Thermo-mechanical contact behavior of a finite graded layer under a sliding punch with heat generation

The problem of a rigid punch contacting with a finite graded layer on a rigid substrate is investigated within the framework of steady-state plane strain thermoelasticity, in which heat generated by contact friction is considered with a constant friction coefficient and inertia effects are neglected. The material properties of the graded layer vary according to an exponential function in the thickness direction. Fourier integral transform method and transform matrix approach are employed to reduce the current thermocontact problem to the second kind of Cauchy-type singular integral equation. Distributions of the contact pressure and the in-plane stress under the prescribed thermoelastic environment with different parameter combinations, including ratio of shear moduli, relative sliding speed, friction coefficient and thermal parameters are obtained and analyzed, as well as the stress singularity and the stress intensity factors near the contact edges. The results should be helpful for the design of surfaces with strong wear resistance and novel graded materials for real applications.     

Indentation of a punch into an elastic strip with friction and adhesion

In the contact interaction between elastic bodies with friction taken into account, the contact region splits, as a rule, into adhesion and sliding regions {xc[1]}. Contact with adhesion and sliding was first considered by L. A. Galin {xc[2]} in the problem of indentation of a punch with a rectilinear foundation into an elastic half-plane, who obtained an approximate solution of this problem [{xc2}, {xc3}]. Galin's problem was further studied in [{xc4}–{xc9}].     

磁电弹复合材料和刚性导电导磁圆柱压头的二维微动接触分析

本文求解平面应变状态下磁电弹复合材料半平面和刚性导电导磁圆柱压头的二维微动接触问题。假设压头具有良好的导电导磁性，且表面电势和磁势是常数。微动接触依赖载荷的加载历史，所以首先求解单独的法向加载问题，然后在法向加载问题的基础上求解循环变化的切向加载问题。整个接触区可以分为内部的中心粘着区和两个外部的滑移区，其中滑移区满足Coulomb摩擦法则。利用Fourier积分变换，磁电弹半平面的微动接触问题将简化为耦合的Cauchy奇异积分方程组，然后数值离散为线性代数方程组，利用迭代法求解未知的粘着/滑移区尺寸、电荷分布、磁感应强度、法向接触压力和切向接触力。数值算例给出了摩擦系数、总电荷和总磁感应强度对各加载阶段的表面接触应力、电位移和磁感应强度的影响。     

制动磨损源大气颗粒物排放的研究进展

交通运输工具种类及数量的持续增长,势必会给环境保护带来严重的影响. 交通运输工具于摩擦制动过程释放的制动磨损颗粒物(即制动粉尘)已成为城市大气颗粒物的重要贡献源,显著影响着城市的空气质量. 为贯彻落实绿色发展理念,探索制动磨损源大气颗粒物排放的控制措施,需深入了解颗粒物排放的准确信息. 基于此,本文中综述了近年来以制动磨损为源头的大气颗粒物排放研究进展. 首先,从机理层面介绍了制动过程中磨屑的衍化,简述了摩擦层的形成机制和制动粉尘的来源及排放特性;其次,重点阐述了制动器结构、材料类型、外界环境、制动速度和制动载荷等因素对制动磨损源大气颗粒物排放的影响,分析了各因素对大气颗粒物排放特性(如颗粒形貌、颗粒尺寸和颗粒浓度等)的影响规律;最后,提出了制动磨损源大气颗粒物排放研究需要加强的几方面内容.      

铸造锌-石墨复合材料的摩擦学特性

作者以高铝锌基合金ZA-27为基体,使之与石墨在熔融状态下复合成为均匀浆料,经过挤压铸造成型,得到了几种石墨含量不同的锌-石墨复合材料。微观结构分析结果表明,金属-石墨界面结合状态良好,石墨分布均匀。这种材料在石墨含量低于5％(wt,下同)时的承载能力比青铜ZQSn6-6-3的高。其线膨胀系数随着石墨含量的增加而下降。在本试验条件下,随着石墨含量的增加,复合材料进入稳定磨损阶段所需要的时间缩短,滑动过程的平稳性增大,摩擦表面温度降低,摩擦系数明显下降,磨损率减小;在石墨含量达到6.2％时,锌-石墨复合材料的减摩性。耐磨性和相对抗咬合性都远比基体合金ZA-27的好,表明锌-石墨复合材科是一种新型的具有良好开发应用前景的减摩耐磨材料。     

Modeling of friction at different scale levels

We construct a model for studying the common influence of the imperfect elasticity of actual bodies, the microgeometry of their surfaces, and their adhesive interaction on the contact characteristics (the contact pressure distribution, the region of actual contact) and on the sliding friction force. The model is based on the solution of a plane contact problem of sliding of a rigid body with a regular relief on the boundary of a viscoelastic foundation with surface molecular attraction in the gap between the surfaces taken into account. We analyze the influence of the surface microgeometry parameters at different scale levels on the character of the surface interaction (the saturated or discrete contact) and the friction force for different sliding velocities of the contacting bodies.     

