Atomistic Simulations of Dislocations in Confined Volumes

AbstractInternal microstructural length scales play a fundamental role in the strength and ductility of a material. Grain boundaries in nanocrystalline structures and heterointerfaces in nanolaminates can restrict dislocation propagation and also act as a source for new dislocations, thereby affecting the detailed dynamics of dislocation-mediated plasticity. Atomistic simulation has played an important and complementary role to experiment in elucidating the nature of the dislocation/interface interaction, demonstrating a diversity of atomic-scale processes covering dislocation nucleation, propagation, absorption, and transmission at interfaces. This article reviews some atomistic simulation work that has made progress in this field and discusses possible strategies in overcoming the inherent time scale challenge of finite temperature molecular dynamics.

Download Full-text

Length Scale Effects in Materials Deformation of Nano and Microscale Au Structures

Volume 11: Mechanics of Solids, Structures and Fluids ◽

10.1115/imece2009-12077 ◽

2009 ◽

Author(s):

Jie Lian ◽

Junlan Wang

Keyword(s):

Mechanical Properties ◽

Elastic Modulus ◽

Size Effect ◽

Sample Size ◽

Atomistic Simulation ◽

Scale Effects ◽

Elastic Recovery ◽

Boundary Effect ◽

Dislocation Nucleation ◽

Atomistic Simulations

In this study, intrinsic size effect — strong size dependence of mechanical properties — in materials deformation was investigated by performing atomistic simulation of compression on Au (114) pyramids. Sample boundary effect — inaccurate measurement of mechanical properties when sample size is comparable to the indent size — in nanoindentation was also investigated by performing experiments and atomistic simulations of nanoindentation into nano- and micro-scale Au pillars and bulk Au (001) surfaces. For intrinsic size effect, dislocation nucleation and motions that contribute to size effect were analyzed for studying the materials deformation mechanisms. For sample boundary effect, in both experiments and atomistic simulation, the elastic modulus decreases with increasing indent size over sample size ratio. Significantly different dislocation motions contribute to the lower value of the elastic modulus measured in the pillar indentation. The presence of the free surface would allow the dislocations to annihilate, causing a higher elastic recovery during the unloading of pillar indentation.

Download Full-text

Atomic-Scale Modeling of the Annihilation of Jogged Screw Dislocation Dipoles

MRS Proceedings ◽

10.1557/proc-578-217 ◽

1999 ◽

Vol 578 ◽

Cited By ~ 7

Author(s):

T. Vegge ◽

O. B. Pedersen ◽

T. Leffers ◽

K. W. Jacobsen

Keyword(s):

Molecular Dynamics ◽

Screw Dislocation ◽

Atomic Scale ◽

Atomistic Simulations ◽

Elastic Band ◽

Screw Dislocations ◽

Scale Modeling ◽

Band Method

AbstractUsing atomistic simulations we investigate the annihilation of screw dislocation dipoles in Cu. In particular we determine the influence of jogs on the annihilation barrier for screw dislocation dipoles. The simulations involve energy minimizations, molecular dynamics, and the Nudged Elastic Band method. We find that jogs on screw dislocations substantially reduce the annihilation barrier, hence leading to an increase in the minimum stable dipole height.

Download Full-text

Study of Nanocutting Using Atomic Model

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.33-37.963 ◽

2008 ◽

Vol 33-37 ◽

pp. 963-968

Author(s):

Chun Yi Chu ◽

Chung Ming Tan ◽

Yung Chuan Chiou

Keyword(s):

Molecular Dynamics ◽

Energy Minimization ◽

Atomic Scale ◽

Scale Model ◽

Atomistic Simulations ◽

Cutting Depth ◽

Cutting Deformation ◽

Simulation Results ◽

Model Approach

The stress induced in a workpiece under nanocutting are analyzed by an atomic-scale model approach that is based on the energy minimization. Certain aspects of the deformation evolution during the process of nanocutting are addressed. This method needs less computational efforts than traditional molecular dynamics (MD) calculations. The simulation results demonstrate that the microscopic cutting deformation mechanism in the nanocutting process can be regarded as the instability of the crystalline structure in our atomistic simulations and the surface quality of the finished workpiece varies with the cutting depth.

