二维多粗糙峰粘着接触问题的有限元分析

应用Barquins理论的圆柱体粘着接触理论和Maugis-Dugdale模型以及有限元方法分析了圆柱形粗糙峰的刚性粗糙表面与半无限弹性表面的二维微观粘着接触问题。研究了粗糙峰间距,粗糙峰曲率半径和外载荷等参数对金属材料微观粘着接触问题接触压力和接触区域von Mises应力分布的影响。结果表明,在零载荷下,改变粗糙峰间距对于粘着接触没有影响,而改变曲率半径则影响较大。在外载荷作用下,改变粗糙峰间距和曲率半径均会影响粘着接触的压力分布和应力分布。     

材料属性温度相关热弹塑性接触问题研究

应用有限元方法建立了可考虑屈服应力温度相关效应的粗糙表面热弹塑性接触模型.研究了摩擦力和不同热输入情况下圆柱体与弹塑性平面的接触力学特性.求解了考虑屈服应力温度相关效应的粗糙表面热弹塑性接触问题,探讨了摩擦热效应对表面温升、接触压力、平均间隙及接触体应力分布的影响.提出了考虑热膨胀系数温度相关效应的热弹塑性接触模型.通过刚性圆柱体与半无限大平面的热弹塑性接触研究了热膨胀系数温度相关效应对接触体应力分布的影响.     

材料属性温度相关热弹塑性接触问题研究

应用有限元方法建立了可考虑屈服应力温度相关效应的粗糙表面热弹塑性接触模型。研究了摩擦力和不同热输入情况下圆柱体与弹塑性平面的接触力学特性。求解了考虑屈服应力温度相关效应的粗糙表面热弹塑性接触问题,探讨了摩擦热效应对表面温升、接触压力、平均间隙及接触体应力分布的影响。提出了考虑热膨胀系数温度相关效应的热弹塑性接触模型。通过刚性圆柱体与半无限大平面的热弹塑性接触研究了热膨胀系数温度相关效应对接触体应力分布的影响。
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含角接触球轴承和粗糙间隙表面滑动轴承关节的平面柔性多连杆机构动态误差分析与优化设计

传统旋转间隙关节接触模型假定衬套和销轴的接触面是光滑的并仅考虑接触区域的初始接触点的影响,常忽略接触区域中其它接触点的作用,不可避免导致模型分析精度下降.为此,提出一种含角接触球轴承和粗糙间隙表面滑动轴承关节的平面柔性多连杆机构动力学建模、分析与优化的计算方法.考虑粗糙旋转间隙关节多点接触状态,建立了一个新颖粗糙间隙接...     

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。     

基于PFC3D的研磨片研磨过程离散元仿真

针对研磨片研磨过程中工件表面粗糙峰去除和研磨片磨粒涂覆层磨粒脱落的问题,将离散元技术应用到研磨片研磨过程微观表面变化研究中。以PFC3D软件为平台,对研磨片的研磨过程进行了建模与仿真,将模型简化为理想梯形凸起的粗糙峰层和磨粒-结合剂混合层的相互接触摩擦过程,通过双轴试验表征了模型微观参数,开展了单元接触点不平衡力的变化规律、单元脱落过程、磨粒涂覆层中结合剂结合强度以及砂结比对研磨过程的影响分析。研究结果表明,接触点处的不平衡力呈现散射样式逐步减弱,不平衡力峰值为5.9×103N;磨粒平行粘结强度为723 Pa,砂结比为1∶6时研磨效果最好,粗糙峰可以有效去除,表层钝化磨粒可以有效脱落。     

