter on the bearing stability performance are discussed. The results show that with a critical shear stress of zero, an increase in the stability threshold can be achieved with a higher value of the nondimensional slip length and a smaller extent of the slip region on the bearing surface.     

Optimum shape design for surface of a porous slider bearing lubricated with couple stress fluid

Porous-bearing performance can significantly benefit from optimally designing the shape of the bearing. The present paper introduces an approach for designing the optimum shape of a slider bearing using an inverse method. The proposed approach utilises a sequential quadratic programming algorithm to minimise friction subject to load and centre of pressure requirements specified by the designer. Bearing characteristics, such as friction, load and centre of pressure, are obtained by solving a modified Reynolds-type equation numerically using the finite difference method. The modified Reynolds equation is derived on the basis of Stokes' microcontinuum theory of couple stress fluids, which is used to study non-Newtonian lubricants. Results show that the optimisation approach reduces the coefficient of friction. In addition, the dimensionless slip parameter is shown to be the most significant parameter affecting optimal friction. Copyright © 2008 John Wiley & Sons, Ltd.     

Analytical analysis and optimisation of the Rayleigh step slider bearing

In tribology, the Rayleigh step is known as a bearing with the highest load capacity amongst all other possible bearing geometries. In classical resources on tribology, it is also shown that there is an optimum geometry for the Rayleigh step providing the highest load capacity. However, the analyses are confined to a special case where the effect of hydrostatic pressure is neglected. Furthermore, the possible optimum parameters in terms of the friction force and/or friction coefficient as well as the lubricant flow rate have not been discussed. In this study, the Rayleigh step is comprehensively analysed including the effect of variations of pressure at the boundaries on the optimum parameters. In addition, the bearing is also optimised considering lubricant flow rate, friction force and friction coefficient. It is shown that the optimum bearing parameters are strictly dependent on the variations of the pressure at the boundaries. It is also verified that the optimum point(s) in terms of load capacity are not necessarily equal to the optimum point(s) considering friction coefficient and/or lubricant flow rate even though if there is no pressure difference between bearing endings.     

关节轴承摩擦温度场计算方法

以推力型关节轴承为研究对象,分析了轴向载荷下的接触应力,并根据试验所得摩擦力矩反推出了动态摩擦因数。结合接触应力及摩擦因数求出了摩擦热流率,并将其作为第二类边界条件进行了轴承非定常温度场有限元分析,最后利用红外热像仪拍摄了摩擦过程中轴承侧表面温度分布,检验仿真结果的可靠性。仿真与试验结果表明：该计算方法解决了球面摩擦副摩擦因数的精确计算和热流率的空间分配问题,建模时忽略球面间隙会直接影响接触应力分布并造成温度场分布出现较大误差,考虑球面间隙可以更精确地计算轴承摩擦温度场。     

表面织构对水润滑轴承混合润滑性能的影响

为分析表面织构对水润滑轴承混合润滑性能的影响,基于平均Reynolds方程及JFO空化边界条件建立带有表面织构的水润滑轴承混合润滑模型并数值求解,获得不同织构参数下水润滑轴承的Stribeck曲线。研究结果表明:表面织构是否能改善润滑性能与其深径比及面密度参数密切相关,织构的引入并不一定能降低水润滑轴承的摩擦因数;表面织构的面密度和深径比存在最优值,能使水润滑轴承获得最大的膜厚比与最小的摩擦因数,并在较低的转速下由混合润滑状态进入流体动压润滑状态。     

Parametric study of texturing in convergent bearings

The effect of textured surfaces in hydrodynamic bearings is assessed using a mass-conserving numerical analysis that allows for arbitrary geometry and multiple regions of cavitation. The texture investigated consists of regularly spaced rectangular pockets through an (infinitely) long linearly convergent or parallel bearing. This arrangement leads to nine independent non-dimensional parameters including operating conditions. The effectiveness of texture at improving load support and reducing friction over a corresponding plain bearing is described in relation to these parameters and the important interaction between parameters is highlighted. The beneficial or detrimental effect of texture is explained in terms of the fundamental mechanisms of hydrodynamic pressure generation including inlet suction.     

Some Observations on Frictional Force During Fretting Fatigue

Frictional force behavior during fretting fatigue and its interdependence on other fretting variables are investigated. Both coefficient of static friction and the normalized frictional force (i.e., the ratio of frictional force and normal contact load) increase during the earlier part of a fretting fatigue test and then both reach to a stabilized value. The variation of temperature in the contact region and normalized frictional force with increasing cycle numbers and bulk stress show similar trend implying that normalized frictional force represents the average friction in the contact region during a fretting fatigue. An increase in bulk stress, relative slip, and hardness of pad material results in an increase of the normalized frictional force, while an increase in contact load, frequency and temperature decreases the normalized frictional force. The normalized frictional force is also affected by the contact geometry. On the other hand, coefficient of static friction increases with an increase in the hardness of mating material, temperature and roughness from shot-peening treatment, but is not affected by contact geometry and displacement rate. Further, the normalized frictional force is not affected by the contact geometry, roughness and applied bulk stress level when fretting fatigue test is conducted under slip controlled mode, however it increases with increasing applied relative slip and decreasing contact load in this case.