薄膜粗糙表面有摩擦接触问题的数值计算研究

采用ANSYS的APDL语言编程通过参数化变量方式实现了薄膜粗糙表面有摩擦接触问题的整个建模与分析过程,其中包括参数化生成满足高斯分布的随机粗糙表面与计及摩擦因数和薄膜/基体弹性模量比变化情况下的自动有限元分析过程。计算结果表明:当摩擦因数一定时,随着薄膜/基体弹性模量比的增大,应力分布逐渐向基体深处扩展,粗糙表面上各点接触压力一致减小,接触压力峰值减小的最大幅度为9.0%;当弹性模量比一定时,摩擦因数的变化对基体部分应力分布的影响不大,然而随着摩擦因数的增加,粗糙表面上各点接触压力增大,接触压力峰值增加的最大幅度为13.2%,可见摩擦因数和弹性模量比对薄膜粗糙表面的接触应力有明显影响。     

Adhesive Contribution to the Coefficient of Friction Between Rough Surfaces

The contribution of adhesive bridges between micro-asperities to the macroscopic coefficient of friction of two rough elastic bodies is calculated in the framework of Greenwood and Williamson’s model. An analytical expression for the coefficient of friction as a function of the mean square slope of the surface profiles, the roughness, the elastic moduli, and the surface energy, is established.     

Chemical Modification of Friction Surfaces in Boundary Lubrication

The influence of the nature and structure of chemically active additives on the chemical modification temperature of friction surfaces was investigated using a KT-2 four-ball machine with various metal and lubricant-additives combination. A synergistic effect of detergent and antioxidant additives on the critical and chemical modification temperature of oil was found.     

两种测度方法表征粗糙表面的效果研究

为了比较结构函数与均方根2种测度方法对粗糙表面的分形表征效果,模拟了具有不同理论分形维数的表面轮廓曲线,然后用结构函数和均方根2种方法对它们进行分形特性表征和分形维数计算,并对表征结果进行了理论分析。研究表明,2种测度方法均具有较好的表征效果。与结构函数测度方法相比,均方根测度方法的分维计算精度高,表征曲线的线性度好,反映分形特征的无标度区间宽,分形表征效果显著。另外,均方根测度方法还具有物理意义明确和分维计算简单的优点。因此均方根测度方法不失为粗糙表面分形表征的一种有效方法。     

Adhesion and Friction Enhancement of Film-Terminated Structures against Rough Surfaces

A number of biomimetic and bioinspired micron-scale surface structures have been developed in recent years with unique surface properties such as highly enhanced and switchable adhesion and friction against smooth surfaces. However, few studies have examined the effect of roughness on mechanisms for property enhancement, although this is of critical importance for applications. Here, we investigate the effect of roughness on adhesion and friction of a family of film-terminated fibrillar and ridge/channel microstructures. Although increasing roughness uniformly attenuates adhesion and friction, we find that the film-terminated structures maintain their enhancement compared to flat controls against a variety of rough surfaces (including natural stones). The principal mechanisms underlying property enhancement against smooth surfaces remain operative against rough surfaces. We show how the effect of roughness on surface mechanical properties of structured surfaces can be understood as a combination of known effects due to structure and roughness.     

外界压力对粗糙表面摩擦与接触的影响研究

为研究外界压力对粗糙表面摩擦的影响,建立斜面滑块在不同真空度下的模型并进行试验测量在不同真空度下不同摩擦副配伍材料发生初始滑动时的斜面倾角。试验结果表明：随着外界压力增加,滑块发生初始滑动时的倾角增大,静摩擦力也增大。对于硬度小、重量轻以及接触面积大的摩擦副材料和零部件,其所受外界压力的影响更大。当外界压力从真空度-0.095 MPa增加到0 MPa,轴承钢/轴承钢的最大静摩擦力增大11%、轴承钢/聚碳酸酯增大12%,而聚碳酸酯/聚碳酸酯增大39%。由于通常情况下物体间的摩擦性能总是会受到外界压力的影响,因此真实摩擦角应在绝对真空环境下进行测量,而在大气中进行的测量都存在误差。同时可用文中方法测量两物体的实际接触面积。试验表明随着载荷增加实际接触面积增加,跟摩擦学的经验理论一致。     

双粗糙面滑动过程摩擦因数的变化分析

采用W-M函数建立具有分形特征的三维双粗糙面接触模型,考虑了接触界面间的黏着效应,在滑动速度、法向载荷及界面剪切强度等参数变化下,运用有限元方法探讨了粗糙体在滑动过程中摩擦因数的变化情况。结果显示,滑动速度、法向载荷及界面剪切强度等参数对摩擦因数的变化有一定的影响,边界润滑工况下平均摩擦因数为0.28,无润滑工况下平均摩擦因数为0.713,最大界面剪切强度时的平均摩擦因数为0.73;随着界面剪切强度的减小、法向载荷的增大、滑动速度的增加,滑动摩擦因数有所减小。与相关文献结论或实验结果进行比较,证明了上述结果的正确性。分析结果可为摩擦学设计和摩擦材料的制备提供理论参考。     

About Joint Deformations of Asperities and the Destruction of Rough Surfaces During Friction

The mechanics of the deformations and the destruction of the asperities of rough surfaces has been considered, taking into account the mutual influence of the elastic constants of the materials participating in the friction couple.

