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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. 相似文献
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针对润滑状态下结合面的接触刚度问题,建立一种混合润滑状态下粗糙表面接触刚度等效薄层模型,将接触界面的总刚度等效为固体接触刚度和润滑剂接触刚度之和,研究不同实际接触面积下的表面形貌和润滑剂类型对法向接触刚度的影响,并讨论固体刚度和润滑剂刚度占总法向刚度的比例。结果表明:粗糙界面的法向接触刚度随法向载荷的增加而增加,且混合润滑状态下的接触刚度大于干接触条件下的接触刚度;在初始接触时,法向接触刚度敏感地依赖于润滑性能;随着实际接触面积的增大,表面形貌对接触刚度的影响变得更加明显。 相似文献
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基于分形理论,利用双变量Weierstrass-Mandelbrot函数模拟三维分形结合面,建立尺度相关的三维分形结合面法向接触刚度模型。推导出各等级微凸体发生弹性、弹塑性以及完全塑性变形的存在条件。确定结合面上各等级微凸体的面积分布密度函数,推导出法向接触刚度和法向接触载荷的解析表达式。计算结果表明:当结合面上的微凸体只能发生弹性变形,即自身等级小于弹性临界等级的微凸体,该部分微凸体引起的法向接触刚度和对应法向载荷关系呈非线性。当微凸体的等级大于弹性临界等级,在结合面接触过程中,微凸体弹性变形引起的法向接触刚度与对应的法向载荷关系为线性,非弹性变形引起的法向接触刚度与法向载荷关系为非线性。微凸体的等级范围对结合面的刚度影响较大,在相同的法向载荷作用下,高等级微凸体的结合面产生较高的法向接触刚度,即结合面越平整,结合面的法向刚度越高。 相似文献
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An improved elastic contact model for a single asperity system is proposed accounting for both the effects of bulk substrate
and asperity deformations. The asperity contact stiffness is based on the Hertzian solution for spherical contact, and the
bulk substrate stiffness on the solution of Hertzian pressure on a circular region of the elastic half-space. Depending on
the magnitude of the applied load, as well as the geometrical and physical properties of the asperity and bulk materials,
the bulk substrate could have considerable contribution to the overall contact stiffness. The proposed single asperity model
is generalized using two parameters based on physical and geometrical properties, and is also verified using finite element
analysis. A parametric study for a practical range of geometric and physical parameters is performed using finite element
analysis to determine the range of validity of the proposed model and also to compare it with the Hertz contact model. The
single asperity model is extended to rough surfaces in contact and the contact stiffness from the proposed model and the simpler
Greenwood–Williamson asperity model are compared to experimental measurements. 相似文献
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A temperature analysis of dry sliding fully plastic contact is extended to calculate the asperity temperatures between a sliding lubricated rigid smooth plane and a stationary elastic rough surface. First, surface roughness is generated numerically to have a Gaussian height distribution and a bilinear autocorrelation function. Lai and Cheng's elastic rough contact computer program is then used to determine the asperity contact loads and geometries of real contact areas. Assuming different frictional coefficients for shearing the lubricant film at the noncontact areas, shearing the surface film at the asperity contacts and shearing the oxide film as the asperity temperature exceeds a critical temperature, asperity temperature distributions can be calculated. Eight cases in Durkee and Cheng's scuffing tests of lubricated simple sliding rough contacts are simulated by using 20 computer-generated rough surfaces. The results show that scuffing is correlated to high-temperature asperities which are above the material-softening temperature. 相似文献
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基于各向异性分形几何理论,考虑微凸体变形特点、表面微凸体承受法向载荷的连续性和光滑性原理,以及区分微凸体分别处于弹性、塑性变形时的一个微凸体实际微接触面积,建立固定结合部法向接触力学模型。采用二变量Weierstrass-Mandelbrot函数模拟各向异性三维分形轮廓表面。推导出划分弹塑性区域的临界弹性变形微接触截面积、结合部量纲一法向载荷、结合部量纲一法向接触刚度的数学表达式。数值仿真结果表明:当表面形貌的分形维数、分形粗糙度一定时,真实接触面积随着结合部法向载荷的增大而增大;结合部法向接触刚度随着真实接触面积、结合部法向载荷、相关因子或材料特性参数的增大而变大;当分形维数由1变大时,结合部法向接触刚度随着分形维数的变大而增大;当分形维数增加到趋近于2时,结合部法向接触刚度有时却会随着分形维数的增加而降低。结合部法向接触力学模型的构建,有助于分析固定接触表面间的真实接触情况。 相似文献
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A model of molecularly thin lubricant layer behavior for rough, sliding contact is presented in this work as a function of lubricant layer morphology. Building on previous work by the authors where the lubricant layer was assumed to be uniform in thickness and morphology, lubricant contributions to contact are presently treated at the asperity level and the effects of lubricant bonding ratio and coverage are accounted for. Effective stiffnesses for lubricated asperities are used to calculate the bearing and shear forces, while variable surface energy is modeled at the asperity level and used within an improved continuum adhesive formulation. Contributions from asperities in lubricant and solid contact for partial coverage are determined within the context of a statistical mechanics model. The proposed model can be used to study the mixed nanolubrication regime expected during light contact or “surfing” recording in magnetic storage, where sustained nanolubricant contact would partially deplete mobile molecules from the contact interface. 相似文献
