双粗糙接触模型的表面温度在滑动摩擦过程中变化分析

建立三维双粗糙体分形表面的热力耦合接触模型,在固定滑动速度工况下综合考虑了钛合金材料的磨损失效、界面粘着及接触过程中的热力耦合,动态探讨了粗糙体在滑动过程中接触表面的温度变化情况。运用有限元方法对滑动过程的温度场进行模拟仿真并得出:滑动摩擦初始时刻摩擦表面接触温度急剧上升,随着滑动距离的增加,最高接触温度处于波动状态;界面剪切强度越大,最高温度越高。通过研究接触表面的温度场分布情况,以探索滑动过程钛合金材料摩擦磨损的真正起因。将结果与相关文献实验进行比较,得出了模拟仿真的合理性。     

弹塑性粗糙体/刚体平面滑动摩擦过程热力耦合分析

建立一具有三维分形特性的弹塑性粗糙表面与一理想刚性平面接触的热力耦合模型,充分考虑粗糙表面接触微凸体间的相互作用及接触界面摩擦热流耦合等的影响.运用大型有限元软件ANSYS中的非线性有限元多物理场方法,数值模拟并分析了滑动摩擦过程粗糙实体的热、力分布规律.发现由于速度的突变,滑动初始摩擦表面最高温度急剧升高,而匀速滑动中温升缓慢;整个滑动摩擦过程中粗糙表面的VonMises等效应力分布极其不均,且在接触凸点后方距表面一定深度处存在一拉应力区;在滑动瞬间及其闪点温度形成时,粗糙实体表面的VonMises等效应力发生明显变化,且最大拉应力值及其拉应力层厚度明显增大,此结果为材料裂纹萌生及扩展提供了一定的理论依据.     

热力耦合下微接触点塑性应变沿深度变化分析

在考虑粗糙实体弹塑性变形、热力耦合、微凸体间相互作用和摩擦热流耦合等影响下,运用有限元法数值模拟具有三维分形特性的粗糙面与刚性平面间滑动摩擦过程,分析了粗糙实体接触凸点塑性变形随深度变化情况。发现：在速度的突变和闪点温度形成时,摩擦接触表层等效塑性应变增大明显;在这一摩擦表层,过不同接触点的纵向剖面塑性应变沿深度分布不同：有的是接触表面塑性变形最大,有的是在接触微凸体表面下某一深度塑性变形最严重,而接触凸点表面的塑性应变稍小些。这与相关文献用SEM研究干摩擦后金属摩擦表层变形照片后发现的结果一致。滑动摩擦过程中,金属粗糙摩擦接触表层塑性变形的不断累积,将会导致材料表层中的夹杂或微观缺陷周围萌生微孔和裂纹源。     

双粗糙面滑动过程考虑黏着时的摩擦学性能分析

建立了二维双粗糙体分形表面的接触模型,在固定滑动速度工况下考虑材料的磨损失效,针对是否考虑接触过程中的黏着因素,动态探讨了粗糙体在滑动过程中的摩擦磨损变化情况。运用有限元方法对滑动过程的摩擦磨损进行模拟仿真,得出考虑黏着因素的界面剪切强度τ=σy/3(σy为材料的屈服应力)时的摩擦因数平均值为0.48;对滑动过程是否考虑黏着因素的磨损率及振动情况进行分析比较,引入快速傅里叶函数对摩擦振动进行变换得到功率谱,结果发现,考虑黏着因素的情况下,相应的磨损率较大,功率谱低频成分较多,振动相对比较平缓,所需要的能量也相应比较大。将模拟仿真结果与实验进行比较,验证了模拟仿真的合理性,也加深了对摩擦磨损过程物理图像的理解。     

滑动摩擦中不同润滑条件对应力层的影响研究

真实工程表面接触时,微凸体将产生弹塑性变形。建立了在不同润滑条件下二维双粗糙弹塑性分形模型,分析了润滑对滑动摩擦中应力层的分布影响情况。在完全润滑和边界润滑时材料表层下方出现易断裂的循环应力区域,干摩擦时循环应力层消失。     

粗糙表面基于G-W接触的三维瞬态热结构耦合

工程表面是粗糙的,其对磨损有较大影响.为了研究磨损过程的热动力学,文中基于G-W (Greenwood-Williamson)接触模型,将两个粗糙表面简化为一规则形状微凸体与一理想平面,分析在移动热源作用下接触面的边界条件,着重考虑摩擦滑动过程中两物体的弹性变形以及摩擦接触温度与接触区域应力的耦合问题,利用热-结构顺序耦合建立三维瞬态有限元计算模型.从而揭示粗糙表面滑动摩擦副的温度和热应力分布规律,为进一步研究热-机械失效问题及磨损机理奠定理论基础.     