摩擦粒子填充材料对高速列车闸片制动性能的影响

在自行研制的制动缩比试验台上,对中心孔填充不同材料的高速列车制动闸片摩擦粒子进行拖曳制动试验,并采用有限元分析方法进行制动系统复特征值和接触应力分析,探讨填充不同材料对磨损特性、振动噪声和热分布的影响. 结果表明:原始摩擦粒子中心孔填充材料后,对制动系统的摩擦系数和模态耦合特性未产生显著影响,但对界面磨损行为和系统振动噪声特性产生明显影响. 填充粉末冶金后排屑行为下降,磨损行为更为复杂,制动系统产生的噪声增大;而填充紫铜、石墨和铸铁后的制动噪声均有所降低,尤其填充铸铁后表面磨损相对均匀,其摩擦学性能相较于其他粒子得到一定的改善. 填充材料产生的磨屑及相应的界面磨损行为是影响制动摩擦振动噪声和表面热分布的关键因素,填充合理的材料有助于降低制动噪声和改善制动界面磨损行为及表面热分布.      

摩擦信号分形维数与载荷和速度的关系研究

在立式万能摩擦磨损试验机上对GCr15/45#钢摩擦副进行不同接触载荷和滑动速度下的摩擦磨损试验,对初始滑动距离1 000 m内的摩擦系数信号进行数据采集,运用结构函数测度方法对摩擦系数信号进行分形表征,计算不同载荷和速度下的分形维数,研究摩擦信号的分形维数随载荷和速度的变化规律.结果表明,摩擦系数信号具有显著的分形特征,其分形维数随载荷和速度而变化.在相同载荷下,分形维数随滑动速度增加而增大;在相同速度下,分形维数随着接触载荷增加而增大.磨损率与摩擦系数信号的分形维数正相关.     

超高分子量聚乙烯/Al_2O_3生物摩擦学特性的研究

在自制销 -盘摩擦磨损试验机上评价了超高分子量聚乙烯 (UHMWPE)与 Al2 O3陶瓷摩擦副在干摩擦和生理盐水、蒸馏水及人血浆润滑条件下的摩擦学特性 ,用扫描电镜观察试样磨损表面形貌并分析磨损机理 .结果表明 :在干摩擦和生理盐水及蒸馏水润滑条件下的起始摩擦系数较接近 ,血浆润滑条件下的起始摩擦系数最低 ;稳态摩擦系数在干摩擦时最大 ,蒸馏水润滑条件下最小 ,生理盐水和人血浆润滑条件下较接近并比蒸馏水润滑下的高 ;干摩擦下UHMWPE的磨损率最大 ,血浆润滑条件下的最小 .干摩擦下 UHMWPE磨损表面可见大量不规则的细小纤维状磨屑 ,蒸馏水润滑下 UHMWPE磨损表面可见明显的塑性变形和疲劳剥落迹象 ,而血浆润滑条件下 UHMWPE磨损表面则可见大量的疲劳微裂纹     

Double frictional receding contact problem for an orthotropic layer loaded by normal and tangential forces

With the increasing research in the field of contact mechanics, different types of contact models have been investigated by many researchers by employing various complex material models. To ascertain the orthotropy effect and modeling parameters on a receding contact model, the double frictional receding contact problem for an orthotropic bilayer loaded by a cylindrical punch is taken into account in this study. Assuming plane strain sliding conditions, the governing equations are found analytically using Fourier integral transformation technique. Then, the resulting singular integral equations are solved numerically using an iterative method. The weight function describing the asymptotic behavior of the stresses are investigated in detail and powers of the stress singularities are provided. To control the trustworthiness and correctness of the analytical formulation and to compare the resulting stress distributions and contact boundaries, a numerically efficient finite element method was employed using augmented Lagrange contact algorithm. The aim of this paper is to investigate the orthotropy effect, modeling parameters and coefficients of friction on the surface and interface stresses, surface and interface contact boundaries, powers of stress singularities, weight function and to provide highly parametric benchmark results for tribological community in designing wear resistant systems.

