Research On The Normal Contact Model Of Joints Considering The Surface Anisotropy

With the rapid progress of modern science and technology,the demand for machinery in the manufacturing industry is increasing to high speed,high efficiency and high precision,which puts forward higher requirements for the static and dynamic performance of general machine tools,CNC machine tools,machining centers and other mechanical equipments.The jionts universally exist in the mechanical system,mechanical structure and mechanical parts,and its static and dynamic characteristics are important factors affecting the whole machine's performence.Therefore,the study of the basic characteristics of the mechanical joints for the promotion of high-end equipment manufacturing capacity and precision has very important academic significance and application value.In this paper,the basic characteristic parameters of the joints such as the contact load,the contact area,the contact stiffness and the contact damping are studied,considering the anisotropic properties of the rough surfaces.Starting with asperity modeling,based on the normal static loading,unloading contact model of the anisotropic joints,the static and dynamic theoretical contact models of the joint considering single rough surface contact,asperity interaction,double rough surfaces contact and double rough surface contact with asperity interaction are established respectively.The main innovation achievements and research contents are as follows:(1)Anisotropic rough surface theory modeling.The mathematical model of the multidimensi--onal gaussian probability density function for anisotropic rough surface is established by using simplified calculations and derivation of various random variables on the rough surface,autocorrelation functions,and assumptions of the power spectrum moments that satisfy the surface anisotropy.The statistical parameters related to the rough surface of anisotropy can be obtained,which lays a foundation for the study of the contact model of anisotropy joints.(2)Study on normal contact model of anisotropic joint.A normal statistical contact model for(9)Supported by the National Natural Science Foundation of China(No.51275407).the static loading and unloading of anisotropic joints is established,which takes into account the asperity's elastic,elastoplastic and plastic deformation,and the single rough plane hypothsis made up of equivalent rough surface and smooth rigid plane.After the dimensionless normal contact model is simulated,the influence of normal static loading and contact deformation on the contact area and contact stiffness of anisotropic joints is analyzed.The curve change law of the contact parameters of anisotropic joints is consistent with that of isotropy,greater than isotropic in dimensionless values.During loading,the contact area and contact stiffness increase with the increase of contact load and contact deformation,and the changing curve of contact stiffness presents a non-linear increase.While during unloading,the contact load depends on the maximum value of the contact load.And due to the existence of residual deformation,with the constant decrease of contact load,the normal contact area is larger than the contact area at the time of loading,and the contact stiffness is also greater than the load contact stiffness.(3)Study on the normal dynamic contact model of anisotropic joint.Based on the anisotropic joint surface normal static loading and unloading statistical contact model,the normal dynamic contact stiffness and contact damping calculation model of the anisotropic joint surface is established.The influence of the normal contact load,the dynamic relative displacement amplitude and the vibration frequency on the contact dynamic stiffness and the contact damping of anisotropic joint is analyzed.The results show that the normal contact stiffness of anisotropic or isotropic interface is very close to the static contact stiffness,with the normal dynamic relative displacement amplitude nonlinear growth,but not with the vibration frequency changing.The normal contact damping with the normal dynamic relative displacement amplitude increases,but with the increase in vibration frequency and decrease,and the relation with the contact load presents an approximate linear phenomenon.(4)Study on the normal contact model of the anisotropic joint considering the asperity interaction.Based on the principle of asperity interaction,a normal contact deformation model of asperity is established,then the normal static and dynamic contact model of the anisotropic joint is introduced to establish the anisotropic joint normal contact model considering the asperity interaction assumption.The variation of the normal static parameters,contact dynamic stiffness,contact damping are analyzed respectively and compared with the single rough plane hypothesis.Analysis show that considering the asperity interaction,the changing trend of each parameter is the same as the single rough plane hypothesis,but the static contact load,contact area,and contact stiffness will be large under the same deformation.The value of the normal dynamic contact stiffness is similiar,but the increment of the normal dynamic relative displacement amplitude is more obvious.Under the same normal preload,the contact damping with the dynamic relative displacement amplitude,the vibration frequency is smaller than that ofthe single rough surface.It shows a slight nonlinearity with the increase of the normal contact load,and the contact damping value is greater in the anisotropy than in the isotropic case.(5)Study on normal contact model of anisotropic joints considering double rough contact surfaces.The equivalent single rough surface is extended to the double rough surface contact.Then the normal static and dynamic contact model of the anisotropic joint considering the assumption of the double rough contact surface is established.The relationship between the normal static and dynamic contact stiffness and the contact damping is analyzed,compared with the assumption of the single rough plane and the asperity interaction.The results show that after considering the contact of double rough surfaces,the interaction of each parameter is assumed to be the same as that of the single rough plane and the asperity interaction.The value of the contact load is smaller,the contact area increase with contact load is smallest and but the contact stiffness are largest.The normal dynamic contact stiffness increases with the increase of different variables,and is greater than the other two assumptions;the change law of normal contact damping is similar,and the assumption of the asperity interaction is numerically similar,and the anisotropic damping value greater than isotropic case.(6)Study on the normal contact model of the anisotropic joint considering the asperity interaction and the double rough surfaces assumption.The principle of asperity interaction and the side contact theory are organically combined to establish a normal static and dynamic contact model for the anisotropic joint considering the double hypothesis of double rough surfaces and asperity interaction.The curve relationship to the static and dynamic parameters is analysied and compared with other single assumption.It was found that the normal contact load of the double hypothesis is the biggest on the same deformation.And the contact area is similar to the double rough surface assumption under the same contact load,and the contact stiffness is smaller than the assumption of a single rough plane.The dynamic contact stiffness trend is consistent with the rest of the single hypothesis and smaller than the single rough plane hypothesis.The normal contact damping is also similar and numerically in the middle of all other hypotheses.(7)The experiment of normal and dynamic characteristic parameters of the jonit.The rough surface of different processing methods are selected,and static and dynamic experiments are performed on the experimental platform for the basic characteristic parameters of the joint,to obtain the trend of normal static stiffness with contact pressure,dynamic contact stiffness and contact damping with normal pressure,amplitude and vibration frequencies,respectively.The surface morphology was obtained with a Leica white light copolymerization interference microscope.The surface power spectrum moment was obtained by extraction calculation.The theoretical simulation of the normal and static contact model of the joint was performed using this power spectrum moment and compared with the experimental results.