考虑界面粗糙度动态变化的点接触弹流润滑特性研究

针对点接触弹流润滑的粗糙度效应,建立了考虑表面粗糙度动态变化的点接触弹流润滑模型,实现了油膜厚度和压力分布的快速求解. 对点接触弹流润滑下的粗糙表面弹性变形进行了定性和定量研究,同时分析了表面均方根粗糙度、载荷、相对运动速度和滑滚比对最小膜厚和最大压力的影响,以及表面形貌动态变化对膜厚比的影响. 结果表明:形貌变化改变了弹流油膜和压力分布特性,相对于光滑表面,表面粗糙度总体上提高了最大接触压力、降低了最小膜厚,在轻载工况下表面粗糙度对油膜厚度的削弱更加显著,而不同速度下粗糙度的影响程度基本相同,呈现线性变化趋势,膜厚比随载荷增大呈现先增后减的变化趋势,并在530 MPa左右达到峰值.      

渐开线斜齿轮非稳态弹流润滑数值模拟研究

建立了渐开线斜齿轮啮合的弹流润滑计算模型,将斜齿圆柱齿轮啮合的齿面接触等效为有限长线接触的弹流润滑问题.考虑斜齿轮啮合的实际因素,将斜齿轮啮合过程中的等效曲率半径和齿面载荷的变化反映到弹流润滑计算模型中,应用统一Reynolds方程方法求得轮齿在1个完整啮合周期内的瞬时弹流润滑数值解.结果表明：斜齿轮啮合线上各点处的膜厚、压力均有较大不同,各接触点处的油膜厚度受综合曲率半径的影响较大;斜齿轮传动非稳态效应相对较弱;小齿轮齿根附近和节点位置处润滑状态较差;适当增大压力角可以改善齿轮的润滑.     

原子尺度摩擦行为的分子动力学模拟

应用大规模分子动力学方法,模拟了具有原子级光滑和原子级粗糙形貌的刚性球形探头与弹性平面基体的干摩擦行为,研究了无/有粘附条件下的载荷与摩擦力、载荷与真实接触面积,以及摩擦力与真实接触面积之间的关系,对纳米尺度下的摩擦行为规律进行了分析。几种系统的真实接触面积－载荷关系都与相应的连续力学接触模型定性的一致,它们分别是Hertz光滑表面接触模型、Greenwood-Williamson粗糙表面接触模型和Maugis-Dugdale粘着接触模型。无论是由光滑表面还是粗糙表面构成的摩擦系统,在无粘附条件下摩擦力与载荷成正比,而摩擦力与真实接触面积之间没有一个简单的关系;在粘附条件下摩擦力与真实接触面积成正比,而摩擦力与载荷之间表现为Maugis-Dugdale模型预测的亚线性关系。我们的研究表明,当表面作用从无粘附到粘附时,控制摩擦力的决定因素从载荷转变为接触面积,摩擦行为从载荷控制摩擦转变为粘着控制摩擦。     

两表面速度均为任意方向的非牛顿椭圆接触等温弹流润滑分析

提出了一种简单易行的方法用于进行两表面速度均为任意方向的等温点接触弹流润滑分析;建立了等温非牛顿椭圆接触弹流润滑的数学模型,综合考虑了两表面速度同向、反向及不共线且与椭圆短轴成一定角度的工况,并得到了两表面速度均为任意方向的等温数值解.结果表明:随着两表面速度方向的改变,合卷吸速度的方向不断变化,接触椭圆在计算域内的倾斜角度也随之改变;由于接触椭圆与坐标轴成一定角度,油膜的压力和膜厚不再与Y=0平面对称,Y=0平面内第二压力峰和油膜颈缩出现在出口区,而在X=0平面内第二压力峰和油膜颈缩出现在入口区.     

基于载荷分担理论的渐开线斜齿轮热混合弹流润滑分析

沿接触线把斜齿轮分成许多小薄片,每一薄片看成具有当量角速度的直齿轮,根据欧拉方程得到任一接触点处的曲率半径和表面速度.然后基于载荷分担、弹流润滑和粗糙线接触理论,建立了考虑表面粗糙度的斜齿轮传动混合热弹流润滑模型.研究了斜齿轮传动稳态载荷分布下牛顿流体和Carreau流体时的润滑特性.结果表明:牛顿流体和Carreau非牛顿流体模型下,中心油膜厚度、油膜承载比例、油膜温升随时间和接触线的变化规律相同.牛顿流体下的摩擦系数较工程实际偏大.Carreau非牛顿流体模型下摩擦系数和工程实际相符,其随接触线啮合位置的变化规律与油膜厚度正好相反.     