Fe3Al基复合材料摩擦表面的分形特性研究

利用结构函数法对Fe3A l基复合材料干滑动摩擦表面的分形特性进行了研究,并计算其分形维数。结果表明Fe3A l基复合材料摩擦表面具有明显的分形特征,分形维数和摩擦因数以及磨损率之间有着密切相关性,随着分形维数的增大,摩擦因数和磨损率都逐渐减小,磨损率尤为明显,说明材料摩擦表面形貌特征对其摩擦学性能具有显著影响。     

CrNiMo钢在高速干滑动条件下摩擦表面的组织变化研究

在MMS-1G型高速干滑动摩擦磨损试验机上,采用CrNiMo钢作为销试样,与H96黄铜盘配副,进行了高速干滑动摩擦磨损试验,研究其高速干滑动摩擦磨损性能。对试验后的试样沿纵切面进行微观组织分析,探讨摩擦表面在试验前后及不同试验参数条件下的组织变化。结果表明,在高速干滑动条件下,CrNiMo钢材料的摩擦磨损性能随滑动速度的增加存在突变,其微观组织摩擦后沿纵切面发生了较大变化,且摩擦表面组织随滑动速度增加,发生了回复再结晶及碳化物的析出和长大。     

20 vol％SiCp/Al复合材料—硬质合金摩擦磨损表面形貌研究

以YG6X硬质合金为对磨材料,借助MMUD-5摩擦磨损试验机研究了载荷、转速和温度对20vol%SiC_p/Al复合材料干滑动摩擦磨损性能的影响,并采用SH-4000M扫描电镜和VHX-2000三维超景深光学显微镜对试样的摩擦磨损带进行观察。结果表明:当载荷小于150N时,表面质量较好,只有轻度涂覆现象;当载荷大于200N时,随着载荷的增加,表面质量越来越差,表面磨损主要为犁沟和剥离;在较低转速下,表面磨损主要是剥离和犁沟;在较高速度下,材料表面因较高的温度产生塑性形变,出现了裂纹和粘着磨损;当温度超过100℃后,磨损表面产生塑性变形,且随着温度升高,表面磨损由犁沟和剥离转变成粘着磨损和颗粒拔出等损伤。     

粗糙表面扭动微动磨损数值研究

基于三维W-M分形函数利用SolidWorks建立三维粗糙表面,同时利用Abaqus用户子程序Umeshmotion引入能量磨损准则,建立了三维球-粗糙面接触下的扭动微动数值模型,研究初始表面粗糙度对扭动微动摩擦磨损过程的影响。首先利用G-W模型的无量纲化接触面积解析解验证了粗糙面模型的合理性,同时通过与实验的磨损结果进行对比,进而验证了数值模型对扭动微动磨损预测的精确性和有效性。分析结果表明：表面粗糙度的改变对于扭动微动磨损有着显著的影响,其中磨损体积、摩擦耗散能以及磨损率都随着表面粗糙度的增加而增加,即在同等微动条件下会加剧表面磨损;摩擦激活能随着表面粗糙度的增加而减小,越粗糙的表面磨损激活的阙值越低,故减小初始表面粗糙度可有效降低扭动微动磨损。     

ANALYSIS OF THERMAL-ELASTIC STRESS OF WHEEL-RAIL IN ROLLING-SLIDING CONTACT

A coupling thermo-mechanical model of wheel/rail in rolling-sliding contact is put forward using finite element method. The normal contact pressure is idealized as the Hertzian distribution, and the tangential force presented by Carter is used. In order to obtain thermal-elastic stress, the ther-mal-elastic plane stress problem is transformed to an elastic plane stress problem with equivalent fictitious thermal body force and fictitious boundary distributed force. The temperature rise and ther-mal-elastic stress of wheel and rail in rolling-sliding are analyzed. The non-steady state heat transfer between the contact surfaces of wheel and rail, heat-convection and radiation between the wheel/rail and the ambient are taken into consideration. The influences of the wheel rolling speed and wear rate on friction temperature and thermal-elastic stress are investigated. The results show the following: ① For rolling-sliding case, the thermal stress in the thin layer near the contact patch due to the friction temperature rise is severe. The higher rolling speed leads to the lower friction temperature rise and thermal stress in the wheel; ② For sliding case, the friction temperature and thermal stress of the wheel rise quickly in the initial sliding stage, and then get into a steady state gradually. The expansion of the contact patch, due to material wear, can affect the friction temperature rise and the thermal stress during wear process. The higher wear rate generates lower stress. The results can help under-stand the influence of friction temperature and thermal-elastic stress on wheel and rail damage.     

