Lev Zuev

On the kinetics of localized plasticity domains emergent at the pre-failure stage of deformation process

The behavior of localized plasticity domains occurring at the final stage of the plastic flow process has been investigated. A series of runs was conducted on materials differing in the crystal lattice type which disclosed regular features exhibited by the flow process upon transition to macroscopic necking and viscous failure. It is found that the most distinctive regularity is the occurrence of flow domains that are moving in a concerted manner towards the pole of the bundle of domain trajectories plotted in the time-space coordinates. The deformation patterns are found to be related to the kinetics of nucleation and motion of localized plasticity fronts. The probable origin of the observed effects is considered.

Effect of Hydrogen on Plastic Strain Localization of Construction Steels

The effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested specimens of austenitic stainless and low-carbon steels have been studied using a double exposure speckle photography technique. The main parameters of plastic flow localization at various stages of the deformation hardening have been determined in steels electrolytically saturated with hydrogen in a three electrode electrochemical cell at a controlled constant cathode potential.

Acoustic parameters as the material formability criteria

Two methods of non-destructive evaluation of material condition are presented in this paper. These methods are based on careful measurement of Rayleigh wave propagation velocity with a frequency of 5 MHz. Preliminarily investigations were carried out in order to relate the ultrasound propagation velocity to the mechanical characteristics of the deforming material. The first method allows estimating the strength limit by Rayleigh wave velocity measurement during elastic loading of the specimen. Since machine parts operate under elastic stress, this method can be used directly on working machine parts and frameworks. The second method is connected with the forming process and can be used for the definition of a criterion of elastic-plastic transition of metal products.

Elastoplastic transition in the material with sharp yield point

A study was made of the processes involved in the nucleation and propagation of Chernov–Luders bands in low carbon steels. It is found that the deformation bands are nucleated in the deforming sample at stress levels that are significantly lower relative to the upper yield limit. A sharp yield point is found to occur on the deformation curve, with its ascending and descending branches corresponding to the band nucleus “ingrowth”. Following the sharp yield point, a mobile Chernov–Luders band proper is observed for the yield plateau. The rate of deformation band fronts has been determined for both the band “ingrowth” and the band propagation stage. The occurrence of mobile band front(s) is considered. Thus, the conventional assumption that the deformation front is a boundary separating deformed and non-deformed material regions represents facts only approximately.

Evolution of Macro-Scale Plastic Flow Localization of Tri-Layered Stainless Steel - Low Carbon Steel - Stainless Steel Metal with Digital Image Correlation Method

Evolution of localized plastic deformation in tri-layered metal material casting consistng of the working part (layer) from austenitic stainless steel and bearing part from low-carbon steel was investigated. The pictures of localization of the plastic flow during the process of uniaxial tension were obtained by means of the digital image correlation method (DIC). Using optical microscopy methods, the changes in the fracture surface were investigated. The deformation diagrams were examined for deformed samples of tri-layered metal. These were found to show all the plastic flow stages: the linear, parabolic and pre-failure stages would occur for the respective values of the exponent n from the Lüdwik-Holomon equation. The analysis of the plastic flow stages and localized plastic deformation parameters was performed.

Velocity and attenuation of ultrasound waves under cyclic loading of low-carbon steel

The results of the research of ultrasound wave velocity and attenuation in low-carbon steel during low-cycle fatigue tests have been presented in this work. It has been found that the dependencies of acoustic parameters on the number of cycles have three stages. The first stage is connected with dislocation density growth in a specimen. The transition from the second stage to the third one can be used as a criterion of fatigue wear of metalworks and implemented for nondestructive ultrasound lifetime estimation.

On the kinetics of mobile Chernov–Lüders band fronts

The elastic-plastic transition occurs in materials having a sharp yield point simultaneously with the nucleation and propagation of Chernov–Luders bands (CLBs). It is found that the time it takes for a given CLB to be nucleated differs by about an order of magnitude from its propagation rate. The CLB fronts would travel in a concerted manner, so that their motion rates taken together at any time would make up a constant value. An increase in the deformation rate would bring about a nonlinear increase in the motion rates of CLB fronts.

On the plastic flow localization of martensitic stainless steel saturated with hydrogen

The deformation behavior of tensile tested corrosion resistant high-chromium steel electrically saturated with hydrogen has been investigated. The studies were performed for high-temperature tempered steel with sorbitic structure and after electrolytic hydrogenation for 6 and 12 hours. It was found that hydrogen has markedly reduced the breaking stress and elongation leading to the fracture of the specimen. Using the method of double-exposed speckle photography, it was found that the plastic flow of the material had localized character. The evolution of localized-strain center distributions follows the law of plastic flow. The autowave parameters (autowave velocity and autowave length) were measured for every state of high-chromium steel under investigation and the difference between them is of great significance.

Plastic flow inhomogeneities in metals

The paper provides research data on macroscopic plastic flow inhomogeneities in metals: Chernov–Luders bands and Portevin—Le Chatelier effect. Their evolution regularities and motion kinetics are analyzed, showing that Chernov–Luders fronts and Portevin–Le Chatelier jump-like straining can be treated respectively as macroscopic auto-wave processes of switching and excitation in deformed media of various origins.

Variation in Mechanical Properties Due to The Effect of Electric Potential

Metal microhardness as a function of electric potential was investigated experimentally for the test samples of aluminum, zirconium and siliceous iron. The effects of electric potential proper and of contact potential difference, which are due to metals having different electron densities, are compared in terms of variation in metal microhardness. Two sets of microhardness data obtained for the test samples are analyzed. Both effects are found to cause a significant enhancement in metal microhardness (up to 20%); therefore, in a qualitative sense, these effects are considered equivalent.