Due to the low viscosity of water, water-lubricated bearings are susceptible to significant wear and noise in demanding operating conditions. It has been demonstrated that a small quantity of secondary lubricating medium can improve the lubrication performance of water-lubricated contact surfaces and achieve the purpose of temporary risk aversion. As a further step, the feasibility of the proposed idea is experimentally validated on a water-lubricated bearing test bench. A numerical model that couples the N–S equation and the VOF model is then developed to investigate the behavior of the flow field lubricated by pure water and water with a small quantity of the secondary lubricating medium. This model provides the predictions of important quantities such as the load-carrying capacity, the secondary lubricating medium volume fraction and the contact pressure under different lubricated conditions. The results show that the secondary lubricating medium can enter into the contact region and improve the lubrication performance of water-lubricated bearings, especially at lower shaft rotational speeds. Therefore, the feasibility of our proposed idea is verified, which provides a promising approach to reduce the wear and friction of water-lubricated bearings when they encounter short-time severe working conditions.

The axle box bearing is a crucial component of high-speed electric multiple units (EMU) and is exposed to harsh working conditions, making it susceptible to subsurface-induced rolling contact fatigue (RCF) under long-term alternating stress. The objective of this paper is to develop a damage-coupled elastic–plastic constitutive model that can accurately predict the RCF life of EMU axle box bearings made from AISI 52100 bearing steel. The total damage is divided into elastic damage related to the shear stress range and plastic damage associated with plastic deformation. Material parameters are determined based on experimental data from the literature, and validation is conducted to ensure the validity of the model. Finally, the RCF behavior of the EMU axle box bearing, including crack initiation, crack propagation, and spalling, is simulated, and reasonable results are obtained. This study provides valuable insights into the RCF behavior of EMU axle box bearings and contributes to the accurate prediction of the fatigue life.

This study investigates the film formation mechanism of lubrication using a small quantity of lubricating medium in a water environment. A roller-on-disc test rig combined with a fluorescent technique is employed to directly measure and observe the film formation behavior when a small amount of lubricating medium is introduced into the water. Additionally, a surface-modified disc is used to examine the impact of wettability gradients on the film-forming capability of the lubricating medium. The results indicate that the film thickness between the roller and the disc increases with the injection of two types of lubricating oils into the water at varying disc speeds, both for the original and modified discs. During the 10-second oil supply period, the spreading behavior of the lubricating oil on the lubricating track influences the film thickness stability. Furthermore, the surface-modified disc demonstrates an enhanced film thickness compared to the original disc, and viscosity becomes a key factor limiting the film-forming capability of the lubricating oil as the disc speed increases for both disc types. This research offers valuable insights for the design of new water-lubricated bearings.

Previous research has revealed that introducing a secondary lubricating medium can temporarily enhance water-lubricated bearing performance, thereby reducing the risk of lubrication failure under challenging conditions. This study aims to identify the optimal injection point for the secondary lubricating medium and evaluates oil supply rate effects. Experiments are conducted using a block-on-ring test rig, complemented by computational fluid dynamics (CFD) simulations to elucidate the underlying mechanisms. Three oil supply settings, upstream, inlet and outlet of the contact region, are compared. Results show that upstream oil supply led to a lower critical speed at which the added oil loses any effect compared to the inlet oil supply and outlet oil supply. The effect of oil supply rates on friction reduction varies among the oil supply settings and ring rotational speeds. In conclusion, the most effective oil supply setting positions the injector at the outlet of the contact region, outperforming placement at the entrance of the contact region.