| The joint surfaces are common in the mechanical structure and the dynamic characteristics of the joint surfaces have an important influence on the dynamic characteristics of the whole mechanical system,which affects the characteristics of friction and wear,lubrication and seal,stiffness and damping,vibration and noise of the mechanical system.For many years,experts and scholars from all over the world have studied dynamic characteristics from the perspective of macro contact and parameter identification,or from microscopic perspectives on different scales.A lot of theoretical,finite element simulation and experimental research are carried out on the typical interfaces of the machine,and many calculation models and solving methods are put forward.Due to the continuous development of the static and dynamic characteristics of modern machinery towards high speed,high precision and lightweight,this makes how to calculate the dynamic characteristics of joint surfaces become the key issue of today's mechanical design.At present,there are two major theoretical factions about how to establish a theoretical contact model for analyzing the dynamic characteristics of the typical joint surfaces:one is statistical theory,the other is fractal theory.The statistical theory is limited by the accuracy and sampling length of the measuring instrument,and fractal theory can describe all the information of the surface topography and is not affected by the measuring instrument.The surface of mechanical components that look like smooth from the macroscopic view,while if viewed from a microscopic view,there are numerous and irregular asperities on surface from different measurement scales.The asperity forms the surface roughness of the component.Moreover,the distribution of these asperities show self-similar characteristics,so it is more appropriate to describe them using fractal theory.The contact between the joint surfaces of the assembled parts is actually the contact between the asperities,so the mechanism of contact deformation determines the dynamic characteristics of the joint surfaces.In this paper,under the support of the National Natural Science Foundation of China and the Fundamental Research Funds for Central Universities,the contact characteristics and the dynamic characteristics of vibration-friction coupling of the joint surfaces are studied.The dynamic characteristics of the joint surfaces affect the static and dynamic performance of the whole machine,and then affect the start and stop accuracy,running accuracy,machining accuracy,and vibration stability of the whole machine.Based on the modified three-dimensional fractal contact theory,the dynamic characteristics of the joint surfaces are modeled,and the fractal prediction models such as contact stiffness,contact damping,friction force,and wear are presented,so as to start the study from the perspective of micro influence macro.This idea not only provides a basis for the subsequent overall theoretical modeling of the system,but also provides a reference for understanding and improving the vibration-friction coupling characteristics of the macro system.The main contents of this paper are as follows:(1)The normal and tangential contact stiffness models,normal and tangential contact damping models,as well as the static friction coefficient model and sliding friction model of the joint surfaces are established;the influence of interface parameters on each model is analyzed.Based on the fractal theory and Hertz theory,the three-dimensional fractal characteristics of the surface topography,the elastic-plastic transitional deformation mechanism of the asperity and the influence of the dynamic friction coefficient between the interfaces are considered,the effects of parameters such as fractal dimension,fractal roughness,maximum asperity contact area,and dynamic friction factor on relevant fractal model are analyzed.(2)The normal and tangential contact stiffness models and the normal and tangential contact damping models between cylindrical surfaces and spherical surfaces are established;the influence of fractal parameters and geometric size parameters on each model is analyzed.Based on the fractal contact models established in the previous paper,the fractal contact models of cylindrical and spherical surfaces are established;the influence of fractal parameters D,G,friction factor ?,material characteristic parameter ?,contact line length L,cylinder radius R and different contact forms is analyzed in detail.(3)A vibration transmission path model with interface topography,an adhesive contact fractal model,a wear fractal model,and an interface instantaneous temperature fractal model are established,the nonlinear response and thermal instability characteristics of interface vibration are analyzed.Based on the microscopic three-dimensional contact topography characteristics,the frequency responses of interface vibration transmissibility and interfacial penetration loss rate are analyzed in detail.The effects of interface fractal dimension D,fractal roughness G and friction factor ? on the contact fractal models are analyzed.(4)A typical modal coupling model of vehicle braking system is established.The vibration and friction coupling analysis of plane joint surfaces is completed.Based on the vehicle braking system in engineering,it is abstracted into a typical modal coupling model with two degrees of freedom.The stability and non-linear characteristics of the flutter system under the influence of the interface stiffness ratio,friction factor and damping ratio are analyzed.The finite element analysis and measured test of the vibration and noise of the flutter system are given,and the theoretical analysis and verification of the measured results are completed.Through the above research,the main conclusions of this paper are summarized,the innovations and shortcomings are pointed out,and the future research directions are also prospected. |
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