| Contact surface of maching parts or friction pair has a certain roughness.The contact behavior of rough surfaces plays a vital role for the real carrying capacity,friction and wear of contact parts.About 80% damaged parts are caused by various forms of wear or failure.Therefore,to research mechanical behavior of cyclic micro-contact between rough surfaces,to explore frictional characteristics and evaluation methods of sliding friction interface,are providing theoretical and experimental basis for high reliability and long lifetime frictional contact parts.It is of great significance for the development of national economy and human daily life.1)The rough surface morphology characterization parameters of statistical method and fractal theory were determined,the fitting surface was established.By means of composition of the surface roughness and measuring results,the asperities height distribution of 2D or 3D rough surface was obtained.According to measuring point data and profile height distribution,2D or 3D fitting surface could be obtained by least mean square method and paraboloid fitting method.The results showed that,Parabolic approximation curves of the rough profile obtained by the least mean squares approach could approximate original surface profile preferably.Meanwhile,it could be suitable for asperity contact loading and unloading model better.2)A multilevel contact model of rough surfaces is established for point contact and line contact,and verified by experiment and simulation method.At first,by means of single asperity supporting load,it is connected the global and the asperity level model,a multilevel contact model of rough surfaces is established for point contact and line contact.Through cyclic normal loading test of line contact or point contact,combined with finite element simulation,the relationship of normal loading,real contact area and interference was explored.Real contact behavior of rough surface was researched.Research results show that the model results are similar to test and finite element simulation results.It had practical guiding significance to research contact behavior and morphology evolution caused by elastic-plastic deformation from micro-scale.3)Based on loading-unloading multi-level model of rough surface,tangential function of sliding friction was introduced,multi-scale sliding friction model of ball-disc friction pair was set up.Considering the increased wear loss of frictional interface with sliding cycles at macroscopic scales,this model divided total tangential friction into plowing friction and shear friction.Taking rotational speed and normal load as main influencing factors,grinding polishing surface,circumferential textured and radial textured surfaces were built.By means of sliding friction experiment,the influencing factors of steady state friction coefficient and tangential force were analyzed.Finite element modeling of ball-disc friction pair was established by using ABAQUS to calculate Mises stress,equivalent plastic strain,plowing force and shear force,and the model and test were verified quantitatively.Multi-scale coupling problem of macro friction pair parts and microscopic surface morphology was solved.The results show that steady-state frictional coefficient of sliding friction are positively correlated with wear rate.Steady-state frictional coefficient of different surfaces in descending order are circumferential texture,untextured and radial texture.Regardless of the initial surface morphology,frictional coefficient decreases first and then increases with the increase of revolving speed.With the increase of normal loading,it presents an upward trend.Deeper or wider textured surface has higher frictional coefficient and larger instantaneous fluctuation.Moreover,frictional coefficient also associates with the selection of friction pair material.4)Based on initial wear rate and stable wear rate of ball-disc friction pair,characterizing method of sliding wear about rough surface was proposed,and adaptation law of wear behavior and friction characteristics was obtained.According to wear mass loss of sliding friction test,sliding wear characterization method was established to obtain the relationship curve of mass loss,wear rate,wear coefficient and wear time.Based on test results of different working conditions,the influence of normal loading,sliding velocity and initial surface on wear was analyzed.Particle size distribution of wear debris and wear conditions was explored.The results showed that,for anisotropy rough surface,textured direction would influence the tribological characteristics of sliding friction pair.Moreover,with the increasing mass loss,the wear rate,stable friction coefficient and wear debris size would be increased. |
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