渗氮钢粗糙表面的弹塑性接触研究

利用弹塑性有限元和单纯形法求解弹塑性接触模型，分别模拟了屈服强度呈梯度变化的渗氮钢、未经处理的匀质材料和硬涂层材料粗糙表面的弹塑性接触行为。与未经处理的匀质材料相比，渗氮钢可承受更大接触载荷。在相同载荷作用下，渗氮钢表面粗糙峰接触面积较小，平均间距较大，接触体内材料不易发生屈服，从而显著提高接触性能。和硬涂层材料相比，渗氮钢接触体内等效von Mises应力分布平缓，没有应力突变。最后讨论了渗氮层和硬涂层的厚度对粗糙表面接触特性的影响。     

单粗糙峰通过接触区全过程的时变热弹流数值仿真

建立了带单粗糙峰的表面滚滑工况的点接触时变热弹流模型，数值模拟了钢与钢接触、快速表面带单粗糙峰通过接触区的全过程。结果表明，接触区内的粗糙峰会引起局部高压，当粗糙峰较高时，润滑膜会变得极薄，这对润滑的可靠性是不利的，而局部压力高峰也会严重降低材料的表面疲劳寿命。     

基于JKR模型的粗糙圆柱表面线黏着接触分析*

利用粗糙平面接触模型,假定表面单个微凸体的接触采用JKR黏着接触模型,同时考虑圆柱体表面的整体变形,建立了粗糙圆柱表面线黏着接触模型,推导出表面等效压力分布方程。把压力方程量纲一化,采用修正Newton-Raphson法对方程进行迭代求解,计算出粗糙圆柱表面存在表面力作用下的等效压力分布曲线。结果表明外载荷不小于零时,接触中心压力为正,微凸体被压缩;而接触边缘处压力为负,微凸体被拉伸,表明黏着区域主要分布在接触边缘。同时计算出接触半宽随外载荷的变化曲线,当外载荷为拉伸力并大于某一临界值时,表面分开。并且与经典的接触模型进行了对比,发现低载时模型之间的差别较大,而载荷比较大时趋于一致。     

织构化滑动轴承混合润滑与磨损耦合数值模型

基于统计学模型建立织构化轴承混合润滑与磨损的计算模型,通过生成轴瓦虚拟粗糙表面,分别利用平均流量雷诺方程、K-E弹塑性接触模型、Boussinesq积分、Archard型磨损方程求解油膜压力、粗糙峰接触压力、轴瓦的弹性变形和轴瓦表面磨损量。通过有限差分法和牛顿下山法对模型进行数值模拟,得到不同偏心率下的油膜压力、油膜厚度、轴瓦弹性变形、轴瓦表面粗糙峰接触压力及磨损量,并与其他混合润滑模型进行对比,验证了该模型的有效性。以圆形凹坑织构为例,研究在多种工况下,润滑状态转化以及织构对磨损过程的影响。研究表明:织构可以形成二次润滑,有利于流体润滑;随偏心率增大,进入混合润滑状态后,承载能力、粗糙峰接触载荷迅速增加,摩擦因数出现拐点;在混合润滑状态下,磨损过程前期表面织构会造成轴承承载性能降低和增大磨损,随着滑动轴承进一步磨损,表面织构可以起到减磨作用。     

A Model for Wear and Friction in Cylinder Liners and Piston Rings

Abstract

A one-dimensional elstohydrodynamic mixed lubrication wear and friction model is developed. The model can predict the effects of surface roughness, asperity contact, temperature-pressure-viscosity on wear, lubrication, and friction of the piston rings and cylinder liner. Wear is predicted based on the surface asperity contact pressure. The cylinder bore wear and the ring pack friction during an engine break-in are simulated and compared with the experimental results. The influence of cylinder wall temperature and surface roughness on friction and wear is investigated. The ring pack friction due to oil viscous shearing and asperity contact is found to reach its minimum at a certain oil temperature.     

