Measurements of friction in strip drawing under thin film lubrication

Strip drawing is used to investigate the friction behaviour under thin film lubrication in metal forming with plastic deformation. Friction coefficients are measured under a wide range of tribological conditions. The surface roughness is measured on an interferometric profilometer. The results show that the friction coefficient decreases with increasing oil film thickness h_w, as estimated using a formula appropriate for smooth tool and workpiece. Measurements of the surface topography show that change in friction is associated with a change in contact ratio between the tool and strip. The effect of strip reduction, strip roughness and die roughness on the friction coefficient is also investigated.     

水溶性3-(N,N-二正丁基二硫代氨基甲酸基)酸衍生物的摩擦学性能

通过摩擦学实验和表面分析研究了两种酸衍生物，3-(N，N-二正丁基二硫代氨基甲酸基)丙酸及3-(N，N-二正丁基二硫代氨基甲酸基)丙二酸的摩擦学性能及作用机理。实验表明：两种酸衍生物均具有优良的承载能力和抗磨性能．并能显著提高水基液的烧结负荷．且3-(N，N-二丁基二硫代氨基甲酸基)丙二酸的摩擦学性能优于3-(N，N-二正丁基二硫代氨基甲酸基)丙酸，其抗磨作用机理是在摩擦表面形成了吸附膜和化学反应膜，两类膜的共同作用有效地阻止了摩擦失效的发生。     

Tribochemical Reactions and Lubricating Effects of Fluorinated Methanes for Al2O3 Ceramic

It has been found that CF₃CH₂F (HFC-134a) gas is an effective lubricant for several ceramics because of the formation of fluorine-containing tribochemical products. To understand the influence of the molecular structure of fluorine-containing gases on the lubricating characteristics, the lubricating effects and tribochemical reactions of some fluorinated methanes for Al₂O₃ ceramic were studied. X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) were used to identify the chemical structure of tribochemical products. It was found that the friction and wear of Al₂O₃ ceramic were dependent on the molecular structure of the reacting fluorocarbon gases. The lowest friction was obtained in CH₂F₂. CHF₃ showed the best anti-wear effect. The results of surface analyses indicate that greater amounts of tribochemical products are produced when Al₂O₃ rubs in CH₂F₂ than in CF₄ and CHF₃ gases. C–C/C–H/carbon and AlF₃, which are mainly formed on the sliding surface in CH₂F₂, are responsible for the low friction. The mechanism of tribochemical reactions of the different environmental molecules on the nascent surface of Al₂O₃ was also discussed.     

Multilevel solution for thermal elastohydrodynamic lubrication of rolling/sliding circular contacts

A fast multigrid approach is presented for the analysis of thermal elastohydrodynamic lubrication (EHL) under rolling/sliding circular contacts at high loads and high slip ratios with low computing time on a personal computer. This fast solver combines directiteration, multigrid, Newton-Raphson, Gauss-Seidel iteration, and multilevel multi-integration methods into one working environment that can reduce the computational complexity from O(n³ to O(nlnn) for the thermal EHL problem under rolling/sliding circular contacts. Since the couped Reynolds and energy equations are simultaneously solved by the Newton-Raphson scheme, the iteration for the convergence solution is less than those of the classical approach. Results show that thermal effects on the pressure profile and film thickness are significant for a wide range of loads, speeds and slip ratios. The maximum midfilm and surface temperature rise in the Hertzian contact region increases with increasing slip ratio, dimensionless speed, and load. The minimum film thickness decreases with increasing load and slip ratio, and decreasing dimensionless speed.     

In Situ Study of Metal Oleate Friction Modifier Additives

There has been debate for many years as to whether long-chain surfactant friction modifier additives reduce friction by forming adsorbed films of monolayer thickness or whether they form films equivalent to several or many multilayers thick. In the work described in this paper, a series of metal oleate friction modifier additives has been synthesized and their film-forming properties compared in rolling-contact conditions by means of ultrathin film interferometry. It has been found that some of these additives form thick boundary films while others do not. It is concluded that thick boundary-film formation results from the formation of insoluble iron(II) oleate on the rubbing surfaces and that, for metal oleates, this occurs only for metals lower than iron in the electrochemical series and is due to a redox reaction involving iron from the steel surface and the metal oleate.     

基体状态对FeS层固体润滑性能的影响

研究了不同基体硬度的模具钢渗硫层和不锈钢渗硫层减摩耐磨行为及其机理，结果表明硬度高的模具钢渗硫层固体润滑性明显强于不锈钢渗硫层。其机理为在其它条件相同的情况下，基体越硬，越能够抵抗对摩件表面微凸体的刺伤和刮擦破坏，从而给予渗硫层更好的支撑。     

有序薄膜润滑的速度场

基于有序膜分子模型分析薄膜润滑中的速度场分布。薄膜润滑中有序膜分子的取向与向列相液晶分子有类似性,可用“向矢”表示。利用液晶理论可以分析薄膜润滑的速度场和润滑剂分子的取向,为分析薄膜润滑的特性提供依据。薄膜润滑区别于弹流润滑之处在于有序膜分子的弹性。粘弹比可以很好地表征这种差异。给出了不同粘弹比下的“向矢”角度和等效粘度的分布情况以及速度场的分布情况。     

航空发动机主轴圆柱滚子轴承弹流动态性能仿真

基于现代弹流理论和弹性力学理论建立了圆柱滚子轴承等温稳态、非等温时变及其接触面粗糙的热弹流分析模型和应力分析模型,用数值分析方法对模型进行了求解,并对圆柱滚子轴承弹流动态性能和滚动体接触应力进行了仿真。仿真结果表明,轴承速度、载荷、粗糙度是影响轴承弹流性能的主要因素;在不考虑其它因素情况下,接触区内中部的接触应力最高。     

Film thickness and roughness of ZDDP antiwear films

The two experimental techniques, spacer layer interferometry imaging (SLIM) and atomic force microscopy (AFM), have been used to measure the thickness and roughness of zinc dialkyl dithiophosphate (ZDDP) reaction films formed in a rolling-sliding minitraction machine (MTM) tribometer. The AFM method has been complemented by a novel ZDDP film removal method based on ethylenediaminetetraacetic acid (EDTA) solution. It has been found that the two approaches measure very similar ZDDP film thickness values, lending credence to both methods. However the AFM approach measures much rougher ZDDP reaction films than MTM-SLIM and it is believed that SLIM underestimates the film roughness. Based on this, the use of MTM-SLIM is recommended for monitoring the evolution of antiwear film thickness during rubbing, while AFM should be employed for studying the morphology of antiwear films.     

Experimental simulation of chemical reactions between ZDDP tribofilms and steel surfaces during friction processes

Friction tests are performed in a controlled environment (Ultra High Vacuum), between steel surfaces and a ZDDP tribofilm at different contact severities. According to AES analyses, evidence of chemical reactions activated by friction is given. The reaction of the ZDDP tribofilm with the native iron oxide could partially explain its antiwear behavior.