Tribological Properties of the Porous Liquid Storage Medium with Different Pore Depths

The porous liquid storage medium exhibits excellent self-lubricating performance because of its outstanding capability of store and release lubricating medium due to the unique pore structures. Under some special working conditions such as oil-free lubrication and inconvenient maintenance, it can meet the interface protection requirements of friction reduction, wear-resistance, and maintenance-free. One of the important factors affecting the lubrication performance of the porous liquid storage medium is the pore parameters, and therefore by optimizing pores parameters, the hydrodynamic lubrication effects and tribological performances of the porous liquid storage medium can be enhanced. In this study, the influencing mechanism of the pore depth on the tribological properties of porous storage medium was investigated by the method of both simulation calculation and experiment. In the beginning, the motion state of the fluid in the pores and the fluid pressure distribution at the friction interface of the porous liquid storage medium with different pore depths were probed by the computational fluid dynamics (CFD). In consideration of the meniscus force at the gas-liquid interface and the Laplace-Young's equation, the gas-liquid bearing model of the porous liquid storage medium with different pore depths and the distribution of the minimum pressure difference on the gas-liquid two-phase were studied. In the following, based on the calculation results, the porous liquid storage media with different pore depths were prepared by 3D printing, and then the effect of the pore depths on the tribological performance of the porous liquid storage medium was further investigated by conducting the friction tests with a self-developed ring-block tribological tester. Theoretically, the viscous fluid can enter into the convergent gap generated due to the porous structure on the surface of the porous liquid storage medium, which can thus generate a hydrodynamic lubrication effect and effectively improve the lubricating lift force of the lubricant. The results of CFD simulation showed that the lubricating lift force of the porous liquid storage medium increased first and then decreased with the increase of the pore depth. When the pore depth was 7.5 mm, the lubricating lift force of the porous storage medium reached the maximum. The hydrodynamic lubrication effect of the porous liquid storage medium could be enhanced with an appropriate pore depth. A shallow pore depth led to an inadequate lubrication lift, while a deep pore depth might cause a backflow phenomenon of the fluid in the pores and thereafter weaken the wedge effect. When the lubricant was not fully filled or partially consumed due to the service in the porous liquid storage medium, the gas entered into the pores and the gas-liquid two-phase was then formed, which could bear loads under the action of the meniscus force. The maximum bearing capacity of the gas-liquid two-phase in the pores of the porous liquid storage medium increased first and then became stable with the increasing pore depth, and the increment decreased with the increase of the pore depth. The tribological tests demonstrated that the friction coefficient of the porous liquid storage medium was first decreased and then increased with the increase of the pore depth, which was consistent with the simulation results. During the friction process, the surface abrasion of the porous liquid storage medium was dominated by the grain-abrasion adhesive wear with few adhesive wear. Compared with the non-porous sample, the wear loss of the porous liquid storage medium was reduced by 35.24%~90.52%, indicating the improved wear resistance. It was also found that that the hydrodynamic lubrication effect of the porous liquid storage medium and the gas-liquid two-phase bearing capacity could be affected by the pore depths, thereby the tribological behaviors of the porous liquid storage medium could be regulated. This work provides a theoretical guidance for the topology optimization design of the porous liquid storage medium, and also lays a foundation for the continued research on the lubricating mechanism of the porous liquid storage medium. Copyright ©2022 Tribology. All rights reserved.