Contact Characteristics Modeling Of Joint Surfaces Based On Multi-stage Contact Theory

Joint surfaces are important parts of machine tools system,and the contact characteristics such as the static friction factor,tangential stiffness and contact thermal conductance of the joint surface greatly affect the working performance of the machine tool.Therefore,it is crucial to establish an accurate and reliable joint surface contact model in the design stage of the machine structure to predict the characteristics of the machine structure correctly.At present,most of the joint surface contact models based on fractal geometry theory consider that the actual deformation of the asperity is equal to its own height,without taking into account that the actual deformation of the asperity changes during loading process,which is not consistent with the classical contact mechanics.In view of this,this paper carries out the modeling and simulation of the static friction factor,tangential stiffness and contact thermal conductance of the joint surface based on the multi-stage contact theory of the joint surface,which strictly distinguishes the height and deformation of the asperity.The main research works are as follows:(1)Aiming at the problem of inconsistent study results between the statistical model and the fractal model of the static friction factor of the joint surface in the existing literature,based on the multi-stage contact theory of the joint surface,the height and deformation of the asperity are strictly distinguished,and the maximum tangential load that the joint surface can withstand is first derived based on the segmental function of the actual deformation of the asperity and the distribution function of the length of the base of the asperity.Based on the definition of the static friction factor,a fractal model of the static friction factor of the joint surface was established,and through the simulation of the proposed model,the influence law of normal load,fractal dimension and characteristic length scale parameters on the static friction factor of the joint surface was analyzed,and then the simulation results of the model were compared with the previous static friction factor models and example data to verify the correctness of the model.(2)Based on the multi-stage contact theory of the joint surface,the fractal model of the joint surface tangential stiffness was established by combining the single asperity tangential contact stiffness model,the model was simulated and the effect of normal load,fractal dimension and characteristic length scale parameters on the tangential stiffness of the joint surface was analyzed,and then compared with the experimental results.The results show that the fractal model of joint surface tangential stiffness based on multi-stage contact theory is more consistent with the experimental results,which shows the correctness of the model.(3)Based on the multi-stage contact theory of the joint surface,a fractal model of contact thermal conductance of the joint surface is established in combination with a single asperity contact thermal conductance model,and the effects regularity of normal load,fractal dimension,and characteristic length scale parameters on the contact thermal conductance are simulated and analyzed for the proposed model,the results show that the contact thermal conductance of the bond surface increases with increasing normal load.