In this work, deformation behavior of porous ceramics ZrO2 - 5.5 wt.% Y2O3 with a different morphology of the pore space under axial quasi-static compression is studied by the method of digital image correlation (DIC). Two stages of the deformation behavior of ceramics have been identified, namely, the controlled accumulation of microcracks and the formation of block structures. It has been found that an increase in the average pore size leads to the decrease of the tensile strength and the effective elasticity modulus and the increase of the ultimate deformation, while the nature of the deformation macrolocalization changes from ordered to chaotic one. It is shown that the rate of accumulation of local deformations in the central part of the deformable sample with a pore size of 68 mu m is several times higher than in the sample with a pore size of 29 mu m.

The authors studied the nature of mobile fronts of localized deformation that generate and propagate during deformation of metastable austenitic-martensitic TRIP steel VNS9-Sh along the entire length of the loading curve from the yield point to fracture. A joint research of the nature of the deformation fronts movement and kinetics of the magnetic phase accumulation made it possible to establish that the fronts under consideration are the fronts of the thermoelastic phase transformation of metastable austenite into martensite. This transformation is realized firstly by formation of the Chernov–Lüders bands and then the Portevin–Le Chatelier bands. Both processes are consistent with staging of the deformation curve, which contains a pseudo-plateau, a section with an increasing hardening coefficient, and a section with a decreasing hardening coefficient. It is shown that the deformation-induced phase transformation corresponds to the fronts propagating on the pseudo-plateau and on the section of loading curve with an increasing hardening coefficient. The Portevin–Le Chatelier bands, which are formed in the section of the loading diagram with a decreasing hardening coefficient, are not associated with “austenite-martensite” transformation and have a twin nature. The kinetics of thermoelastic transformation fronts, as well as deformation fronts in materials with a shear mechanism of shaping, can be described in terms of the autowave concept. On the yield plateaus, the phase transformation occurs through generation and propagation of localized plasticity switching autowaves. In the section with an increasing hardening coefficient, it continues through generation and movement of excitation autowaves. The propagation regions of excitation autowaves are limited in the sample space. They are set by the zones of origin and annihilation of primary switching autowaves which were formed on the yield plateau.

The kinetics of Chernov–Lüders and Portevin–Le Chatelier deformation processes at the yield plateau in an aluminum-magnesium alloy is analyzed. It is established that the deformation is localized in moving deformation fronts. In general, the movement of the fronts proceeds discretely and only in the phase of abrupt unloading of the sample. Continuous movement of deformation fronts is possible if the rate of recovery of the operating stresses applied by test device is greater than or equal to the rate of stress decline controlled by internal processes at a lower structural-scale level. The kinetics of the motion of deformation fronts, both in the Chernov–Lüders and Portevin–Le Chatelier processes, can be described within the autowave concept of plastic flow, and the fronts themselves represent excitation autowaves.

The regularities of the formation of localized plastic flow autowaves in metals upon Lüders and Portevin–Le Chatelier deformations are considered taking into account the difference in the microscopic plastic flow mechanisms of these phenomena. Regularities in the development of these effects are studied. It has been established that the features of deformation characteristic for them are determined by the difference in the properties of the active media formed in the materials under study upon plastic deformation. The conditions for generating a switching autowave under Lüders deformation and an excitation autowave for the Portevin–Le Chatelier effect in deformable materials are considered.

In this work, the deformation behavior of ZrO2-5.5 wt.% Y2O3 ceramics with porosity from 30 to 50% during axial compression tests using the digital image correlation method was studied. A comparative analysis of the deformation curves and dependences of the averaged accumulation of local deformations < exx > along the axis of compressive stresses x and < eyy > along the axis of tensile stresses y , calculated by the methods of correlation of digital images in different parts of deformable samples from the test time, was carried out. It has been established that the process of deformation and fractures of porous zirconia ceramics develops in stages. In this case, the change in the curves of accumulation of local strains < exx > and < eyy > during the test correlates with the strain hardening index obtained from the deformation curves "stress - strain". It has been established that the deformation of zirconia proceeds macroscopically localized. An inhomogeneous distribution of local deformations over different areas of the studied porous ceramics was found. Spatiotemporal patterns of the distribution of instantaneous local strains exx along the loading axis x , obtained from the surface of deformable specimens during loading by the digital image correlation method, correlate with macropatterns of fracture of porous ceramics.

