Research On The Shear Contact Stiffiness And Damping Model Of Solid-liquid Interface

With the development of modern industry,the requirements of high-end mechanical equipment for precision,high speed,high efficiency,integration and intelligence are higher and higher.The joint surface connecting various parts is an important factor in the design and analysis of mechanical equipment,and its stiffness and damping characteristics account for 50% and 80%of the total stiffness / damping of mechanical equipment.It is self-evident that the importance of considering the joint surface in the design analysis and simulation optimization of mechanical equipment.Throughout the research of modern scholars,a lot of research has been done on the dry friction interface and its normal contact characteristics,but there is no research on the tangential characteristics of oil-bearing interface(solid-liquid interface),and the tangential characteristics are equally important for the optimization analysis of the whole machine.The important direction of this paper is to study its theoretical model and provide data support.In this paper,the solid and fluid contact parts of the solid-liquid interface are modeled separately,and then the two parts are paralleled and extended to the whole interface through the statistical theory to obtain the theoretical simulation model.The static,dynamic and macro relative motion characteristics of the solid-liquid interface are verified through the comparison of simulation and experiment.The main research contents are as follows(1)According to the lubrication state of solid-liquid interface,the contact model is assumed,and the tangential static boundary lubrication contact model of solid-liquid interface is established on the basis of closed oil pit and Newton’s viscosity law.Mindlin,Fujimoto and Ke contact models are integrated in the solid-solid contact part,and the closed oil pit model and its quivalent contact model are established in the solid-liquid contact part.Finally,through MATLAB simulation,the relationship between tangential contact stiffness and normal deformation,normal contact load,lubricant viscosity is obtained,and the simulation results are discussed and analyzed.The results show that the solid-liquid interface and the solid-liquid interface have similar contact characteristics under static state.For the tangential contact stiffness of the solid-liquid interface,the tangential contact stiffness of the closed oil pit is dominant when the load is small,and gradually the tangential contact stiffness of the asperity is dominant with the increase of the load.The tangential contact stiffness of solid-liquid interface is higher than that of solid-liquid interface.(2)The theoretical modeling of the tangential mixed lubrication contact model of the solidliquid interface under tangential excitation is carried out.The solid-solid contact part is based on Mindlin,Fujimoto,Ke fusion model.In the fluid contact part,the average Reynolds equation with contact probability factor is applied to the micro fretting layer.The tribological performance parameters are obtained by using the finite difference method,and the stiffness and damping of the oil film in the small disturbance state are calculated by using the difference model of stiffness and damping.The tangential dynamic contact model of the solid-liquid interface is obtained by paralleling the two parts.The relationship between the characteristic parameters of the interface and normal contact load,excitation frequency,tangential dynamic displacement amplitude and lubricant viscosity is obtained by MATLAB simulation.The simulation results show that the greater the viscosity of lubricating oil,the greater the tangential contact stiffness of oil film;The tangential contact stiffness of oil film increases with the increase of normal contact load,and the higher the excitation frequency is,the faster the slope of linear increase is;With the increase of the amplitude of the tangential dynamic displacement,the tangential contact stiffness of the fluid part decreases nonlinearly.The tangential damping coefficient of fluid decreases nonlinearly with the increase of excitation frequency,and the amplitude of dynamic displacement does not affect the change of tangential damping coefficient;The tangential contact damping coefficient increases with the increase of normal contact load,and the larger the excitation frequency is,the slower the increase is.(3)The previous solid-solid contact fusion model is no longer suitable for the solid-liquid interface in the macro moving state,so the savkoor asperity adhesion sliding friction contact model is adopted.The four contact stages of a pair of asperities in time domain and the relationship between the corresponding tangential force and time are described.On this basis,the analytical formulas of the tangential force,the tangential contact stiffness,the normal contact load and the normal deformation of the asperities in time domain are derived by using the mathmatic method,Considering the height distribution of micro convex body,the contact of single micro convex body is extended to the whole joint surface by statistical theory,and the tangential contact stiffness model of macro relative motion solid consolidation joint surface is obtained.The fluid contact part is modeled by stiffness damping difference method.Then,the relationship between tangential contact characteristics of solid-liquid interface and normal contact load and macro moving speed is obtained by MATLAB simulation.The results show that the tangential contact stiffness of the fluid increases nonlinearly with the normal load and linearly with the macro moving speed;The tangential contact stiffness of solid-liquid interface increases nonlinearly with the increase of normal contact load,and decreases nonlinearly with the increase of macro moving speed;The contact characteristics of solid-liquid interface and solid-liquid interface are similar,and the tangential contact stiffness of solid-liquid interface is greater than that of solid-solid interface.(4)The theoretical model of tangential contact stiffness / damping of static / dynamic solidliquid interface is compared with the experimental data.In accordance with the established theoretical model,the rough joint of EDM is selected,and the # 220 machine tool guide oil is selected as the intermediate medium of solid-liquid interface.Through experiments,the relationship between the tangential contact stiffness of the solid-liquid interface and the normal surface pressure under static condition and the relationship between the tangential contact stiffness and damping coefficient of the solid-liquid interface and the normal surface pressure,excitation frequency and tangential displacement under dynamic condition are obtained.The experimental data are fitted with the appropriate function and compared with the theoretical model.