     

Two-dimensional thermoelastic contact problem of functionally graded materials involving frictional heating

The two-dimensional thermoelastic sliding frictional contact of functionally graded material (FGM) coated half-plane under the plane strain deformation is investigated in this paper. A rigid punch is sliding over the surface of the FGM coating with a constant velocity. Frictional heating, with its value proportional to contact pressure, friction coefficient and sliding velocity, is generated at the interface between the punch and the FGM coating. The material properties of the coating vary exponentially along the thickness direction. In order to solve the heat conduction equation analytically, the homogeneous multi-layered model is adopted for treating the graded thermal diffusivity coefficient with other thermomechanical properties being kept as the given exponential forms. The transfer matrix method and Fourier integral transform technique are employed to convert the problem into a Cauchy singular integral equation which is then solved numerically to obtain the unknown contact pressure and the in-plane component of the surface stresses. The effects of the gradient index, Peclet number and friction coefficient on the thermoelastic contact characteristics are discussed in detail. Numerical results show that the distribution of the contact stress can be altered and therefore the thermoelastic contact damage can be modified by adjusting the gradient index, Peclet number and friction coefficient.     

高速列车制动闸片摩擦块形状对制动界面摩擦学行为的影响

在自行研制的高速列车制动缩比试验台上,对六边形、五边形和圆形摩擦块进行拖曳制动试验,研究摩擦块形状对高速列车制动界面摩擦学行为的影响,并采用有限元方法分析了不同摩擦块形状下制动界面接触行为的差异,探讨了摩擦块形状对接触压力分布及表面热分布的影响. 结果表明:摩擦块形状显著影响了制动界面磨损特性及接触压力分布,使得制动盘产生不同的温度分布现象. 在本试验条件下,六边形摩擦块表面磨损轻微,接触平台大小较为均匀,而五边形和圆形摩擦块表面呈现明显的犁沟和剥落特征,且大接触平台占比较高;六边形摩擦块与制动盘拖曳制动过程,界面具有较大的接触面积,使得接触压力分布较为均匀,表现出较好的接触行为,而五边形和圆形摩擦块的接触行为相对较为复杂,与之对摩的制动盘产生明显的热聚集现象.      

干摩擦条件下Al18B4O33晶须增强AC4C铝基复合材料的摩擦磨损特性

利用环－块磨损试验机,在干摩擦条件下研究了铸态与Ｔ６处理态Ａｌ１８Ｂ４Ｏ３３晶须增强ＡＣ４Ｃ铝基复合材料的摩擦磨损行为。结果表明：与铸态复合材料相经,Ｔ６处理态复合材料的耐磨性较差;晶须与基体间的界面化学反应影响复合材料的摩擦磨损特性,在本文试验载荷范围内,复合材料发生了由轻度磨损向严重磨损的转化;在高载荷下,除 了产生擦伤和粘着,在表层和次表层发生的应变硬化还会导致界面开裂、晶须断裂和分离;在低     

A unified model for adhesive interfaces with damage,viscosity, and friction

A general framework for models describing adhesive contact between rigid bodies is proposed. The intensity of adhesion is supposed to decrease under the action of prescribed tangential and normal relative displacements. The reduction is attributed to progressive damage, and comes with energy dissipation. Additional dissipation due to viscosity and friction is also taken into account. The response of the interface is described by a single state variable. It is determined by general laws expressing a mechanical version of the first two laws of thermodynamics, combined with a set of phenomenological assumptions.     

氧化锆陶瓷/碳纤增强聚醚醚酮在水润滑下的摩擦磨损特性研究

在材料端面摩擦试验机上对氧化锆陶瓷与碳纤增强聚醚醚酮(CFRPEEK)配副在水润滑条件下的摩擦磨损特性进行了试验研究,探讨了滑动速度和接触压力对材料摩擦磨损的影响规律.发现氧化锆陶瓷与CFRPEEK配副在水润滑条件下的摩擦系数随速度增加而减小,在速度较低时,存在明显的磨合过程;速度较高时,摩擦系数较小且随滑动过程变化很小,CFRPEEK的磨损率随速度变化不大.压力为0.4和0.5 MPa时,CFRPEEK的摩擦系数和磨损率均较小,但当压力达到0.8 MPa时,摩擦系数显著增加且剧烈振荡,并发生严重磨损.CFRPEEK的磨损机理主要是黏着磨损,氧化锆陶瓷磨损的主要机理是应力引起的点蚀.     

