含多粗糙峰涂层等效应力的有限元分析

研究刚性平面与含粗糙峰涂层在二维与三维模型下的弹性接触问题,采用有限元法分析涂层弹性模量比、涂层厚度、粗糙峰间距、刚性平面压下深度对涂层粗糙峰表面、涂层/基体界面分布及基体等效应力分布的影响。计算结果表明压下深度对三维涂层粗糙峰表面最大应力的影响最大,涂层厚度、涂层/基体弹性模量比、粗糙峰间距的变化对应力值影响逐渐减小;增大涂层厚度、减小压下深度和粗糙峰间距、降低弹性模量比会使得三维接触模型最大等效应力值显著降低;增加涂层粗糙峰数和涂层厚度、同时降低涂层弹性模量有助于提高涂层/基体界面结合强度。相对于二维接触模型来说三维接触模型在粗糙峰表面的等效应力增大,造成这种变化的主要原因是由于涂层表面粗糙峰之间的等效应力叠加引起的。该研究为涂层粗糙峰及涂层/基体界面强度的应力分析提供依据。     

铝硅聚苯酯封严涂层切向载荷作用下应力分布的有限元分析

在封严涂层弹性模量试验的基础上,建立封严涂层摩擦有限元模型,对民航发动机铝硅聚苯酯封严涂层的摩擦过程进行有限元分析。分析了摩擦系数、涂层厚度和粘结层厚度等参数对涂层/粘结层/基体系统应力分布的影响。分析结果表明:在切向载荷的作用下,随着摩擦系数的增大,涂层表面、涂层与粘结层的界面以及粘结层和基体界面处的应力峰值均增大;随着涂层厚度的增大,涂层表面及两界面处的应力峰值均减小,但当涂层厚度达到一定程度后,继续增加涂层厚度对降低应力峰值的效果不明显;粘结层厚度在一定范围内的变化对涂层表面和涂层与粘结层界面处的应力变化影响不大,但随着粘结层厚度的减小,粘结层与基体界面处的应力峰值均增大。     

夹杂物对轴承滚动接触应力场的影响分析

建立基于无限边界的含夹杂物滚动轴承赫兹接触有限元模型,分析夹杂物位置深度、夹杂物与基体材料的弹性模量比和不同类型夹杂物对轴承滚动接触应力分布的影响,分析脂润滑状态下夹杂物对滚动接触应力场的影响,探究了接触区摩擦因数对次表层应力场的影响。结果表明:夹杂物对应力场的影响随其位置深度的增加而减弱;软夹杂物产生的应力集中效应随其弹性模量增大而减小,硬夹杂物产生的应力集中效应随其弹性模量增大而增大;在其他参数相同时,具有不规则棱角边缘的AlN夹杂物对应力场的影响更明显;切向摩擦力导致最大Von Mises应力位置向零件表面偏移,当接触区摩擦因数增大到一定数值后,轴承中最先发生微观疲劳裂纹的位置从夹杂物附近转移到零件表面。     

滚动接触状态下固体润滑薄膜界面损伤失效行为分析

以内聚力模型（CZM）为基础建立薄膜-基体承载系统的有限元分析模型,采用双线性本构关系描述薄膜-基体结合界面的承载及损伤失效行为,通过分析法向和切向载荷作用下界面的承载状态,研究了摩擦因数、薄膜弹性模量、膜厚对薄膜-基体承载系统的界面应力、分离位移、能量释放率的影响,结果表明：摩擦因数增大会导致接触前沿界面承载状态恶化,从而增加界面损伤和脱附失效的风险;薄膜弹性模量增大可以减小接触前沿界面损伤区域和损伤程度,当薄膜弹性模量小于基体弹性模量时界面承载性能急剧恶化;随膜厚增大,界面切向损伤区域和损伤程度先减小后增大,膜厚为0.2倍接触半宽时有利于提升薄膜-基体结合界面的承载性能。     

