Research On Modeling Method Of Joint Based On Real Rough Surface Contact Analysis

Joint characteristics have significant effect on mechanical system performance.The main difference of performance analysis between mechanical system and mechanical part is that mechanical system performance analysis needs to consider the influence of joint characteristics.In this paper,the author studied the contact characteristics of real rough surface by theoretical,experimental and numerical simulation methods based on the existing research results and experimental data.And then,the author studied the influence of joint characteristics on mechanical system performance.What’s more,a finite element modeling method of joint is presented.The main researches can be presented in following aspects:Firstly,the analysis of contact characteristics based on real 3D rough surface profile data.The contour data of metal grinding surface were measured by white light confocal interference focusing microscope and atomic force microscope.Then,the rough surface contact model based on real contour data was established in the finite element software.Furthermore,the influence of different sampling resolution on the contact characteristics was analyzed.The analysis results show that the proportion of real contact area to nominal contact area and the contact stiffness decreases with the increase of sampling resolution,but the contact stress increases with the increasing of sampling resolution.With the increasing of the sampling frequency,the relationship between the normal load and the real contact area tends to be linear.The relationship between normal load,real contact area and the contact stress of the contact layer is no longer affected by sampling resolution when the sampling resolution increases to a certain extent.Moreover,the relationship between the normal load and the real contact area is linear when the normal load does not exceed the material yield stress.Secondly,an orthotropic constitutive relation and finite element modeling of joint surface.By analyzing the geometric characteristics,physical structure and mechanical properties of the contact surface,it is found that the contact layer has orthotropic property.This paper presents a method for modeling the contact layer based on the widely used isoparametric element in finite element analysis.In this method,the contact layer is equivalent to a virtual material with equal thickness,homogeneity and orthotropic property.The expressions of the material parameters in the constitutive equation of the virtual material are determined by analyzing the distributions of real contact surface and the change rules of contact stiffness.According to the constitutive equation of the virtual material,an experimental model is established in the finite element software.And,the finite element analysis results are compared with experimental results.It is showed that the orthotropic material can reflect the anisotropic contact property of the joint surface,and has good software adaptability.Thirdly,the dynamic characteristics of heavy vertical milling machine were analyzed.In this part,the author studied the influence of the joint characteristics on the dynamic performance of the whole machine.The modal analysis of the whole machine tool,the impulse response analysis of the whole machine considering the surface profile of the joint and the impulse response analysis of the whole machine without considering the surface contour of the joint.The natural frequencies and mode shapes of the machine tool obtained by the three methods are compared correspondingly.By comparison,the results of the dynamic analysis of the whole machine tool without taking into account the characteristics of the joint and the results obtained by considering the characteristics of the joint are very different.Therefore,the joint model should be suitably established according to the actual structure.