Thermo-electro-mechanical contact behavior of a finite piezoelectric layer under a sliding punch with frictional heat generation

The thermal contact problem of a piezoelectric strip with heat supply generated by the frictional tangential traction under the action of a rigid sliding punch is investigated. The inertial effects are considered. It is convenient to introduce the Galilean transform. Whole cases of the root distribution of the corresponding characteristic equation are detailed. Appropriate fundamental solutions that can lead to real solutions of the thermo-electro-mechanical quantities are derived for the piezoelectric governing equation. The stated problem is reduced to Cauchy singular integral equation of the second kind finally. Numerical results are also presented. The solutions have a reduced dependence on the material properties. The singular behaviors at the edges of the punch are revealed. The stress distribution and temperature distribution above the punch with the variations of the relative sliding speed, the frictional coefficient and the thickness are plotted. The effects of the material constants on the stress distribution and temperature distribution above the punch are presented.     

基于表面织构技术改善摩擦学性能的研究进展

利用表面织构技术改善材料表面摩擦学性能已被大量应用于许多工程领域. 然而,通过表面织构技术提高材料表面的减摩耐磨性能的确切机理仍不清楚,因此,研究人员进行了大量表面织构几何特征和工况条件的优化来研究表面织构技术的机理及应用范围. 本文作者回顾了近年来表面织构技术在控制摩擦方面的主要研究成果,从不同润滑条件下的减摩机制与理论模型展开讨论,重点从表面织构的几何特征和实际工况条件两个方面来评述改善材料表面摩擦学性能的最新进展,其中,几何特征包括表面织构的纹理形状、直径、深度、面密度和排列方式;实际工况条件取决于摩擦形式及操作条件,根据摩擦系数、磨损量、承载能力、阻力系数及升力系数等体现摩擦学性能的参数,对改善表面摩擦学性能的参数和条件进行分析和总结. 深入研究精确的理论模型和普适性的模拟方法并开发改善摩擦学性能的参数优化方法是未来的研究重点和方向.      

磨合过程中液体润滑实现超低摩擦的混合模型研究

针对球-盘滑动试验,在磨合过程中获得超低摩擦的液体润滑状态,建立耦合流体润滑、粗糙接触力学、Archard磨损方程和相关物理参数(液体黏度、表面粗糙度和磨损系数)时变函数的混合模型,研究磨合过程中液体润滑的摩擦系数演化. 通过数值模拟结果可知:在磨合过程中,润滑介质等效黏度增大,形成流体动压润滑薄膜,有效隔开粗糙表面;其次在磨合过程中,新生成的表面粗糙度降低,减少粗糙峰承载比,实现超低摩擦润滑状态;最后在适当的液体黏度和提高表界面效应减少边界摩擦系数,可进一步实现液体超低摩擦润滑状态. 为磨合过程宏观液体润滑性能演化所建立的混合数值模型对提高液体润滑超低摩擦设计效率具有重要价值意义.      

Sliding frictional contact between a rigid punch and a laterally graded elastic medium

Analytical and computational methods are developed for contact mechanics analysis of functionally graded materials (FGMs) that possess elastic gradation in the lateral direction. In the analytical formulation, the problem of a laterally graded half-plane in sliding frictional contact with a rigid punch of an arbitrary profile is considered. The governing partial differential equations and the boundary conditions of the problem are satisfied through the use of Fourier transformation. The problem is then reduced to a singular integral equation of the second kind which is solved numerically by using an expansion–collocation technique. Computational studies of the sliding contact problems of laterally graded materials are conducted by means of the finite element method. In the finite element analyses, the laterally graded half-plane is discretized by quadratic finite elements for which the material parameters are specified at the centroids. Flat and triangular punch profiles are considered in the parametric analyses. The comparisons of the results generated by the analytical technique to those computed by the finite element method demonstrate the high level of accuracy attained by both methods. The presented numerical results illustrate the influences of the lateral nonhomogeneity and the coefficient of friction on the contact stresses.     

Determination of optimal shape of a moving punch with friction taken into account

The optimization problem for the contact interaction between a rigid punch and an elasticmediumis considered. It is assumed that that the punch is under the action of some prescribed forces and momenta and moves along a surface bounding a half-space filled with an elastic medium. It is also assumed that themotion is quasistatic and the friction forces arising in the region of contact are taken into account. The punch shape is considered as the desired design variable, and the integral functional characterizing the discrepancy between the pressure distribution in the region of contact that corresponds to the optimized shape of the punch and a given goal distribution of pressure is taken as the minimizing criterion. The optimal shape can be determined efficiently by solving the following two problems: first, to obtain the optimal pressure distribution and then to solve a boundary value problemfor the elastic half-space under the action of the obtained normal pressure and friction forces. By way of example, the optimal shape is analytically determined for a punch of rectangular shape in horizontal projection.