Numerical Analysis For Fractal Theory-Based Model Of Micro-Point Contact In Partial Lubrication Condition

Along with the development of machine tool in the direction of high precision and microminiaturization, the dynamic characteristics of the guide joint surface is playing an important role of the machine. Therefore, it is of great both theoretical and practical significance to explore the micro-scale dynamic characteristics of guide joint surface of the machine tool.The dynamic characteristics are based on the static characteristics which mainly start with the contact problem between rough surfaces, and more of them are from the macroscopic aspects now, while the micro-scale studies have few literature reports. The fractal-based description of rough surfaces could not be restricted by scale, however, the lubrication of the joint surface did not take into consider in the contact model. In the field of lubrication, the parameters of elastohydrodynamic lubrication problem between rough surfaces were involved in the macroscopic quantity. The descriptions of the rough surface were limited to the surface roughness that assumes a sine or cosine distribution, the micro parameters related to the material surface roughness were not involved.Based on the above situation, using W-M fractal function simulate the rough texture of the rough surfaces, this paper finds the connection between traditional roughness and the fractal characteristics. Through the average Reynolds equation which was derived by Patir N. and Cheng H.S. of3D rough surfaces, according to the flow continuity conditions in the contact area, this paper establishes the equations which described as fractal theory-based model of micro-point contact in partial lubrication condition, in order to objectively reflect the fractal rough surface lubrication regularity, and to further perfect the joint surface fractal contact model which takes the lubrication problem into consideration. Because elastohydrodynamic lubrication equations are partial differential equations that are difficult to solve, and considered the difficulty of direct iteration, so referring to the previous fixed parameters and using Fortran language, by adopting the method of multiple grid computing pressure distribution and multiple grid integral method to calculate oil film thickness, the numerical calculations complete numerical solution are obtained. In addition, by changing the parameters of roughness, viscosity, speed and load for multiple sets of numerical calculation, using Origin software display and analysis of the results of numerical calculation, this paper discusses these impacts on micro point contact in partial elastohydrodynamic lubrication. Summarizing the results, this paper can get the following conclusion:(1) When considering the surface roughness, the stress distribution has obvious difference with traditional Hertz stress distribution. As the root-mean-square value of roughness increasing, the average film thickness decreases, and the film pressure is showing a tendency of increase.(2)As the original viscosity of the oil increasing, it will make the average film thickness increases, and the film pressure decreases. In addition, the film thickness and pressure distribution have obvious fluctuation with the changing of viscosity. The smaller viscosity is, the more obvious pressure fluctuation is, and the less obvious film thickness fluctuation is.(3) Increasing speed parameters can make the average film thickness increases and necking phenomenon more obvious. While the film pressure decreases, the outlet pressure peak moves to the entrance area and its value increase as well. In addition, the changes of the dimensionless velocity will also make the film thickness and pressure fluctuating and is similar to the effect of viscosity.(4) As the load parameter increasing, the average film thickness will reduce while the film pressure is opposite, and the outlet pressure peak moves to the exit area with its value decreasing. The changes of the dimensionless velocity will also make the film thickness and pressure fluctuating and is opposite to the effect of viscosity and velocity.