| Mechanical friction between the contact surfaces have a significant impact on the power consumption, failure life and reliability of equipment. It is an important research subject that how to reducing wear, increasing energy utilization and prolonging service life. Recently, as a new method of surface treatment, surface texture reveals a great advantage in the area of friction reducing and anti-wear than smooth surface. The lubrication condition can be improved and the friction and wear can be reduced by surface texturing on the surface of equipment. In order to further enrich the research of surface texture, the effect of topography and arrangement of surface texture on tribological properties has been studied systematically and in-depth in this paper.First, the hydrodynamic lubrication model was made for textured surface with spherical dimples, and the effect of radius, depth, area ratio and relative sliding speed on the friction coefficient and the bearing capacity of hydrodynamic pressure were studied. The results of simulation show that the coefficient of friction is inversely proportional to area ratio and depth of surface texture, and the depth is an important factor affect to friction coefficient. Bearing capacity is mainly related to the depth and relative sliding speed, the bearing capacity increases with the increase of depth, and reaches the highest value when the dimensionless depth equal to 15.Second, the properties of lubricating and friction-reducing for textured surface with cylinder shaped dimples have been studied using simulation method, the interaction between adjacent texture units is considerd in the CFD model, and the influence of depth, radius, offset ratio and relative sliding velocity on coefficient friction and bearing capacity have been analyzed. The results show that the offset ratio has significant influence on the bearing capacity between two contact surfaces. The increase of pressure coefficient is almost 34.9 times when the offset ratio increase from 0 to 0.5, meanwhile, friction coefficient increases slightly, but the increase of it is only about 0.59%. The other conclusion is that the increase of texture area can not only increases bearing capacity but also decreases the coefficient of friction.For the texture with isotropous geometry, such as cylinder shaped texture, the effect of inclination angle on tribological properties isn’t need to be considered during the process of research. But for the texture with anisotropic geometry, such as elliptical dimple, it is an important factor which must be considered in the process of texture design that the interaction of the inclination angle, offset ratio and patterns on tribological properties. The model of hydrodynamic lubrication was built for textured surface with elliptical dimples, and the effects of area ratio, inclination angle, offset ratio and patterns on the characteristic of friction and bearing capacity were considered in using orthogonal design to optimize the geometry parameters in the simulation process. The CFD results show that the coefficient of friction decreases significantly with increasing area of texture unit, and the coefficient of friction was minimum when the inclination angle equal to 90 degree(the long axis of ellipse along the direction of sliding). The inclination angle and offset ratio have strong effect on the bearing capacity of friction couple. The results of test show that the inclination angle and offset ratio have great effect on the friction coefficient, and the optimize bitch of texture units is 1500 μm. The inclination angle for minimize friction was 0 degree under low speed and light load condition and 90 degree under high speed and heavy load condition, respectively. By comparing the tribological properties of three textured surfaces with different patterns of texture units, we found that the textured surface with P2 pattern has the optimize friction reducing properties among all the three patterns mentioned in this work.The geometry structure of ring shaped texture is complex and should be regard as a groove bending its shape along a circle path, which has the characteristics of discrete dimple and continuous groove, simultaneously. The simulation result shows that the friction reducing characteristic of the surface with ring shaped texture superior to that of cylinder texture surface under the same conditions, and the coefficient of friction decreases with the increasing area ratio of texture unit. The conclusion that ring shaped texture has an advantage in debris capture than the surface with cylinder shaped texture can be drown from streamline analysis. The friction test for surface with ring shaped texture were performed on variable loads friction-wear tester, and the results show that the width of ring shaped texture has great influence on the friction of texture surface, the optimal width value of ring shaped texture is about 200 μm. The friction decreases with the increasing of offset ratio. The tribological properties of ring shaped texture seems to be quite sensitive to the geometry parameters, coefficient of friction can greater than or less than that of smooth surface. |