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Different statistical micro-contact models including Greenwood–Williamson (GW), Chang–Etsion–Bogy (CEB), Zhou–Maietta–Chang (ZMC), Kogut–Etsion (KE) and Jackson–Green (JG) are employed together with the bulk deformation of the bounding solids to predict dry rough line-contact characteristics such as the apparent pressure profile, contact width and real area of contact. The approach involves solving the micro-contact models and separation formulas simultaneously. Comparison of different contact models reveals that the use of elastic–plastic micro-contact models predicts a lower maximum normal pressure and a greater contact width and real contact area compared to the GW model. Further, based on the results of numerical simulations, useful relationships are provided for the prediction of the maximum contact pressure, contact width, real area of contact and pressure distribution. 相似文献
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Contact modeling of two rough surfaces under normal approach and with relative motion is carried out to predict real area
of contact and surface and subsurface stresses affecting friction and wear of an interface. When two macroscopically flat
bodies with microroughness come in contact, the contact occurs at multiple asperities of arbitrary shapes, and varying sizes
and heights. Deformation at the asperity contacts can be either elastic and/or elastic-plastic. If a thin liquid film is present
at the interface, attractive meniscus forces may affect friction and wear. Historically, statistical models have been used
to predict contact parameters, and these generally require many assumptions about asperity geometry and height distributions.
With the advent of computer technology, numerical contact models of 3-D rough surfaces have been developed, particularly in
the past decade, which can simulate digitized rough surfaces with no assumptions concerning the roughness distribution. In
this article, a comprehensive review of modeling of multiple-asperity contacts in dry and wet conditions is presented. Contact
models for homogeneous and layered, elastic and elastic-plastic solids with and without tangential loading are presented.
The models reviewed in this paper fall into two groups: (a) analytical solutions for surfaces with well-defined height distributions
and asperity geometry and (b) numerical solutions for real surfaces with asperities of arbitrary shape and varying size and
height distributions. Implications of these models in friction and wear studies are discussed.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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J. I. McCool 《摩擦学汇刊》2013,56(3):431-440
The details are given of a computer model for performing a state-of-the-art tribological assessment of the performance of a lubricated concentrated rolling/sliding/spinning/contact comprising general anisotropic rough surfaces. The name chosen for this program is TRIBOS. It computes: 1. The contact ellipse dimensions and area 2. The elastohydrodynamic (EHD) film thickness both at the plateau and at the constriction that forms at the rear of a lubricated concentrated contact under fully flooded (un-starved) and isothermal lubricant inlet conditions 3. The apportionment of the applied load between the asperities and the lubricant film 4. The magnitude and direction of the tractive force transmitted between the contacting bodies by the combined effects of (a) shearing of the fluid film and (b) coulomb friction between contacting asperities 5. The mean number of asperity contacts and the real contact area, i.e. the total contact area of the elastically deformed asperities 6. A film thickness correction factor accounting for lubricant starvation in the contact inlet 7. A film thickness correction factor accounting for a viscosity decrease of the inlet oil due to fluid heating 8. An index of surface fatigue behavior The program is a synthesis of computational tools from the current literature for the computation of fluid film thickness and traction, and a general asperity simulation model for the elastic contact of anisotropic rough surfaces. In the example given, it is used to perform a comparative evaluation of the performance of 18 combinations of 9 surface roughnesses and 2 lubricants in a traction drive contact. 相似文献
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在涉及微凸体侧接触的粗糙表面接触建模过程中,通常需要假定微凸体之间侧接触的角度分布规律。提出一种考虑微凸体水平距离分布及相互作用的结合面法向接触刚度建模方法,该方法不再需要假定角度分布规律,而是基于首次发现的单个粗糙表面微凸体水平距离正态分布规律,根据统计学理论进行考虑微凸体相互作用的结合面法向接触刚度建模。对模型进行数字仿真发现:结合面法向接触刚度与接触载荷均随着微凸体水平距离标准差的减小而增大,并且考虑微凸体相互作用会使得结合面的法向接触刚度减小。结合面法向接触刚度随弹性模量的增大而减小,随材料硬度的增大而增大。通过有限元仿真结果与模态试验结果对比可知,基于模型的有限元仿真前三阶固有频率与试验所得结果基本吻合,并且误差相对GZQ模型更小。旨在通过研究单个粗糙表面微凸体水平距离分布,突破侧接触建模时接触角度分布函数仍需假设的理论瓶颈,为更加准确地预测结合面接触特性奠定基础。 相似文献
