Research On Surface Texture Design And Tribological Properties Based On Fractal Geometry

Friction exists widely in the field of mechanical engineering and directly affects the working performance and service life of mechanical equipment.How to reduce the friction and wear of equipment and prolong the service life is an urgent problem in the field of machinery.It is found that machining micro-texture on the surface of friction pair can obviously improve the interface lubrication performance and reduce the friction and wear.But at present,the surface texture design is mainly based on experience and lack of relevant theories and design criteria.In order to further enrich the scientific research in the field of surface texture,fractal geometry theory is introduced in this paper,and the geometric morphology of the surface texture is designed,and the lubrication simulation and friction and wear test of the texture interface are carried out,which lays a theoretical and reference foundation for the study of surface texture design.Firstly,based on the fractal theory,the fractal characteristics of rough surface with self-affine and self-similarity are expounded,which shows that it is necessary to introduce fractal geometry theory into the topography of rough surface.By comparing the fractal dimension of common fractal graphs,it is found that the larger the fractal dimension is,the more complex the graph is.In order to analyze the relationship between rough surface and fractal dimension,four methods of measuring fractal dimension are analyzed in detail,and two dimensional rough contour and three dimensional rough topography are simulated by W-M function.The results show that fractal dimension and characteristic scale can characterize the roughness of rough surface.Then,based on the basic equations of fluid mechanics,the common fractal geometric functions are introduced.Two functions based on texture design are selected by comparison.In addition,40 kinds of models with the fractal characteristics of Sierpinski triangle and Sierpinski carpet are established by taking five micro-geometric shapes as units.Five best fractal patterns of Sierpinski carpet with large fractal dimension and porosity between 16% and 38% are selected through analysis.On this basis,Reynolds equation was simplified and the microfluidic infiltration control of five texture interfaces was studied by COMSOL software.The results show that the seepage velocity of the interfacial fluid increases with the decrease of the tortuosity of the micro-pits.Through the analysis of seepage velocity and pressure difference,it is found that the fractal pattern of circular micro-geometric element has the best friction performance.Finally,five kinds of fractal textures with different morphologies were machined on the surface of No.45 steel specimen by laser processing technology,and the interface friction and wear tests were carried out.The results show that the friction coefficients of the samples with five textures are lower than those without texture.Among the five surface textures,the friction coefficient of circular microgeometric element takes the shortest time from initial fluctuation to stability.The friction coefficient of circular microgeometric element is the lowest among the five textures.The results show that the friction coefficient of the interface can be reduced by machining the surface texture of a certain shape,which is consistent with the results of seepage simulation,indicating that the simulation of interfacial microfluidic infiltration can reveal the mechanism of surface texture wear reduction to a certain extent.The fusion of surface texture and fractal geometry theory ensures the diversity of surface texture topography design and promotes the traditional empirical design to the theoretical design.Therefore,fractal geometry theory,as the theoretical basis of surface texture design,not only enriches the scientific research in the field of surface texture,but also extends the tribology theory of surface texture,providing theoretical reference and design basis for surface texture design in practical engineering.