A. V. Kolubaev

Using acoustic emission for the analysis of wear processes during sliding friction

The acoustic response of two friction pairs, in which brittle fracture and intense plastic deformation take place during friction, has been studied. The acoustic signals have been analyzed by calculating median frequencies using the window Fourier transform technique.

Analysis of acoustic emission during sliding friction of manganese steel

The process of acoustic emission during the sliding friction of X120Mn12 (DIN EN Standard) manganese steel has been studied. The coefficient of sliding friction has been determined in the absence of lubricants and the parameters of generated sound have been measured. A relationship between the acoustic emission spectrum and the friction coefficient is established.

Generation of shear bands in subsurface layers of metals in sliding

Nanostructuring of the surface of specimens during friction is investigated under the conditions of shear instability of the subsurface layers of the material due to the strong localization of deformation. It is demonstrated that the localization of deformation in the subsurface layers occurs in three stages. The structure of the localization zone is studied. The formation of a nanocrystalline material on the surface due to the shear instability is considered by analogy with the formation of the shear band. The formation of the nanocrystalline material can be responsible for the crossover from the mild wear to the adhesive wear in the absence of mechanisms providing structural adaptability.

General regularities of the microstructure formation during friction stir welding and sliding friction

A comparative metallographic analysis of the formation of the metal microstructure during sliding friction and friction stir welding is performed. It has been shown based on the example of a weld joint made of aluminum alloy fabricated by friction stir welding that the weld microstructure has all signs of the deformed layer of metal formed due to sliding friction, which is accompanied by the seizure of conjugated surfaces.

Effect of elastic excitations on the surface structure of hadfield steel under friction

The structure of the Hadfield steel (H13) surface layer forming under dry friction is examined. The deformation of the material under the friction surface is studied at a low slip velocity and a low pressure (much smaller than the yields stress of H13 steel). The phase composition and defect substructure on the friction surface are studied using scanning, optical, and diffraction electron microscopy methods. It is shown that a thin highly deformed nanocrystalline layer arises near the friction surface that transforms into a polycrystalline layer containing deformation twins and dislocations. The nanocrystalline structure and the presence of oxides in the surface layer and friction zone indicate a high temperature and high plastic strains responsible for the formation of the layer. It is suggested that the deformation of the material observed far from the surface is due to elastic wave generation at friction.

Study of the formation of contact between rough surfaces based on the particle method

A model is proposed for the rough surface of a solid based on the particle method. Although the particle size is selected arbitrarily in this study, the evolution of the actual area of contact and the change in stress at the points of contact show fairly good agreement with concepts derived from experimental investigations. The experiments show that as two surfaces converge, the pressure at the contacts is considerably higher than the nominal value, and this leads to plastic deformation of the surface layers much greater than the bulk deformation. The model clearly shows the controlling factors and how the stressed state of the surface layer is formed. The model can be used to analyze interaction between surfaces, not only for the stationary case, but also when these undergo relative displacement.

The evolution of the surface layers on metals in sliding friction

The methods of speckle-interferometry, electron, optic, and atom-force microscopy were used to study the structure and regularities of deformation of surface layers on metals and alloys in friction. The causes of deformation localization are analyzed. An explanation of the strong wear resistance of Hadfield steel is proposed using data on the evolution of the surface layer structure.

Study of plastic shear deformation in surface layer at friction. Simulation results. Part I. Model description

A one-dimensional macroscopic model of friction is presented which considers changes in elastic characteristics of the material caused by frictional heating and strain hardening. A single act of contact between a microasperity made of a ductile hardenable material and the counterbody was calculated for various contact spot sizes. It is shown that the contact spot size affects considerably the temperature, plastic deformation, and changes in the material elastic characteristics. Shears of surface layers relatively to the base material observed experimentally are explained proceeding from the modeling results.

Sound Generation in Sliding Friction

The process of sound generation in a sliding friction contact in the absence of lubricants has been studied simultaneously with measurements of the friction coefficient. A correlation between the sound intensity, the spectrum of sound generated in the tribological system, and the friction coefficient is established. It is shown that not only do the tribological properties of contacting materials influence the characteristics of the acoustic signal, but the reverse influence may take place as well: the elimination of elastic oscillations accompanied by sound generation in the junction leads to a decrease in the friction coefficient.

Application of fractals to the analysis of friction processes

An attempt is made to estimate the fractal dimension of the lateral surface of a steel sample formed as a result of friction by analyzing an image obtained using a scanning electron microscope.