scholarly journals Size Dependence of Dislocation-Mediated Plasticity in Ni Single Crystals: Molecular Dynamics Simulations

2009 ◽  
Vol 2009 ◽  
pp. 1-10 ◽  
Author(s):  
Xiaoyan Li ◽  
Wei Yang
Keyword(s):  
Slip System ◽  
Single Crystals ◽  
Temperature Effects ◽  
Size Dependence ◽  
Dislocation Dynamics ◽  
Deformation Mechanisms ◽  
Atomistic Simulations ◽  
Single Slip ◽  
System A ◽  
Dynamics Simulations

We investigate the compressive yielding of Ni single crystals by performing atomistic simulations with the sample diameters in the range of 5 nm ∼ 40 nm. Remarkable effects of sample sizes on the yield strength are observed in the nanopillars with two different orientations. The deformation mechanisms are characterized by massive dislocation activities within a single slip system and a nanoscale deformation twining in an octal slip system. A dislocation dynamics-based model is proposed to interpret the size and temperature effects in single slip-oriented nanopillars by considering the nucleation of incipient dislocations.

Uniaxial Stress Deformation Experiment for Validation of 3-D Dislocation Dynamics Simulations

2002 ◽  
Vol 124 (3) ◽  
pp. 290-296 ◽  
Author(s):  
David H. Lassila ◽  
Mary M. LeBlanc ◽  
Gregory J. Kay
Keyword(s):  
Experimental Data ◽  
Single Crystal ◽  
Single Crystals ◽  
High Purity ◽  
Axial Stress ◽  
Uniaxial Stress ◽  
Dislocation Dynamics ◽  
Uniform State ◽  
Dynamics Simulations ◽  
Unconstrained Motion

An apparatus has been developed for performing compression deformation experiments on oriented metallic single crystals to provide data for validation of 3-D dislocation dynamics simulations. The experiment is performed under conditions that allow unconstrained motion of the upper and lower compression platen, and thus a relatively uniform state of axial stress is maintained during the deformation. Experiments have been performed on high-purity Mo single crystal and polycrystalline Cu. Various aspects of the experimental procedures and results are presented. Possible usages of the experimental data for the validation of 3-D dislocation dynamics simulations are discussed.

Three-Dimensional Continuum Dislocation Dynamics Simulations of Dislocation Structure Evolution in Bending of a Micro-Beam

MRS Advances ◽  
2016 ◽  
Vol 1 (24) ◽  
pp. 1791-1796 ◽  
Author(s):  
Alireza Ebrahimi ◽  
Thomas Hochrainer
Keyword(s):  
Dislocation Density ◽  
Slip System ◽  
Evolution Equations ◽  
Three Dimensional ◽  
Dislocation Dynamics ◽  
Structure Evolution ◽  
Internal Variables ◽  
Plastic Shear ◽  
Continuum Dislocation Dynamics ◽  
Dynamics Simulations

ABSTRACTA persistent challenge in multi-scale modeling of materials is the prediction of plastic materials behavior based on the evolution of the dislocation state. An important step towards a dislocation based continuum description was recently achieved with the so called continuum dislocation dynamics (CDD). CDD captures the kinematics of moving curved dislocations in flux-type evolution equations for dislocation density variables, coupled to the stress field via average dislocation velocity-laws based on the Peach-Koehler force. The lowest order closure of CDD employs three internal variables per slip system, namely the total dislocation density, the classical dislocation density tensor and a so called curvature density.In the current work we present a three-dimensional implementation of the lowest order CDD theory as a materials sub-routine for Abaqus®in conjunction with the crystal plasticity framework DAMASK. We simulate bending of a micro-beam and qualitatively compare the plastic shear and the dislocation distribution on a given slip system to results from the literature. The CDD simulations reproduce a zone of reduced plastic shear close to the surfaces and dislocation pile-ups towards the center of the beam, which have been similarly observed in discrete dislocation simulations.

