The Study Of Fractal Contact And Friction Vibration On Rotating End-face Based On Stribeck Friction Model

Friction is a complex,nonlinear and uncertain natural phenomenon.Frictional vibration is a double-edged sword,which can not only provide services for people,but also damage the system and make environmental noise.In engineering application,the vibration and noise caused by friction are the hotspot and difficulty of current research,and their mechanisms need further study.In this paper,the rotating end-face friction system is taken as the research object.Around the contact vibration of dry friction,the dynamic characteristics of the system containing friction are studied deeply.The dynamic adaptability of the frictional pair system is discussed through combining theories and experiments.The purpose is to enrich the theoretical research and experimental support of friction dynamics,and improve the interaction between contact and friction in the system dynamic analysis model.At the same time,the research results are applied to the friction dynamic characteristics of the compressor crankshaft system,and the design guidance of antifriction and vibration reduction is put forward.The main contents of this paper are as follows:(1)The relationship curve between the real contact area and the contact load is given in the basis of the M-B fractal contact model.Considering the influence of friction on the deformation of contact micro convex,the critical contact area of elastic-plastic deformation is modified.Combined with the experimental results of surface fractal parameters,the fractal models of the normal contact stiffness and tangent contact stiffness between rough surfaces obtained on the basis of Hertz theory are modified.(2)Based on the Stribeck friction effect,the normal fractal contact stiffness is introduced to establish the friction torque model.According to the mechanical and kinematic analysis of the system,the Lagrange equations and the differential equations are established to analyze the system stability and characteristic frequencies.The results show that the unstable vibration of the friction pair system occurs in a certain speed range;the larger the Stribeck coefficient is,the larger the unstable range is;increasing the contact load will expand the instability trend of the system,but rising the contact surface smoothness properly can reduce the system instability;enlarging the contact load and the relative sliding speed will raise the normal vibration of the system.However,the higher speed will reduce the tangential vibration frequency,and the radial vibration frequency is determined by the intrinsic parameters of the system.(3)Design and build the friction experiment platform independently;put forward the overall layout of the test device and experimental design requirements;specifically design the structural parts being processed and manufactured according to the mechanical design principle and mechanical design manual,and draw the design drawings.In the design of the experimental platform,it is necessary to ensure that the constraint state of the friction parts is basically consistent with the theory.The spring is used as the normal load of the contact surface to cleverly design the loading device.Improving the processing and assembly accuracy of the parts to ensure the smooth fit of the two contacted surfaces.On account of the theoretical research,the specific friction testing schemes and requirements are carried out.(4)The dynamic responses of four groups of friction pairs are studied.The results indicate that different friction pairs have similar frictional responses.The vibration frequencies are concentrated from 2000 Hz to 7000 Hz.The rich harmonics in this frequency band are produced by the surface collision.There are three or four main frequencies in this frequency band.The amplitude of friction vibration response of containing 45~#steel is much higher than that without45~#steel.The effects of contact load and relative sliding speed on the response of the system are studied.The results imply that increasing the load and speed will make the response amplitude larger,and the high-frequency vibration is more prominent.It is also revealed that the system is unstable between 500 rpm and 3000 rpm.In order to explain the phenomenon of friction vibration,the modal analysis is carried out.It is demonstrated that the response frequency of the system vibration caused by friction is highly consistent with the system resonance frequency,which means the resonance frequency is excited by the friction.The resonance frequency is rising with the increase of the load and speed,which is accordant with the theory.(5)Based on the theoretical and experimental achievements,the friction dynamic characteristics of the compressor crankshaft system are analyzed by the ADAMS software.The results indicate that the dry friction causes the system unstable collision and excites the resonance frequency of the system.The damping coefficient and contact stiffness are used to simulate the state of surface lubrication.It is found that there is a critical value that can significantly reduce the unstable impact of the system.Taking the maximum vibration acceleration of the system as the research index,the critical state of the stable vibration of the system is determined through DOE analysis,which provides design guidance for the antifriction and vibration reduction.