表面织构在脂润滑条件下的摩擦性能研究

采用声光调Q二极管泵浦Nd:YAG激光加工系统在H13钢表面加工出不同密度的织构,以润滑脂作为润滑剂,利用MMW-1A型微机控制万能摩擦磨损试验机考察表面织构在不同载荷、不同转速条件下的摩擦磨损特性。实验结果表明:在脂润滑条件下表面织构能有效改善摩擦副表面的摩擦性能;与光滑无织构试样相比,表面织构试样的摩擦因数显著降低;一定范围内,随着织构密度的增加,平均摩擦因数呈现出先减小后增大的趋势,且织构密度为10%时的平均摩擦因数最小,最小平均摩擦因数为0.18,较光滑无织构试样减小32.23%;摩擦因数随着试验载荷的增大而减小,但随着转速的增加呈现出先减小后增大的变化趋势。     

线接触条件下微动摩擦特性的研究

通过试验研究了线接触微动摩擦特性。研究表明：线接触微动摩擦因数变化与点接触形式相同；位移幅值在部分滑移区时，表面粗糙度对表面磨损有影响。磨痕分析表明，承载区域接触不均匀，存在虚接触区域，其大小与表面粗糙度有关，而接触区域没有不磨损的粘着区，不同于点接触形式。     

面接触润滑条件下表面形貌对动压润滑的影响

利用课题组自主研发的面接触光干涉油膜厚度测量系统,对表面凹槽滑块的流体动压润滑油膜厚度进行了试验测量.试验中以静止的微型凹槽滑块平面和旋转的光学透明圆盘平面构成润滑副,且两润滑平面始终保持平行;在载荷固定的条件下,对油膜厚度—速度曲线进行测量.结果表明凹槽的宽度、深度、方向和位置等因素对油膜厚度有着重要影响.     

面接触边界润滑模型研究

根据经典的热传导公式,求解面接触边界润滑条件下的接触温度,再根据吸附热和摩擦因数、接触温度之间的关系建立一种求解边界润滑摩擦因数的模型。利用模型计算一个实例,通过分析发现,在载荷较低时,摩擦因数随滑动速度或载荷的变化变动很小,载荷较高时,摩擦因数随滑动速度或载荷的增大而增加;摩擦因数随接触温度的增加而增加;相对油亏量和摩擦因数有着基本一致的变化规律。通过在自制滑块-摩擦盘机构上的实验证实,实验结果和理论结果有相似的变化规律。     

边界润滑条件下表面微细织构减摩特性的研究

表面织构(Surface texture)已被证明是一种提高表面承载力和改善表面摩擦学特性的有效方法。然而在边界润滑条件下,织构对表面摩擦性能的影响机制仍未明确。利用纳米压痕仪在碳钢表面制作了具有不同密度和深度(125~500nm)的划痕的点阵,并通过改进的四球试验机对其在边界润滑下的摩擦性能进行了评价。试验载荷为100~300N,相对滑动速度为0.19~1.33m/s。研究发现:在边界润滑条件下,深度为125nm的低密度"划痕"点阵具有良好的减摩效果。     

面接触下水合羟乙基纤维素的润滑特性研究

以羟乙基纤维素(HEC)作为水基润滑添加剂,研究面接触条件下HEC润滑液的润滑特性。采用红外光谱仪分析HEC化学组成,结合分子动力学模拟分析HEC与水分子的相互作用,采用白光干涉三维表面形貌仪测量试样的表面形貌,借助微摩擦磨损试验机(UMT-2)探究转速、载荷、质量分数对润滑液润滑特性的影响。结果表明:HEC可以与水分子形成中、高强度的氢键;转速变化在摩擦副入口处对润滑液的成膜过程产生影响,进入摩擦副的润滑膜可以保持稳定的润滑状态,摩擦因数随转速增大几乎不变;增大载荷,润滑液在摩擦副间分布更加均匀,提升润滑性能,摩擦因数随载荷增大而减小;随润滑液质量分数增大,摩擦因数先减小后增大,质量分数为1.00%时摩擦因数最小。提出羟乙基纤维素水基润滑模型,模型包括水分子层和水合羟乙基纤维素层,其中水合羟乙基纤维素层起主要作用。     

定量供油条件下面接触油膜润滑特性的数值分析

建立定量供油条件下的面接触流体润滑理论模型,数值分析面接触副的膜厚-速度特性以及各工况参数对接触区润滑的影响。研究结果表明:供油量一定时,乏油现象会在某个卷吸速度下出现,并随卷吸速度增加逐渐恶化,而出口膜厚则随着卷吸速度的增加先增加后逐渐达到稳定,且其值接近于供油膜厚,与实验的结果具有良好一致性;供油量越小,或润滑油黏度越大,出口膜厚随卷吸速度的改变量越小。     

