粘塑性流体的界面滑移对润滑性能的影响研究

首先指出经典润滑理论中的边界无滑移条件已不再适用于具有极限剪应力的粘塑性流体润滑．而后，通过确定最大剪应力位置和加入剪应力边界条件，建立了界面滑移后的润滑方程．在联立求解不同区域的润滑方程基础上，对界面滑移的开始位置及扩展方式进行了分析．最后，讨论了不同膜厚比下滑移对润滑性能的影响．

STUDY ON INFLUENCE OF THE BOUNDARY SLIP OFVISCO-PLASTIC LUBRICANT ON THE LUBRICATIONPROPERTIES

Hydrodynamic lubrication theory based on viscous fluid mechanics has greatly devel-oped the tribology theory. However, because the mechanical equipment is developed with muchhigher speed and larger scale in recent years, lubrication failure occurs frequently. In electric gen-erator sets and mill trains, accidents caused by lubrication failure cost great lost. According tostatistics of the former Soviet Unions, 60 percent of the accidents in hydroelectric generator setsare caused by lubrication failure. The lubrication failure has also happened in some hydroelectricstations of China~[l]. The burning of bearing bushes in the mill train is frequent. Because thehappening of lubrication failure is unpredictable and with destructive effect, to study and solvethis problem is very important.It should be pointed out that most of lubrication failure accidents happened under the con-ditions that the bearing had passed through the design of the classical hydrodynamic lubricationtheory. This raises the doubt on the correction and rationality of the theory to predict lubricationfailure.The plasticity of solid materials is well known. After the subjected stress reaches the yieldstrength of the solid material, its load carrying capacity cannot increase anymore. The yield regionincreases rapidly until the material is broken.In lubrication theory, it is known that a fluid film can also carry vertical load under thehydrodynamic conditions. However, the research on how the film will be broken is not well studied,yet, especially from the view point of a visco-plastic fluid.Recent high pressure rheological experiments have shown that lubricant possesses plasticity,too~[2]. Therefore, non-Newtonian fluid lubrication becomes a main field to study lubrication failure.Researches~[3-6] show that a slip may occur between fluid and solid with consideration of the limitingshear stress. It may change the distribution of the velocity and weaken the load carrying capacityof lubricant film.In the present paper, it is pointed out that the non-slip boundary conditions in the classicallubrication theory are no longer suitable to the visco-plastic fluid lubrication. By determiningthe position of the maximum shear stress and adding stress boundary condition, slip boundarylubrication equations are deduced. With solving the equations, the happening and expanding ofthe boundary slip are analyzed. Finally, the influences of the boundary slip with different filmratio on the lubrication properties are discussed.