Development of a wear equation for polymer-metal sliding in terms of the fatigue and topography of the sliding surfaces

A wear equation has been derived using the concept of fatigue failure due to asperity interactions in the contact region between sliding bodies. One of the three principal stresses that arise in the contact zone under the effect of a normal as well as a tangential load is of tensile nature. It is this principal stress that has been considered to be responsible for the initiation and propagation of fatigue cracks. It is assumed that the deformation in the contact zone is of elastic nature and that both the contacting surfaces are covered with asperities that have spherical tips. The wear equation involves the asperity height distribution φ(z). The particular distribution for a sliding situation is determined from experimental studies of the topography of sliding surfaces. The wear equation indicates that the wear rate depends upon the fatigue properties of the weaker material, normal load, sliding speed, coefficient of friction, moduli of elasticity of the contacting materials, asperity density, asperity radius of curvature and the distribution and standard deviation of asperity heights. The variation of wear with these parameters as indicated by the wear equation is in agreement with the experimental studies already reported in the literature.     

A Wear Model of Plane Sliding Pairs Based on Fatigue Contact Analysis of Asperities

Wear modeling is essential to predict and improve wear resistance of machine parts. This article presents a fatigue wear model of plane sliding pairs under dry friction. The wear model is constructed through developing a dynamic contact model of surfaces and proposing a mean fatigue damage constant of asperities. It is simpler and more practical than existing fatigue wear models because it describes the quantitative relationship between the wear behaviors of the plane sliding pairs and the main factors including the load and sliding speed, material property, friction property, and surface topography of the pairs. Furthermore, the wear model can predict the wear of each component of the sliding pairs. Reasonability and applicability of the wear model are validated via pin-on-disc wear tests. The wear model is applicable to predict the wear of the plane sliding pairs, which is characterized by friction fatigue of contact surfaces. The wear model can also be used to guide the tribological design of sliding pairs in machinery.     

考虑摩擦的圆柱面切向接触刚度分形模型研究*

为了更准确地计算圆柱面切向接触刚度,本文考虑摩擦因素的影响,在圆柱面分形接触模型的基础上,引入存在摩擦时弹塑性变形的临界面积公式,并利用切向接触刚度的基本理论,推导考虑摩擦的圆柱面切向接触刚度分形模型,并通过Matlab对上述模型进行仿真,研究不同参数(摩擦因数、分形维数、粗糙度幅值 、材料的特性参数、曲率半径)以及接触的形式对切向接触刚度的影响。仿真结果表明：切向接触刚度与法向载荷成正比关系,但随分形维数取值范围的变化分别呈现指数与线性规律。摩擦因数与切向接触刚度成反比关系;材料的特性参数对切向刚度的影响,不仅与分形维数有关,还与自身取值关联;分形维数,粗糙度幅值与切向刚度的关系,受分形维数和材料特性参数的影响呈现正比或反比趋势。另外,内接触比外接触时的切向刚度大;随着曲率半径的变大,切向刚度增加。该研究为后续开展高副结合面动力学分析提供理论 基础。     

Coatings tribology—contact mechanisms and surface design

The fundamentals of coating tribology are presented by using a generalised holistic approach to the friction and wear mechanisms of coated surfaces in dry sliding contacts. It is based on a classification of the tribological contact process into macromechanical, micromechanical, nanomechanical and tribochemical contact mechanisms, and material transfer. The important influence of thin tribo- and transfer layers formed during the sliding action is shown. Optimal surface design regarding both friction and wear can be achieved by new multi-layer techniques which can provide properties such as reduced stresses, improved adhesion to the substrate, more flexible coatings and harder and smoother surfaces. The differences between contact mechanisms in dry, water- and oil-lubricated contacts with coated surfaces is illustrated by experimental results from diamond-like coatings sliding against a steel and an alumina ball. The mechanisms of the formation of dry transfer layers, tribolayers and lubricated boundary and reaction films are discussed.     