钢-钢摩擦副在不同润滑和接触形式下的高温减摩性能的研究

用多功能SRV试验机评价了在干摩擦和油润滑条件下,试验参数对钢-钢摩擦副在点接触和线接触形式下的高温减摩性能的影响。结果表明,在试验范围内,随着试验负荷的增大,钢-钢摩擦副在干摩擦条件下线接触摩擦因数和点接触摩擦因数呈逐渐下降的趋势,这种下降趋势在线接触时尤为明显;但在油润滑条件下,试验负荷的增大对钢-钢摩擦副之间的线接触和点接触摩擦因数的影响不显著。在干摩擦条件下,不论是在点接触还是线接触形式下,试验速度对钢-钢摩擦副之间的高温点接触和线接触摩擦因数的影响并不显著;但在油润滑条件下,试验速度对钢-钢摩擦副的高温线接触和点接触摩擦因数的影响都比较显著,特别是在较高的试验速度时影响更为明显。     

Ag膜在干摩擦、油和脂润滑下的摩擦学性能研究

精密运转部件表面沉积一层软金属银和银基固体薄膜可以有效地降低摩擦、减小磨损。通过钢球/镀Ag膜摩擦盘在干摩擦、4122油和L252脂润滑条件下的球-盘摩擦学试验,研究Ag膜在油和脂复合润滑下的摩擦学性能,分析润滑条件、载荷、速度对Ag膜摩擦因数的影响。试验结果表明:在4 N法向载荷和油、脂润滑下,与干摩擦相比,镀Ag膜摩擦副的最大静摩擦因数分别减小了10.7%和6.1%;在0～2 000 r/min转速范围内,Ag膜摩擦因数随转速增加而减小,与干摩擦相比,油润滑下Ag膜摩擦因数减小9%～48%,脂润滑下Ag膜摩擦因数减小17%～52%。Ag膜在干摩擦、4122润滑油和L252润滑脂复合润滑下,摩擦因数均随载荷增加而降低;Ag膜摩擦副/钢球在油、脂复合润滑下启动摩擦力矩小,摩擦副在宽转速范围内摩擦因数变化小,运转平稳。     

Approximate Formula for the Contact between Truncated Surfaces and Frictional Characteristics of a Journal Bearing in Mixed Lubrication

This paper presents an approximate formula for the contact of a non‐Gaussian distribution of truncated surfaces, which is useful for mixed lubrication theory, and gives a method for the determination of the truncation parameters in this formula from a measured roughness profile. Using this approximate formula for a contact, the approximate formula for the friction coefficient of a journal bearing in mixed lubrication, which was previously proposed by the authors, is modified for truncated surfaces, and the frictional characteristics are demonstrated for various parameters of truncated roughness using the modified formula.     

混合润滑下粗糙表面的接触刚度研究*

针对润滑状态下结合面的接触刚度问题,建立一种混合润滑状态下粗糙表面接触刚度等效薄层模型,将接触界面的总刚度等效为固体接触刚度和润滑剂接触刚度之和,研究不同实际接触面积下的表面形貌和润滑剂类型对法向接触刚度的影响,并讨论固体刚度和润滑剂刚度占总法向刚度的比例。结果表明：粗糙界面的法向接触刚度随法向载荷的增加而增加,且混合润滑状态下的接触刚度大于干接触条件下的接触刚度;在初始接触时,法向接触刚度敏感地依赖于润滑性能;随着实际接触面积的增大,表面形貌对接触刚度的影响变得更加明显。     

Experimental Study on the Tribological Properties of Powder Lubrication under Plane Contact

Powder lubrication has been studied using a plane contact tribometer. Four kinds of powders—polytetrafluoroethylene (PTFE), graphite, MoS₂, and ball-like copper—were used during the experiments. The results show that powder can be introduced into frictional clearance without any special treatment. The powder's physical properties significantly influence the tribological characteristics in the powder lubrication. The friction coefficient and wear are obviously decreased when the powders are PTFE, graphite, and MoS₂, which are excellent solid lubricants. At lower load capacity, powder lubrication using ball-like copper had certain antifriction effects, but it rapidly became worse with increasing load capacity. Observation with optical microscopy showed that the lubricant film is dynamically formed on the rubbing surfaces in most experiments.     

基于面接触的粉末润滑实验研究

利用石墨粉末颗粒,基于端面摩擦试验机对粉末润滑方式开展了摩擦学研究。试验了粉末冶金铜合金材料、粘结石墨润滑涂层、PTFE 3层自润滑复合材料3种试样在石墨粉末颗粒流润滑条件下的摩擦因数、温度及表面膜等特性,并与干摩擦和油润滑进行了对比。结果表明:粉末润滑可以实现与固体润滑膜、自润滑材料类似的无油固体润滑效果;利用它的持续补充性,可以实现动态补充和修复的固体润滑膜;但是,粉末润滑膜与基体附着能力较差。     