基于共轭梯度法和快速傅立叶变换的粗糙表面微动接触数值研究

实际工程表面多为粗糙表面,研究粗糙表面的表面形貌对微动接触中压力和应力的影响具有重要意义。本文研究接触过程中法向载荷保持不变,切向载荷为周期性的交变载荷。首先,建立接触算法和模型,算法核心是利用共轭梯度法CGM(Conjugate gradient method)计算微动接触中的表面压力及切向应力并利用快速傅里叶变换FFT(Fast Fourier transform)加快计算速度。然后,对单峰表面、正弦表面和随机粗糙表面的接触进行数值研究。结果表明,表面幅值对切向载荷-位移曲线以及接触过程中的能量耗散有影响,表面幅值越大,相同切向载荷作用下产生的切向位移越大,能量耗散也越大。     

考虑摩擦动力学特性的渐开线齿轮润滑分析

以渐开线齿轮为研究对象,综合考虑齿面摩擦、油膜刚度和阻尼的影响,将摩擦动力学特性和齿面形貌考虑到有限长线接触弹流润滑理论(EHL)中,采用多重网格数值求解法获得了渐开线齿轮在不同啮合位置处的动载荷分布,压力与膜厚分布,并对比分析了干摩擦与润滑条件下压力分布的不同特征以及动载荷对油膜分布的影响.计算结果表明:低速时,动载荷接近稳态分布,在单双齿交替点有明显的高频冲击,随着转速的增加,动载荷变化趋于平缓;与干摩擦相比,润滑油膜可以减小最大压力峰值以及入口区和出口区的压力,但对粗糙峰凹谷处压力有所增加.沿啮合线方向,压力在节点位置附近达到最大值,膜厚受动载荷的影响较小,近似呈线性增加趋势.     

有限长滚子线接触热弹流润滑分析

应用多重网格解法 ,求出了有限长滚子线接触热弹流润滑的完全数值解 .结果表明 :在滚子的中部 ,油膜压力、温度和最小膜厚与无限长线接触热弹流润滑的解几乎一致 ;在滚子端部的圆角处 ,油膜压力、温度和最小膜厚与中部均显著不同 ,且最大油膜压力、最大油膜温度和最小油膜厚度均发生在此处 ,端部圆角半径对弹流润滑性能有显著影响 .同时 ,将有限长线接触热解与有限长线接触等温解进行了比较 .     

多重网格法计算有限长线接触热弹流问题初值对求解过程的影响

对有限长线接触热弹流数值求解中压力初值和温度初值的设置进行调整和改进,采用Hertz压力分布修正和无限长线接触弹流压力作为2种压力初值的设置方案,并提出增加温度初值和设定温度曲线2种温度初值设置方法.结果表明:采用无限长线接触弹流压力作为压力初值更为有效,可以直接计算最大Hertz接触压力pH=1.45 GPa时的重载荷工况;2种温度初值设置方法均能够使程序计算效率得到提高,其中采用设定温度曲线的方法可以使温度分布的总趋势快速显现,迭代次数减少25.5%左右.     

载荷和电压对纯铜滚动载流摩擦学性能的影响

基于FTM-CF100型滚动载流摩擦试验机,研究了纯铜滚动载流摩擦副在不同载荷和外加电压下的性能变化规律,并利用扫描电子显微镜、白光干涉三维形貌仪等对摩擦表面进行微观分析,揭示了稳态运行时性能变化的机理.研究表明:增加载荷和增加电压均促进粗糙接触表面发生形变,真实接触面积的增加降低了接触电阻,摩擦区域粗糙度的改善提高了动态摩擦系数和动态电阻的稳定性.但电阻热促进材料黏着,因而同一载荷下载流摩擦系数高于单纯机械摩擦系数,且随外加电压的增加持续增加.     

弹塑性微凸体侧向接触相互作用能耗

传统的结合面研究多基于光滑刚性平面与等效粗糙表面接触假设,忽略了结合面上微凸体侧向接触及相邻微凸体之间的相互作用,这导致理论模型与实际结合面存在较大出入.针对承受法向静、动态力的机械结合面,从微观上研究了微凸体侧向接触及相互作用的接触能耗.将法向静、动态力分解为法向分力和切向分力,获取弹性/弹塑性/塑性阶段考虑微凸体侧接触及相互作用的加、卸载法向分力-变形和切向分力-位移的关系.通过力的合成定理,从而获取加、卸载法向合力与总变形之间的关系,由于法向分力产生的塑性变形及切向分力产生的摩擦,导致加载、卸载法向合力-总变形曲线存在迟滞回线.通过对一个加、卸载周期内的法向合力-总变形曲线积分,获得一个周期的微凸体接触能耗,包括应变能耗及摩擦能耗.仿真分析表明:微凸体在3个阶段的能耗均随变形的增大而非线性增大.微凸体侧向接触角度越大,能耗越大,且在弹性阶段最为明显.在弹性阶段,仅存在侧向的摩擦能耗,故结合面在低载荷作用下必须采用双粗糙表面假设.在塑性阶段,由于微凸体接触能耗为应变能耗,且接触角对其能耗影响甚微,故结合面在大载荷作用下可采用单平面假设对其进行研究.相对于KE和Etsion模型,本文提出的模型与Bartier的实验结果更吻合.     

