Research On The Contact Characteristics Of Anisotropic Joint Surface Using The Contact Coefficient Of Ellipsoid

In the research on the characteristics of the junction of the rough surface,a large number of literatures on the contact characteristics of the junction usually regard it as an isotropic rough surface.However,in practice,most of the processing planes have been found to have obvious anisotropy characteristics through research.In this paper,a contact stiffness model and a contact damping model with anisotropic characteristics of the joint surface are proposed.In this model,the asperities on the rough surface are equivalent to the ellipsoidal asperities,and the rough surface is equivalent to the anisotropic surface.When constructing the contact analytical model expressing the anisotropic bonding surface,this paper establishes the normal and tangential contact stiffness models of the two ellipsoid asperities varying with the angle of the principal curvature,including the elastic and elastoplastic transition stages.At the same time,corrections were made to the separation of the macro-surface profile features and the micro-protrusion contact in the existing bonding surface contact model.Then,by introducing the contact coefficient of the ellipsoid,the area distribution function in the fractal model of the joint surface contact is improved,and the normal,tangential contact stiffness and contact damping model of the anisotropic joint surface are established.Finally,an experimental model and a finite element model are established for comparison and verification to prove the rationality of the model established in this paper.The research content of the thesis is carried out from the following aspects:(1)A theoretical model of the contact stiffness of the anisotropic bonding surface has been established.it is assumed that the asperities on the joint surface are ellipsoidal asperities and there is a peak-to-peak positive contact between the two asperities.The asperities are established based on the Hertzian contact theory The normal and tangential contact load models of the contact area of the two ellipsoid micro-convex bodies varying with the included angle are presented.Finally,after improving the area distribution function of the fractal model based on the continuous deformation theory,a fractal model of the normal and tangential contact stiffness of the anisotropic bonding surface is established.(2)Numerical simulations are carried out on the anisotropic normal and tangential contact stiffness models established above.The simulation results show that for an anisotropic surface,the normal and tangential contact stiffness will change with the angle of the ellipsoidal asperities.The closer the formed contact surface is to the circle,the normal and tangential contact stiffness will decrease,while the normal and tangential contact stiffness will be approximately linear as the contact coefficient of the ellipsoid surface representing the macro-profile error increases.Increase;improving the flatness of the bonding surface,reducing the roughness of the bonding surface,increasing the normal contact load and increasing the material parameters of the bonding surface material can all improve the normal and tangential contact stiffness between the bonding surfaces.(3)Verify the rationality and superiority of the model in this paper by using the experimental device including joint surfaces.First,the principle and application of the virtual material method for the construction of the contact layer material parameters of the finite element model consistent with the experimental model are explained,and then the experimental model including joint surfaces is constructed,the modal experiment is carried out,and the experimental device is passed.The natural frequencies and the first three modes of the joint surface under different tightening torques are measured.At the same time,a finite element model consistent with the experimental model was established based on the virtual material method,and the contact stiffness fractal model established in the previous chapter was input into the contact layer parameters of the finite element model through APDL language.Finally,after obtaining the first three-order mode shapes and natural frequencies of the experimental model and the finite element model,a comparison was made.The results show that the anisotropic bonding surface contact model established in this paper is consistent with the results measured by the experimental model.Good;the difference between the first three natural frequencies of the finite element model under different tightening torques and the experimental model is within,which proves the correctness of the model established in this paper and can faithfully reflect the contact characteristics of the whole machine.(4)A theoretical model of anisotropic bonding surface contact damping is established.Based on the normal contact load model of the anisotropic bonding surface established in Chapter 2,a fractal model reflecting the normal contact damping of the anisotropic bonding surface was established for the first time.It provides a new theoretical model for the research on anisotropic contact damping of the joint surface.Finally,a finite element model with the same parameters as the experimental model in literature [96] is established,and the theoretical model of contact damping established in this paper is substituted into the finite element model and the literature model for comparison and verification.