Micromechanisms of deformation in γ-TiAl

2002 ◽  
Vol 753 ◽  
Author(s):  
Patrick Veyssière ◽  
Yu-Lung Chiu ◽  
Fabienne Grégori
Keyword(s):  
Single Crystals ◽  
Lamellar Structure ◽  
Deformation Mechanisms ◽  
Slip Systems ◽  
Plastic Properties ◽  
Single Slip ◽  
Self Organisation

ABSTRACTInvestigations conducted in our group on plastic properties of a variety of strained TiAl based alloys and resulting microstructures are reviewed. These include oriented single crystals of Al-rich γ-TiAl and semi-oriented polycrystals with γ + α2 lamellar structure. The wealth of micro-mechanisms encountered in this family of alloys is, to large extent, due to the decomposition of <011] dislocations: <011] ↔ 1/2<112] + 1/2<110]. This transformation sometimes introduces serious uncertainties as to which slip systems were actually operating during deformation. Another transformation involving decomposition is the formation of intralamellar networks during deformation. Mechanisms not involving decomposition include the trailing of faulted dipoles by <011] dislocations and the generation of arrays of prismatic loops of ordinary dislocations. The latter maneuver is at the origin of fundamental processes such as self-organisation in single slip in a variety of crystals.

scholarly journals The Plastic Deformation Mechanisms of hcp Single Crystals with Different Orientations: Molecular Dynamics Simulations

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 733
Author(s):  
Zhi-Chao Ma ◽  
Xiao-Zhi Tang ◽  
Yong Mao ◽  
Ya-Fang Guo
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Phase Transformation ◽  
Molecular Dynamics Simulations ◽  
Single Crystals ◽  
Deformation Mechanisms ◽  
Shear Stresses ◽  
Affecting Factors ◽  
Fcc Phase ◽  
Dynamics Simulations

The deformation mechanisms of Mg, Zr, and Ti single crystals with different orientations are systematically studied by using molecular dynamics simulations. The affecting factors for the plasticity of hexagonal close-packed (hcp) metals are investigated. The results show that the basal <a> dislocation, prismatic <a> dislocation, and pyramidal <c + a> dislocation are activated in Mg, Zr, and Ti single crystals. The prior slip system is determined by the combined effect of the Schmid factor and the critical resolved shear stresses (CRSS). Twinning plays a crucial role during plastic deformation since basal and prismatic slips are limited. The 101¯2 twinning is popularly observed in Mg, Zr, and Ti due to its low CRSS. The 101¯1 twin appears in Mg and Ti, but not in Zr because of the high CRSS. The stress-induced hcp-fcc phase transformation occurs in Ti, which is achieved by successive glide of Shockley partial dislocations on basal planes. More types of plastic deformation mechanisms (including the cross-slip, double twins, and hcp-fcc phase transformation) are activated in Ti than in Mg and Zr. Multiple deformation mechanisms coordinate with each other, resulting in the higher strength and good ductility of Ti. The simulation results agree well with the related experimental observation.

The Temperature and Strain Rate Dependence of the Flow Stress in MoSi2 Single Crystals

1993 ◽  
Vol 322 ◽  
Author(s):  
S.A. Maloy ◽  
T.E. Mitchell ◽  
John J. Petrovic ◽  
A.H. Heuer ◽  
J.J. Lewandowski
Keyword(s):  
Flow Stress ◽  
Slip System ◽  
Strain Rate ◽  
Single Crystal ◽  
Single Crystals ◽  
Stress Exponent ◽  
Deformation Mechanisms ◽  
Strain Rates ◽  
Jump Test ◽  
Stress And Deformation

AbstractThe temperature dependence of the flow stress and deformation mechanisms of single crystal MoSi2 have been determined for compression along three different orientations, [001], [021] and [771], at two different strain rates, 1 × 10−5/s and 1 × 10−4/s, and at temperatures between 900 and 1600°C. The flow stress along [021] is slightly higher than that along [771] while both orientations gave a much lower flow stress than that along [001]. Along [021], slip occurs on the {110} 1/2<111> slip system between 1000 and 1200°C, while at 1300-1400°C, slip occurs on the {013}<100> slip system. Along [771], deformation occurs by the [001]<100> slip system while cross-slip onto {013} and [011] planes is observed at 1000-1300°C except that slip occurs on the {013{1/2<331> slip system at 1000-1100°C for faster strain rates. Along [001], slip occurs on the {013}1/2<331> system at 900-1100°C while slip is observed on the {011} 1/2<111> system at 1300-1600°C. Strain rate jump tests from 1×10−5/s to 5x10−5/s at 1 100°C revealed a stress exponent of 7 along [771] and 20 along [021], while a rate jump test from lx10−5/s to 2x 10−5/s along [001] at 1400°C gave a stress exponent of 3.9.

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