| Friction and wear phenomena of materials or devices in industrial production are unavoidable,and the energy loss and the equipment damage caused by friction and wear are becoming increasingly prominent.In order to solve the problem,scholars have proposed different methods of friction control,such as changing contact forms,changing friction pair materials and changing lubrication state,which bring about some positive efficiency and breakthrough.However,the traditional friction control methods can only unilaterally increase or decrease the surface friction characteristics of the materials or devices,and the friction can not be adjusted online and reversibly according to the environment and operating conditions,which impedes the intelligent development of the instruments and equipments.How to intelligently control the friction between devices,especially the sliding friction between two surfaces,has become the critical problem to be solved urgently.Magnetic-sensitive rubber has excellent magnetic control characteristics,which makes it possible to control friction by the the external magnetic field,optimize the anti-friction and anti-wear properties of devices,and improve the working efficiency and the service life of mechanical equipments.Therefore,the magnetic-sensitive rubber is taken as the research object in this study,aiming at the problems that the magnetically controlled friction mechanisms are not clear and the experiments are not complete.The magnetically controlled sliding friction mechanisms of the magnetic-sensitive rubber are studied based on the macroscopic and microscopic scales.The change of sliding friction mechanisms of the magnetic-sensitive rubber are explained by theoretical model,which provides a theoretical basis for the engineering application of the controllable sliding friction characteristics of the magnetic-sensitive rubber.The main contents of this thesis are as follows:1.The research background and significance of the magnetically controlled friction characteristics of the magnetic-sensitive rubber are expounded.The recent research progress of the magnetic-sensitive rubber is introduced.And the research status of magnetically controlled sliding friction characteristics of the magnetic-sensitive rubber is especially reviewed.In addition,the sliding friction mechanisms of composites under the external magnetic field are summarized.Then the shortcomings of the related researches are pointed out,and the main contents of this thesis are planned.2.The factors that may affect the sliding friction characteristics of the magnetic-sensitive rubber under the external magnetic field are analyzed.And the initial surface morphology of the magnetic-sensitive rubber is observed by white light interferometer.Then the contact mechanical behavior and sliding friction characteristics between the magnetic-sensitive rubber and the friction pair are described based on the contact theory model and the binomial law of friction.The surface roughness and the elastic modulus are selected as important variables which cause the change of the friction characteristics of the magnetic-sensitive rubber under the external magnetic field.Finally,the detailed research plan of the magnetically controlled friction mechanisms is drawn up.3.The finite element model of the magnetic-sensitive rubber is constructed,and the changes of the surface roughness and the elastic modulus are analyzed from the microscopic aspect.The results show that the surface roughness and the elastic modulus of the magnetic-sensitive rubber are changed in different degrees due to the interaction between the ferromagnetic particles under the external magnetic field.Furtherly,the mutual friction model between the magnetic-sensitive rubber and the friction pair is established,and the influence of the surface roughness and the elastic modulus on the sliding friction performance under the external magnetic field is investigated.The simulation results show that the change of surface roughness and the elastic modulus will lead to the change of surface friction characteristics of the magnetic-sensitive rubber.4.The magnetic-sensitive rubber samples with different initial morphologies are prepared,and the experimental platform for surface observation of samples is designed and built.Then the surface profiles,mechanical properties and sliding friction characteristics of the magnetic-sensitive rubber under magnetic field are measured from the macroscopic aspect by using the existing platform in the laboratory.The experimental results show that the surface roughness and the elastic modulus of the magnetic-sensitive rubber will be changed with the action of the magnetic field,and the change trend is consistent with the simulation results.Affected by the change of surface morphology and elastic modulus,the friction coefficients of all samples with different initial morphologies are decreased when the magnetic field is about 250 mT.In addition,the friction coefficient of the samples with the smoother initial surface can be adjusted in a wide range.The friction coefficient of the isotropic magnetic-sensitive rubber with the particle volume ratio of 15% has the most significant change,which is ranged from 0.98 to 0.75,and the change rate is as high as 23.3%.Moreover,the friction coefficient of samples with therougher initial surface can be adjusted in a small range,and the anisotropic magnetic-sensitive rubber with particle volume ratio of 15% has the relatively obvious change,which decreases from 0.52 to 0.47,and the change rate is only 9.7%.5.Based on the magnetic dipole theory,the changes of the surface roughness and the elastic modulus of the magnetic-sensitive rubber under the external magnetic field are analyzed theoretically.Then the simulation and experimental phenomena that the change trend of the surface morphology of the magnetic-sensitive rubber affected by the initial surface roughness are explained,and the increasing trend of the elastic modulus of the magnetic-sensitive rubber is verified.Futhermore,based on the elastic contact theory and the binomial law of friction,the relationship between sliding friction characteristics of the magnetic-sensitive rubber and the surface roughness and the elastic modulus is established.The theoretical analysis shows that the sliding friction characteristics of the magnetic-sensitive rubber with the magnetic field are influenced by the coupling effect of the surface roughness and the elastic modulus.The larger change range of the elastic modulus determines the decreasing trend of the friction coefficient of the magnetic-sensitive rubber,and the change of the surface roughness adjusts the decrease degree of the friction coefficient,which is consistent with the sliding friction experimental results.Finally,the controllable sliding friction mechanisms of the magnetic-sensitive rubber with the magnetic field are revealed. |
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