弹性接触中的表面微滑问题及数值求解

研究法向载荷和切向载荷耦合作用下的三维弹性点接触问题.当切向载荷不足使接触体发生整体滑动时,接触面产生微滑区域.对于异质物体的接触,即使仅有法向载荷作用,由于变形的不协调,接触面同样会产生微滑区域.运用半解析的方法求解微滑接触问题,影响系数通过Green函数得到解析解,压力和切应力的求解基于共轭梯度法和快速傅里叶变换法.算法仅在关心的接触区域划分网格,缩短计算时间.通过对比光滑同质物体接触的数值解和解析解来验证算法.分析正弦异质表面接触的压力分布、切应力分布、粘着区域.结果显示,由于粗糙峰的存在,粘着区域为多个不连通的区域.随着切向力的增加,压力分布沿着切向力相反的方向倾斜,切应力τx逐步变为正值,粘着区域沿着切向力相反的方向移动并逐渐变小.     

滤波截止频率对粗糙表面接触机理的影响

使用基于快速傅里叶变换和共轭梯度法的扩展干接触程序,以及基于Greenwood和Williamson接触模型(G-W模型)的接触求解方法,分析滤波截止频率对粗糙表面接触机理的影响。结果表明,粗糙表面形貌数据再处理时使用的滤波器滤波截止频率,对力－接近量关系有着明显的影响;G-W 接触模型仅适用于波长较大的粗糙表面。因此,在G-W模型的各种应用中,应注意滤波截止频率对粗糙表面接触机理的影响。     

微动接触中分形粗糙表面的接触应力研究

表面粗糙度对微动状态下接触面的接触压力和剪切摩擦力有着显著影响.在这项研究中,创建Python脚本将Matlab中利用Weierstrass-Mandelbrot函数构造的分形表面轮廓坐标导入ABAQUS中,并使用样条曲线拟合轮廓坐标,从而构建包含粗糙表面的二维柱面/平面接触模型.采用有限元方法研究考虑粗糙表面接触的接...     

三维真实粗糙表面弹性接触的全域数值解

本文提出了三维真实粗糙表面弹性接触问题的全域数值求解方法。这种方法采用网格规则划分和局部柔度矩阵存储解决了计算机存储问题;采用求解域收缩和逐次低松弛迭代解决了接触方程求解问题。运用这种方法可以获得真实粗糙表面弹性接触时全接触域内的压力分布与总载荷、接触图象及其实接触面积、接触变形与接触刚度等参数。计算结果与实测结果符合得较好。     

弹性状态下粗糙表面法向接触刚度的研究

粗糙表面接触问题是一类重要和具有实用价值的实际工程问题。采用Ｈｅｒｔｚ理论和粗糙表面随机接触模型, 研究弹性状态下粗糙表面法向接触刚度,推导出在不同接触体的法向接触刚度公式。由推导的理论公式可知,粗糙表面 在随机接触模型中接触刚度跟载荷成正比,与表面粗糙度均方值成反比     

弹性状态下粗糙表面的法向接触刚度

粗糙表面接触问题是一类重要和具有实用价值的实际工程问题。采用Hertz理论和粗糙表面随机接触模型,研究弹性状态下粗糙表面法向接触刚度,推导出在不同接触体的法向接触刚度公式。由推导的理论公式可知,粗糙表面在随机接触模型中接触刚度跟载荷成正比,与表面粗糙度均方值成反比。     

基于NCGM的粗糙表面数值模拟与实验对比

基于时间序列模型、线性变换方法和Johnson转换系统,研究粗糙表面的重构方法。为减少数据储存空间的需求和收敛性要求,采用非线性共轭梯度法（NCGM）求解自相关矩阵,得到高斯型表面及非高斯型表面的数值模拟方法。对不同相关长度及高度分布的高斯型、非高斯型粗糙表面进行数值模拟,并与实际测量结果进行对比。结果表明,所提出的基于NCGM的粗糙表面数值模拟方法能有效地模拟满足高度分布函数与自相关函数的实际加工表面。     

粗糙表面滑动摩擦接触模型研究的进展

对近年来国内外粗糙表面模型的进展进行了概述,根据粗糙表面模型类型的不同,分为粗糙表面和平面接触模型以及双粗糙表面接触模型,在各自模型中按照静载和滑动接触类型的研究进展进行表述,并提出了一些目前研究中遇到的热力耦合的问题以及将来双粗糙分形表面模型的发展.     

