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

本项目旨在通过对表面粗糙度的非稳态和多尺度结构的研究，探索混合润滑中润滑失效的机理，并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。采用超薄薄膜干涉法对溅射纳米粗糙表面和光刻微坑织构表面进行了纯滑动点接触弹流实验。结果表明，磨损区域或微坑的通过引起局部流体流动的变化，从而进一步导致磨损的开始和扩展。同时，设计并建造了一个新的试验室，用于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稳态多尺度表面结构。Haar函数作为母小波。利用小波系数描述了微凸体和凹坑的不规则排列，并将其作为静止表面的微观形貌，应用于简单倾斜滑动轴承流体动力润滑的数值分析。另一个数值分析的机械密封的平面-平面接触的织构表面的流体动力润滑，显示流体动力流动的依赖性的微坑的形状和位置。为了研究润滑油膜中空穴的产生，求解了Navier-Stokes方程，并引入Level Set方法求解气液界面。空泡的形状和位置被确定，这被证明取决于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.