粗糙表面接触研究进展

工程中的任何接触表面都不会是绝对光滑的,对于某些特殊接触问题必须考虑表面形貌的接触效应.粗糙表面接触研究是一门年轻的交叉学科.它主要研究粗糙表面接触力学,接触导电和导热,接触密封,接触振动和噪声,接触刚度,骨关节接触等问题,涉及固体力学,流体力学,随机过程及概率统计,计量学,电学和传热学,振动理论以及生物学等学科知识.本文综述了粗糙表面接触的研究进展.      

Conductance of rough random profiles

Recently, the real contact area and the compliance and electrical resistance for a rough surface defined with a Weierstrass series have been studied under the assumption that superposed self-affine sine waves had well separated wavelengths, extending the celebrated procedures pioneered by Archard [Archard, J.F., 1957. Elastic deformation and the laws of friction. Proc. R. Soc. Lond. A 243, 190–205]. Here, more realistic fractal rough surface profiles are considered, by using the Weierstrass series with random phases, and with much lower separation of the various scales, using a full or a hybrid numerical/analytical technique. A non-linear layer algorithm is developed which is a very efficient approximate tool to study this problem, avoiding the need for averaging over various realizations of profiles with random phases. The multiscale problem is solved by a cascade of 2-scales problems, each of which is solved with a few elements for an imposed contact area, deriving load as a function of indentation and the conductance by differentiation using Barber’s analogy theorem.Dimensionless results for the conductance as a function of applied pressures show that the conductance seems to be close to a power law at low loads, and is nearly linear at intermediate loads (following the normalized single sinusoidal case except at the origin). At high loads, the conductance becomes strongly dependent on fractal dimension because of weak dependence on the contribution of small wavelength scales (higher order terms in the series). Since roughness tends to be squeezed out, the conductance tends to increase more than linearly (more so, the smaller is the fractal dimension). However, another limit could be found in terms of the finite size of the specimen, which may suggest reaching a finite limit. The resulting curves could then be sigmoidal, as confirmed by qualitative comparisons with experiments in the literature.     

Mechanics of advancing pin-loaded contacts with friction

This paper considers finite friction contact problems involving an elastic pin and an infinite elastic plate with a circular hole. Using a suitable class of Green's functions, the singular integral equations governing a very general class of conforming contact problems are formulated. In particular, remote plate stresses, pin loads, moments and distributed loading of the pin by conservative body forces are considered. Numerical solutions are presented for different partial slip load cases. In monotonic loading, the dependence of the tractions on the coefficient of friction is strongest when the contact is highly conforming. For less conforming contacts, the tractions are insensitive to an increase in the value of the friction coefficient above a certain threshold. The contact size and peak pressure in monotonic loading are only weakly dependent on the pin load distribution, with center loads leading to slightly higher peak pressure and lower peak shear than distributed loads. In contrast to half-plane cylinder fretting contacts, fretting behavior is quite different depending on whether or not the pin is allowed to rotate freely. If pin rotation is disallowed, the fretting tractions resemble half-plane fretting tractions in the weakly conforming regime but the contact resists sliding in the strongly conforming regime. If pin rotation is allowed, the shear traction behavior resembles planar rolling contacts in that one slip zone is dominant and the peak shear occurs at its edge. In this case, the effects of material dissimilarity in the strongly conforming regime are only secondary and the contact never goes into sliding. Fretting tractions in the forward and reversed load states show shape asymmetry, which persists with continued load cycling. Finally, the governing integro-differential equation for full sliding is derived; in the limiting case of no friction, the same equation governs contacts with center loading and uniform body force loading, resulting in identical pressures when their resultants are equal.     

Stability of tribotechnical laminated coatings subjected to tracing loads

The problems of surface stability of laminated coatings subjected to the combined effect of tracing surface loads and a stationary temperature field is considered. The material of the layer and the base are considered linearly elastic and trasversally isotropic. Fulfillment of conditions of absolutely rigid force and ideal contacts are assumed between the individual elements of the laminar medium. The subcritical stress state of the laminar medium under consideration is piecewise-homogeneous. Interbranch Engineering Center “Tribotekhnika”, Dnepropetrovsk, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 35, No. 6, pp 32–38, June, 1999.     

