scholarly journals MD Simulations of Compression of Nanoscale Iron Pillars

2011 ◽  
Vol 1369 ◽  
Author(s):  
Con J. Healy ◽  
Graeme J. Ackland
Keyword(s):  
Boundary Conditions ◽  
Deformation Behaviour ◽  
Md Simulations ◽  
Perfect Crystal ◽  
Width Ratio ◽  
Nucleation Sites ◽  
Large Length ◽  
Iron Pillar ◽  
Fixed Boundaries ◽  
Dislocation Sources

ABSTRACTIt is now possible to create perfect crystal nanowires of many metals. The deformation of such objects requires a good understanding of the processes involved in plasticity at the nanoscale. Isotropic compression of such nanometre scale micropillars is a good model system to understand the plasticity. Here we investigate these phenomena using Molecular Dynamics (MD) simulations of nanometre scale single crystal BCC iron pillars in compression.We find that pillars with large length to width ratio may buckle under high strain rates. The type of buckling behaviour depends sensitively on the boundary conditions used: periodic boundary conditions allow for rotation at top and bottom of the pillar, and result in an S shaped buckle, by contrast fixed boundaries enforce a C shape. Pillars with a length to width ratio closer to that used in experimental micropillar compression studies show deformation behaviour dominated by slip, in agreement with the experiments. For micropillars oriented along <100>, slip occurs on <110> planes and localized slip bands are formed. Pillars of this size experience higher stresses than bulk materials before yielding takes place. One might expect that this may be in part due to the lack of nucleation sites needed to induce slip. However, further simulations with possible dislocation sources: a shorter iron pillar containing a spherical grain boundary, and a similar pillar containing jagged edges did not show a decreased yield strength.

Dynamic Response Analysis of Docking Chamber Structure Considering Viscoelastic Boundary Condition

2013 ◽  
Vol 405-408 ◽  
pp. 1939-1944
Author(s):  
Gui Lan Tao ◽  
Li Zhang
Keyword(s):  
Boundary Conditions ◽  
Secondary Development ◽  
Response Analysis ◽  
Elastic Model ◽  
Cross Point ◽  
Finite Element Software ◽  
Structure Response ◽  
Structure Dynamic ◽  
Fixed Boundaries ◽  
Incident Waves

Spring-damper units were set on the boundaries to absorb incident waves and reflected scattering waves to realize viscoelastic artificial boundary (VAB). The equivalent node load input method was used to simulate the VAB and viscoelastic boundary element wave input. Programming is based on APDL secondary development language with ANSYS finite element software. Considering the interaction between chamber structure and the surrounding soil, docking chamber structure dynamic model is established based on the VAB. The linear elastic model was used for concrete structure. The D-P nonlinear model was used for the back soil calculation. Docking chamber structure dynamic analysis under conditions of fixed boundaries and viscoelastic boundaries were conducted. The result indicated that under the viscoelastic boundary conditions, dynamic acceleration response is significant on the top of the lock wall, which is approximately 2.5 times of the value on the bottom of the lock wall. The maximum response stress appears near the cross point of the lock wall and the bottom floor with value of approximately 5620 kPa;.The chamber bottom floor is subjected to tension and maximum stress with the value of approximately 6180 kPa. Usually, the structure response under the fixed boundary conditions is higher than the structure response under the viscoelastic boundary conditions.

Small-to-Large Length Scale Transition of TMAO Interaction with Hydrophobic Solutes

2021 ◽  
Author(s):  
Angelina Folberth ◽  
Swaminath Bharadwaj ◽  
Nico van der Vegt
Keyword(s):  
Molecular Dynamics ◽  
Free Energy ◽  
Md Simulations ◽  
Free Energy Calculations ◽  
Length Scale ◽  
Simulation Data ◽  
Energy Calculations ◽  
Large Length ◽  
Hydrophobic Solutes ◽  
Large Length Scale

We report the effect of trimethylamine N-oxide (TMAO) on the solvation of nonpolar solutes in water studied with molecular dynamics (MD) simulations and free-energy calculations. The simulation data indicate the...