无隔水管泥浆回收钻井系统吸入模块密封胶芯非线性摩擦接触分析

建立无隔水管泥浆回收钻井系统密封胶芯及钻具二维轴对称有限元模型,使用非线性有限元方法计算密封胶芯与钻具间的接触压力大小,验证密封胶芯在无隔水管泥浆回收钻井中的可行性。研究摩擦因数变化对接触压力的影响,分析密封胶芯Mises应力峰值和钻具与胶芯间的摩擦力分布规律。结果表明:摩擦因数与胶芯密封面和钻具间的接触压力成非线性关系,胶芯主密封段接触压力随摩擦因数增大而减小,而胶芯锥形密封段和凸鼻形密封段的接触压力随摩擦因数增大而增大;胶芯Mises应力随摩擦因数增大而变大,且胶芯与钻杆接头上端接触时Mises应力峰值最大,容易导致胶芯破坏;胶芯与钻具间的接触面积基本不随摩擦因数变化而变化,摩擦力随摩擦因数的增大近似成线性增加;胶芯与钻杆接头接触时,摩擦力较大且增长显著,说明胶芯与接头接触时更容易发生磨损。     

宽温度域工况下汽车水泵O形密封圈的密封性研究

针对汽车发动机水泵O形橡胶密封圈宽温度域的工况特点,构建其与温度相关的Mooney-Rivlin材料模型,探讨冷却液温度、压力、摩擦因数等对O形密封圈接触压力、等效应力以及密封性的影响。研究表明：温度的升高将引起接触压力及等效应力的峰值呈幂指数减小,导致密封可靠性降低,但在宽温度域（-40~130℃）工况下,接触压力的峰值始终远大于液体压力,因此该密封圈具有可靠的密封性;液体压力的增大虽然会引起接触压力峰值增大,但其增大的速度比液体压力增大的速度小,因此将引起密封可靠性下降;摩擦因数对密封可靠性的影响不大。     

基于分形理论的滑动摩擦表面接触力学模型

依据分形理论,考虑微凸体变形特征及摩擦作用的影响建立滑动摩擦表面接触力学模型。采用一个三次多项式来表达弹塑性变形微凸体的接触压力与接触面积的关系,从而满足在变形状态转变临界点处的微凸体接触面积与接触压力转化皆是连续和光滑的条件。推导出滑动摩擦表面临界弹性变形微接触面积、临界塑性变形微接触面积、量纲一真实接触面积的数学表达式。理论计算结果表明,表面形貌一定时,真实接触面积随着载荷的增大而增大;载荷一定时,真实接触面积随着特征尺度系数的增大而减小,随着分形维数的增大先增大后减小;当表面较粗糙时,摩擦因数对真实接触面积的影响很小;随着表面光滑程度的增大,摩擦因数对真实接触面积的影响增大,真实接触面积随着摩擦因数的增大而增大,特别是当摩擦因数较大时,真实接触面积增大的幅度也较大。接触力学模型的建立,为研究滑动摩擦表面间的摩擦磨损性能提供了依据。     

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。     

热机耦合作用下冲击螺杆钻具传动轴密封性能分析*

针对高温、三维复合运动(往复+旋转)耦合作用下冲击螺杆钻具传动轴总成密封失效问题,设计氢化丁腈橡胶热老化试验,基于热老化试验数据建立热老化效应冲击螺杆钻具传动轴总成O形密封圈三维有限元模型,采用有限元方法研究流体压力、温度、摩擦因数和往复速度对传动轴总成O形密封圈静密封及动密封性能的影响。结果表明:静密封状态下高应力区位于O形密封圈右侧,高接触压力区位于O形密封圈内接触面、外接触面和侧面,最大von Mises应力和最大接触压力随着流体压力和温度的增大而增大,最大接触压力整体上随着摩擦因数的增大而减小;动密封状态下最大von Mises应力和最大接触压力在往复速度为0.4 m/s和摩擦因数为0.25出现异常规律,最大von Mises应力和最大接触压力随着流体压力和温度的增大而增大。由此建议密封圈在静密封和动密封状态,在往复速度小于0.4 m/s和较小摩擦因数下运行。     