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结合面接触刚度直接影响了机械设备的整机动态特性,为了建立更为准确的接触刚度模型,以分形几何理论为基础,利用单一微凸体承受局部载荷时的弹性变形特性,并基于域扩展因子引入微接触截面积分布函数,推导了考虑表面微凸体相互作用影响的结合面接触刚度分形模型。为了验证所提出模型的准确性,通过三维非接触式测量,获得了试验试样的表面轮廓数据,并根据结构函数法,计算了各个试样的表面分形参数,进而将理论接触刚度与试验结果对比分析,结果表明:法向接触刚度的增长速率与粗糙面表面临界接触面积有关,临界接触面积决定了结合面内的弹性变形占比。考虑微凸体相互作用后,所提出模型的预测曲线更加符合试验中法向载荷与接触刚度的关系。 相似文献
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《Wear》1986,113(3):353-370
The contact mechanism between a cylinder and a rough plate is theoretically analysed for mixed, elastic and plastic contacts of asperities. The analysis leads to the result that the contact pressure, the contact width and the compliance between the cylinder and plate differ considerably from those calculated from the Hertz equation and the Lundberg equation when the surface roughness in contact is greater and the normal load is lower. It is also found that the difference between the calculated contact width and the compliance based on mixed asperity contacts and those based on elastic or plastic asperity contacts is small. To confirm the analysed results, the contact width between the cylinder and the rough steel or rough copper plate was measured by means of evaporated carbon and lamp black film coatings on the rough surfaces. The compliance between the surfaces was also measured using differential transformers. Little difference was found between the analysed results and the experimental results. 相似文献
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新的粗糙表面弹塑性接触模型 总被引:18,自引:3,他引:15
提出一种新型的粗糙表面弹塑性微观接触模型.该模型的建立基于接触力学理论和接触微凸体由弹性变形向弹塑性变形及最终向完全塑性变形的转化皆是连续和光滑的假设.研究单个微凸体在载荷逐渐增加时的变形规律,并重点推出弹塑性变形区间的接触方程.在此基础上应用概率统计理论导出了粗糙表面的接触载荷、平均分离和实际接触面积之间的数学关系式.在不同的塑性指数和载荷条件下,该模型与GW弹性模型和CEB弹塑性模型就实际接触面积和法向距离的预测结果进行了对比.结果表明,在同样塑性指数和载荷条件下比GW模型预测的实际接触面积大但法向距离小,且两者的差距随塑性指数和载荷的增加而增大.因此该模型的预测结果更加符合人们的试验观察和直觉,能够更加科学和合理地描述两个粗糙表面的微观和宏观接触状态. 相似文献
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基于分形几何理论,考虑微凸体因应变硬化而造成弹塑性变形阶段硬度随变形量变化而变化,建立结合面第一、第二弹塑性变形阶段单次加载刚度分形模型。推导出在计入硬度变化的情况下,单个微凸体在弹塑性变形阶段法向接触刚度与接触面积之间的关系式,进而得出结合面在弹塑性变形阶段法向接触刚度与接触面积、接触载荷之间量纲为一的关系式,并通过仿真分析得出相关参数对结合面法向接触刚度的影响。仿真结果显示:考虑硬度变化时,结合面量纲一法向接触刚度的值与法向实际接触载荷、实际接触面积之间存在关系;结合面法向接触刚度随着分形维数D的增大而增大;分形维数一定时,结合面法向接触刚度随表面长度尺度参数G值增大而增大。 相似文献
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This paper presents a relatively complete numerical solution to time-dependent micro-thermoelastohydrodynamic lubrication in line contacts subjected to constant load and entraining velocity. Sinusoidal functions are employed to model the traverse roughness on contact surfaces. The Eyring model is used to describe the non-Newtonian flow of the lubricant. With respect to time, the problem is treated as a periodic one so that most variables, such as pressure, film thickness and temperature, can be considered as periodic functions. An efficient algorithm is developed, and a number of cases are solved. The results indicate that the lubricant squeeze induced by the motion and interaction of rough surfaces significantly affects the solution of micro-thermoelastohydrodynamic lubrication. 相似文献
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The Greenwood and Williamson theory of random rough surfaces in contact has been combined with established elastohydrodynamic theory to provide a theoretical approach to highly loaded lubricated contacts in which the load is shared between hydrodynamic pressure and asperity contact. It is shown that, provided a major part of the load is carried by elastohydrodynamic action, the separation between the two rough surfaces is given (to a first approximation) by the film thickness which would exist between two smooth surfaces under the same conditions of load, speed and lubricant. It then follows that the asperity pressure, both real and apparent, is determined primarily by the ratio of theoretical film thickness to the combined roughness of the two surfaces (ho/σ). A corollary of this result is that an increase in total load, which has only a small influence on the film thickness, is carried by an increase in fluid pressure and only gives rise to a small increase in asperity contact pressure. 相似文献
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The paper considers elastic contact of rough surfaces and develops a simple analytical expression for the stiffness of the contact under tangential loading, which predicts that the contact stiffness is proportional to normal load and independent of Young??s Modulus. The predictions of this model are compared to a full numerical analysis of a rough elastic contact of finite size. The two approaches are found to be in good agreement at low loads, when the asperity spacing is large, but the numerical approach predicts much lower stiffnesses at medium and high loads. It is shown that the overall stiffness cannot exceed that of the equivalent smooth contact, and a simple means of modifying the analytical approach is proposed and validated. 相似文献