Research On Ellipse-plastic Normal Contact Stiffness And Damping Of Joint Surface Based On Anisotropic Fractal Theory

The mechanical interface is widely distributed in various mechanical structures,and the contact behavior of the interface has an important and complex effect on the rigidity and damping of mechanical equipment.The mechanical interface is an important link to be considered in the mechanical design process.The mechanical joint surface is composed of two rough surfaces that are in contact.A single rough surface has certain geometric features on the micro scale.These surface characteristic parameters have a direct impact on the stiffness and damping characteristics of the joint surface.Most processed surfaces have anisotropy,so constructing a reasonable anisotropic joint surface contact model is of great significance to the mechanical structure and the optimization design of the whole machine.Most models are equivalent to micro-convex bodies on the joint surface as spheres,but ellipsoidal micro-convex bodies are more general.To this end,based on the anisotropic fractal geometry theory,the micro-convex body of the joint surface is equivalent to an ellipsoid,and the contact stiffness and contact damping of the joint surface are modeled and studied.The main research work is as follows:(1)Since the micro-contact point of the equivalent ellipsoid micro-convex body is a micro-ellipse surface,there is one more variable compared with the previous circular contact surface.First,through certain reasonable assumptions,the contact model between the micro-convex body on the fractal surface and the rigid plane is established.Furthermore,based on the anisotropic fractal geometry theory,a fractal model of joint normal contact stiffness considering rough surface anisotropy is established.Finally,the model in this paper is compared with previous models to verify the reliability of the modeling method in this paper.In addition,the effect of eccentricity on the stiffness of the joint surface was studied.The simulation results show that the eccentricity of the contact point of the bonding surface has a significant effect on the rigidity of the bonding surface,and the normal contact stiffness of the bonding surface increases as the eccentricity increases.(2)For the elliptical contact surface,the eccentricity actually follows a certain distribution,rather than a specific value.According to the distribution characteristics of the eccentricity of the joint surface,assuming that it follows the Beta distribution,the two-dimensional joint distribution density function about the area of the elliptical contact point and the eccentricity is obtained from the eccentricity distribution density function and the joint surface area size distribution function.Furthermore,based on the research in(1),a probability model of normal contact stiffness of the joint surface based on the anisotropic fractal theory is established.The influence of normal load,fractal dimension,fractal roughness and shape parameters on the normal stiffness of the joint surface was simulated and analyzed,and the model was compared with the experimental data.Studies have shown that for the elliptical contact point of the bonding surface,when the eccentricity or the eccentricity of the bonding surface is subject to Beta(5,5),it is more in line with the actual contact situation.(3)Based on the above research,anisotropic fractal geometry theory and normal contact damping loss mechanism,a probability model of joint normal contact damping based on anisotropic fractal theory is established.Through the numerical simulation of the model,the influence law of the joint surface normal load,fractal dimension,fractal roughness and shape parameters on the normal damping of the joint surface is explored.