Modeling and Simulating Dislocation Dynamics Near Sound Speeds in Cubic Crystals

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

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Microtwinning Evidence For The Apparent Five-Fold Symmetry in T2(Al6Li3Cu)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100125178 ◽

1987 ◽

Vol 45 ◽

pp. 24-25

Author(s):

Kenneth S. Vecchio ◽

David B. Williams

Keyword(s):

Stable Equilibrium ◽

Equilibrium Phase ◽

Convergent Beam Electron Diffraction ◽

Icosahedral Structure ◽

Cubic Crystals ◽

Icosahedral Phases ◽

Heat Treated ◽

Zero Layer ◽

Convergent Beam ◽

Zr Alloy

Since the discovery in 1984 by Shechtman et al. of crystals which display apparent five-fold symmetry, extensive effort has been given to establishing a theoretical basis for the existence of icosahedral phases (eg.2.). Several other investigations have been centered on explaining these observations based on twinning of cubic crystals (eg.3.). Recently, the existence of a stable, equilibrium phase T2Al6 Li3Cu) possessing an icosahedral structure has been reported in the Al-Li-Cu system(4-6).In the present study an Al-2.6wt.%Li-l.5wt.%Cu-0.lwt.%Zr alloy was heat treated at 300°C for 100hrs. to produce large T2 precipitates. Convergent Beam Electron Diffraction (CBED) patterns were obtained from two-fold, three-fold, and apparent five-fold axes of T2 particles. Figure 1 shows the five-fold symmetric zero layer CBED pattern obtained from T2 particles.

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MISORIENTATION DISTRIBUTION FUNCTION FOR CUBIC CRYSTALS

Industrial laboratory Diagnostics of materials ◽

10.26896/1028-6861-2019-85-5-28-32 ◽

2019 ◽

Vol 85 (5) ◽

pp. 28-32

Author(s):

A. S. Kolyanova ◽

Y. N. Yaltsev

Keyword(s):

Distribution Function ◽

Grain Boundaries ◽

Orientation Distribution ◽

Recrystallization Annealing ◽

Misorientation Distribution ◽

Cubic Crystals ◽

Special Boundaries ◽

Pole Figures ◽

Two Samples ◽

Euler Space

A calculation method for obtaining the misorientation distribution function (MDF) for cubic crystals which can be used to estimate the presence or absence of special boundaries in the materials is presented. The calculation was carried out for two samples of Al-Mg-Si alloy subjected to various mechanical and thermal treatments: the first sample is subjected to rolling; the second sample is subjected to recrystallization annealing. MDF is calculated for each sample; the results are presented in the Euler space and in the angle-axis space. The novelty of the method consists in the possibility of gaining data on the grain boundaries from X-ray texture analysis without using electron microscopy. A calculation involving only mathematical operations on matrices was performed on the basis of the orientation distribution function restored from incomplete pole figures. It is shown that no special boundaries are observed in the deformed sample, whereas in the recrystallized alloy, special boundaries are detected at Ʃ = 23, 13, and 17. The shortcoming of the proposed method can be attributed to the lack of accurate data on grain boundaries, since all possible orientation in the polycrystal should be taken into account in MDF calculation.

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ANALYSIS OF SOUND SPEED IN LONGITUDINAL DIRECTION AT REFERENCE MOISTURE CONTENT (w = 12 %) IN SAWMILL ASSORTMENTS (FAGUS SYLVATICA, L.)

Akustika ◽

10.36336/akustika20203745 ◽

2020 ◽

pp. 45-50

Author(s):

Alena Rohanová

Keyword(s):

Moisture Content ◽

Modulus Of Elasticity ◽

Dynamic Modulus ◽

Sound Speed ◽

Longitudinal Direction ◽

Structural Timber ◽

Sound Speeds ◽

Dynamic Modulus Of Elasticity ◽

Round Timber

This paper explores the analysis of sound speeds in the longitudinal direction and their reduction to the reference moisture content w = 12 %. The sound speed cw was determined with Sylvatest Duo device. Moisture content of beech sawmill assortments (round timber: N = 16, logs: N = 2 × 16, structural boards: N = 54) in the range of 12 – 72 % was measured. For the analysis purposes, the sound speed was converted to reference conditions (c12, uref = 12%). A second-degree polynomial (parabola) with a regression equation of the form: c// = 5649 - 27,371 × w + 0.0735 × w2 was used to convert cw to c12, and correction of measured and calculated values was used as well. The sound speeds c12 in sawmill assortments (c12,round, c12,log, c12,board) were evaluated by linear dependences. Dependence was not confirmed for c12,round and c12,board1 (r = 0.168), in contrast for c12,round and c12,log2 the dependence is statistically very significant (r = 0.634). The results of testing showed that the most suitable procedure for predicting quality of structural timber is the first step round timber – log2, the second step: log2 - board2. More exact results of the construction boards were obtained from log2 than from log1. The sound speed is used in the calculation of dynamic modulus of elasticity (Edyn). EN 408 mentions the possibility of using dynamic modulus of elasticity as an alternative method in predicting the quality of structural timber.

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Theory of the deformation of aligned polyethylene

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2015.0171 ◽

2015 ◽

Vol 471 (2180) ◽

pp. 20150171 ◽

Cited By ~ 7

Author(s):

A. Hammad ◽

T. D. Swinburne ◽

H. Hasan ◽

S. Del Rosso ◽

L. Iannucci ◽

...

Keyword(s):

Load Transfer ◽

Tensile Load ◽

Equation Of Motion ◽

Dislocation Dynamics ◽

Viscoelastic Deformation ◽

Transfer Length ◽

Soliton Dynamics ◽

Fluctuation Dissipation ◽

Pull Out ◽

Definition Of

Solitons are proposed as the agents of plastic and viscoelastic deformation in aligned polyethylene. Interactions between straight, parallel molecules are mapped rigorously onto the Frenkel–Kontorova model. It is shown that these molecular interactions distribute an applied load between molecules, with a characteristic transfer length equal to the soliton width. Load transfer leads to the introduction of tensile and compressive solitons at the chain ends to mark the onset of plasticity at a well-defined yield stress, which is much less than the theoretical pull-out stress. Interaction energies between solitons and an equation of motion for solitons are derived. The equation of motion is based on Langevin dynamics and the fluctuation–dissipation theorem and it leads to the rigorous definition of an effective mass for solitons. It forms the basis of a soliton dynamics in direct analogy to dislocation dynamics. Close parallels are drawn between solitons in aligned polymers and dislocations in crystals, including the configurational force on a soliton. The origins of the strain rate and temperature dependencies of the viscoelastic behaviour are discussed in terms of the formation energy of solitons. A failure mechanism is proposed involving soliton condensation under a tensile load.

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Dislocation dynamics prediction of the strength of Al–Cu alloys containing shearable θ′′ precipitates

Journal of the Mechanics and Physics of Solids ◽

10.1016/j.jmps.2021.104375 ◽

2021 ◽

Vol 151 ◽

pp. 104375

Author(s):

R. Santos-Güemes ◽

L. Capolungo ◽

J. Segurado ◽

J. LLorca

Keyword(s):

Dislocation Dynamics ◽

Cu Alloys

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