The case when the destruction is taking place inside of the contact layer is assumed to have the highest probability. The tight bear of the peaks of one body against the valleys of the other and the adhesion phenomena are leading to a mutual deformation of the prevailing number of asperities of both surfaces. This allows one to consider the contact layer as a composite body consisting of two solid phases and voids.

It has been shown that such an approach does not exclude the possibility of shearing off only the soft material of the couple.

For the asperities subject to bending deformations, the mutual influence of the elastic constants is conditioned by the mutual angle of rotation of the cross sections.

In this case consideration of the tangential stresses in the destruction of the short bars (asperities) is essential.     

Theoretical and Finite Element Analysis of Static Friction Between Multi-Scale Rough Surfaces

The current work considers the multi-scale nature of roughness in a new model that predicts the static friction coefficient. This work is based upon a previous rough surface contact model, which used stacked elastic–plastic 3-D sinusoids to model the asperities at multiple scales of roughness. A deterministic model of a three-dimensional deformable rough surface pressed against a rigid flat surface is also carried out using the finite element method (FEM). The accuracy of the deterministic FEM model is also considered. At the beginning of contact, which is surface-point contact, the asperities or peaks are isolated, sharp, and the contact areas consist of an inadequate number of elements and sources of error. In this range of contact, the results are not presented as real or accurate. As the normal load increases, the number of the contact elements become larger, and thus, the results become more accurate. That is, the deterministic FEM results are most accurate at high loads. Spectral interpolation is used to smooth the geometry in between the original measured nodes. The effects of normal load and plasticity index on static friction are then analyzed. The results predicted by the theoretical model are also compared to other existing rough surface friction contact models and the FEM results. They are in a good qualitative agreement, especially for higher loads and higher plasticity indices. The FEM model also has significant error, but it is more accurate at higher loads where the proposed multi-scale static friction model and FEM model are in better agreement.     

Measurement of Friction Noise Versus Contact Area of Rough Surfaces Weakly Loaded

This study presents an experiment to measure the dependence of friction noise versus the nominal contact area. The friction-induced vibration is generated by the sliding of two rough surfaces. The normal load is low leading to a weak contact. The normal load and the sliding velocity are maintained constant. The nominal contact area ranges over two orders of magnitude. It is found that two regimes exist. On the one hand, the vibration energy is proportional to the contact area. But on the second hand, the vibration energy is constant, i.e., does not depend on the contact area.     

Anomalous Low Friction Under Boundary Lubrication of Steel Surfaces by Polyols

We present here anomalous low friction obtained with highly polished steel on steel hard contact lubricated by glycerol under severe mixed and boundary regimes (λ ratio below 1). We investigated the effects of contact pressure, sliding speed, and temperature on friction coefficient and electrical contact resistance. The mechanism of low friction (typically below 0.02) is thought to have two origins: first a contribution of an ultrathin EHL film of glycerol providing easy shear under pressure, second the chemical degradation of glycerol inside the contact when more severe conditions are attained, generating a nanometer-thick film containing shear-induced water molecules. This new mechanism, called “H-bond Network model”, is completely different from the well-accepted “Monolayer” model working with polar molecules containing long aliphatic chains. Moreover, we show outstanding superlubricity (friction coefficient below 0.01) of steel surfaces directly lubricated by a solution of myo-inositol (also called vitamin Bh) in glycerol at ambient temperature (25 °C) and high contact pressure (0.8 GPa) in the absence of any long chain polar molecules. Mechanism is still unknown but could be associated with friction-induced dissociation of inositol and H-bond interactions network of water-like species with steel surface.     

基于多孔介质理论的双粗糙面金属静密封泄漏模型

粗糙面微观几何形貌是影响静密封泄漏特性的重要因素。应用粗糙面的三维点云数据,将粗糙面进行离散化处理,进而将由双粗糙面构成的密封界面等效为三维逾渗栅格模型,基于多孔介质理论计算得到密封界面的孔隙率和渗透率,从而建立了一种双粗糙密封界面的泄漏率模型。搭建金属静密封泄漏率测量试验台,通过对环面金属静密封泄漏特性的试验研究,验证了该泄漏模型的有效性。利用该模型分析了表面纹理方向、粗糙面波动频率与材料特性对金属静密封泄漏特性的影响。结果表明：各向异性粗糙面构成的密封界面具有较好的密封性能;粗糙面波动频率越大,密封性能越好;低硬度材料易于实现有效密封;在重载情况下,粗糙面微观几何形貌对孔隙率与泄漏率的影响不显著。     

