介观双粗糙弹塑性流体动力润滑界面法向接触刚度模型

Model of Normal Contact Stiffness of Mesoscopic Double Rough Elastoplastic Hydrodynamic Lubrication Interface

弹性流体动力润滑状态通常出现在机械高副零部件的点/线接触部位,如齿轮、轴承和蜗轮蜗杆等.宏观上点/线接触在介观层面表现为两粗糙表面的接触,在微观层面上则又表现为微凸体间的接触.由于在中/重载荷作用下,粗糙表面上的微凸体发生接触后会产生弹塑性/塑性变形,从而使得两粗糙表面的弹流润滑接触转变为弹塑性流体动力润滑接触.此外,界面的接触刚度决定了机械装备的整机刚度.为了精确获得弹性流体动力润滑状态下界面法向接触刚度及其主要影响因素,基于界面的法向接触刚度由固体接触刚度和润滑油膜刚度两部分构成的思想,根据固体弹塑性理论和流体动力学理论,分别对界面间微凸体侧接触及部分膜流体动力润滑进行分析,从微观入手揭示双粗糙表面弹塑性流体动力润滑接触机理,进而建立考虑微凸体侧接触弹塑性变形的流体动力润滑界面法向接触刚度模型.通过仿真分析,揭示了法向载荷、卷吸速度、表面粗糙度及润滑介质特性等因素对润滑界面法向接触刚度的影响规律.研究表明:在相同速度、粗糙度及润滑油黏度的工况下,固体接触刚度和油膜接触刚度均随着法向接触载荷的增加呈非线性增大;在相同载荷、速度及润滑油黏度的工况下,接触表面粗糙度越大,表面形貌对于润滑状态的影响较强,固体接触刚度占界面总刚度的主要部分,界面主要由固体承载;在相同载荷、粗糙度及润滑油黏度工况下,随着卷吸速度的增大,固体接触刚度逐渐减小,油膜刚度占界面总刚度的主要部分;在相同载荷、粗糙度及速度工况下,随着润滑油黏度的增大,油膜刚度基本保持不变,固体接触刚度基本不受润滑油黏度的影响.通过理论建模准确获得单位面积弹塑性流体动力润滑结合面法向接触刚度,对改善机械装备动态性能、提高机械装备的可靠性具有重要的理论和实际意义.

Elastohydrodynamic lubrication state usually appears in the point/line contact parts of high mechanical parts,such as gears,bearings,worm wheels.At the macroscopic level,the point/line contact is the contact between two rough surfaces at the mesoscopic level,and the contact between two convex bodies at the microscopic level.The elastoplastic/plastic deformation occurs when the contact of the micro-convex body on the rough surface occurs under medium/heavy load,so the elastohydrodynamic lubrication contact of the two rough surfaces is transformed into an elastoplastic hydrodynamic lubrication contact.In addition,the contact stiffness of the interface determines the overall stiffness of the mechanical equipment.In order to accurately obtain the normal contact stiffness of the interface under elastic hydrodynamic lubrication and its main influencing factors,based on the idea that the normal contact stiffness of the interface is composed of solid contact stiffness and lubricating oil film stiffness,according to solid elastoplastic theory and fluid dynamics theory,the side contact of the slightly convex body between the interface and part of the hydrodynamic lubrication of the film are analyzed respectively.The contact mechanism of elastoplastic hydrodynamic lubrication on double rough surfaces was revealed from the microscopic point of view,and then the normal contact stiffness model of hydrodynamic lubrication interface was established considering the elastoplastic deformation of the side contact of micro convex body.Through simulation analysis,the influence law of factors(normal load,enrolling speed,surface roughness and lubrication medium characteristics)on the normal contact stiffness of lubrication interface was revealed.The results showed that under the condition of the same speed,roughness and viscosity of lubricating oil,the solid contact stiffness and oil film contact stiffness increased nonlinearly with the increase of normal contact load.Under the same conditions of load,speed and lubricant viscosity,the greater the roughness of the contact surface,the stronger the influence of surface topography on the lubrication regime.The contact stiffness of solids accounted for the main part of the total stiffness of the interface,and the interface was mainly borne by solids.Under the same load,roughness and lubricant viscosity conditions,the contact stiffness of solids gradually decreased with the increase of relative velocity,and the oil film stiffness accounted for the main part of the total stiffness of the interface.Under the same load,roughness and speed conditions,the oil film stiffness basically remained unchanged with the increase of lubricating oil viscosity,and the solid contact stiffness was basically not affected by lubricating oil viscosity.It was of great theoretical and practical significance for improving the dynamic performance and reliability of mechanical equipment to accurately obtain the normal contact stiffness of elastic-plastic hydrodynamic lubrication joint surface per unit area through theoretical modeling.