非牛顿润滑的滚滑线接触表面摩擦特性

Frictional characteristics of rolling-sliding coexisting line contact surface with non-newtonian lubricant

线接触粗糙表面的摩擦特性对机械结构表面的润滑设计与润滑状态预测具有重要的意义。为预测混合润滑状态下弹塑性线接触表面的摩擦特性,基于法向外载荷由润滑油膜与微凸体共同承担的载荷分配思想,分别采用Kogut-Etsion微观接触模型(KE模型)和Carreau流变模型描述干摩擦粗糙表面的接触和润滑油的非牛顿特性,建立了一种可快速、准确预测混合润滑状态下滚滑线接触表面的摩擦系数模型。模拟了法向载荷、表面粗糙度、润滑油入口黏度以及微观粗糙接触模型对摩擦系数的影响规律。结果表明:润滑油的剪切稀化行为很大程度上减小了油膜厚度,导致更多微凸体与微凸体间的直接接触,从而引起总摩擦系数的增大;在轻载、粗糙度较小、润滑油入口黏度较大的润滑工况下,表面更易从混合润滑过渡为流体动力润滑状态;当表面处于边界和混合润滑状态时,基于KE模型预测的表面总摩擦系数和微凸体摩擦系数均小于仅考虑微凸体纯弹性变形的模型预测结果,而对于润滑油膜的摩擦系数,该结果是相反的。

The friction characteristics of the line contact rough surface are of great significance for the lubrication design and lubrication state prediction of mechanical structures.To predict the friction behavior of the elastic-plastic line contact surface under mixed lubrication condition,the Kogut-Etsion(KE)model and the Carreau model were utilized to describe the dry contact and the non-Newtonian characteristics of the lubricant respectively.A mixed friction coefficient model for the rolling-sliding coexisting line contact surface was proposed based on the load-sharing concept in which the normal load was shared by the lubricant film and the asperity.The effects of normal load,surface roughness,lubricant inlet viscosity and the micro-contact model on friction coefficient were analyzed.The results showed that the film thickness was reduced by shear thinning behavior of the lubricant film greatly,which caused more asperity to asperity contacts,thereby increasing in the total friction coefficient.With the conditions of light load,small roughness and high inlet viscosity,it was easier to occur that the transition from mixed to hydrodynamic lubrication.In the boundary and mixed condition,the total friction coefficient and the asperity friction coefficient predicted based on KE model were smaller than the results of model only considering the pure elastic deformation of the asperity,while for the hydrodynamic friction coefficient,the result was opposite.