The paper focuses on deformation of ZrO2−5.5 wt.

A model of localized plastic flow development based on the idea about interaction between plasticity carriers and acoustic emission pulses generated by developing elementary plasticity acts is proposed. It is shown experimentally that the plastic flow is always localized on the macroscopic scale level. The volume distribution of the localization zone has the form of different autowave processes and depends on the work hardening law.

The mobile localized deformation fronts formed in elastoplastic transition are considered for materials with dislocational and martensitic plastic flow mechanisms, in the case of active extension at different rates. The motion of the fronts is recorded and described on the basis of correlation methods for digital images. A synergetic approach is adopted. The deformed object is regarded as an open system that is far from equilibrium—that is, an active medium containing distributed potential-energy sources, which are stress microgenerators. Under external perturbation, these concentrators relax by microshear and the object is reshaped. Each microgenerator may be regarded as an active element with two states: metastable elastic stress; and a stable relaxed state. Under external perturbation, only transition from elastic stress to the relaxed state is possible. These are regarded as trigger elements; the active medium is characterized as bistable. In bistable media, switching autowaves are observed; these are mobile boundaries between the metastable and stable states. Within this framework, the localized deformation fronts may be interpreted as switching autowaves. It is found that the form and kinetic parameters of the localized deformation fronts do not depend on the chemical composition, structure, or micromechanisms of deformation; this confirms that they are autowaves. However, the kinetics of switching autowaves must be determined by the parameters of the external perturbation. In fact, the velocity of the localized deformation fronts increases with increase in the extension rate. It is established that the velocity of the localized deformation fronts depends nonlinearly (parabolically) on the strain rate. The exponent of this dependence is less than one and is the same for all the materials considered.

The paper presents the study of the process of deformation-induced γ → α-transformation in TRIP-steel and its effect on the strain-hardening coefficient at the macroscopic level. It is shown that a phase transformation starts with the propagation of Luders bands during the pseudo-plateau, when the strain-hardening coefficient is constant. The boundaries of Luders bands are switching autowaves of localized plasticity. After the annihilation of switching autowaves in the samples in the austenitized state, the phase transformation continues with the movement of deformation fronts of the Portevin–Le Chatelier bands, which are excitation autowaves. In this case, the strain-hardening coefficient increases to a maximum value and then decreases up to fracture. The nucleation and propagation of phase transformation fronts is confirmed by magnetic measurements. After the transition to the stage where the hardening coefficient decreases, the γ → α' phase transformation decays and is no longer the predominant mechanism of plastic flow.

New representations concerning plasticity physics in crystals are discussed. The model of plastic flow is suggested, which can describe its main regularities. With the use of the experimental investigation, it is shown that the plastic flow localization plays the role in the evolution of plastic deformation. Obtained data are explained with the application of the principles of nonequilibrium-systems’ theory. The quasi-particle is introduced for the description of plasticity phenomenon. It is established the relation between plasticity characteristics of metals and their position in Periodic table of the elements. A new model is elaborated to address localized plastic-flow evolution in solids. The basic assumption of the proposed model is that the elementary plasticity acts evolving in the deforming of medium would generate acoustic emission pulses, which interact with the plasticity carriers and initiate new elementary shears. As found experimentally, the macrolocalization of plastic flow involves a variety of autowave processes. To address the phenomenon of localized plastic-flow autowaves, a new quasi-particle called ‘autolocalizon’ is introduced; the criterion of validity of the concept is assessed.

We consider the regularities of a plastic flow in materials with strain-induced phase transformation in titanium nickelide and trip steel as examples. The experimental analysis of plastic deformation processes has been carried out using the technique of digital correction of speckle images, which makes it possible to describe quantitatively the behavior of plasticity fronts associated with phase transformation in the given materials. The mechanisms of formation of the Lüders fronts as well as the Portevin–Le Chatelier fronts at different stages of the plastic flow are considered.

