scholarly journals Effect of Twin Boundary Motion and Dislocation-Twin Interaction on Mechanical Behavior in Fcc Metals

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2238
Author(s):  
Jaber Rezaei Mianroodi ◽  
Bob Svendsen
Keyword(s):  
Twin Boundary ◽  
Partial Dislocation ◽  
Shear Loading ◽  
Dislocation Nucleation ◽  
The Other ◽  
Boundary Motion ◽  
Normal Loading ◽  
Fcc Metals ◽  
Boundary Orientation ◽  
Normal Twin

The interplay of interface and bulk dislocation nucleation and glide in determining the motion of twin boundaries, slip-twin interaction, and the mechanical (i.e., stress-strain) behavior of fcc metals is investigated in the current work with the help of molecular dynamics simulations. To this end, simulation cells containing twin boundaries are subject to loading in different directions relative to the twin boundary orientation. In particular, shear loading of the twin boundary results in significantly different behavior than in the other loading cases, and in particular to jerky stress flow. For example, twin boundary shear loading along ⟨ 112 ⟩ results in translational normal twin boundary motion, twinning or detwinning, and net hardening. On the other hand, such loading along ⟨ 110 ⟩ results in oscillatory normal twin boundary motion and no hardening. As shown here, this difference results from the different effect each type of loading has on lattice stacking order perpendicular to the twin boundary, and so on interface partial dislocation nucleation. In both cases, however, the observed stress fluctuation and “jerky flow” is due to fast partial dislocation nucleation and glide on the twin boundary. This is supported by the determination of the velocity and energy barriers to glide for twin boundary partials. In particular, twin boundary partial edge dislocations are significantly faster than corresponding screws as well as their bulk counterparts. In the last part of the work, the effect of variable twin boundary orientation in relation to the loading direction is investigated. In particular, a change away from pure normal loading to the twin plane toward mixed shear-normal loading results in a transition of dominant deformation mechanism from bulk dislocation nucleation/slip, to twin boundary motion.

scholarly journals Evolution of Friction and Permeability in a Propped Fracture under Shear

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-13 ◽  
Author(s):  
Fengshou Zhang ◽  
Yi Fang ◽  
Derek Elsworth ◽  
Chaoyi Wang ◽  
Xiaofeng Yang
Keyword(s):  
Normal Stress ◽  
Shear Loading ◽  
Particle Crushing ◽  
Normal Loading ◽  
Fracture Surfaces ◽  
Frictional Strength ◽  
Transport Response ◽  
Shear Slip ◽  
High Normal Stress ◽  
Proppant Embedment

We explore the evolution of friction and permeability of a propped fracture under shear. We examine the effects of normal stress, proppant thickness, proppant size, and fracture wall texture on the frictional and transport response of proppant packs confined between planar fracture surfaces. The proppant-absent and proppant-filled fractures show different frictional strength. For fractures with proppants, the frictional response is mainly controlled by the normal stress and proppant thickness. The depth of shearing-concurrent striations on fracture surfaces suggests that the magnitude of proppant embedment is controlled by the applied normal stress. Under high normal stress, the reduced friction implies that shear slip is more likely to occur on propped fractures in deeper reservoirs. The increase in the number of proppant layers, from monolayer to triple layers, significantly increases the friction of the propped fracture due to the interlocking of the particles and jamming. Permeability of the propped fracture is mainly controlled by the magnitude of the normal stress, the proppant thickness, and the proppant grain size. Permeability of the propped fracture decreases during shearing due to proppant particle crushing and related clogging. Proppants are prone to crushing if the shear loading evolves concurrently with the normal loading.

ATOMISTIC SIMULATION OF TORSIONAL VIBRATION AND PLASTIC DEFORMATION OF FIVE-FOLD TWINNED COPPER NANOWIRES

2014 ◽  
Vol 11 (supp01) ◽  
pp. 1344010 ◽  
Author(s):  
Y. G. ZHENG ◽  
Y. T. ZHAO ◽  
H. F. YE ◽  
H. W. ZHANG ◽  
Y. F. FU
Keyword(s):  
Plastic Deformation ◽  
Torsional Vibration ◽  
Partial Dislocation ◽  
Dislocation Nucleation ◽  
Activation Process ◽  
Torsional Angle ◽  
Wire Radius ◽  
Wire Length ◽  
Deformation Behaviors ◽  
The Wire

In this paper, atomistic simulations have been conducted to investigate the torsional mechanical behaviors of five-fold twinned nanowires (FTNs), including the torsional vibration properties, elasto-plastic deformation behaviors and activation process of the first partial dislocation nucleation. Simulation results show that the fundamental torsional vibration frequency is inversely proportional to the wire length and is independent of the wire radius. Provided that an effective shear modulus of FTNs is used, the classic elastic torsional theory may be applicable to nanoscale. Furthermore, it is found that the plastic deformation of FTNs is dominated by partial dislocation activities. The normalized critical torsional angle corresponding to the onset of plastic deformation increases with the decrease of the wire radius and temperature, while it is almost independent of the wire length and loading rate. In addition, the activation energy of the first partial dislocation nucleation is about several electric voltages and decreases with the increase of the wire radius and applied torsional load.

