Proceedings of SerbiaTrib '13

which is responsible for one of the reasons for thedeviation of the real surface of the crystal from theinitially smooth and the emergence of so-callednatural roughness [3]. Such modifications ofsurface geometry are sub roughness, whichsignificantly exceeds the atomic scale roughnessarising at vibrations of the atoms or molecules dueto thermal fluctuations.The most appropriate criterion for selectingmaterials for the parts of tribosystems can be takenminimum value of frictional work [4].Friction work calculated by the formula [5]Wfr fFS , (2)frwhere F – normal force of friction pair elementsinteraction; f – a friction coefficient; S fr – frictiontrack.Tribosystem are open thermodynamic systemsthat exchange energy and matter with theenvironment. Friction is the process of convertingthe external mechanical energy into internal energyin the form of vibration and wave motion ofparticles of tribosystem followed by thermal,thermionic, acoustic, and other phenomena. Most ofthis energy is converted into heat and is given to theenvironment, the other - is to change the physicaland chemical state of the surface layers of thematerial. Dissipation of energy corresponds to anincrease of entropy (dS > 0).Energy balance of tribosystem according to thefirst law of thermodynamics describes by theequation.Wfr q W. (3)where q – energy of heat exchange with theenvironment, ΔW – change of internal energy is thesum of the energy used to change the structure ofthe material and energy of heating.At the same time, the work of the friction forceis the sum of the work of plastic deformation,hysteresis loss and the elastic deformation of thedispersion, that is, the work expended in theformation of new surfaces and associated with thesurface energy of solids [6, 7].The basis of the thermodynamic approach tofracture and wear of solids is energy mechanicalanalogy (deformation) and thermal (melting andsublimation) of failure.The energy spent on the deformation andfracture of solid bodies, compared with one of thethermodynamic characteristics of the material (heatof sublimation enthalpy of the solid and liquid state,latent heat of fusion). In this case, it is assumed thatthermodynamic properties are independent of thestructure of the material. The body is treated as acontinuous, homogeneous, isotropic medium with astatistically uniformly distributed structuralelements.Plastic deformation is considered as acombination of a large number of acts ofmicroscopic atomic-molecular rearrangementsassociated with the generation of sources ofdeformation (dislocations).Plastic deformation of the surface temperaturebelow the recrystallization temperature leads towork hardening of the surface layer and itsstrengthening. At widely differing hardnessstructural components of the material and repeatedexposure of loading occurs initially high wear ofsoft base; specific pressures acting on the solidcomponent thereby increasing, solid componentsare pressed into a soft base, some of them arebroken up and moved further under the forces offriction. As a result of such selective wear surfaceenriched solid structural components and gets stitchstructure that during wear of babbit, for example,according to research of M. M. Khrushchov andA. L. Kuritsyna [8].As a result of the interaction of the interfacedparts new surfaces are formed, which is followedby the energy release, γ ef , consumed for itsforming [6]: f F,Rz HV , (4)ef ,where F – the normal force of friction pair elementsinteraction; Rz – ten point height ofirregularities [9].Rough surface can be considered as a set ofirregularities randomly located on a perfect surfaceand having a random size, in other words, as therealization of the random field. This approachmakes it possible to represent the surface as a scalarrandom function [10]z = z(t, ω), (5)where the parameter t runs through the set of valuesof T, defined by the spatial arrangement of therough surface; ω – elementary event of aprobability space Ω.To determine the surface characteristics requiredfor calculations in tribology, often enoughknowledge only first two derivatives of the functionz(t, ω). Thus there is a need to calculate the densityof the joint distribution of several random variables.Quantify the contact of rough surfaces is animportant step in the development of physicalmodels of frictional interaction. It requiresconsideration of both the characteristics of theroughness, and the specific properties of thecontacting bodies, depending on their internalstructure, loading time and environmentalconditions.196 13 th International Conference on Tribology – Serbiatrib’13