基于ANSYS的直齿圆柱齿轮摩擦特性分析

基于CATIA平台,通过参数化方法建立渐开线直齿圆柱齿轮模型,以IGES文件格式导入ANSYS,对齿轮齿廓进行摩擦特性分析。在只改变摩擦因数的情况下,分析齿轮啮合过程中轮齿受到的接触应力、摩擦力和接触压力的变化规律。结果表明:当摩擦因数小于0.3时,随着摩擦因数的增加,接触应力、摩擦力以及接触压力都明显增加;当摩擦因数在0.3~0.8之间时,接触应力、摩擦力以及接触压力随摩擦因数的增加而变化的幅度变小,但是总体趋势是增加的。而齿轮接触应力、摩擦力和接触压力的增加都会加速轮齿失效和缩短齿轮疲劳寿命,因此,减小摩擦因数是提高齿轮抗点蚀能力和延长疲劳寿命的一种可行方法。     

The maximum tensile stres on a hard coating under sliding friction

In the friction of a hard coating the maximum tensile stress in the sliding direction generated at the friction surface is important for predicting crack propagation in the coating. The finite element method is employed to evaluate the stress field in the hard coating and the substrate under frictional loads, and the ratio between the values of maximum tensile stress and the maximum contact pressure is calculated under various contact conditions. Finally, a simple equation is introduced for the calculation of the maximum tensile stress at the friction surface. This equation is a function of friction coefficient, maximum contact pressure, coating thickness, contact width and elastic moduli of coating and substrate, and gives the value of the maximum tensile stress which is affected by the existence of the substrate.     

Stress analysis of cushion form bearings for total hip replacements.

Cushion form bearings comprise a thin layer of low elastic modulus material on the articulating surface of the bearing, which can deform to help preserve a film of lubricant between the bearing surfaces and therefore reduce friction and wear. The long-term function of this type of bearing is dependent on the strength and durability of this compliant layer. Finite difference and finite element methods have been used to analyse the stress distribution in the compliant layer of cushion form bearing for artificial hip joints under physiological loading conditions. A good agreement between finite difference and finite element methods was found. Under normal loading, the highest value of the maximum shear stress was found to be at the interface between the compliant layer and the more rigid substrate close to the edge of the contact. The values of maximum shear stress in the centre of the contact close to the articulating surface were lower than in the equivalent Hertzian contact. A friction force acting at the surface had little effect on the stress distribution for coefficients of friction less than 0.05. However, for higher values of friction coefficient (larger than 0.2), corresponding to inadequate lubrication, the maximum shear stress increased by a factor of four and was found to be located at the surface. The analysis predicts that the mode of failure will be at the interface with the substrate under fluid film or mixed lubrication conditions and at the articulating surface when the bearing runs dry with higher levels of friction. Both failure modes have been observed experimentally under the conditions specified.     

A multiscale mechanics approach for modeling textured polycrystalline thin films with nanothickness

A multiscale method is proposed for calculating elastic constants of textured polycrystalline thin films of nanothicknesses. In this method the molecular simulation and finite element method are hierarchically employed. The elastic constants for each single crystal are first calculated through the simulations of on- and off-axis tension tests of the single crystal using molecular statics. Subsequently, the constitutive relations for the single crystal are used in conjunction with a finite element code to study the macro-mechanical deformation and stresses in textured polycrystalline nanofilms. The result indicates that both film thickness and grain size influence the macro-Young's modulus and Poisson's ratio of the nanofilm. Specifically, for nickel, the value of the macro-Young's modulus decreases as film thickness decreases and increases as grain size decreases. The value of the macro-in-plane Poisson's ratio increases as the thickness decreases or grain size increases.     