Download Full-text

Domain Reduction Method for Periodic Nanostructure Modeling: Gold Nanorods, Carbon Nanotubes and Graphene Applications

Volume 9: Mechanics of Solids, Structures and Fluids ◽

10.1115/imece2010-40541 ◽

2010 ◽

Author(s):

Eduard G. Karpov ◽

Dong Qian

Keyword(s):

Atomistic Simulation ◽

Reduction Method ◽

Atomistic Simulations ◽

Fine Scale ◽

Coarse Scale ◽

Benchmark Data ◽

Domain Reduction ◽

Interfacial Boundary ◽

Nanocrystalline Structures ◽

Domain Reduction Method

A domain-reduction approach for the simulation of one- and two-dimensional nanocrystalline structures is demonstrated. In this approach, the domain of interest is partitioned into coarse and fine scale regions and the coupling between the two is implemented through a multiscale interfacial boundary condition. The atomistic simulation is used in the fine scale region, while the discrete Fourier transform is applied to the coarse scale region to yield a compact Green’s function formulation that represents the effects of the coarse scale domain upon the fine/coarse scale interface. This approach facilitates the simulations for the fine scale, without the requirement to simulate the entire coarse scale domain. Robustness of the proposed domain-reduction method is demonstrated via comparison and verification of the results with benchmark data from fully atomistic simulations. Demonstrated applications include deformation of crystalline Au (111) nanorods, CNT bending and buckling, and graphene nanoindentation.

Download Full-text

Determination of Ionic Diffusion Mechanisms in Solids

MRS Proceedings ◽

10.1557/proc-527-443 ◽

1998 ◽

Vol 527 ◽

Author(s):

John Corish

Keyword(s):

Molecular Dynamics ◽

Diffusion Coefficient ◽

Atomistic Simulation ◽

Atomistic Simulations ◽

Ionic Diffusion ◽

Simulation Studies ◽

Lattice Statics ◽

Monte Carlo Techniques ◽

Diffusion Mechanisms

ABSTRACTThe experimental and atomistic simulation methodologies by which microscopic diffusion mechanisms can be determined in solids are described. Measurement of the Haven Ratio requires evaluation of the diffusion coefficient and of the ionic conductivity for the species in pure and doped specimens and is, in practice, limited to simpler materials. Atomistic simulations using lattice statics, molecular dynamics and Monte Carlo techniques can yield very detailed information on the pathways followed by migrating ions and are being utilised more extensively for this purpose. Examples of such experimental and simulation studies are discussed.

Download Full-text

Molecular Dynamics Simulation of Surface Effect on Tensile Deformation of Single Crystalline Copper

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.620.61 ◽

2014 ◽

Vol 620 ◽

pp. 61-66 ◽

Cited By ~ 1

Author(s):

Qiang Gao ◽

Yong Bo Guo ◽

Ying Chun Liang ◽

Qing Chun Zhang

Keyword(s):

Molecular Dynamics ◽

Tensile Deformation ◽

Surface Effect ◽

High Energy ◽

Dislocation Nucleation ◽

Atomic Scale ◽

Dynamics Simulation ◽

Crystal Plane ◽

Single Crystalline ◽

Tensile Process

Based on molecular dynamics method, the tensile process of single crystalline Cu nanorod and single crystalline Cu bulk were simulated at atomic scale. The motion of atoms, total energy of atom-strain curves and number of dislocation atom-strain curves during the tensile process were acquired. The results shown that surface effect has a significant effect on the tensile mechanical properties of single crystalline Cu nanorod. For single crystalline Cu nanorod, the energy of atoms in the edges and surface were higher than the energy of atoms inside the nanorod. Dislocations nucleation in the edges that with high energy and extend along the {111} crystal plane. The nanorods produce plastic deformation and shows excellent ductility under the "dislocation nucleation-energy rising and dislocation layers cross-slip" mechanism of the alternating cycle. For single crystalline Cu bulk, dislocation nucleation randomly and extend to the entire simulation model along the {111} crystal plane quickly. The single crystalline bulk Cu produce fracture under the "microscopic vacancy-microscopic hole-penetration of microscopic holes-fracture" mechanism.

