Study On Frictional Calculation Of Random Rough Surfaces Contacting

Friction is a common phenomenon during relative movement between contact pairs;it is a seemingly simple phenomenon,but it is closely related to our life and production economic benefit.And many scholars are firmly committed to the field of tribology.After a long time of accumulation and development,tribology has become a multidisciplinary subject.The classical laws of macro tribological have been widely used in engineering practice.However,with modern equipments and products' incline to miniaturization and ultra-precision,macro friction laws have been unable to meet the accuracy requirements in the micro scale.In recent decades,with the emergence of micro friction testing instruments,such as atomic force microscope and surface force apparatus,people have made a great progress in the study of micro/nano friction.Most previous research on micro/nano friction are based on the deterministic models of surface topography,however,the friction contact surfaces have a certain roughness in engineering.Morphology,structure,material properties,working conditions and the friction process are random in practice.To get more in line with the actual situation of friction analysis results,we need to establish the random friction model.However,at present,there is little research on random friction,and the qualitative research methods of experiment and measurement are in the majority;the quantitative research methods of calculation and analysis are very few,due to the excessive influence factors of random friction process.Friction material properties,temperature,structure and other factors are relatively stable in the ordinary progress of friction,but the surface morphology is a mainly random factor in the friction process.Therefore,this paper mainly focuses on the study of the influence of morphology parameters on friction mechanism,and sets up the calculation models for the random rough surfaces contact.The main research contents are as follows:(1)On the basis of the potential barrier of contact surfaces and the stochastic properties of contact surface morphology,a new calculation model of sliding friction force loaded on nano-scale rough surface is established.Then,the model is used to numerically calculate the sliding friction force of the same material friction pair with rigorous stationary process.The results show that the normal load is linear to the mean sliding friction force obtained by the presented model and is exponential to the average surface separation;and that the average normal force increases linearly with the standard deviation of roughness height distribution at the same average surface separation.In addition,the calculation results are consistent with the existing research conclusions,which means that the presented model is effective and feasible.With this model,the mean sliding friction force can be predicted according to the distribution parameters of contact interface morphology,material parameters and normal load.(2)Adopting the precision finite element analysis results of a sphere-flat contact of Kogut and Etsion,and combining with rough surfaces contact statistical theory of Greenwood and Williamson,we set up two kinds of random friction force calculation models based on composite-oscillator model and interface barrier theory respectively,and two kinds of calculation models are compared.The results show that: under the same friction conditions,the predicted friction force based on the composite-oscillator model is smaller than that based the contact interface barrier with low normal load;when the normal load exceeds a certain value,the calculated result curves of the two models intersect,then tend to be consistent with the increase of normal load;the friction force decreases with the increase of plasticity index.(3)Based on the view of the system and energy and the Greenwood and Tripp contact model,a calculation model for elastic-plastic spherical contact of nominal level rough surface is presented.The friction experiment between AFM ball probe and rough surface samples were taken.The results show that the deviation between the theoretical values and the experimental values is small under a low plasticity index,while larger with the increase of plasticity index.(4)A new static friction model for random rough surfaces contact is presented.This model analyzes the static friction with the energy dissipation mechanism that the change of the potential of contact surfaces causes the friction.And this model incorporates the analyses of interfacial potential for a spherical contact in a statistical representation of surface roughness.A comparison between the present model and several previously published models shows that the energy dissipation mechanism is a feasible solution for predicting the static friction of rough surfaces contact.The prediction results of present model are in good agreement with that of the KE friction model and the CKE friction model at low plasticity index.(5)This paper establishes formulas between the bearing area ratio and friction coefficient for dry and lubricated friction,investigates the relationship between the bearing area ratio curve and roughness parameters,and subsequently explains the influence mechanism of the roughness parameters on the friction and wear by the bridge of the bearing area ratio.Finally,dry and lubricated pin-on-disc tests were performed on samples with different roughness parameters,and the experimental results verify that the established formulas and the explanation of the influence mechanism are feasible and reasonable.