边界膜剪切弹性模量对于微接触性能的影响

INFUENCE OF THE BOUNDARY FILM SHEAR ELASTIC MODULUS ON THE PERFORMANCE OF A MICRO CONTACT

建立接触模型,理论分析了微接触中边界膜剪切弹性模量对于接触性能的影响.接触区由两平行平面形成,属一维接触.上接触表面为粗糙表面,具有矩形微凸体.下接触表面为光滑平面.两接触表面均处理成刚性表面.微接触区中充满流体.它分成两个子区,在微接触的出口区由于极小的接触间隙充满边界膜,在微接触的入口区由于接触间隙较大充满流体膜.边界膜和流体膜行为决定整个微接触性能.当膜厚较大时,这里边界膜可看成纳米级薄膜.由于上接触表面处有限的剪应力承受能力,边界膜可于上接触表面滑移.设下接触表面处剪应力承受能力很大而边界膜在下接触表面不滑移.由于边界膜-接触表面间相互作用,边界膜黏度、密度和剪切弹性模量均沿膜厚变化,在理论分析中使用它们的等效值,这些值与边界膜厚度有关.流体膜在两个接触表面均不发生滑移,分析中不考虑流体膜剪切弹性模量.流体膜采用传统分析法.给出了理论分析和若干变工况参数下的计算结果.

A contact model is developed to theoretically analyze the influence of shear elastic modulus of the boundary film on the performance of a micro contact.The contact is one-dimensional and formed by two sliding parallel planes.The upper contact surface is rough with rectangular micro projections,while the lower contact surface is smooth.Both of the contact surfaces are treated as rigid.The micro contact is filled with fluid.It consists of two sub-zones.In the outlet zone,the micro contact is distributed with boundary film because of the nanometer-scale contact separation,while in the inlet zone,the micro contact is distributed with fluid film because of the relatively high contact separation.The performance of the micro contact is determined by the behaviors of the boundary film and the fluid film.When the film thickness is relatively high,the boundary film here can be considered as the nanometer-scale thin film.Because of the limited shear stress capacity at the upper contact surface,the boundary film can slip at the upper contact surface.It is assumed that the shear stress capacity at the lower contact surface is high enough so that the boundary film can not slip at the lower contact surface.Because of the interaction between the boundary film and the contact surface,the viscosity, density and shear elastic modulus of the boundary film are all varied across the film thickness;their equivalent values,which are dependent on the boundary film thickness,are used in theoretical analysis.The analytical approach proposed by the author and his colleagues is used for analyzing the boundary film behavior.The fluid film is assumed not to slip at both of the contact surfaces.The effect of the shear elastic modulus of the fluid film is neglected in the analysis.The conventional approach is used for analyzing the fluid film behavior. The present paper gives the theoretical analysis and some of the computational results for different operating conditions.