Influence of the Wetting Properties of Liquids on the Tribological Behavior of Selected Sliding Materials in Mechanical Seals

Theoretical investigations are carried out for a plain journal bearing considering the influence of thermal effects on non-Newtonian lubrication. With reasonable assumptions, the steady state and dynamic characteristics are presented using a thermohydrodynamic analysis of a bearing lubricated by a nonlinear, i.e., cubic, fluid model.

Experiments are conducted on a rig to study the steady state and dynamic performance of a full journal bearing with different types of non-Newtonian lubricants. Experiments include the measurements of eccentricity ratio, critical speed, and stability limit.

The theoretical investigation reveals that the interaction of the non-Newtonian effect and the thermohydrodynamic effect is strong for friction, and the interaction effect is negligible in the case of eccentricity ratio, attitude angle, and lubricant flow rate. Further, for relatively high values of non-Newtonian parameter, α_n , the effect due to the non-Newtonian parameter is not negligible.     

Tribological Properties of Lubricating Films on the Al-Si Alloy Surface via Laser Surface Texturing

Dimpled textures were prepared by using a pulse solid laser on the surface of Al-Si alloy. The combination of laser surface texturing (LST) and MoS₂ solid lubricant as well as their tribological properties were investigated in this article. The obtained friction and wear data were critically analyzed to investigate how the parameters of texture influence the tribological performance of Al-Si alloy. Furthermore, morphological investigations of the transfer layers on the worn surfaces were performed and the wear mechanisms are discussed. The results show that the combination of LST and solid lubricant improves the tribological characteristics of Al-Si alloy. The friction coefficient of Al-Si alloy: steel friction pairs can be reduced to 0.15 under dry friction. The lubrication mechanism is attributed to a synergetic effect of providing solid lubricant and traps wear debris in the dimples. It was found that the optimum density of structure was 37% for excellent tribological properties.     

Surface Films and Soluble Degradation Products Formed in a PFPAE Fluid and Their Implications to the Wear of Steel

The soluble degradation products were generated in a linear perfluoropolyalkylether (PFPAE) fluid in boundary lubrication. Perfluoropolyalkylether carboxylic acid species were found in the residual fluids from the sliding tests by vibration spectroscopy. Surface-bound organic and inorganic reaction products were identified by vibration microspectroscopy with a grazing angle objective attachment and X-ray photoelectron spectroscopy (XPS), respectively. Inorganic surface films were found to be composed primarily of FeF₃. A monodentate perfluorocarboxylate surface species was found on the sliding surfaces in 50° and 100°C tests but not found in 150°C tests. The higher friction and wear in 150°C tests as compared to 50° and 100°C tests were attributed to the absence of the perfluorocarboxylate species over the sliding surfaces at high temperatures.     

Effect of the Anion on the Tribological Properties of Ionic Liquid Nano-Films on Surface-Modified Silicon Wafers

The films of three kinds of 3-butyl-1-methylimidazolium base ionic liquids with thickness of 2 nm were prepared on hydroxyl-terminated and amino-terminated Si substrates by dip-coating method. As anions, tetrafluoroborate, hexafluorophosphate, and adipate, respectively, were chosen. The tribological performances of these thin films were examined by the determination of the film durability and friction coefficient by means of a UMT-2MT tribometer using a steel ball as counterpart. The morphologies of worn surfaces were investigated by a non-contact interferometric microscope. The findings showed that 3-butyl-1-methyl-imidazolium hexafluorophosphate having the poorest hydrophilicity of the ionic liquids exhibited the best tribological properties on aminated Si surface at 0.4 N and 4 Hz.     

Effects of Magnesium Borate Whiskers on the Antiwear and Mechanical Performance of Natural Rubber

Magnesium borate whiskers (MgBWs) are utilized to improve the antiwear and mechanical performance of natural rubber (NR). The results suggest that the wear resistance of the vulcanizates was increased significantly and the mechanical performance of the vulcanizates was increased to some extent with the inclusion of MgBW. Bis-(3-[triethoxysilyl]-propyl)-tetrasulfide (Si-69) and tea polyphenols (TPs) were used to improve the inferior interface between MgBW and the NR matrix and their effectiveness and the relationship of structures and the properties were explored. The micrographs illustrate that the interfacial interactions between the whiskers and matrix were obviously enhanced after surface modification by Si-69. With the incorporation of TP, the wear resistance of the vulcanizates was further increased. The present investigations attribute the improvement of antiwear properties of NR to the high antiwear ability of whiskers and the improved mechanical performance of the vulcanizates.     

The Influence of Longitudinal and Transverse Profile on the Load Capacity of Pivoted Pad Bearings

An extension of previous work on the effects of surface profile on the load capacity of pivoted pad thrust bearings. Numerical solutions are presented for a square pad having profiles consisting of (a) longitudinal curvature, (b) transverse curvature, and (c) a combination of (a) and (b). Improved load capacity over the flat pad with optimum pivot location is found for some operating conditions including the case of the centrally pivoted pad.     