It is shown in the work that plastic flow in solids develops always in localized manner. A macroscopic scale ~ 10-2 m characterizes the localization. The localized flow zones form the pattern of localized strain, which is the projection of the autowave processes of plastic flow, developing in the volume, on the observed surface of the tested specimen. One can observe the pattern with the help of speckle-photography method. The investigations of various materials allowed to establish that the pattern of localized deformation is the information source for a kinetics of deformation processes. A general characteristic of localized plastic flow in solids is the elastic-plastic invariant of deformation which couples the typical characteristics of localized plastic flow autowaves with the same for the elastic waves in crystal lattice. The quantity of the invariant ratio is defined for nearly forty various materials (BCC, FCC, HCP metals and alloys, alkali-halide crystals, ceramics, rocks) studied in the conditions of active elongation and compression at the temperature range 143-420 K. The physical considerations are presented to explain the invariant origination and its relation to other physical characteristics of crystal lattice, in particular, the Debye temperature. In the light of these considerations, it is possible to explain the meaning and the origin of the invariant, and to derive numerous consequences from them. In fact, the set of these consequences comprehend all the regularities of developed plastic flow processes and allows to consider the elastic-plastic invariant of deformation as the master equation for developing this day autowave approach to physical theory of plastic deformation.

The regularities of plastic flow in materials with deformation-induced phase transformations on the example of titanium nickelide and TRIP steel are studied. For experimental analysis of plastic deformation processes, the method of digital image correlation has been used, which allows us to quantitatively describe the behavior of plasticity fronts associated with the course of phase transformations in the materials under study. The mechanisms of formation of Lüders bands and Portevin-Le Chatelier bands at different stages of plastic flow are considered.

The kinetics of deformation processes on the yield plateau is studied in aluminum alloy 1550. It is found out that in the general case, the Lüders band fronts move discretely and only in the phase of specimen unloading. A continuous motion of the deformation fronts is possible if the relaxation rate of the applied stresses due to the test machine is higher than or equal to the rate of their decrease controlled by the internal processes at a lower scale level. The discrete motion of the Lüders fronts in the 1550 alloy suggests that they are not purely switching autowaves.

This paper discusses the kinetics of the fronts of localized plastic deformation in TRIP steel using a combination of DIC methods and magnetization measurements. It is shown that the kinetics of deformation fronts, which is mainly determined by the stages of the hardening curve, is consistent with changes in the phase composition. A phase transformation starts with the propagation of Luders bands and then proceeds through the formation and propagation of Portevin-Le Chatelier bands, but only in the region of increasing strain hardening coefficient. After the transition to the stage where the hardening coefficient decreases, the gamma -+ alpha' phase transformation decays and is no longer the predominant mechanism of jerky flow. Both types of plastic instability in TRIP steel can be described using the autowave concept of localized plasticity.

The kinetics of deformation processes at the yield plateau in the aluminum alloy 1550 studied. It is established that in the general case, the motion of the Lüders band fronts occurs discretely and only in the phase of sample unloading. Continuous motion of the deformation fronts is possible if the rate of relaxation of the applied stresses due to the test machine is greater than or equal to the rate of their decline, controlled by internal processes at a lower scale level. The discrete motion of the Lüders fronts in the 1550 alloy suggests that they are not pure autowaves of switching.

The present work is aimed at studying plastic strain localization in the technically pure polycrystalline nickel (with the nickel content of no less than 99.5%) at room temperature. Plastic strain localization under uniaxial tension at a constant rate is accompanied by discontinuous flow. It is shown that the plastic flow is entirely manifested by Portevin–Le Chatelier strain bands, whose origin is associated with a stress drop in the stress-strain curve. The kinetics regularities of these bands are established, as well.

In this paper, a study of the deformation behavior of zirconia ceramics with porosity of 27 and 42% under diametral compression tests (the Brazilian test) using the digital image correlation method was carried out. Spatiotemporal patterns of strain localization across the loading axis of the deformed sample (epsilon(yy)) are obtained. It was found that the strain in porous zirconia ceramics occurs macroscopically localized. With increasing porosity, the character of formation of spatiotemporal patterns of strain localization changes. The change in the rates of averaged accumulation of local strain epsilon(yy) correlates well with the type of "stress-displacement" curves.