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Experimental and theoretical studies have been completed in this paper to investigate the interface effect in the lubrication performance of a step slider bearing. Oleophobic fluorine-containing diamond-like carbon (F-DLC) coatings were prepared on the step slider to provide low affinity to lubrication films. With an optical slider bearing test rig, it is revealed that the F-DLC coating presents an increase in the film thickness/load-carrying capacity and a decrease in the coefficient of friction (COF), which is quite different from the common idea that both the load-carrying capacity and the COF are reduced at the same time. Contact angles measurement on the step slider shows that the affinity to the lubricant of the inlet step surface is lower than that of the outlet land, which can be attributed to the rougher surface of the step surface by the laser ablation. Theoretical analyses show that various interfacial slip velocities on the inlet step and the outlet land can generate different change in the load-carrying capacity and the COF. When the step surface presents lower interfacial slip velocity of the film than the land surface, increase in load-carrying capacity and decrease in the COF can be theoretically found to support the experiments finds.
In this paper it was demonstrated that a small quantity of silicone oil could be employed as a secondary lubricant to assist water lubrication when there appear short-time sever working conditions. With a deliberately fabricated fiber-guide nozzle a short-time injection of silicone oil to water lubricated block-on-ring contact in the mixed lubrication could reduce friction of the contact markedly. With increase of the ring speed the friction reduction ratio decreases first and then slightly increase thereafter. Measurements of the wear track displayed more wear reduction under higher ring speeds and larger viscosity. It was proposed that the friction and wear reduction could be attributed to the water-excluded lubrication film formation in the whole contact zone by silicone oil, which was validated by optical interferometry measurement of the lubrication films. In addition, through fluorescence technique it was found that water environment can reduce the wettability of the silicone oil on the lubrication track so that the oil replenishment on the track is enhanced and the film thickness increases.
Under limited lubricant supply condition, the lubrication of a slider bearing can be enhanced by discontinuous oil droplets on the lubrication track induced by poor surface wettability. This experimental finding is contrary to the general perception that strong surface wettability favors lubricating film build up. Theoretical lubrication models with the lubricant supply in the forms of oil droplets (ModelⅠ) and uniform oil layer (ModelⅡ) are established to clarify the odd experimental observation. Results show that oil supply in the form of droplets can achieve better lubrication performance than the uniform oil layer, which are correlated to the experimental finding. The mechanism is probably due to the early film pressure initiation when oil droplets enter the bearing contact.
An ultra-low friction and high load capacity could be obtained on the surfaces grafted by a polymer brush even at relatively slow friction speeds in aqueous lubrication environments, which has attracted widespread attention to study the lubrication mechanism of polymer brushes; however, it has yet to be fully understood. The macroscopic tribological performance of two different polymer brushes, which were prepared by the method of “grafting to” and “grafting from” and named as PLL-g-PEG and PSPMA, respectively, were investigated. The friction results demonstrated that PLL-g-PEG obtained a lower friction coefficient than polymer brush PSPMA, which was ascribed to its unique “self-healing” behavior. The lubrication film was in situ observed and the film thickness induced by the polymer brush was measured using a laboratory set for film thickness measurement apparatus based on interference technology. It was found that PSPMA exhibited excellent lubrication performance not found in PLL-g-PEG, and two film-forming mechanisms highly dependent on velocity were revealed, which may be important to interpret the lubrication mechanism of polymer brushes in aqueous lubricants.
The water-lubricated bearing in ship propulsion system is easily impacted by sea wave shock, which is a great threat to the smooth start-up of the bearing system. Therefore, in the present research, the Euler equations, average Reynolds equation, and sea wave shock function are combined together to build the start-up model of water-lubricated bearing. The influences of amplitude, direction, and entry time of sea wave shock on the start-up performance of bearing are studied. The result shows that the shaft has a strong instantaneous vibration under the influence of friction force at the initial start-up stage, and the shock load with appropriate direction and amplitude can suppress or even eliminate this vibration phenomenon. The earlier the shock enters the start-up process, the more serious asperity contact gets, and the worse the system’s stability becomes. The increase of the shock load amplitude and the advance of the shock load entry time can help the shaft rapidly lift off. This study can provide a reference for the smooth start-up of ship propulsion system in a sea wave environment.
Effective oil replenishment to the lubrication track of a running bearing is crucial to its sustainable operation. Reliable practical solutions are rare despite numerous theoretical studies were conducted in the last few decades. This paper proposes the use of surface effect, wettability gradient, to achieve the goal. This method is simple and can be nicely implemented using femtosecond laser ablation. A periodic comb-tooth-shaped pattern with anisotropic wetting capability is devised and its effect on the anisotropic spreading behaviour of an oil droplet is studied. Results show that the comb-tooth-shaped pattern enables the rearrangement of oil distribution, thereby escalating oil replenishment to the lubrication track. The effect is due to the unbalanced interfacial force created by the surface pattern. The influence of the shape and the pitch of teeth, which are the two governing factors, on oil transport is also reported. The effects of the newly devised surface pattern on lubrication are experimentally evaluated under the conditions of limited lubricant supply. These results are promising, demonstrating the reduction in bearing friction and the increase in lubricating film thickness.
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本研究组位于青岛市黄岛经济技术开发区青岛理工大学嘉陵江校区内，依山傍水。研究组人员包括固定教师、博士后及博士和硕士研究生，主要从事薄膜润滑的研究工作。 薄膜润滑作为一种减小摩擦和避免磨损的重要手段，在保证各类装置的正常工作中担任重要角色，如高速精密机械、微机电系统以及人工器官等。专注于该领域，我们研发了一系列液体润滑薄膜测量系统，这些测量系统使我们能够准确测量到纳米尺度到微米尺度润滑油膜；同时，我们还开发了高效的数值算法，对薄膜润滑的详细过程进行大量的理论模拟，对其中的细节部分，如薄膜的压力及流动等进行相对完整研究。 借助于薄膜润滑的研究，我们和工业界的合作伙伴一起开发了新的润滑技术，用于提高机器运行的效能。
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