Download Full-text

A Hybrid Molecular Dynamics/Atomic-Scale Finite Element Method for Quasi-Static Atomistic Simulations at Finite Temperature

Journal of Applied Mechanics ◽

10.1115/1.4025807 ◽

2013 ◽

Vol 81 (5) ◽

Cited By ~ 3

Author(s):

Ran Xu ◽

Bin Liu

Keyword(s):

Finite Element Method ◽

Finite Element ◽

Finite Temperature ◽

Simulation Method ◽

Atomic Scale ◽

Atomistic Simulations ◽

Single Wall Carbon Nanotubes ◽

Equilibrium Configurations ◽

Quasi Static Process ◽

Element Method

In this paper, a hybrid quasi-static atomistic simulation method at finite temperature is developed, which combines the advantages of MD for thermal equilibrium and atomic-scale finite element method (AFEM) for efficient equilibration. Some temperature effects are embedded in static AFEM simulation by applying the virtual and equivalent thermal disturbance forces extracted from MD. Alternatively performing MD and AFEM can quickly obtain a series of thermodynamic equilibrium configurations such that a quasi-static process is modeled. Moreover, a stirring-accelerated MD/AFEM fast relaxation approach is proposed in which the atomic forces and velocities are randomly exchanged to artificially accelerate the “slow processes” such as mechanical wave propagation and thermal diffusion. The efficiency of the proposed methods is demonstrated by numerical examples on single wall carbon nanotubes.

Download Full-text

Atomic-Scale Simulation in Materials Science

MRS Bulletin ◽

10.1557/s0883769400066331 ◽

1988 ◽

Vol 13 (2) ◽

pp. 28-35 ◽

Cited By ~ 27

Author(s):

Michael Baskes ◽

Murray Daw ◽

Brian Dodson ◽

Stephen Foiles

Keyword(s):

Molecular Dynamics ◽

Statistical Mechanics ◽

Atomistic Simulation ◽

Materials Science ◽

Vibrational Energy ◽

Equations Of Motion ◽

Atomic Scale ◽

Wide Range ◽

Scale Properties ◽

Computer Power

Realistic simulation of the atomic-scale properties of complex systems has long been a goal of scientists interested in the behavior of condensed matter. Until recently, the role of atomistic simulation techniques has been to address rather idealized problems in statistical mechanics. Treatment of more realistic materials has been uncommon not because suitable approaches toward simulating such materials were unknown, but rather because the computer power available was inadequate. Recently, major advances have occurred in the complexity of systems subject to atomistic simulation, primarily due to a dramatic increase in availability of computer power. These new capabilities have driven the development of atomic-scale descriptions of real materials accurate enough for atomistic simulation of a wide range of specific materials science problems.In this section, we will outline several of the techniques used to simulate the microscopic behavior of an atomistic system. The first method introduced for atomistic simulation was the molecular dynamics technique, in which Newton's equations of motion for the individual atoms are integrated numerically for given interatomic and external forces. One of the first uses of this technique was the study, by Fermi, Pasta, and Ulam, of randomization of vibrational energy in a one-dimensional chain of atoms. Although the results of this initial application were to some extent unsatisfactory, the molecular dynamics technique has since been applied to a wide range of problems in the statistical mechanics of condensed media.

Download Full-text

Molecular Dynamics Simulations of Dislocation Nucleation From Bicrystal Interfaces in FCC Metals

Materials ◽

10.1115/imece2005-82092 ◽

2005 ◽

Cited By ~ 1

Author(s):

Douglas E. Spearot ◽

Karl I. Jacob ◽

David L. McDowell

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulations ◽

Tensile Deformation ◽

Dislocation Nucleation ◽

Atomistic Simulations ◽

Structural Units ◽

Fcc Metals ◽

Deformation Response ◽

Dynamics Simulations

Atomistic simulations are used to study dislocation nucleation from <001> tilt bicrystal interfaces in copper subjected to a tensile deformation. Specifically, three interface misorientations are examined, including the Σ5 (310) interface, which has a high density of coincident atomic sites. The initial interface configurations, which are discussed in terms of structural units, are refined using energy minimization techniques. Molecular dynamics simulations are then used to deform each interface in tension. The role of boundary conditions and their effect on the inelastic deformation response is discussed in detail. Molecular dynamics simulations show that the interface structural units are directly involved in the partial dislocation nucleation process. The maximum tensile strength of the Σ5 (310) interface shows a modest increase in the case where lateral confinement of the interface is an important consideration.

Download Full-text