V. E. Rubtsov

Shear Instability in the Subsurface Layer of a Material in Friction

The shear instability in subsurface layers of a material in friction has been investigated. As the friction surface is approached, several characteristic regions can be distinguished in the bulk of the metal: the region of plastic deformation and texturing (I), the region of severe fragmentation (II), the region of turbulent flow (III), and the region of laminar flow (IV). Regions I and II can be referred to as regions of conventional plastic deformation, whereas regions III and IV correspond to regions of the development of shear instability of the Kelvin-Helmholtz type at the shear boundary. The possibility of implementing this phenomenon within the hydrodynamic approach has been evaluated.

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.

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.

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.

Structure and tensile fracture of 1570C aluminum alloy

Both deformation and fracture tensile studies on orientation dependence of 1570C aluminum alloys samples with respect to rolling direction have been carried out. As revealed, the viscous fracture mechanism is more inherent to the samples with orientation transversal to the rolling direction while samples oriented along the rolling direction revealed quasi-brittle areas on the fracture surfaces. Despite practically the same level of the yield stress there is 10% difference I the ultimate stress.

Effect of friction stir welding parameters on defect formation

Friction stir welding is a perspective method for manufacturing automotive parts, aviation and space technology. One of the major problems is the formation of welding defects and weld around the welding zone. The formation of defect is the main reason failure of the joint. A possible way to obtain defect-free welded joints is the selection of the correct welding parameters. Experimental results describing the effect of friction stir welding process parameters on the defects of welded joints on aluminum alloy AMg5M have been shown. The weld joint defects have been characterized using the non-destructive radioscopic and ultrasound phase array methods. It was shown how the type and size of defects determine the welded joint strength.

Effect of heat generation due to plastic deformation on behavior of surface-layer material during sliding

Sliding friction of materials differing in their deformation hardenability is simulated using a modified macroscopic model which allows taking into account of frictional heating, as well as additional heat generation in the material surface layer due to its plastic deformation. Taking into consideration additional heat generation is shown to have an effect on the heat conditions and shear deformation in the surface layer when the deformation hardenability of the material falls within a certain range. Comparative calculations performed with and without consideration of additional heat generation exemplify the quantitative and qualitative differences of heating and plastic deformation of the surface layer.

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.

Structure and properties of fixed joints formed by ultrasonic-assisted friction-stir welding

This paper deals with structure and properties of aluminum alloy 7475 and its joints obtained by friction stir welding including under ultrasonic action. Microhardness measurements show that ultrasonic action increases strength properties of the joints. Optical and transmission electron microscopy reveals that this effect is related to the precipitation of tertiary coherent S-and T-phase particles.

Radioscopy of remnant joint line in a friction stir welded seam

The possibilities of the radioscopic detection of defects such as remnant joint lines, which occur during friction stir welding, have been evaluated. In addition to common radioscopy, a microfocus source of X-ray radiation and metallography were applied to attain high geometric magnification. It was shown that this defect type can be detected using high geometric magnification; defects such as foreign inclusions may occur as a result of tool wear.