Abstract
Thin film lubrication (TFL), a lubrication regime that fills the gap between boundary lubrication (BL) and elastohydrodynamic lubrication (EHL) regimes, was proposed 20 years ago. Since it was first recorded in the literature, TFL has gained substantial interest and has been advanced in the fields of theoretical and experimental research. Following the revelation of the TFL phenomenon and its central ideas, many studies have been conducted. This paper attempts to systematically review the major developments in terms of both the history and the advances in TFL. It begins with the description and definition of TFL, followed by the state-of-art studies on experimental technologies and their applications. Future prospects of relevant studies and applications are also discussed.
Highlights
Numerous attempts have been made and documented to illuminate the lubrication mechanism, such as the revelation of the elastohydrodynamic lubrication (EHL) regime [1, 2] and boundary lubrication (BL) regime [3]
In the EHL regime, the film thickness is dominated by elastohydrodynamic factors, i.e., the rolling speed, contact pressure, viscosity of lubricant etc., while in the BL regime, the properties of the lubricant films are dominated by chemical action between substrate surfaces and lubricant molecules
It has been recognized that the lubrication between solid surfaces will be dominated by different regimes under different conditions, mainly involving hydrodynamic lubrication (HDL), elastohydrodynamic lubrication (EHL), thin film lubrication (TFL), and boundary lubrication (BL).The lubrication map shown in Fig. 2 [36] is obtained by using the ratio h/Ra to describe the lubrication regime, where h is the lubricating film thickness and Ra is the combined surface roughness of the two surfaces
Summary
Numerous attempts have been made and documented to illuminate the lubrication mechanism, such as the revelation of the elastohydrodynamic lubrication (EHL) regime [1, 2] and boundary lubrication (BL) regime [3]. Gupta et al [29] succeeded with revealing the microscopic behavior of lubricant films ranging from 1 to 10 nm by examining various contributions to the disjoining pressure. Both the van der Waals force and the structural force resulting from the molecular orientation and packing have been emphasized. In 1994, the physical model of thin film lubrication (TFL) was respectively proposed by Luo and Wen [4, 5], indicating that the combined effect of molecules attached on surfaces and in the thin lubricating film resulted in a distinct lubrication performance. From that time forth, growing interest has been stimulated to reveal the origins and characteristics of thin film lubrication models, bringing numerous advances to both experimental [23, 24, 30, 31] and theoretical studies, as Hu et al [33−35] reported
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