A statistical model of elasto-plastic asperity contact between rough surfaces

This work models statistically elasto-plastic contact between two rough surfaces using the results of a previous finite element analysis of an elasto-plastic sphere in contact with a rigid flat. The individual asperity contact model used accounts for a varying geometrical hardness effect that has recently been documented in previous works (where geometrical hardness is defined as the uniform pressure found during fully plastic contact). The contact between real surfaces with known material and surface properties, such as the elastic modulus, yield strength, and roughness are modeled. The asperity is modeled as an elastic-perfectly plastic material. The model produces predictions for contact area, contact force, and surface separation. The results of this model are compared to other existing models of asperity contact. Agreement exists in some cases and in other cases it corrects flaws, especially at large deformations. The model developed by Chang, Etsion and Bogy is also shown to have serious flaws when compared to the others. This work also identifies significant limitations of the statistical models (including that of Greenwood and Williamson).     

Contact width and compliance between cylinders and rough plates

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.     

Fractal prediction model of thermal contact conductance of rough surfaces

The thermal contact conductance problem is an important issue in studying the heat transfer of engineering surfaces,which has been widely studied since last few decades,and for predicting which many theoretical models have been established.However,the models which have been existed are lack of objectivity due to that they are mostly studied based on the statistical methodology characterization for rough surfaces and simple partition for the deformation formats of contact asperity.In this paper,a fractal prediction model is developed for the thermal contact conductance between two rough surfaces based on the rough surface being described by three-dimensional Weierstrass and Mandelbrot fractal function and assuming that there are three kinds of asperity deformation modes:elastic,elastoplastic and fully plastic.Influences of contact load and contact area as well as fractal parameters and material properties on the thermal contact conductance are investigated by using the presented model.The investigation results show that the thermal contact conductance increases with the increasing of the contact load and contact area.The larger the fractal dimension,or the smaller the fractal roughness,the larger the thermal contact conductance is.The thermal contact conductance increases with decreasing the ratio of Young’s elastic modulus to the microhardness.The results obtained indicate that the proposed model can effectively predict the thermal contact conductance at the interface,which provide certain reference to the further study on the issue of heat transfer between contact surfaces.     

Transient Heat Conduction Between Rough Sliding Surfaces

When two rough bodies slide against each other, asperities on the opposing surfaces interact with each other, defining a transient contact and heat conduction problem. We represent each body by a Greenwood and Williamson asperity model with a Gaussian height distribution of identical spherical asperities. The heat transfer during a typical asperity interaction is analyzed, and the results are combined with the height distributions to determine the mean heat flux and the mean normal contact pressure as functions of the separation between reference planes in the two surfaces. We find that the effective thermal conductance is an approximately linear function of nominal contact pressure, but it also increases with the square root of the sliding speed and decreases with the 3/4 power of the combined RMS roughness. The results can be used to define an effective thermal contact resistance and division of frictional heat in macroscale (e.g., finite element) models of engineering components, requiring as input only the measured roughness and material properties.     

Temperature Analysis in Lubricated Simple Sliding Rough Contacts

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.     

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.     

Effect of asperity interactions on rough surface elastic contact behavior: Hard film on soft substrate

An improved elastic micro-contact model of rough surfaces accounting for asperity interactions is proposed. The contact behavior of a single asperity system is composed of a stiffer hemi-spherical asperity deformation and bellowing softer substrate deformation, which is then extended to rough surface contact including asperity interactions. Using the solution of substrate deformation, normal positions of individual asperities are adjusted during quasi-static contact, from which surface interactive forces are obtained. Analytical simulations are performed using the proposed rough surface contact model, whose results are compared to Greenwood-Williamson-based models and with experimental measurements.     

Analysis of plane and rough contacts, subject to a shearing force

We analyse the surface traction conditions induced in plane contact between two bodies whose surfaces are rough. It is assumed that the roughness may be idealised by a surface of regularly spaced cylindrical “bumps”, and the overall geometry may be in the form of a cylinder, flat ended punch or wedge. The stick-slip regime experienced by each individual asperity contact is found, and hence it is shown how the applied shearing force produces concentrated regions of surface damage. Conditions for crack initiation are then discussed, and compared with equivalent results found for nominally smooth contacts.