Spatiotemporal Ordering at Plastic Flow of Solids

Зуев, Л. Б.; Данилов, В. И.; Семухин, Б. С.

doi:10.15407/ufm.03.03.237

Cited by 31 publications

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“…The localization obeys the law of plastic flow, i.e., it is determined by deformation stages of stress-strain curves of materials [1,2]. It is shown in [3] that a peculiar shape of the localization patterns is characteristic of the prefracture stage where the behavior of the localized plastic deformation domains enables the point of subsequent fracture to be predicted. The results were obtained for bcc and hcp polycrystals.…”

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confidence: 99%

Kinetics of localized plastic flow during deformation and fracture of a D1 alloy

2007

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The stress-strain curve of a polycrystalline duralumine (D1) is studied to find three basic deformation stages: linear hardening, parabolic hardening (n = 1/2), and prefracture (n < 1/2). The results obtained show special features of macrolocalization of the plastic flow of the alloy under review. The distribution patterns of localized plastic flow domains develop according to deformation stages. The prefracture stage is characterized by selfcorrelated motion of the domains to the point of subsequent fracture. It follows from an analysis of the plastic flow localization kinetics that both hardening and softening domains coexist in the specimen in the prefracture stage. The domains move with a constant velocity inherent to each of them and linearly dependent on the position of their nucleation point.

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Section: Introductionmentioning

confidence: 99%

Kinetics of localized plastic flow during deformation and fracture of a D1 alloy

2007

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“…Zr-Nb alloy also obey this dependence. Hence, there are grounds to assume that this parameter is independent of the crystalline lattice type, structural state, chemical composition, and micromechanism of plastic shear; this parameter is determined by the balance of hardening and relaxation processes at the microscopic level, as was shown, e.g., in [14]. Additional evidence of the latter statement can be the data on the wave process of localization in tin.…”

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confidence: 89%

“…To study the kinetics of the evolution of macrolocalization patterns, we used the representation of X local sites in the sample as a function of strain or time (under active extension, ε ∼ t). It was shown [14] that such a procedure applied to distributions with spatial-temporal periodicity (wave distributions) makes it possible to determine the spatial λ and temporal T periods of the process and also the velocity of deformation sites V = dX/dt.…”

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“…In the present work, the autowave character of localization was also observed in all cases with the stage of linear hardening: in Mg-Mn-Ce and V-Zr-C alloys and in pure Sn, though their crystallographic structure is absolutely different. According to [14], f.c.c. materials have an inversely proportional dependence of localization autowave velocity V II on the hardening rates θ at the linear stage II normalized to shear moduli.…”

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“…4, is within the range of values extrapolated by curve 2 rather than curve 1. It was noted [14] that this group of points is composed by velocities of autowaves at the stages of easy slipping of single crystals and yield areas of polycrystalline samples. The main factor of resistance to deformation, which is the contact interaction of dislocations of various slipping systems, is absent in the stages considered; therefore, hardening is not large, and the lattice friction of dislocations plays the leading role [17].…”

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Types of Localization of Plastic Deformation and Stages of Loading Diagrams of Metallic Materials with Different Crystalline Structures

