scholarly journals Plasticity of crystals and interfaces: From discrete dislocations to size-dependent continuum theory

2010 ◽  
Vol 37 (4) ◽  
pp. 289-332 ◽  
Author(s):  
Sinisa Mesarovic
Keyword(s):  
Unsolved Problem ◽  
Continuum Theory ◽  
Elastic Interaction ◽  
Interface Energy ◽  
Crystalline Materials ◽  
Size Dependent ◽  
Dislocation Mechanics ◽  
Pile Up ◽  
Slip Planes ◽  
Discrete Dislocations

In this communication, we summarize the current advances in size-dependent continuum plasticity of crystals, specifically, the rate-independent (quasistatic) formulation, on the basis of dislocation mechanics. A particular emphasis is placed on relaxation of slip at interfaces. This unsolved problem is the current frontier of research in plasticity of crystalline materials. We outline a framework for further investigation, based on the developed theory for the bulk crystal. The bulk theory is based on the concept of geometrically necessary dislocations, specifically, on configurations where dislocations pile-up against interfaces. The average spacing of slip planes provides a characteristic length for the theory. The physical interpretation of the free energy includes the error in elastic interaction energies resulting from coarse representation of dislocation density fields. Continuum kinematics is determined by the fact that dislocation pile-ups have singular distribution, which allows us to represent the dense dislocation field at the boundary as a superdislocation, i.e., the jump in the slip filed. Associated with this jump is a slip-dependent interface energy, which in turn, makes this formulation suitable for analysis of interface relaxation mechanisms.

scholarly journals Dopants Modulate Crystal Growth in Molten Salts Enabled by Surface Energy Tuning

2021 ◽  
Author(s):  
Xiaoqiao Li ◽  
Linming Zhou ◽  
Han Wang ◽  
Dechao Meng ◽  
Guannan Qian ◽  
...  
Keyword(s):  
Crystal Growth ◽  
High Temperature ◽  
Surface Energy ◽  
Molten Salts ◽  
Rational Approach ◽  
Temperature Synthesis ◽  
Crystalline Materials ◽  
Size Dependent ◽  
High Temperature Synthesis ◽  
Energy Tuning

Crystalline materials are routinely produced via high-temperature synthesis and show size-dependent properties; however, a rational approach to regulating their crystal growth has not been established. Here we show that dopants...

USE OF STRAIN GRADIENT THEORY FOR MODELING THE SIZE-DEPENDENT PULL-IN OF ROTATIONAL NANO-MIRROR IN THE PRESENCE OF MOLECULAR FORCE

2013 ◽  
Vol 27 (18) ◽  
pp. 1350083 ◽  
Author(s):  
Y. TADI BENI ◽  
M. ABADYAN
Keyword(s):  
Strain Gradient ◽  
Continuum Theory ◽  
Strain Gradient Theory ◽  
Gradient Theory ◽  
Cross Sectional ◽  
Size Dependent ◽  
Proposed Model ◽  
Molecular Force ◽  
Intrinsic Material Length ◽  
Material Length

Experiments reveal that mechanical behavior of nanostructures is size-dependent. Herein, the size dependent pull-in instability of torsional nano-mirror is investigated using strain gradient nonclassic continuum theory. The governing equation of the mirror is derived taking the effect of electrostatic Coulomb and molecular van der Waals (vdW) forces into account. Variation of the rotation angle of the mirror as a function of the applied voltage is obtained and the instability parameters i.e., pull-in voltage and pull-in angle are determined. Nano-mirrors with square and circular cross-sectional beams are investigated as case studies. It is found that when the thickness of the torsional nano-beam is comparable with the intrinsic material length scales, size effect can substantially increase the instability parameters of the rotational mirror. Moreover, the effect of vdW forces on the size-dependent pull-in instability of the system is discussed. The proposed model is able to predict the experimental results more accurately than the previous classic models and reduce the gap between experiment and previous theories.

A continuum theory of stress gradient plasticity based on the dislocation pile-up model

2014 ◽  
Vol 80 ◽  
pp. 350-364 ◽  
Author(s):  
Dabiao Liu ◽  
Yuming He ◽  
Bo Zhang ◽  
Lei Shen
Keyword(s):  
Stress Gradient ◽  
Continuum Theory ◽  
Gradient Plasticity ◽  
Pile Up

Hot Spots from Dislocation Pile-up Avalanches

2005 ◽  
Vol 896 ◽  
Author(s):  
William Grisé
Keyword(s):  
Hot Spots ◽  
Hot Spot ◽  
Energetic Material ◽  
Shear Banding ◽  
Dislocation Dynamics ◽  
Circular Loop ◽  
Dislocation Mechanics ◽  
Pile Up ◽  
Localized Heating ◽  
Realistic Assessment

AbstractThe model of localized adiabatic heating associated with release of a dislocation pile-up avalanche is described and re-evaluated. The model supplies a fundamental explanation of shear banding behavior in metal and non-metal systems. Now, a dislocation dynamics description is provided for more realistic assessment of the hot spot heating, for both straight dislocation pile-ups and circular loop pile-ups. Such a localized heating effect was overestimated in the earlier work, in part, to show the dramatic enhancement of the work rate, and the corresponding temperature build-up, potentially occurring in the initial pile-up release, say, at achievement of the critical dislocation mechanics-based stress intensity for cleavage. Proposed applications are to potentially brittle metal, ionic, and energetic material systems.

scholarly journals Dislocation Nucleation and Pileup under a Wedge Contact at Nanoscale