A Truly Generalized Plane Strain Meshless Model for Combined Normal and Shear Loading of Fiber Reinforced Materials

2010 ◽  
Author(s):  
Eisa Ahmadi ◽  
M. M. Aghdam
Keyword(s):  
Direct Method ◽  
Micromechanical Model ◽  
Computation Time ◽  
Integral Form ◽  
Shear Loading ◽  
Interface Condition ◽  
Fiber Reinforced ◽  
Equilibrium Equations ◽  
Normal Loading ◽  
Fiber Reinforced Materials

A truly meshless method based on the integral form of equilibrium equations is formulated. A micromechanical model is developed to study micro-stresses in normal and shear loading of unidirectional fiber reinforced composites. A small repeating area of composite including a fiber surrounded by matrix called representative volume element (RVE) is considered as solution domain. A direct method is proposed for enforcement of the appropriate periodic boundary conditions for shear and normal loading. Especially transverse shear loading is considered in this analysis. Fully bonded interface condition is investigated and the continuity of displacements and traction is imposed to the fiber-matrix interface. Comparison of the predicted results shows excellent agreement with results in available literature. Results of this study also revealed that the presented model can provide highly accurate predictions with respectively small number of nodes and small computation time without the complexity of mesh generation.

The Morphology of Grain Boundary Interactions with Twins in YBa2Cu3O7−δ

1993 ◽  
Vol 319 ◽  
Author(s):  
Jenn-Yue Wang ◽  
A. H. King
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Twin Boundary ◽  
Interfacial Energy ◽  
Coincidence Site Lattice ◽  
The Other ◽  
Twin Boundaries ◽  
Site Lattice ◽  
Dislocation Arrays

AbstractVarious morphologies are observed where twins meet grain boundaries in YBa2Cu3O7−δ. Twins may be “correlated” at the boundary (i.e. twin boundaries from one grain may meet a twin boundary from the other grain in a quadruple junction) and the twins may be narrowed or “constricted” at the boundary. These effects are determined by the interfacial energy. We estimate the energy of the various interfaces by determining the dislocation arrays they contain, using the constrained coincidence site lattice (CCSL) model and Bollmann's O2-lattice formalism. Our approach indicates that there are significant changes in the energy of the interfaces and is thus able to explain the variety of observed morphologies.

Real-time observation of twin boundary motion in organic crystal (TMTSF)2X

2001 ◽  
Vol 251 (1) ◽  
pp. 199-205 ◽  
Author(s):  
Kazushige Kawabata ◽  
Yasuyoshi Hosokawa ◽  
Takashi Kawauchi ◽  
Takashi Sambongi
Keyword(s):  
Real Time ◽  
Twin Boundary ◽  
Organic Crystal ◽  
Boundary Motion ◽  
Time Observation ◽  
Real Time Observation

Plasticity in the Thickness Direction of Paperboard Under Combined Shear and Normal Loading

2001 ◽  
Vol 123 (2) ◽  
pp. 184-190 ◽  
Author(s):  
N. Stenberg ◽  
C. Fellers ◽  
S. O¨stlund
Keyword(s):  
Mechanical Behavior ◽  
Test Piece ◽  
Yield Function ◽  
Shear Loading ◽  
Plastic Behavior ◽  
Thickness Direction ◽  
Initial State ◽  
Normal Loading ◽  
Elastic Plastic ◽  
Out Of Plane

Creasing and offset printing are both examples of paperboard converting operations where the stress state is multiaxial, and where elastic-plastic deformation occurs in the thickness direction. Optimization of paperboard for such operations requires both advanced modeling and a better understanding of the mechanical behavior of the material. Today, our understanding and modeling of the out-of-plane properties are not as well established as our knowledge of the in-plane behavior. In order to bridge this gap, a modification of the Arcan device, which is well known in other fields, was developed for the experimental characterization of the out-of-plane mechanical behavior of paperboard. A fixture attached to the Arcan device was used to control the deformation in the test piece during loading. The test piece was glued to the device with a high viscosity adhesive and left stress-free during curing to achieve an initial state free of stresses. The apparatus proved to work well and to produce reliable results. Measurements of the mechanical behavior in combined normal and shear loading generated data points for the determination of the yield surface in the stress space. The elastic-plastic behavior in the thickness direction of paperboard was modeled assuming small-strain orthotropic linear elasticity and a quadratic yield function. Simulations using this yield function and an associative flow law showed good agreement with the test results.

Nonuniform twin-boundary motion in Ni–Mn–Ga single crystals

2004 ◽  
Vol 84 (20) ◽  
pp. 4071-4073 ◽  
Author(s):  
Miguel A. Marioni ◽  
Samuel M. Allen ◽  
Robert C. O’Handley
Keyword(s):  
Single Crystals ◽  
Twin Boundary ◽  
Boundary Motion

Theoretical Study of Twin Boundary Motion in Heusler Ni-Mn-Ga Alloys Using Monte Carlo Method

2012 ◽  
Vol 190 ◽  
pp. 327-330
Author(s):  
K.I. Kostromitin ◽  
Vasiliy D. Buchelnikov ◽  
V.V. Sokolovskiy ◽  
P. Entel
Keyword(s):  
Magnetic Field ◽  
Monte Carlo ◽  
Monte Carlo Method ◽  
Monte Carlo Simulations ◽  
Twin Boundary ◽  
Constant Temperature ◽  
Theoretical Study ◽  
Heusler Alloys ◽  
Boundary Motion ◽  
Different Temperatures

The twin boundary motion in Ni-Mn-Ga Heusler alloys has been investigated using Monte Carlo simulations. The Hamiltonian of system includes magnetic and elastic parts and two magnetoelastic terms. It is shown that the twin boundary shifts in a magnetic field at the constant temperature. The spin and strain volume fractions have been obtained at different temperatures.

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