Tribological Properties of Potassium Titanate in the Brake Friction Material; Morphological Effects

The tribological characteristics of brake friction materials containing different shapes of potassium titanate were investigated. They contain typical ingredients of a non-asbestos organic based friction material, including potassium titanate in the shapes of whiskers, platelets, and splinters. A Krauss type friction tester is used to obtain thermal stability and wear resistance of the friction materials at elevated temperatures. The results showed that the morphology of potassium titanate plays an important role in the formation of contact plateaus and transfer films on the rubbing surfaces, which are closely associated with tribological properties. The friction material with splinter shape potassium titanate shows better friction stability and improved wear resistance compared to those containing other types of potassium titanate due to larger contact plateaus and stable friction films at the sliding interface. On the other hand, the transfer films produced by the friction materials with platelet or whisker potassium titanate are not sustainable at elevated temperatures since they are easily detached during sliding, resulting in poor wear resistance.     

Tribophyiscal scaling effects in friction and wear of polymers on small‐ and large‐scale tests

Coefficients of friction and wear rates for polyacetal and polytetrafluoroethylene are measured on small‐scale cylinder‐on‐plate tests and large‐scale flat‐on‐flat tests. Three models for extrapolation between small‐ and large‐scale test results, which are based on experimental parameters, are presented: (i) one single mechanical parameter (normal load), (ii) the contact‐pressure–sliding‐velocity model (temperature limit), and (iii) a macroscopic geometry model. The last model is most extensively evaluated and considers thermal effects, sample geometry and contact conditions. After correction for the thermal sliding regime and viscoelastic deformation, the coefficients of friction can be extrapolated while the wear rates are more sensitive to the contact situation. High‐temperature tests on small scale are not representative for high‐load tests on large scale. Besides mechanical effects such as stress concentrations and debris mobility, variations in polymer structure under sliding (formation of rigid amorphous phase) and chemical interactions (wear debris polymerisation) also change with testing scale. The latter effects are explicitly illustrated from spectroscopic measurements on the worn surfaces. Copyright © 2008 John Wiley & Sons, Ltd.     

柱塞泵配流副滑摩界面摩擦磨损及热力耦合分析

针对轴向柱塞泵配流副滑摩过程中由摩擦温升所引起的摩擦磨损问题,建立配流副轴对称非稳态热传导方程,利用ABAQUS有限元软件进行配流副摩擦磨损及热力耦合特性分析,并利用端面摩擦磨损试验机进行试验验证。结果表明:在滑摩初期,相比于中低压力,高压力工况更易发生磨粒磨损;随着滑摩进行,材料表面粗糙峰被磨平,加之温度上升,材料强度下降,高转速取代高压力成为接触面温度和摩擦系数增大的主要影响因素,此时的磨损机制主要为黏着磨损;在滑摩过程中,外径出现了应力集中现象,且接触压力高于内径;转速及压力对配流副摩擦温升及磨损特性的影响是非线性的,在相同PV值下,转速比压力的影响更为显著。     

Wear resistance of coating materials under the frictional heating conditions

The problem of the wear of an elastic coating due to a rigid body sliding over the coating surface and heating due to contact friction has been considered. The solution of the quasi-static problem has been constructed in the form of a series over eigenvalues. The area of unstable solutions of the problem, where the thermoelastic instability of a sliding contact takes place, has been determined in the dimensionless parameter space. The wear resistance of a coating has been studied for different kinds of materials depending on the following parameters: the relative sliding velocity of contact surfaces, the mode of the contact interaction of the friction surfaces, the coating thickness, etc. taking into account the temperature and stresses developing at the contact interface.     

Effect of deformation of the contact surface on wear and friction—a study on clarification of the mechanism of abrasive wear

The cutting action due to a protuberance between the rubbing surfaces in abrasive wear might be susceptible to adhesion at the rake surface in the direction of sliding.

In the present paper we discuss an approach to clarify the abrasive wear mechanism, which is dominated by the effect of the difference in the contact deformation between both surfaces on wear and friction related with abrasive wear, on the basis of experiments conducted under ultrahigh vacuum.

Although in practice it is generally very difficult to obtain a characteristic surface during sliding, we carried out experiments on surfaces that were as clean as possible to investigate the effect of the size of the deformed contact surface on the abrasive wear.

Consequently, we were able to confirm that the friction differs according to which of the test pieces is the harder and, if the friction pair is composed of the same material, because the contact surface is deformed differently in each case.