Mechanisms of lubrication failure due to non-steady multi-scale surface structure and applied technology

本项目旨在通过关注表面粗糙度的非稳态多尺度结构，从实验和理论两方面研究润滑膜局部失效导致宏观润滑失效的过程，探索混合润滑中润滑失效的机理。采用超薄膜干涉法对光刻法制备的微凹坑表面和溅射纳米粗糙表面进行了纯滑动点接触EHL实验。发现磨损区或微凹坑的通过会引起局部流体流动的变化，进而导致磨损的产生和扩大。同时，设计并搭建了一个新的试验箱，研究了环境气体对空腔形成的影响。在分析方面，为了描述非稳态多尺度表面结构，引入了离散小波变换。采用Haar函数作为母小波。利用小波系数给出凹凸不平点的不规则排列，并将其作为静止表面的微形貌，用于简单倾斜滑块轴承流体动力润滑数值分析。对机械密封平面接触时织构表面的流体动力润滑进行了数值分析，发现微凹坑的形状和位置与流体动力流动有关。为了研究润滑油膜中空腔的产生，采用水平集法求解Navier-Stokes方程，求解气液界面。空泡的形状和位置取决于空泡的形状和空泡压力。

This project aims at exploring mechanisms of lubrication failure in mixed lubrication by focusing on non-steady and multi-scale structure of surface roughness, and studying both experimentally and theoretically processes in which local failure of lubricating films leads to macroscopic lubrication failure. Pure sliding point contact EHL experiments were made with ultra-thin film interferometry for sputtered nano-roughness surfaces and textured surfaces having micro-pits produced with photo etching. It was found that that passage of worn area or micro-pits caused changes in local fluid flow, which further led to initiation and expansion of wear. Also, a new test chamber was designed and built to study effects of environmental gas on formation of cavities. In the analytical side, the discrete wavelet transform was introduced in order to describe non-steady multi-scale surface structures. Haar function was employed as a mother wavelet. Irregular alignment of asperities and pits was given by wavelet coefficients, which was then used as microtopography of stationary surface in the numerical analysis of hydrodynamic lubrication of a simple inclined slider bearing. Another numerical analysis was made on hydrodynamic lubrication of textured surfaces in flat-flat contact of mechanical seals, which showed dependence of hydrodynamic fluid flow on shape and location of the micro-pits. In order to investigate generation of cavities in lubricant films, Navier-Stokes equations were solved whereby the Level Set Method was introduced to seek gas-liquid interface. Shape and location of cavities were determined, which were shown to depend on shape of pits and cavitation pressure.