Seepage Behavior Analysis of Porous Self-Lubricating Surface under Solid-Liquid Two-Phase Action

Porous self-lubricating materials are widely used in advanced lubrication technologies, such as porous bearings, gears prepared by powder metallurgy, and bionic self-lubricating materials, due to their self-lubricating properties. The seepage behavior of lubricating fluid on porous surfaces has an important impact on the quality of surface lubrication. Unfortunately, the existing research does not pay enough attention to this topic, and the complex solid-liquid two-phase coupling mechanism is still unclear. In this paper, the porous self-lubricating materials were taken as the research object for analyzing the deformation of porous matrix and the flow characteristics of lubricating liquid in porous matrix under the effect of the external load. The change of seepage velocity with loading time on the porous surface was discussed. The seepage and lubrication behavior of porous surfaces under solid-liquid dual-phase action were studied. The results showed that the porous matrix was deformed under load. The lubricating fluid stored in the pores was forced to flow, and the flow behavior of infiltration and precipitation occurred on the porous surface. The lubricating fluid penetrated into the porous matrix in the contact area and precipitated out to the porous surface at the entrance of the contact area. Under a constant load, the lubricating fluid on both sides of the inlet did not maintain a stable seepage phenomenon, but showed a process of diffusion, fluctuation, and stability finally with the loading time. In the vertical direction in the porous material, the maximum fluid pressure occurred on the upper surface, and the maximum solid force occurred at the subsurface close to the upper surface. On the porous surface, the solid stress and fluid pressure were symmetrically distributed along the y-axis, and the solid stress and fluid pressure were the largest in the center of the contact area. After long-time loading, the solid stress distribution on the porous surface was similar to the analytical solution of the traditional Hertz contact theory, which indirectly verifies the effectiveness of the numerical model established in this paper. During the loading process, the bearing capacity of the liquid phase in the friction interface first increased and then decreased. Contrary to the liquid phase, the bearing capacity of the solid phase first decreased and then increased. After long loading, the bearing capacity of the liquid-phase decreased to zero, and all the external loads were borne by the solid-phase material. Appropriately increasing the load can increase the dialysis rate of the lubricating fluid on the porous surface and improve the lubrication state, but it also make the fluctuation of the seepage velocity more violent. The fluctuation of normal seepage velocity on both sides of the contact area may affect the stability of lubricating oil film at the friction interface. How to control the fluctuation amplitude and duration of normal seepage velocity is worthy of further exploration.