Research On Modeling For Contact Stiffness And Static Friction Coefficient Of Joint Surfaces

Joint surfaces are ubiquitous in the structure of machine tools.Their contact characteristics have important influences on the working performance of the machine tools.The establishment of a scientific and reasonable joint surface contact model is of great significance to the correct prediction of the static and dynamic characteristics of the machine tool structure in the design stage.This paper aims at the problems and shortcomings of the current theoretical modeling research on the contact stiffness and static friction coefficient of the joint surface.Through the method of combining theoretical research and experimental verification.Carried out the modeling research work of the normal contact stiffness and static friction factor of the joint surface.The influence of different morphology parameters of the bonding surface on the contact characteristics is also discussed.The work of this paper is summarized as follows:(1)For the previous model of normal contact stiffness of the joint surface,there are problems that the stiffness of the asperity is discontinuous and smooth in the elastoplastic stage and the calculated stiffness is not zero in the plastic stage.Two new elastoplastic contact stiffness models are proposed to solve this problem.The two models respectively use the cubic polynomial function and the template function interpolation method in mathematics to describe the relationship between the stiffness and deformation of the elastoplastic interval of a single asperity.On this basis,a statistical model of the normal contact stiffness of the joint surface is established.Furthermore,the contact stiffness value of the joint surface calculated by the simulation of the mathematical model was compared with the experimental data of the existing literature.Verify the correctness of the model.(2)The current method of using Tresca yield theory to calculate the maximum tangential load when a single asperity is subjected to a normal force has certain deficiencies.This article is based on elastoplastic mechanics and statistical theory.A new formula for calculating the maximum static friction force of a single asperity under load is proposed based on the von-Mises yield theory.On this basis,a new calculation model of static friction factor is proposed.The numerical simulation calculation of the model reveals the relationship between the static friction factor and the normal load under the standard deviation of different asperity heights.Furthermore,it is compared with the experimental data of static friction factor in the existing literature.It shows the correctness and validity of the built model.(3)According to the existing fractal model of static friction factor of joint surface in Chinese and foreign literature,it is predicted that the static friction factor will increase with the increase of normal load.Problems that are inconsistent with experimental research conclusions and statistical model results.This article defines the size of the asperity based on the scale level.Strictly distinguish between the height and deformation of the asperity.Delimit the range of grades in which each deformed state occurs.The relationship between the normal load and the contact area of the asperity under different deformation states in different scale intervals is constructed.At the same time,combining the asperity edge stress equation and the plastic yield theory,the relationship between the maximum tangential load and the contact area under the corresponding normal deformation is derived.Taking the contact area as the intermediate variable of the associated normal and tangential load,On these basis,a three-dimensional fractal model of static friction coefficient related to the scale level was established in conjunction with the contact area distribution function,and a fractal model of static friction coefficient considering the change of material hardness with depth was further established.The validity of the model is proved by comparing the calculated results of the built model with the experimental data of static friction coefficient obtained by the predecessors.