弹流润滑条件下织构表面亚表层特性研究

为研究在弹流润滑状态下表面形貌对亚表层特性的影响,利用激光加工方法获得2种微凹坑型织构表面形貌,通过将实测的表面形貌坐标输入弹流润滑数值计算程序得到油膜压力和膜厚分布;以对应工况的油膜压力作为表面法向压应力,利用Rabinowicz经验公式算出剪切应力;将表面法向压应力和切向剪应力叠加后对弹流润滑界面亚表层特性进行仿真研究。结果表明：表面织构使亚表层应力分布发生显著改变;微凹坑直径、卷吸速度对亚表层应力的大小与分布有不同的影响;亚表层变形在摩擦过程中呈现随深度增加先缓慢减小后快速下降的规律,研究结果将为通过表面形貌设计改善轴承等零件受力状况提供理论支持。     

Friction and Wear Properties of Micro Textured DLC Coated Surfaces in Boundary Lubricated Sliding

In the present study, the friction and wear properties of boundary lubricated textured surfaces were investigated. The capability to feed lubricant into the interface of a sliding contact and to isolate wear particles was related to the shape, size and orientation of the texture patterns. Well-defined surface textures of square depressions or parallel grooves of different widths and distributions were produced by lithography and anisotropic etching of silicon wafers. Subsequently the wafers were PVD coated with thin, wear resistant DLC coatings, retaining the substrate texture. The surfaces were evaluated in reciprocating sliding against a ball-bearing-steel ball under starved or amply lubricated boundary lubrication conditions.     

Influence of grease composition on rolling contact wear: Experimental study

This paper presents an experimental study on the influence of grease composition on rolling contact wear (RCW). Experimental tests for three greases and correspondent base oils were carried out on a twin-disc machine under pure rolling conditions. The following parameters were varied: base-oil viscosity, percentage of soap concentration and the presence of additives. The second aim of these tests is to analyse the use of artificial dents as a technique to evaluate RCW: prior to the tests, artificial dents were printed on one of the contacting surfaces. These dents were used to calculate the wear volume that is removed from the surfaces, based on the assumption that when the material is removed, the diameter of these dents diminishes. For each stop, images obtained using video-microscopy were analysed and the diameter of the dents, at a given number of cycles, was calculated. It was found that tests with different lubricants resulted in different damaged areas around the dents. Based on this, a comparison of this area growth throughout the fatigue cycles was used as a way to compare the influence of grease composition on RCW.     

Rolling Contact Fatigue Performance of Vibro-Mechanical Textured Surfaces

The rolling contact fatigue (RCF) performance of vibro-mechanical textured surfaces in a point elastohydrodynamic lubrication (EHL) condition is investigated. Two dimple designs, small (100 μ m × 100 μ m) and large (240 μ m × 100 μ m), are compared with a nontextured sample. Experimental RCF tests show that the textured surfaces exhibit a significantly reduced number of cycles to failure compared with the nontextured sample for the high load, pure rolling conditions evaluated. In order to understand these results, numerical models are used to calculate the lubrication and contact pressure conditions and the subsurface stress distribution. The fatigue failure trends observed experimentally are compared with the simulation results with good agreement. It is determined that RCF performance is related to the presence and size of the generated dimple.     

润滑油添加剂对陶瓷球接触疲劳的影响

利用自制的球-棒疲劳试验机研究了4种润滑油添加剂对Si3N4与GCr15钢摩擦副接触疲劳性能的影响，并借助于扫描电镜(SEM)和X射线能量色散谱(EDAX)分析了Si3N4陶瓷球表面疲劳成因及不同添加剂的抗疲劳机理。结果表明，4种添加剂都不同程度地提高了Si3N4陶瓷球的接触疲劳寿命，其中以极压抗磨剂效果较好；点蚀剥落是Si3N4陶瓷球的主要失效形式；添加剂抗疲劳的主要原因是在钢表面形成反应膜，在陶瓷球表面形成转移膜，降低了滑动摩擦力。     

水润滑条件下转速对车轮钢滚动接触疲劳和磨损性能的影响

为探究水润滑条件下转速对车轮钢滚动接触疲劳和磨损性能的影响,利用滚动接触摩擦磨损试验测试不同转速下车轮试样的剥离寿命、摩擦因数和磨损率,并结合磨损形貌和裂纹扩展形貌观察,对比分析不同转速下摩擦磨损和剥离寿命的影响因素。结果表明:随转速提高,车轮材料氧化程度加剧,导致摩擦因数逐渐增加;当转速由250 r/min增至500 r/min时,摩擦因数增幅较小,应变速率增加导致磨损率下降,当转速由500 r/min增至1000 r/min时,摩擦因数急剧增加,导致材料磨损率增加;随转速提高,剖面塑性流动层厚度、裂纹扩展角度、裂纹分叉深度和最大扩展深度均呈现减小趋势。转速增加带来的摩擦因数的增加,一方面缩短裂纹萌生寿命,另一方面减小了裂纹发生向上转折的深度,最终导致滚动接触疲劳寿命随转速的增加而减小。