基于Advantedge仿真的具有表面功能结构的刀具设计

表面功能结构又称表面微观结构已经在改善材料加工性能方面,如表面摩擦性能和表面承载能力等,得到了广泛的认可,改善了刀具性能。通过设计带有微结构的刀具,用于改善钛合金的切削加工过程中刀具的磨损状况,延长刀具的使用寿命。并且在设计的过程中借助先进的有限元仿真软件Third wave AdvantEdge FEM进行仿真模拟。通过软件仿真替代大量的试切,避免试切过程中材料的浪费,更重要的是,可以在实际切削实验进行前对刀具的设计进行预测评价,节省了设计时间。     

Experimental Study on the Friction Characteristics of Textured Steel Surface with Ring-Shaped Pits under Lubricated Sliding Conditions

Surface texturing has been recognized to be an effective approach to modify the tribological performances of sliding surfaces. A ring-shaped texture has been fabricated on the surface of AISI1045 steel using a pulse laser, and reciprocating sliding tests were performed on a variable load tribometer (VLT). Frictional force of the textured surfaces was investigated under various geometrical parameters (inner radius, external radius, pitch, and offset ratio of texture units) and operating conditions (velocity and load). The results show that the width of the ring-shaped texture has a significant influence on antifriction, an optimum width for minimum friction is about 200 µm, and the staggered array of texture units is an effective way of reducing frictional force and wear.     

Numerical Simulation of the Influence of the Bulges around Laser Surface Textures on the Tribological Performance

To improve the tribological performance of mating surfaces such as journal bearings, dimples with different shapes were introduced through laser surface texturing. In laser surface texturing processes, bulges are always induced around the dimples and may influence the tribological performance of the surface. In this article, the influence of the bulges on the tribological performance of a journal bearing is numerically investigated. Variations in both the friction coefficient and the eccentricity ratio of a journal bearing with the width and height of the bulges are studied. The influence of the radius of the dimples on the tribological performance of a journal bearing is also investigated. Results show that the friction coefficient increases with both the width and the height of bulges in the case of journal bearing under light and moderate loading conditions, which is in accord with the experimental results in previous works. The linear variation in the friction coefficient with the height of the bulges indicates that the wear rate of the bulges may be investigated by monitoring the friction coefficient. The abnormality of friction coefficient variation with the width of the bulges in the case of heavy loading condition indicates that introducing the bulges is an effective approach for reasonable tribological performance. From the results for the influence of the dimple radius, it can be concluded that although the introduction of dimples can improve the tribological performance, it also has some disadvantages such as decreasing the load-carrying capacity.     

碳纤维表面处理对单向C/C复合材料强度的影响

通过对碳纤维表面进行适当的氧化处理 ,改善纤维 /基体之间的界面结合 ,能在复合材料中得到较好的纤维强度利用率 ,提高材料性能。本文在不同条件下对碳纤维进行液相氧化和空气氧化处理 ,并测定了所制备的单向 C/C复合材料的强度 ,研究了不同氧化工艺条件对复合材料拉伸强度的影响 ,对采用氧化后纤维制备材料断裂机制的改变进行了讨论 ;研究发现液相氧化处理对 C/C复合材料的性能影响较为显著。     

测量表面粗糙度的激光高分辨率传感器的设计

文中介绍了一种测量表面粗糙度的高分辨率传感器,该设计应用聚集探测和光电技术,具有非接触、响应快和性能可靠的特点。     

Influence of Lubricant Additive and Surface Texture on the Sliding Friction Characteristics of Steel under Varying Speeds Ranging from Ultralow to Moderate

A newly developed tribometer that undergoes significant changes in sliding speed, ranging from ultralow (5 μm/s) to moderate (17 cm/s), was used to study the lubricated friction characteristic of steel. In this study, the friction characteristics of stearic acid-formulated oil were studied to clarify the effects of surface roughness or surface roughness texture on friction. Several kinds of specimens having isotropic and anisotropic surface roughness with different textures were used. For an isotropic surface, a rougher surface resulted in low friction under low-speed conditions. The same surface produced high friction under high-speed conditions, where macroscopic hydrodynamic action was predominant. Remarkably less friction was observed in the transverse than in the longitudinal direction when the specimen had anisotropic roughness. This difference was particularly notable under ultra-low-speed conditions. Two other parameters of skewness and kurtosis of roughness distributions show that low friction was obtained when surface roughness distribution approached normal. It appears that the low friction observed with a rough surface or a transverse roughness direction could be explained by the microscopic hydrodynamic action of fluid together with the lubricity of the adsorbed molecular layer.