Anticlastic Curvature of Elastically Bent Crystals for Sagittal Focusing

1993 ◽  
Vol 307 ◽  
Author(s):  
J. P. Quintana ◽  
V. I. Kushnir ◽  
P. Georgopoulos
Keyword(s):  
Finite Element ◽  
Aspect Ratio ◽  
Boundary Conditions ◽  
Width Ratio ◽  
Crystal Length ◽  
Poisson Coefficient ◽  
Anticlastic Curvature ◽  
Bent Crystals

ABSTRACTFinite element results are presented for the case of an elastically bent isotropic rectangular crystal with clamped boundary conditions. Results show that the anticlastic curvature can be eliminated in the center of the crystal provided the crystal length to width ratio fits a “golden aspect ratio” which is dependent on the Poisson coefficient ν. For ν=0.262 (appropriate for Si(111)), this ratio is approximately equal to 1.42.

scholarly journals Derivation of boundary conditions for the artificial boundaries associated with the solution of certain time dependent problems by Lax–Wendroff type difference schemes

1982 ◽  
Vol 25 (1) ◽  
pp. 1-18 ◽  
Author(s):  
John C. Wilson
Keyword(s):  
Partial Differential Equations ◽  
Differential Equations ◽  
Boundary Conditions ◽  
Numerical Solution ◽  
Time Dependent ◽  
Finite Region ◽  
Partial Differential ◽  
Artificial Boundaries ◽  
Fixed Boundaries ◽  
Time Dependent Problems

Many problems involving the solution of partial differential equations require the solution over a finite region with fixed boundaries on which conditions are prescribed. It is a well known fact that the numerical solution of many such problems requires additional conditions on these boundaries and these conditions must be chosen to ensure stability. This problem has been considered by, amongst others, Kreiss [11, 12, 13], Osher [16, 17], Gustafsson et al. [9] Gottlieb and Tarkel [7] and Burns [1]

scholarly journals Numerical Exploration of the Defect’s Effect on Mechanical Properties of Nanowires under Torsion

2011 ◽  
Vol 335-336 ◽  
pp. 498-501 ◽  
Author(s):  
Hai Fei Zhan ◽  
Yuan Tong Gu ◽  
Cheng Yan ◽  
Prasad K.D.V. Yarlagadda
Keyword(s):  
Mechanical Properties ◽  
Surface Defects ◽  
Torsional Rigidity ◽  
Stacking Faults ◽  
Md Simulations ◽  
Numerical Exploration ◽  
Deformation Processes ◽  
Dislocation Sources ◽  
Torsion Deformation

Molecular dynamics (MD) simulations have been carried out to investigate the defect’s effect on the mechanical properties of single-crystal copper nanowire with different surface defects, under torsion deformation. The torsional rigidity is found insensitive to the surface defects and the critical angle appears an obvious decrease due to the surface defects, the largest decrease is found for the nanowire with surface horizon defect. The deformation mechanism appears different degrees of influence due to surface defects. The surface defects play a role of dislocation sources. Comparing with single intrinsic stacking faults formation for the perfect nanowire, much affluent deformation processes have been activated because of surface defects, for instance, we find the twins formation for the nanowire with a surface 45odefect.

FEM Analysis of Active Reduction of Torsional Vibrations of Clamped-Free Beam by Piezoelectric Elements for Separated Modes

2015 ◽  
Vol 39 (4) ◽  
pp. 639-644 ◽  
Author(s):  
Elżbieta Augustyn ◽  
Marek S. Kozień ◽  
Michał Pracik
Keyword(s):  
Cross Section ◽  
Rectangular Cross Section ◽  
Fem Analysis ◽  
Width Ratio ◽  
Torsional Vibrations ◽  
Fem Simulations ◽  
Natural Modes ◽  
Piezoelectric Elements ◽  
Large Length ◽  
Free Beam

Abstract Beams with rectangular cross-section, with large length-to-width ratio, can be excited to torsional vibrations. If the piezoelectric elements are mounted to the beam in pairs at the same cross-section with two separated elements positioned on the same side of the beam, and the voltages applied to them are in the opposite phase, they produce twisting moments which can be applied to reduce the torsional vibrations. Results of FEM simulations are presented and analysed in the paper. All analyses are performed for a steel free-clamped beam. The piezoelectric elements made of PZT material are mounted in pairs on one side of the beam. The analyses are done for separated natural modes.

scholarly journals Atomic Simulation of Nanoindentation on the Regular Wrinkled Graphene Sheet

Materials ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1127
Author(s):  
Ruonan Wang ◽  
Haosheng Pang ◽  
Minglin Li ◽  
Lianfeng Lai
Keyword(s):  
Mechanical Properties ◽  
Boundary Condition ◽  
Boundary Conditions ◽  
Young’S Modulus ◽  
Young's Modulus ◽  
Md Simulations ◽  
Force Microscopy ◽  
Atomic Simulation ◽  
Atomic Force ◽  
Surface Wrinkling

Surface landscapes have vague impact on the mechanical properties of graphene. In this paper, single-layered graphene sheets (SLGS) with regular wrinkles were first constructed by applying shear deformation using molecular dynamics (MD) simulations and then indented to extract their mechanical properties. The influence of the boundary condition of SLGS were considered. The wrinkle features and wrinkle formation processes of SLGS were found to be significantly related to the boundary conditions as well as the applied shear displacement and velocity. The wrinkling amplitude and degree of wrinkling increased with the increase in the applied shear displacements, and the trends of wrinkling wavelengths changed with the different boundary conditions. With the fixed boundary condition, the degree of graphene wrinkling was only affected when the velocity was greater than a certain value. The effect of wrinkles on the mechanical characterization of SLGS by atomic force microscopy (AFM) nanoindentation was finally investigated. The regular surface wrinkling of SLGS was found to weaken the Young’s modulus of graphene. The Young’s modulus of graphene deteriorates with the increase in the degree of regular wrinkling.

