Investigation Into The Contact Characteristics And Nonlinear Vibration Mechanisms Of Rough Contact Interfaces

High speed railway brake disc,aero motor and automobile gearbox,which consist of a series of different parts and components,are the key equipment in the field of mechanical manufacturing.Bolted joint is the most common connection in mechanical systems.Two independent parts are connected by bolts to form a contact interface.The mechanical behavior of the contact interface can lead to fundamental changes in the vibration,wear characteristics and reliability of the mechanical system.It is important to study the contact characteristics and vibration mechanism of rough contact interface for improving the dynamic behaviours and reliability of mechanical equipment.The mechanical behavior of the contact surface is affected by the surface morphology,material properties and operation conditions.There is no macroscopic relative movement at the contact surface.However,under the normal loads,the contact interface with micro rough shape is mechanically deformed,resulting in interface contact stiffness.The contact interface with tangential friction is not completely viscous,which will slip tangentially at the micro level.In addition,the mixed lubrication contact interface will be formed after the lubricant is added into contact surface.Therefore,the contact interface has complex contact characteristics under the coupling action of roughness,contact deformation,tangential friction,mixed lubrication and other factors.The mechanical behavior of the contact interface has typical nonlinear characteristics.Three aspects of contact surface are studied in this paper,including interface contact modeling,quantitative characterization of contact surface parameters and the nonlinear vibration response of contact surface.The above research reveals that the nonlinear relationship among the micromorphology parameters,operating condition parameters and vibration response of contact surface,which provides theoretical basis for accurate predicting and improving the dynamic performance of mechanical equipment.The specific researches are as follows:(1)For the problem of non-mo notonic and non-continuous changes of the contact parameters of the exsiting asperity micro-contact model,considering the asperity undergoes the regimes of elastic-elastoplastic-plastic deformation,a low-order elliptic function-based asperity contact model is proposed to achieve monotonous,continuous and smooth change of contact varaibles in different deformation regimes.Considering the influences of surface roughness,material properties and nominal contact area,the power-law characteristics of the normal contact stiffness with the contact load are quantitatively characterized.Then,the explicit analytical expression of the normal contact stiffness with respect to the contact load is constructed,which overcomes the shortcomings of the existing statistical model that the expression of the contact parameter is complicated and only the numerical solution can be obtained.For different statistical models,the maximum error between analytical solutions and numerical solutions of contact stiffness is less than 12%.(2)For the rough contact interface with tangential micro-slip,the existing contact model cannot accurately describe the nonlinear relationship between interface properties and contact stiffness.A new method for calculating the contact stiffness ratio of tangential micro-slip interface is proposed.By deriving the stress-strain constitutive equation of micro-contact asperity,the influences of morphology of asperity and normal load on the contact stiffness ratio are revealed.Based on the tangential micro-slip model of asperity,the quantitative relationship between micro-slip coefficient of rough interface and contact stiffness is also obtained.In the aspect of experimental measurement,considering the attenuation of acoustic reflection coefficient at the contact interface,the original measurement model is improved.For the steel samples with different roughness,as the normal load is 400MPa,the differences between the measured value of the original ultrasonic model and the predicted value of the statistical model is 1.04GPa/μm,and the difference between the improved value and the predicted value is 0.08 GPa/μm.Therefore,the experimental measurement accuracy of the normal contact stiffness is improved.(3)For the rough contact interface in mixed lubrication,based on the existing interface contact model,it is difficult to describe the nonlinear relationship between interface characteristic and contact stiffness accurately.A new method for calculating contact stiffness of mixed lubrication interface based on the equivalent thin layer is proposed.The solid-liquid coupling stiffness of lubricated interface is seprated,and the differences of contact stiffness between interface wiythout lubricant and luborcated interface are compared.The influences of surface morphology,lubricant properties,interfacial separation and actual contact area on the total stiffness of lubricated interface are revealed.Results show that the effects of lubricant properties on contact stiffness are obvious at the initial contact.With the increment of real contact area,the influence of surface morphology on contact stiffness increases.By establishing the finite element model based on the property parameters of equivalent thin-layer materials,the natural frequencies and theoretical mode shapes are compared with the measured results of modal tests to verify the effectiveness of the proposed method.(4)For the contact surface with initial loads,the nonlinear vibration response of the rough contact interface is investigated.The function of the nonlinear restoring force with respect to the equivalent deformation is derived.The influence of surfaceroughness on the interface restoring force and the contact natural frequency is also analyzed.Considering the displacement of the static equilibrium position of the interface,the normal contact vibration model of the bolted interface is established.The variation of the natural frequency of the vibration system with the initial displacement of the interface is studied.The nonlinear relationship between the micro-contact parameters and the macro vibration response characteristics of the interface is revealed.Results show that the restoring force and natural frequency characteristics of the rough interface are affected by the surface topographies.Amplitude-frequency response of the contact vibration system exhibits nonlinear characteristics.The phenomenon of amplitude jump is observed.As the roughness of the contact interface decreases or preload increases,the nonlinear degree of the vibration response for the bolt interface is effectively decreases.