介观双粗糙弹塑性流体动力润滑界面法向接触刚度模型

弹性流体动力润滑状态通常出现在机械高副零部件的点/线接触部位,如齿轮、轴承和蜗轮蜗杆等. 宏观上点/线接触在介观层面表现为两粗糙表面的接触,在微观层面上则又表现为微凸体间的接触. 由于在中/重载荷作用下,粗糙表面上的微凸体发生接触后会产生弹塑性/塑性变形,从而使得两粗糙表面的弹流润滑接触转变为弹塑性流体动力润滑接触. 此外,界面的接触刚度决定了机械装备的整机刚度. 为了精确获得弹性流体动力润滑状态下界面法向接触刚度及其主要影响因素,基于界面的法向接触刚度由固体接触刚度和润滑油膜刚度两部分构成的思想,根据固体弹塑性理论和流体动力学理论,分别对界面间微凸体侧接触及部分膜流体动力润滑进行分析,从微观入手揭示双粗糙表面弹塑性流体动力润滑接触机理,进而建立考虑微凸体侧接触弹塑性变形的流体动力润滑界面法向接触刚度模型. 通过仿真分析,揭示了法向载荷、卷吸速度、表面粗糙度及润滑介质特性等因素对润滑界面法向接触刚度的影响规律. 研究表明:在相同速度、粗糙度及润滑油黏度的工况下,固体接触刚度和油膜接触刚度均随着法向接触载荷的增加呈非线性增大;在相同载荷、速度及润滑油黏度的工况下,接触表面粗糙度越大,表面形貌对于润滑状态的影响较强,固体接触刚度占界面总刚度的主要部分,界面主要由固体承载;在相同载荷、粗糙度及润滑油黏度工况下,随着卷吸速度的增大,固体接触刚度逐渐减小,油膜刚度占界面总刚度的主要部分;在相同载荷、粗糙度及速度工况下,随着润滑油黏度的增大,油膜刚度基本保持不变,固体接触刚度基本不受润滑油黏度的影响. 通过理论建模准确获得单位面积弹塑性流体动力润滑结合面法向接触刚度,对改善机械装备动态性能、提高机械装备的可靠性具有重要的理论和实际意义.      

A Simplified Model for Calculating Hydrodynamic Lubrication Film Thickness in Elastoplastic Line Contacts

The present paper proposes a simplified model for calculating hydrodynamic lubrication film thickness in elastoplastic line contacts. According to the Saint-Venant’s principle, the pressure in the contact is taken as uniformly distributed, this gives the contact surface elastic deformations in the inlet zone far away from the contact center close to real ones while gives those close to the contact center greater than real ones. This treatment is validated for hydrodynamic lubricated elastic contacts for relatively light loads and high rolling speeds. It gives the film thickness at the contact center a little higher than that calculated based on the real elastic model. The treatment is extended to a hydrodynamic lubricated elastoplastic line contact. The contact surfaces in the inlet zone are assumed as elastic and their deformations are calculated based on the uniform pressure distribution in the elastoplastic contact area. An inlet zone analysis is taken for obtaining the calculating equation of the hydrodynamic film thickness at the contact center. The equation overestimates the central film thickness but gives a satisfactory film thickness prediction for the heavy load which gives significant plastic deformations in the elastoplastic contact. It is found that when the load is lighter than 0.6 w _pc , the contact can be taken as elastic when calculating the central film thickness, while when the load is heavier than 0.6 w _pc , the contact can be taken as fully plastic; Here w _pc is the critical load for the contact fully plastic deformation. The plastic deformation in an elastoplastic line contact is found to reduce the hydrodynamic lubrication film thickness in the contact. This reduction is greater for higher rolling speeds and heavier loads. However, it is significantly dropped with increasing surface hardness.     

周期性载荷对非牛顿热弹性流体动力润滑的影响

本文应用数值方法分析了周期性动载荷对线接触热弹性流体动力润滑的影响,使用Ree-Eyring流变模型来描绘润滑剂的非牛顿性质。结果显示,周期性动载可以阻滞油膜的变化并在一定程度上增加膜厚。频率很高的动载可以显著改变压力和温度的分布规律,但润滑剂的非牛顿性质在中轻载条件下并不重要。     

690合金管在室温干态下的冲击微动磨损特性研究

采用小载荷冲击试验机研究了690合金传热管与405不锈钢块在室温干态不同载荷条件下的微幅冲击磨损行为.其中管采用悬臂梁式固定,与冲击配副采取线接触方式,冲击频率为10 Hz,循环次数为106次,试验载荷选取5、10、20和40 N.结果表明:在室温干态条件下,随着载荷的增加,690合金管的磨损体积增大;加工硬化效应增强,磨损表面硬度增加越大.冲击磨损过程中材料表面发生摩擦氧化行为,690合金管的冲击磨损机制主要是磨粒磨损、剥落,且随着载荷增加,磨粒磨损及氧化行为加剧.