Experimental Study and Modeling of the Intermediate Section of the Nonisothermal Constrained Vapor Bubble

1998 ◽  
Vol 120 (1) ◽  
pp. 166-173 ◽  
Author(s):  
M. Karthikeyan ◽  
J. Huang ◽  
J. Plawsky ◽  
P. C. Wayner
Keyword(s):  
Liquid Film ◽  
Vapor Bubble ◽  
Thermal Conductance ◽  
Width Ratio ◽  
Operating Pressure ◽  
Governing Parameter ◽  
Constrained Vapor Bubble ◽  
Operating Limits ◽  
Large Length ◽  
Intermediate Section

The generic nonisothermal constrained vapor bubble (CVB) is a miniature, closed heat transfer device capable of high thermal conductance that uses interfacial forces to recirculate the condensate on the solid surface constraining the vapor bubble. Herein, for the specific case of a large length-to-width ratio it is equivalent to a wickless heat pipe. Experiments were conducted at various heat loads on a pentane/quartz CVB to measure the fundamental governing parameter fields: temperature, pressure, and liquid film curvature. An “intermediate” section with a large effective axial thermal conductivity was identified wherein the temperature remains nearly constant. A one-dimensional steady-state model of this intermediate section was developed and solved numerically to yield pressure, velocity, and liquid film curvature profiles. The experimentally obtained curvature profiles agree very well with those predicted by the Young-Laplace model. The operating temperature of the CVB was found to be a function of the operating pressure and not a function of the heat load. Due to experimental design limitations, the fundamental operating limits of the CVB were not reached.

Dislocation Dynamics Simulations

2012 ◽  
Vol 736 ◽  
pp. 13-20 ◽  
Author(s):  
Karri V. Mani Krishna ◽  
Prita Pant
Keyword(s):  
Boundary Conditions ◽  
Strain Hardening ◽  
Deformation Behaviour ◽  
Dislocation Dynamics ◽  
Clear Correlation ◽  
Rigid Boundary ◽  
Rate Of Increase ◽  
Dislocation Densities ◽  
Dynamics Simulations ◽  
Film Substrate

Dislocation Dynamics (DD) simulations are used to study the evolution of a pre-specified dislocation structure under applied stresses and imposed boundary conditions. These simulations can handle realistic dislocation densities ranging from 1010 to 1014 m-2, and hence can be used to model plastic deformation and strain hardening in metals. In this paper we introduce the basic concepts of DD simulations and then present results from simulations in thin copper films and in bulk zirconium. In both cases, the effect of orientation on deformation behaviour is investigated. For the thin film simulations, rigid boundary conditions are used at film-substrate and film-passivation interfaces leading to dislocation accumulation, while periodic boundaries are used for bulk grains of Zr. We show that there is a clear correlation between strain hardening rate and the rate of increase of dislocation density.

Analysis of the Deformation Behaviour of Cu Processed by High Pressure Torsion

2006 ◽  
Vol 114 ◽  
pp. 101-108 ◽  
Author(s):  
Vil D. Sitdikov ◽  
Roza G. Chembarisova ◽  
Igor V. Alexandrov
Keyword(s):  
High Pressure ◽  
Structural Changes ◽  
High Pressure Torsion ◽  
Deformation Behaviour ◽  
Applied Pressure ◽  
Dislocation Model ◽  
Sources And Sinks ◽  
Dislocation Sources ◽  
Pure Cu ◽  
Misorientation Angles

In the investigation the 3D version of the Estrin-Tóth dislocation model was used to analyze deformation behaviour of pure Cu, subjected to high pressure torsion (HPT) under pressures equal to 0.8, 2, 5, 8 GPa. As a result of the computer simulation, the nature and reasons for strain hardening are analyzed, the dislocation density evolution versus degree of SPD and graincell size versus degree of SPD curves were plotted. It is shown that the model adequately reflects the acting deformation mechanisms and structural changes during HPT at different applied pressures. It has been stated that an increase of the applied pressure at HPT leads to an increase in the activity of dislocation sources and sinks in the grain-cell walls. Misorientations between boundaries are estimated. It is revealed that an increase of the applied pressure contributes to a growth of the misorientation angles between neighbouring grain-cells.

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