2008 ◽  
Vol 2008 ◽  
pp. 1-5 ◽  
Author(s):  
Y. F. Gao ◽  
J. Lou
Keyword(s):  
Image Force ◽  
Interaction Force ◽  
Dislocation Nucleation ◽  
Peierls Stress ◽  
Crystalline Materials ◽  
Dislocation Mechanics ◽  
Experimental Findings ◽  
Raphson Method ◽  
Critical Contact ◽  
Nucleation Of Dislocations

Indentation responses of crystalline materials have been found to be radically different at micrometer and nanometer scales. The latter is usually thought to be controlled by the nucleation of dislocations. To explore this physical process, a dislocation mechanics study is performed to determine the conditions for the nucleation of a finite number of dislocations under a two-dimensional wedge indenter, using the Rice-Thomson nucleation criterion. The configurational force on the dislocation consists of the applied force, the image force, and the interaction force between dislocations. Dislocations reach equilibrium positions when the total driving force equals the effective Peierls stress, giving a set of nonlinear equations that can be solved using the Newton-Raphson method. When the apex angle of the wedge indenter increases, the critical contact size for dislocation nucleation increases rapidly, indicating that dislocation multiplication near a blunt wedge tip is extremely difficult. This geometric dependence agrees well with experimental findings.

Size-dependent reversal of the elastic interaction energy between misfit nanostructures

2013 ◽  
Vol 25 (7) ◽  
pp. 075802 ◽  
Author(s):  
L Persichetti ◽  
A Sgarlata ◽  
M Fanfoni ◽  
A Balzarotti
Keyword(s):  
Interaction Energy ◽  
Elastic Interaction ◽  
Size Dependent

scholarly journals Accommodation of large plastic strains and defect accumulation in nanocrystalline Ni grains

2007 ◽  
Vol 22 (8) ◽  
pp. 2241-2253 ◽  
Author(s):  
X.L. Wu ◽  
E. Ma
Keyword(s):  
Deformation Behavior ◽  
Boundary Migration ◽  
Temperature Deformation ◽  
Plastic Strains ◽  
Domain Structures ◽  
Transmission Electron ◽  
Defect Accumulation ◽  
Pile Up ◽  
Slip Planes ◽  
The Stability

A transmission electron microscopy (TEM) study has been carried out to uncover how dislocations and twins accommodate large plastic strains and accumulate in very small nanocrystalline Ni grains during low-temperature deformation. We illustrate dislocation patterns that suggest preferential deformation and nonuniform defect storage inside the nanocrystalline grain. Dislocations are present in individual and dipole configurations. Most dislocations are of the 60° type and pile up on (111) slip planes. Various deformation responses, in the forms of dislocations and twinning, may simultaneously occur inside a nanocrystalline grain. Evidence for twin boundary migration has been obtained. The rearrangement and organization of dislocations, sometimes interacting with the twins, lead to the formation of subgrain boundaries, subdividing the nanograin into mosaic domain structures. The observation of strain (deformation)-induced refinement contrasts with the recently reported stress-assisted grain growth in nanocrystalline metals and has implications for understanding the stability and deformation behavior of these highly nonequilibrium materials.

Analysis of cantilever NEMS in centrifugal-fluidic systems

2016 ◽  
Vol 30 (22) ◽  
pp. 1650148
Author(s):  
Mohsen Mohsen-Nia ◽  
Fateme Abadian ◽  
Naeime Abadian ◽  
Keivan Mosaiebi Dehkordi ◽  
Maryam Keivani ◽  
...  
Keyword(s):  
Angular Velocity ◽  
Ritz Method ◽  
Continuum Theory ◽  
Angular Speed ◽  
Lumped Parameter Model ◽  
Dispersion Forces ◽  
Liquid Media ◽  
Size Dependent ◽  
D’Alembert Principle ◽  
Lumped Parameter

Electromechanical nanocantilevers are promising for using as sensors/detectors in centrifugal-fluidic systems. For this application, the presence of angular speed and electrolyte environment should be considered in the theoretical analysis. Herein, the pull-in instability of the nanocantilever incorporating the effects of angular velocity and liquid media is investigated using a size-dependent continuum theory. Using d’Alembert principle, the angular speed is transformed into an equivalent centrifugal force. The electrochemical and dispersion forces are incorporated considering the corrections due to the presence of electrolyte media. Two different approaches, i.e., the Rayleigh–Ritz method (RRM) and proposing a lumped parameter model (LPM), were applied to analyze the system. The models are validated with the results presented in literature. Impacts of the angular velocity, electrolyte media, dispersion forces, and size effect on the instability characteristics of the nanocantilever are discussed.

Material grain size and crack size influences on cleavage fracturing

2015 ◽  
Vol 373 (2038) ◽  
pp. 20140124 ◽  
Author(s):  
Ronald W. Armstrong
Keyword(s):  
Grain Size ◽  
Fracture Mechanics ◽  
Crack Size ◽  
Size Dependent ◽  
Silicon Crystals ◽  
Pile Up ◽  
Crack Tip Plasticity ◽  
Material Grain Size ◽  
Stress Behaviour ◽  
Relationship Of

A review is given of the analogous dependence on reciprocal square root of grain size or crack size of fracture strength measurements reported for steel and other potentially brittle materials. The two dependencies have much in common. For onset of cleavage in steel, attention is focused on relationship of the essentially athermal fracture stress compared with a quite different viscoplastic yield stress behaviour. Both grain-size-dependent stresses are accounted for in terms of dislocation pile-up mechanics. Lowering of the cleavage stress occurs in steel because of carbide cracking. For crack size dependence, there is complication of localized crack tip plasticity in fracture mechanics measurements. Crack-size-dependent conventional and indentation fracture mechanics measurements are described also for results obtained on the diverse materials: polymethylmethacrylate, silicon crystals, alumina polycrystals and WC-Co (cermet) composites.

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