Direct observation of the impact of water droplets on oil replenishment in EHD lubricated contacts

Abstract

Water is one of the most significant causes of lubrication failure. There is little research on the direct observation of the impact of water on lubrication properties. In this study, the influence of water on oil replenishment under different elastohydrodynamic (EHD) lubricating conditions is evaluated using optical interferometry and infrared microscopy, and a dimensionless criterion when water influences the film thickness is proposed. Evidence shows that the scour displacing effect and emulsification of water/oil are the main reasons for the reduction in film thickness. Once a water droplet enters an oil reservoir around the critical contact zone, it hardly moves away. This aggravates starvation, reduces the center film thickness of the contact, and leads to lubrication failure of the mechanical components.

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Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 51805505, 52075514, and 51605460).

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Correspondence to Lu Huang or Dan Guo.

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Xiang LIU. He received his Ph.D. degree in 2015 from State Key Lab of Tribology, Tsinghua University, Beijing, China. He studied the mechanism of oil lubrication during Ph.D. period. Now he is an associate research fellow in National Institute of Metrology, Beijing, China. His research area mainly focuses on the volume and density metrology method.

Jintao WANG. He received his bachelor, master, and doctor degrees from Xi’an Jiaotong University in 1998, 2001, and 2006, respectively. He is working for Volume and Density Laboratory of National Institute of Metrology as a research fellow, and the main research field is volume and density metrology method.

Lu HUANG. She received her Ph.D. degree in 2016 from State Key Lab of Tribology, Tsinghua University, Beijing, China. She studied the mechanism of grease and oil lubrication during Ph.D. period. Now she is an associate research fellow in National Institute of Metrology, Beijing, China. Her research area mainly focuses on the evaluation of lubricants and matierials, and nano-particle characterization.

Dan GUO. She received the M.S. degree in engineering mechanics in 1995 from Xi’an Jiaotong University, Xi’an, China and Ph.D. degree in engineering mechanics in 1999 from Tsinghua University, Beijing, China. She joined the State Key Laboratory of Tribology at Tsinghua University from 1999. Her current position is a professor and the deputy director of the laboratory. Her research areas cover the properties of friction at the micro/nano-scale, mechanism of interaction among nanoparticles and surface in ultra-smooth surface planarization, and the formation and lubricayion failure in harsh conditions.

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Liu, X., Wang, J., Huang, L. et al. Direct observation of the impact of water droplets on oil replenishment in EHD lubricated contacts. Friction (2021). https://doi.org/10.1007/s40544-020-0466-0

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Keywords

  • free water droplet
  • point contact
  • starved condition
  • film thickness