应毛军红教授的邀请，香港城市大学机械与生物医学工程系Dr. WONG, P.L., Patrick来校进行学术讲座交流，特请感兴趣的师生届时光临。学术讲座安排如下：

题目：传统光学弹流润滑技术的扩充

时间：2014年10月17日（周五）下午4：00-5：00

地点：机械学院第一会议室

Title: EXTENSION OF CONVENTIONAL OPTICAL ELASTOHYDRODYNAMIC LUBRICATION TECHNIQUE

Abstract: The term “conventional” optical elastohydrodynamic lubrication (EHL) technique refers to the simple mechanical set up of a steel ball rolling or sliding on a partially Cr-coated glass disc and illuminated using monochromatic light source, as firstly introduced by Cameron’s group in Imperial College in UK in the 1960s. EHL studies can be carried out by utilizing the phenomenon of optical interference which is formed by the reflections from the interfaces of a lubricated contact of a steel ball and a partially Cr-coated glass disc. The technique has been widely used in experimental studies of EHL since its introduction. It gains its popularity not only because of the provision of detailed mapping of the highly pressurized and stressed EHL contact but also its simplicity which, as we recognize, is the beauty of the technique. The film thickness is inferred from the known order of interference fringes, which limits the minimum thickness measurement only down to a quarter the wavelength of the light source at about 200 nm. Attempt was made to infer the film thickness from the fringe intensity based on the two-beam interference method, but it may induce significant errors in the measurement. A theoretical analysis which includes consideration of the effects of both multi-beam interference and optical absorption within the Cr film and the steel surface has been conducted, which enables a wide range of lubricant film thickness measurements at a resolution of 1 nm and offers a practical minimum detectable film thickness as thin as 1 nm. The mathematical derivation, at the first look, may be very complicated since it consists of multiplications of complex numbers and lengthy expressions. However, the calculation is quite straight forward and can be readily completed using an ordinary spreadsheet, such as Excel. It is noted that the mechanical set up of the technique and the interferograms obtained are exactly the same as the one introduced in the 1960s. Thus this current extension of the technique does not obliterate the beauty of its simplicity which is, after all, one of the key considerations in experimental studies as repeatedly stressed on by the late Prof. A. Cameron.

Biography:Dr. Patrick Wong obtained his PhD from the University of Hong Kong in 1990, and his BSc from City University, London in 1983. Dr. Wong started his academic career in the City University of Hong Kong since 1990. He is currently an Associate Professor in the Department of Mechanical and Biomedical Engineering in the City University of Hong Kong. His research interests include rolling element bearings, micro/nano magnetic technologies, interfacial phenomena, and lubrication. He has published over 60 international peer-reviewed journals. He is a member of editorial board of the Journal of Industrial Lubrication and Tribology.