Numerical And Experimental Study On Friction And Wear In Elastic Contact

Tribology,as a fundamental interdisciplinary discipline,has been widely concerned by many researchers.However,due to its complexity and limitations of human knowledge,many tribological problems have not been solved yet.Friction mechanics lays the foundation of engineering sciences.A deep understanding of the contact problem in tribology plays an important role in constructing safe and energy-saving mechanical parts.In view of the current situation of more experimental research and less numerical calculation methods in the field of tribology,the purpose of this dissertation is to quantitatively study the contact problems in friction and wear by mathematical methods,and verify these results by experiments.The dissertation mainly focused on the problems of normal and tangential contact of non-Gaussian rough surface,energy dissipation of rough surfaces under preload,contact pressure under dry friction,prediction of wear and in-situ observation of stress field during wear in an initial line contact.Simultaneously,some MATLAB~?calculation codes were given at the end of this dissertation.The Pearson distribution function,which can independently give skewness and kurtosis values,was used to describe the height distribution of rough surfaces.Based on the single-asperity elastic-plastic contact model,a formula for calculating the normal force of the contact interfaces was derived by combining the statistical method.At the same time,the formula for calculating tangential force was derived from the Mindlin's stick-slip model.Then the influence of skewness and kurtosis on normal and tangential contact was analyzed,and the values of tangential contact stiffness at the initial slip were compared with the pubilshed experimental results.In addition,the Iwan model was used to analyze energy dissipation of lap joints under cyclic loading,to which preload had been applied,and the critical slip force distribution function of Jenkins elements based on real physical parameters was derived.Compared with previous studies by other researchers,the greatest advantages of this function are that the distribution function was derived under fewer assumptions,so that it is no longer a phenomenological description of experimental phenomena and the parameters of the function need not be calibrated by experiments.There have been many reports on wear prediction under dry friction.The key point of numerical prediction is the solution of contact pressure between friction pairs.Most of the previous studies have solved the contact pressure through the elastic contact theory,but there are few reports on whether the environmental pressure will affect the contact pressure.In this dissertation,the contact pressure between interfaces under dry friction was solved by using the Reynolds equation modified by FK-Boltzmann from the point of view of gas lubrication.At this time,the normal load is assumed by the contact of asperities and the gas lubrication effect.The unified reynolds equation with low viscosity,low density and significant rarefaction effect was successfully solved by using the mixed lubrication method.Finally,the effects of normal load,entrainment velocity and ambient pressure on the gas loading ratio were studied.It is found that ambient pressure have a significant impact on contact pressure only under high pressure,high speed and light load condition,and elastic contact theory is still usefull to solve the problem under general working conditions.The influence of friction force on contact pressure and wear is largely omitted in the study of wear prediction.In this dissertation,the contact pressure between interfaces was obtained not only by solving the singular integral equation but also conjugate gradient method,and the results were compared with the theoretical under smooth line contact.A variable discrete step function was designed for the phenomenon that the contact pressure changes dramatically and then gently in the process of wear in an initial line contact.Finally,combined with photoelastic experimental technology,the in-situ variation of maximum shear stress field during wear process under linear contact was observed,and the corresponding interference fringe simulation method was established to analyze the change of subsurface stress.