Lubricants

Lubrication performance dominates the rating life of grease-lubricated pitch bearings. Conventionally, the life modification factor is determined using base oil viscosity, whose validity is rarely verified. This work presents an effective viscosity-based method for life evaluation of wind turbine pitch bearings. The effective viscosity of grease is measured under actual operating conditions, and a comparative study is conducted against the conventional base oil viscosity method. The rationality of the proposed approach is validated by bearing life tests. Results indicate that the life modification factor calculated from effective viscosity agrees significantly better with test data. Adopting effective viscosity can substantially improve the accuracy of bearing life prediction. The proposed method provides a reliable and practical way to assess the lubrication performance and fatigue life of pitch bearings.

As key components in efforts to achieve green and sustainable development in machinery, water-lubricated stern bearings are increasingly replacing traditional oil-lubricated bearings. However, water’s inherent properties—such as low viscosity and poor film-forming ability—can induce severe friction-induced vibration and noise under specific operational conditions. These issues not only accelerate wear but also compromise the vessel’s reliability and acoustic stealth, thereby limiting their wider application. This paper provides a comprehensive review of the research progress relating to friction-induced vibration in water-lubricated bearings. It delves into the underlying mechanisms, critiques the primary methodologies used in numerical simulations, summarizes key experimental approaches, and synthesizes the prevailing vibration suppression strategies. Finally, the study clearly outlines existing challenges and proposes directions for future research.

A novel deep eutectic solvent (DES) formulated from choline hydroxide has been investigated as an additive for advanced aqueous lubrication. Comprehensive characterization of the DES enabled the determination of its viscosity, wettability, and key spectroscopic features, providing insight into its physicochemical behavior. The tribological performance of the water-based lubricants was evaluated using a pin-on-disc configuration with a stainless steel–sapphire tribopair. The resulting friction and wear data demonstrate a significant improvement in performance, particularly for the lubricant containing 10 wt.% DES, which exhibited the most favorable reduction in wear rate, achieving an 80% decrease compared to water. Electrochemical measurements, together with surface analysis by Raman microscopy, confirmed the formation of various iron oxide phases on the wear track that influence tribological performance. These oxides contribute to the development of a protective tribolayer that enhances the overall tribological response. Complementary X-ray-based analytical techniques (EDX and XPS) further substantiated the presence, composition, and stability of this tribolayer. Therefore, the study highlights the potential of the choline hydroxide-based DES as an effective component for formulating novel water-based lubricants.