Theoretical And Experimental Study Of Normal Contact Characteristics Of Non-gaussian Rough Surfaces Under Mixed Lubrication

The contact characteristics of mechanical joint surface directly affect the machining performance of machine tool,so it is always a hot topic in mechanical research.Early studies on the contact theory of mechanical joint surfaces mainly assumed that the height of micro-convex body presented Gaussian distribution,and the contact between two rough surfaces was equivalent to the contact between rigid plane and rough surface.However,the height of micro-convex body on the actual machining surface generally showed non-Gaussian distribution,and the parts showed double rough surface contact on the mesoscopic level.The mechanical bonding surface can be divided into fixed bonding surface without lubrication and relative moving bonding surface with lubricating medium according to whether there is macroscopic relative motion.At present,remarkable achievements have been made on the contact characteristics of the nonlubricated fixed joint surfaces,but the research on the relative moving mechanical joint surfaces is a little insufficient,so it is still difficult to accurately obtain the contact stiffness and damping parameters between the relative moving joint surfaces,which has become a key factor restricting the development of high precision machinery equipment.Therefore,in order to establish a contact model of mechanical bonding surface more in line with actual working conditions,and accurately reveal the contact mechanism of mechanical moving bonding surface and the key influencing factors and rules of its response characteristics under mixed lubrication,this paper studies the normal contact characteristics of moving bonding surface in mechanical equipment under mixed lubrication.Considering the velocity of the joint surface and the non-Gaussian property of the convex surface,the normal contact model of the joint surface of mixed lubrication under the action of static and dynamic external forces was established,and the experimental platform of the joint surface of mixed lubrication relative motion was established,and the theoretical model was verified.The main research work is as follows:(1)Modeling and simulation of normal static contact stiffness of mixed lubrication joint surface.Based on the statistical theory,the constitutive relations of the contact elasticity,elastoplasticity and plastic deformation of a single pair of micro-convex surfaces were analyzed for the solid contact part under static normal load.The normal static solid contact stiffness model of the joint surface was established for the non-Gaussian distribution of the height of the micro-convex surfaces.For the contact part of the fluid,the lubrication equation of the partial film under steady state condition was established,and the flow factors and contact factors in the equation with the non-Gaussian distribution of the convex body height were obtained.The distribution of the oil film pressure and film thickness on the bonding surface was simulated and analyzed,and the normal steady-state fluid contact stiffness model was established based on the ultrasonic spring model.Finally,the normal static contact stiffness model of the joint surface of mixed lubrication was constructed by connecting the fluid and the solid part in parallel.The results show that the normal contact stiffness of the joint surface increases nonlinearly with the increase of normal surface pressure,and the solid contact stiffness is dominant.The normal contact stiffness of the joint surface decreases with the increase of the relative sliding velocity and the viscosity of the lubricating medium.The normal contact stiffness of joint surface decreases with the increase of surface skewness.Under low load,the normal contact stiffness of joint surface decreases with the increase of surface kurtosis value.Under high load,the normal contact stiffness of joint surface increases with the increase of surface kurtosis value.(2)Modeling and simulation of normal dynamic contact stiffness and damping of mixed lubrication joint surface.When the mechanical j oint surface is subjected to dynamic normal load under mixed lubrication,a single pair of contact normal stiffness model is established for the contact part of the solid.Based on the statistical theory,the contact normal stiffness model of the joint surface is established for the non-Gaussian distribution of the micro-convex body.According to the relation between contact energy loss and damping characteristics,the solid contact equivalent viscous damping is obtained.For the contact part of the fluid,the lubrication equation of the unsteady part of the film was established to obtain the relationship between the thickness of the contact oil film with time.According to the small disturbance method,the normal average contact stiffness and average contact damping of the fluid in an exciting period were obtained.Finally,the normal dynamic contact stiffness and damping model of the joint surface of mixed lubrication was constructed by connecting the fluid and the solid parts in parallel.The simulation results show that the normal dynamic contact stiffness and damping of the j oint surface increase with the increase of the normal dynamic load.The solid contact stiffness is dominant,and the fluid damping determines the contact damping of the joint surface.The normal dynamic contact stiffness decreases with the increase of viscosity,excitation force amplitude and sliding velocity,but the change of frequency has no effect on it.The normal contact damping of the joint surface increases with the increase of viscosity and sliding velocity,and decreases with the increase of frequency and amplitude of excitation force.The normal dynamic contact stiffness of joint surface decreases with the increase of surface skewness.Under low load,the normal dynamic contact stiffness decreases with the increase of the surface kurtosis value.Under high load,the normal dynamic contact stiffness increases with the increase of the surface kurtosis value.The normal contact damping of joint surface decreases with the increase of surface skewness and kurtosis.(3)Experimental study on normal contact characteristics of kinematic j oint surface of mixed lubrication machinery.The experimental platform of normal contact characteristics of the moving joint surface was designed and developed,and a test system with m+p dynamic signal acquisition and analysis system as the core was constructed.The motion control program and humancomputer interaction interface of the experimental platform were designed.Experiments on static and dynamic contact characteristics of a given moving joint surface were carried out to verify the correctness of the normal contact stiffness and damping model of the static/dynamic j oint surface.