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

本课题旨在通过研究表面粗糙度的非稳态和多尺度结构，从实验和理论两个方面研究混合润滑中润滑膜局部失效导致宏观润滑失效的过程，从而探索混合润滑中润滑失效的机理。用超薄膜干涉法对溅射纳米粗糙表面和光刻产生微坑的织构表面进行了纯滑动点接触弹流润滑实验。研究发现，磨损区或微坑的通过引起了局部流体流动的变化，进而导致了磨损的萌生和扩展。此外，还设计并建造了一个新的试验室来研究环境气体对空洞形成的影响。在分析方面，引入离散小波变换来描述非定常多尺度表面结构。采用Haar函数作为母小波。利用小波系数给出了凹凸凹陷的不规则排列，并将其作为静止表面的微观形貌，对简单倾斜滑动轴承的动压润滑进行了数值分析。另外，对机械密封平面-平面接触中纹理表面的流体动力润滑进行了数值分析，结果表明流体的流动与微坑的形状和位置有关。为了研究润滑膜中空穴的产生，采用水平集方法求解N-S方程，寻找气液界面。确定了空穴的形状和位置，这取决于凹坑的形状和空化压力。

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.