工程粗糙表面接触摩擦热力学研究进展

对近年国内外工程粗糙表面微观热力学的数值模拟的进展作了综述,介绍了工程粗糙表面的表征、接触模型、表面温升的计算模型与方法的研究现状,并提出了当前相关研究中所遇到的问题及今后研究发展方向.     

粗糙表面三体接触理论研究

摩擦表面间往往存在着硬质颗粒从而形成三体接触,而以前关于表面接触的理论和试验研究都停留在二体接触。通过理论分析得到了三体接触中接触副表面间距离、塑性变形量与第三体的粒度分布、外载荷、接触副表面微观几何参数及材料硬度间的关系,并进行了相应的数值计算和分析。结果表明,选择合适的表面粗糙度可使接触副的塑性变形量最小。     

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.     

Analysis of the Fretting Conditions in a Contact Between an Epoxy Thermoset and a Glass Counterface

The fretting conditions in a contact between an epoxy thermoset and a glass counterface have been investigated using a specific device which allows in situ observation of the contact area. The critical displacement for transition from partial slip to gross slip conditions was investigated by the in situ detection of the micro-displacements and by the analysis of the fretting loops. Experimental results were in good relation with the theoretical predictions derived from Mindlin's approach of incipient sliding. Depending on the loading conditions, a progressive change from gross slip to partial slip conditions was found to occur during the early stages of the fretting loading, i.e., before the appearance of any macroscopic damage such as cracking or particle detachment. These fretting conditions were synthesized in a fretting map giving the boundary between various fretting regimes as a function of the normal load, the imposed displacement and the number of cycles.     

The Effect of Scale-Dependent Hardness on Elasto-Plastic Asperity Contact between Rough Surfaces

Statistical methods are used to model elasto-plastic contact between two rough surfaces using a recent finite element model of elasto-plastic hemispherical contact and also recent advances in strain gradient modeling. The elasto-plastic hemispherical contact model used to model individual asperities accounts for a varying hardness effect due to deformation of the contact geometry that has been documented by other works. The strain gradient model accounts for changes in hardness due to scaling effects. The contact between surfaces with hypothetical material and surface properties, such as the elastic modulus, yield strength, and roughness are modeled. A model is also constructed to consider a variable asperity contact radius to evaluate if the strain gradient model will affect it differently. The models produce predictions for contact area, contact force, and surface separation. The strain gradient effects decrease the real area of contact and increase the average contact load in comparison to the model without these effects. The strain gradient model seems to have a larger influence on the predictions of contact load and area than does considering a variable asperity contact radius for the cases considered in this work.     

Analyzing Elastic-Plastic Real Rough Surface Contact in Running-in

A numerical method is presented for evaluating the elastic-elastic contact of real rough surface contacts during running-in. For the surface contact, an elastic-plastic model based on the variational method is applied to analyze the pressure distribution and contact area of worn surfaces during running-in. In conjunction with the classical statistic model of Greenwood and Williamson, the numerical result showed that the plasticity index Ψ was decreased to one in the elastic range as running-in proceeded. In comparison with the Hertzian solution, the influence of the asperities is very significant on the pressure distribution, thereafter causing a higher peak value of contact pressure. For the subsurface, the interior stress from the von Mises criterion was calculated to evaluate the subsurface stress field subject to both normal and tangential forces. In the calculated of the interior stress, the total stress is decomposed into a fluctuating component and a smooth component. The fluctuating part is solved by using FFT from the concept of the convolution theorem while the smooth part is obtained directly by analytical solution. Calculations of contact area and subsurface stress on experimentally produced surfaces whose topography has been determined using an atomic force microscope and friction coefficient front sliding have been carried out. The results showed that asperities and friction coefficient gave rise to stress increase in the near-surface stress field and produced a high stress zone towards the surface. As a result, transverse asperity cracking was produced. The calculations and supporting experimental evidence clearly confirmed that the reduction of peak pressure during running-in decreased the plastic deformation of contact.     