Effect of friction and adhesion on the load–displacement of a spherical probe in contact with a compliant incompressible elastic coating

The mechanical properties of thin films are extracted from the measured load displacement relation in a contact test conducted using micro or nano instruments. At this micro or nano force scale, the adhesion and friction operating between the test tip and thin film surface will contribute to the deformation. The well established Johnson–Kendall–Roberts (JKR) theory provided a relationship between the normal load and elastic central displacement for the adhesion contact. But because of its semi-infinite half-space hypothesis, the standard JKR theory is not applicable to thin film contact problem. Experimental verification demonstrates the numerical version of JKR theory is suitable for compliant thin film adhesion analysis, but it does not include the friction effect. In this paper, the load–displacement relation of totally bonded friction contact with adhesion is studied and compared with that of frictionless case. The practical thin film contact will lie in these two limits. The effect of friction to load and displacement seems very small except for the transition range from film to substrate response. Empirical expressions for the contact compliance are obtained from the detailed finite element study.     

Soft EHL for transversely isotropic materials

The elastohydrodynamic lubrication (EHL) characteristics of transversely isotropic materials are investigated. A finite element method (FEM) is utilized to solve the Reynolds equation, elastic equation, and load balance equation simultaneously on a ball-on-plane equivalent model. A simplified problem related to cornea and contact lens during blinking is studied. The pressure and oil film thickness distributions, surface deformation, and friction coefficient are discussed for various material properties (Young's modulus) and operating conditions (sliding velocity and load). Results reveal that the effects of soft transversely isotropic materials on lubricating performances are significant, which are helpful to further investigate the biomechanical interactions between a keratoconic cornea and a lens during blinking.     

纳米级混合润滑研究

混合润滑是机械中广泛存在的润滑状态。从试验方面研究了由接触、边界润滑和薄膜润滑组成的点接触区混合润滑状态的特性,提出使用动态接触率来描述混合润滑状态,并研究了各种参数对动态接触率的影响。结果表明,在混合润滑状态下,动态接触率与接触中心平均膜厚成指数函数关系。速度和粘度的增大会减小动态接触率,载荷的增加则会增大接触率,极性添加剂分子的使用会减小实际粗糙峰之间的接触,从而降低动态接触率。另外,低速下,综合粗糙度小的摩擦副表面的接触率要大于粗糙度大的表面的接触率;随着卷吸速度的提高,粗糙度小的表面的动态接触率小于粗糙度大的表面的动态接触率。     

An analysis of elasto-plastic sliding spherical asperity interaction

This work seeks to characterize the component of friction, which arises from energy being dissipated via elasto-plastic deformation during sliding contact (as apposed to adhesive mechanisms). The sliding interaction between spheres is analyzed using two approaches (a semi-analytical and finite element simulation). These analyses are used to formulate empirical equations, which describe the average tangential and normal forces resulting from the sliding interaction. A parametric study of the properties of typical metals is then used to help verify the effectiveness of the empirical equations. The study shows that the effective friction coefficient between spherical asperities increases with the elastic modulus, decreases with yield strength, and increases with the interference between the contacts (dependant on the normal load).     

The investigation of contact ratio in mixed lubrication

In order to describe the mixed lubrication in nano-scale which is constituted from dry friction, boundary lubrication, and thin film lubrication, a contact ratio between surfaces of a glass disk and a steel ball in a pure rolling process has been measured by the technique of Relative Optical Interference Intensity (ROII) with a resolution of 0.5 nm in the vertical direction and 1 μm in the horizontal direction. The relationships between the contact ratio and its influence factors have been investigated. Experimental results indicate that the contact ratio in the static state is related to the combined surface roughness, maximum Hertz pressure, and the combined elastic module of tribo-pair in an exponential function. The decrease of rolling speed or lubricant viscosity, and the increase of the pressure will enhance the dynamic contact ratio which is the contact ratio measured in the rolling process. The addition of polar additives into basic oil will reduce the contact ratio. The contact ratio between rough surfaces is larger than that between smooth surfaces in the higher speed region. However, the former becomes smaller than the later after speed decreases below a critical value. A formula for calculating the dynamic contact ratio is given in the end of the paper.     

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

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。     

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。