scholarly journals Multiscale Modeling of Dislocation Processes in Bcc Tantalum: Bridging Atomistic and Mesoscale Simulations

2000 ◽  
Vol 653 ◽  
Author(s):  
L. H. Yang ◽  
Meijie Tang ◽  
John A. Moriarty
Keyword(s):  
Plastic Deformation ◽  
Multiscale Modeling ◽  
Activation Enthalpy ◽  
Analytic Form ◽  
Simulation Method ◽  
Dislocation Dynamics ◽  
Atomic Scale ◽  
Interatomic Potentials ◽  
Screw Dislocations ◽  
Stress Dependent

AbstractPlastic deformation in bcc metals at low temperatures and high-strain rates is controlled by the motion of a/2<111> screw dislocations, and understanding the fundamental atomistic processes of this motion is essential to develop predictive multiscale models of crystal plasticity. The multiscale modeling approach presented here for bcc Ta is based on information passing, where results of simulations at the atomic scale are used in simulations of plastic deformation at mesoscopic length scales via dislocation dynamics (DD). The relevant core properties of a/2<111> screw dislocations in Ta have been obtained using quantum-based interatomic potentials derived from model generalized pseudopotential theory and an ab-initio data base together with an accurate Green's-function simulation method that implements flexible boundary conditions. In particular, the stress-dependent activation enthalpy for the lowest-energy kink-pair mechanism has been calculated and fitted to a revealing analytic form. This is the critical quantity determining dislocation mobility in the DD simulations, and the present activation enthalpy is found to be in good agreement with the previous empirical form used to explain the temperature dependence of the yield stress.

Multiscale Modeling of Two Dimensional Rough Surface Contacts

2004 ◽  
Vol 841 ◽  
Author(s):  
Binquan Luan ◽  
Sangil Hyun ◽  
Mark O. Robbins ◽  
Noam Bernstein
Keyword(s):  
Multiscale Modeling ◽  
Contact Area ◽  
Simulation Method ◽  
System Size ◽  
Adhesive Contact ◽  
Scale Dependence ◽  
Atomic Scale ◽  
Two Dimensional ◽  
Plastic Materials ◽  
Frictional Forces

ABSTRACTA hybrid simulation method is used to study non-adhesive contact between two-dimensional self-affine rough surfaces. We find strong scale dependence as the contact dimensions decrease to the atomic scale. Both purely elastic and plastic materials are considered, and show different trends with system size. In all cases the contact area rises linearly with applied load, but the slope is substantially different from continuum predictions. We also examine the effect of commensurability between contacting surfaces. Contact area and frictional forces can be very different for commensurate and incommensurate surfaces, particularly for plastic materials.

scholarly journals Robust quantum-based interatomic potentials for multiscale modeling in transition metals

2006 ◽  
Vol 21 (3) ◽  
pp. 563-573 ◽  
Author(s):  
John A. Moriarty ◽  
Lorin X. Benedict ◽  
James N. Glosli ◽  
Randolph Q. Hood ◽  
Daniel A. Orlikowski ◽  
...  
Keyword(s):  
Transition Metals ◽  
Multiscale Modeling ◽  
Density Functional ◽  
Large Scale ◽  
Dislocation Core ◽  
Dislocation Dynamics ◽  
Interatomic Potentials ◽  
Dynamic Simulations ◽  
Wide Range ◽  
Dynamics Simulations

First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in transition metals and alloys within density-functional quantum mechanics. In the central body-centered cubic (bcc) metals, where multi-ion angular forces are important to materials properties, simplified model GPT (MGPT) potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect, and mechanical properties at both ambient and extreme conditions. Selected applications to multiscale modeling discussed here include dislocation core structure and mobility, atomistically informed dislocation dynamics simulations of plasticity, and thermoelasticity and high-pressure strength modeling. Recent algorithm improvements have provided a more general matrix representation of MGPT beyond canonical bands, allowing improved accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed for dynamic simulations, and the development of temperature-dependent potentials.

scholarly journals Twisting of a Pristine α-Fe Nanowire: From Wild Dislocation Avalanches to Mild Local Amorphization

Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1602
Author(s):  
Yang Yang ◽  
Xiangdong Ding ◽  
Jun Sun ◽  
Ekhard K. H. Salje
Keyword(s):  
Plastic Deformation ◽  
Probability Distribution Function ◽  
Power Laws ◽  
Dislocation Nucleation ◽  
Dislocation Dynamics ◽  
Deformation Mechanisms ◽  
Strongly Correlated ◽  
Power Law Distribution ◽  
Screw Dislocations ◽  
Dynamics Simulations

The torsion of pristine α-Fe nanowires was studied by molecular dynamics simulations. Torsion-induced plastic deformation in pristine nanowires is divided into two regimes. Under weak torsion, plastic deformation leads to dislocation nucleation and propagation. Twisting-induced dislocations are mainly 12<111> screw dislocations in a <112>-oriented nanowire. The nucleation and propagation of these dislocations were found to form avalanches which generate the emission of energy jerks. Their probability distribution function (PDF) showed power laws with mixing between different energy exponents. The mixing stemmed from simultaneous axial and radial dislocation movements. The power-law distribution indicated strongly correlated ‘wild’ dislocation dynamics. At the end of this regime, the dislocation pattern was frozen, and further twisting of the nanowire did not change the dislocation pattern. Instead, it induced local amorphization at the grip points at the ends of the sample. This “melting” generated highly dampened, mild avalanches. We compared the deformation mechanisms of twinned and pristine α-Fe nanowires under torsion.

Disorientations in dislocation structures: Formation and spatial correlation

2002 ◽  
Vol 17 (9) ◽  
pp. 2433-2441 ◽  
Author(s):  
Wolfgang Pantleon
Keyword(s):  
Plastic Deformation ◽  
Spatial Correlation ◽  
Distribution Functions ◽  
Scaling Behavior ◽  
Dislocation Dynamics ◽  
Slip Systems ◽  
Experimental Findings ◽  
Good Agreement

During plastic deformation, dislocation boundaries are formed and orientation differences across them arise. Two different causes lead to the formation of two kinds of deformation-induced boundaries: a statistical trapping of dislocations in incidental dislocation boundaries and a difference in the activation of slip systems on both sides of geometrically necessary boundaries. On the basis of these mechanisms, the occurrence of disorientations across both types of dislocation boundaries is modeled by dislocation dynamics. The resulting evolution of the disorientation angles with strain is in good agreement with experimental observations. The theoretically obtained distribution functions for the disorientation angles describe the experimental findings well and explain their scaling behavior. The model also predicts correlations between disorientations in neighboring boundaries, and evidence for their existence is presented.

Atomic-scale structural evolution in amorphous Nd9Fe85B6 subjected to severe plastic deformation at room temperature

2009 ◽  
Vol 94 (23) ◽  
pp. 231904 ◽  
Author(s):  
Wei Li ◽  
Xiaohong Li ◽  
Defeng Guo ◽  
Kiminori Sato ◽  
Dmitry V. Gunderov ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
Room Temperature ◽  
Structural Evolution ◽  
Atomic Scale

scholarly journals Comparative Studies on Water Self-Diffusivity Confined in Graphene Nanogap: Molecular Dynamics Simulation

2016 ◽  
Author(s):  
Mohammad Moulod ◽  
Gisuk Hwang
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Surface Energy ◽  
Water Transport ◽  
Surface Interactions ◽  
Bulk Water ◽  
Water Desalination ◽  
Atomic Scale ◽  
Dynamics Simulation ◽  
Interatomic Potentials

Fundamental understanding of the water in graphene is crucial to optimally design and operate the sustainable energy, water desalination, and bio-medical systems. A numerous atomic-scale studies have been reported, primarily articulating the surface interactions (interatomic potentials) between the water and graphene. However, a systematic comparative study among the various interatomic potentials is rare, especially for the water transport confined in the graphene nanostructure. In this study, the effects of different interatomic potentials and gap sizes on water self-diffusivity are investigated using the molecular dynamics simulation at T = 300 K. The water is confined in the rigid graphene nanogap with the various gap sizes Lz = 0.7 to 4.17 nm, using SPC/E and TIP3P water models. The water self-diffusivity is calculated using the mean squared displacement approach. It is found that the water self-diffusivity in the confined region is lower than that of the bulk water, and it decreases as the gap size decreases and the surface energy increases. Also, the water self-diffusivity nearly linearly decreases with the increasing surface energy to reach the bulk water self-diffusivity at zero surface energy. The obtained results provide a roadmap to fundamentally understand the water transport properties in the graphene geometries and surface interactions.

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