考虑摩擦因素的两圆柱体表面接触承载能力的分形模型研究

为了建立更为准确的两圆柱表面接触承载能力分析的分形接触模型,以M-B模型为基础,利用存在摩擦时的弹塑性变形临界接触面积的计算理论,并结合前期获得的两圆柱体接触面积分布公式,推导考虑摩擦因素的圆柱体表面接触承载能力的分形模型。通过Matlab仿真,获得模型中主要参数对分形接触模型影响的预测分析,结果表明:减小摩擦因数,降低粗糙度幅值以及提高材料的特性参数,有利于提高接触承载能力,并改善接触面间的力学特性;分形维数对接触承载能力的影响,不是一个简单线性关系,而是存在一个分形维数的最优值。该模型的研究为后续进行齿轮等相关产品的接触承载分析提供新的理论参考。     

盐溶液条件对边界润滑添加剂在带电表面吸附行为的影响

为揭示盐溶液条件对边界润滑添加剂聚醚接枝聚羧酸盐(Poly(carboxylate ether),PCE)吸附行为的影响,利用表面力仪在一种商业PCE的多种水溶液中直接测量带电云母表面之间的法向作用力.力一距离测量表明PCE从0.1 mol/L K2SO4溶液中微弱地吸附于云母表面,其边界吸附薄膜(厚度约50 (A))...     

真实粗糙表面接触模型的研究

真实工程表面并不是完全光滑的。当两物体相互接触时 ,真实表面实际上是微凸体间的接触。分析真实粗糙表面间的接触对研究摩擦、磨损和润滑起着非常关键的作用。合理地描述润滑状态和摩擦热边界条件也取决于对真实接触状态的求解。本文从 3个方面研究了粗糙表面接触计算模型的主要构成 :粗糙表面轮廓的描述、确定接触压力和表面位移之间关系的计算公式以及求解几何非线性接触问题的方法。最后给出了算例     

无极性油润滑下摩擦面间边界膜的电特性

考察了无极性石蜡基油润滑下摩擦面间的自生电势及外加电压时摩擦面间边界润滑膜的电特性。用摩擦面的氧化作用解释了施加不同方向电压时边界润滑膜表现出的整流效果,并就如何有效利用该氧化作用提出建议。     

An Experimental Study of Friction and Durability of a Thin PTFE Film on Rough Aluminum Substrates

Frictional and durability characteristics of 1-µm-thick polytetrafluoroethylene (PTFE) films deposited by hot filament chemical vapor deposition on aluminum substrates were investigated. A universal microtribotester was used to examine the frictional and durability properties using the ball-on-plate and ball-on-disk configurations, respectively. Effects of normal force (2.5, 5, 10, 15 N), sliding speed (0.1, 1, 5 mm/s), and surface roughness of the aluminum substrate (R_a = 0.01, 0.57, 1.28, 2.34 µm) on the coefficient of friction (COF) and the effects of normal force (2.5, 5 N), sliding speed (0.42, 4.19 mm/s), and surface roughness on the durability were investigated. It was shown that the COF of the PTFE-coated interface increases with increasing surface roughness or sliding speed. The COF depends on the normal force to a lesser extent than the other two parameters. The medium-level, O(0.5 µm), roughness of the substrate provides the longest durability, whereas the smoothest or very rough surface provides shorter durability. Analysis of variance (ANOVA) indicates that the surface roughness has the most significant effect on the COF and durability. In the case of a smooth interface, a relationship between COF, sliding speed, and normal force can be predicted. Results indicate an optimal surface roughness for improving durability.     

Elasto-Plastic Contact of Rough Surfaces

An isothermal elasto-plastic asperity contact model is developed and presented in this paper, which deals with micro plastic flows of materials and the influence of the elasto-plastic deformation of materials on the behavior of contacting surfaces. The model is solved with the incremental form of a simplex-type algorithm. The von Mises yield criterion is used to determine the onset of the plastic deformation. The effectiveness and validity of the model are studied through analyzing a Hertzian contact problem. Substrate stresses are calculated and differences are observed. Furthermore, the contact pressure, real area of contact, and average gap of real rough surfaces under the elastic, elastic-perfectly-plastic, and the elasto-plastic contact conditions are numerically investigated and the results are compared.     

粗糙表面计算机模拟

粗糙表面的计算机模拟是建立粗糙表面模型进而对粗糙表面间相互作用进行模拟研究的前提。提出一种基于时间序列模型、数字滤波技术和Johnson转换系统的粗糙表面模拟方法,分别模拟了各向同性与各向异性、高斯与非高斯分布条件下具有不同形式自相关函数的粗糙表面,并对复杂合成粗糙表面的模拟进行了尝试。最后,对粗糙表面模拟过程中的误差进行了初步分析。结果表明,提出的粗糙表面模拟方法能快速有效地模拟具有指定自相关函数的高斯或非高斯随机粗糙表面;在一定的条件下模拟表面的统计特征与规定值误差很小,但当相关长度比较大的时候,误差比较明显。