Данилов

Зуев

Letakhova

et al. 2006

J Appl Mech Tech Phys

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Macrolocalization, which accompanies the process of plastic deformation beginning from the yield point and ending by fracture, is determined by the staged character of material-loading diagrams. The evolution of localization patterns in a plastic flow of body-centered cubic vanadium alloy, hexagonal close-packed magnesium alloy, tetragonal tin, and face-centered cubic submicrocrystalline aluminum is analyzed within this concept.Introduction. It was found [1-3] that macrolocalization accompanies the process of shape variation of all materials, independent of their chemical nature, crystallographic state, and real structure, over the entire process from the yield point to fracture. The types of deformation localization have a uniform dependence on the law of strain hardening of the material (loading diagram) and uniformly change from one stage to another. The number of such types is limited. Four types are known at the moment [3]: 1) single moving deformation fronts (autowaves of excitation or switching); 2) equidistant moving zones of deformation localization (phase autowave); 3) spatially periodic steady distributions of deformation-localization sites (stable dissipative structures); 4) high-amplitude motionless deformation sites. The first type is typical of stages of easy slip of single crystals and yield areas of polycrystalline materials. The stages of linear hardening correspond to the second type of localization in the form of phase autowaves. The third type of localization arises at stages of parabolic hardening. High-amplitude steady zones of deformation localization in regions of future viscous fracture were observed when the strain before the beginning of neck formation was several percent of the total strain. The evolution of localization patterns rigorously follows the stages of the strain curves. If some stage is absent, the corresponding type of localization is absent as well. Therefore, it was only the third type of macrolocalization that was observed in all experiments without any exceptions, which were performed with single and polycrystals, pure metals and high alloys, ordered structures, materials with dislocation and twinning mechanisms of deformation, alloys with phase-change plasticity, and substances with viscous and quasi-brittle fracture [3]. The phenomenology of transformation of the first to the second type of localization [4] and from the second to the third type of localization [5] has been described. It remains unclear, however, how a steady dissipative structure (third type) is transformed to a distribution with one high-amplitude maximum.

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Plastic flow instability at the necking stage in zirconium alloys

Poletika

Kolosov

Narimanova

et al. 2006

J Appl Mech Tech Phys

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Regular features in plastic-strain macrolocalization are examined at the parabolic stage of strain hardening in theÉ635 and Zircaloy-2 zirconium alloys. Instability of the plastic flow is observed, which is manifested as a periodic variation of space-time distributions of local strain as revealed by means of speckle interferometry. The data obtained are discussed within the framework of a synergetic model for the plastic flow evolution at the final stage. Introduction.Macrolocalization is known to accompany the plastic flow at all stages of the process [1, 2]. It has been found that both wave and stationary space-time patterns of plastic-strain localization can be observed during the deformation of single-crystal and polycrystalline samples. Emergence of either pattern is governed by the strain-hardening law acting at the corresponding stage of deformation [1,2].In the present work, we examine the regular features of development of plastic strain localization at the parabolic stage of the plastic flow and at the prefracture stage in samples of the commercial zirconium alloysÉ635 (an alloy contains by weight 1% Nb; 1.3% Sn; 0.4% Fe; rest Zr) and Zircaloy-2 (an alloy contains by weight 1.2% Sn; 0.5% Fe-Ni-Cr; rest Zr) traditionally used in manufacturing fuel-cell tubes for nuclear reactors [3].It was found previously that the flow curves of zirconium alloys immediately above the yield point can be fitted with parabolas σ ∼ ε n , where n is the parabolicity factor [4-6]. We will call this deformation stage the parabolic stage. The parabolic stage displays an intricate behavior and the corresponding strain curve can be divided into several segments approximated by parabolas with decreasing parabolicity factors running through the values form 0.1 to 0.7. The minimum value of n refers to the beginning of formation of a visible macroscopic neck. Of special interest here is the related evolution of the space-time patterns of plastic-strain localization [4][5][6]. For instance, a stable stationary strain localization pattern with a constant spatial period λ is typical only of strain patterns with parabolicity factors n 0.5 in the law σ ∼ ε n . A typical feature of segments with n < 0.5 in the parabolic strain curve is the motion of localized strain nuclei with a varying spatial period, which is accompanied by periodic strain accumulation at a localized nucleus that transforms to a neck by the end of the parabolic stage.Physical reasons for the observed evolution of localization at the final stage of the plastic flow in zirconium alloys remain unclear; therefore, strain-localization features resulting in the loss of stability of the plastic flow and in subsequent fracture call for a further study. The knowledge of the specific features of generation and development of plastic-strain localization finally resulting in fracture under plastic deformation is of considerable practical significance, in particular, in estimating the technological plasticity margin of zirconium alloys heavily strained in production of finished arti...

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Spatiotemporal Ordering at Plastic Flow of Solids

Cited by 31 publications

References 54 publications

Kinetics of localized plastic flow during deformation and fracture of a D1 alloy

Kinetics of localized plastic flow during deformation and fracture of a D1 alloy

Types of Localization of Plastic Deformation and Stages of Loading Diagrams of Metallic Materials with Different Crystalline Structures

Plastic flow instability at the necking stage in zirconium alloys

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