风电转盘轴承径向微动磨损的数值模拟

以某1.5MW转盘轴承为研究对象,应用ABAQUS软件建立三维球(GCr15轴承钢)/滚道(42CrMo钢)接触弹塑性有限元模型,通过改变滚珠与滚道接触时的曲率比,实现球、滚道接触的径向磨损模式,研究了不同曲率比对滚珠与滚道之间接触应力、相对滑移量和动力学曲线等摩擦学关键参数的影响规律。研究结果表明:滚道的塑性变形主要发生在第一次加载卸载过程中,后续加载循环塑性变形并不明显;随着曲率比的增加,滚道的变形增大,磨损区域减少;模型的最大应力不在接触表面产生,出现在距离接触表面深度1mm处,这与实际损伤结果相符。     

Influence of Mixed-Lubrication and Rough Elastic-Plastic Contact on the Performance of Small Fluid Film Bearings

A previously developed deterministic elastohydrodynamic (EHD) numerical model for small fluid film bearings functioning in the mixed lubrication regime is extended in this work by considering the rough contact. Several simplifying hypotheses are made: the shaft is considered rigid and smooth, turning at low speeds (isothermal regime), and the pad is assumed to have an elastic-perfectly-plastic behavior. The Reynolds equation is solved on a very fine mesh and the elasto-plastic pad deformation caused by the hydrodynamic pressure is taken into account. A deterministic active set-based method is used for determining the contact pressure, the contact extent, and the corresponding deformation. The results are presented for a partial journal bearing configuration, with a linear shaft velocity of 0.47 m/s under specific pressures varying up to 50 MPa. Two pad materials are considered, and the lubricant is either isoviscous or piezoviscous oil. The simulation results, presented as a function of the bearing specific pressure, include eccentricity, the film thickness, the friction torques, the contact extent, etc. Stribeck curves showing the evolution of the friction coefficient in the hydrodynamic and mixed lubrication regimes are also discussed.     

Fretting corrosion of tin-plated contacts

The susceptibility of tin-plated contacts to fretting corrosion is a major limitation for its use in electrical connectors. The present paper evaluates the influence of a variety of factors, such as, fretting amplitude (track length), frequency, temperature, humidity, normal load and current load on the fretting corrosion behaviour of tin-plated contacts. This paper also addresses the development of fretting corrosion maps and lubrication as a preventive strategy to increase the life-time of tin-plated contacts. The fretting corrosion tests were carried out using a fretting apparatus in which a hemispherical rider and flat contacts (tin-plated copper alloy) were mated in sphere plane geometry and subjected to fretting under gross-slip conditions. The variation in contact resistance as a function of fretting cycles and the time to reach a threshold value (100 mΩ) of contact resistance enables a better understanding of the influence of various factors on the fretting corrosion behaviour of tin-plated contacts. Based on the change in surface profile and nature of changes in the contact zone assessed by laser scanning microscope (LSM) and surface analytical techniques, the mechanism of fretting corrosion of tin-plated contacts and fretting corrosion maps are proposed. Lubrication increases the life-time of tin-plated contacts by several folds and proved to be a useful preventive strategy.     

Fretting fatigue of zinc coated low carbon steel EN H320 M

The object of the present study was to investigate the influence of zinc coatings on steel sheets during fretting fatigue and fatigue tests. The influence of the fatigue stress range, normal pressure and amplitude of slip, on the fracture life was studied for both coated and uncoated EN H320 M steel. The wear produced by fretting was measured and compared with the fracture life evolution for different values of slip amplitude. The wear scars and the fracture surfaces were examined by scanning electron microscopy to identify the degradation mechanism. Although zinc films do not influence the fatigue life of the tested steel, when fretting is superposed on to a fatigue stress the coating markedly improves the fracture life.