Dislocation Extraction Algorithm Research Articles

Deformation and boundary motion analysis of a faceted twin grain boundary

In this article, molecular dynamics simulations are used to understand how a nickel bicrystal with faceted incoherent Σ3 grain boundaries responds to uniaxial tensile loading. The deformation response is studied over a wide range of temperatures (100 – 900 K) and strain rates (107 – 1010 s−1). The dislocation extraction algorithm and common neighbor analysis are employed to identify the deformation mechanisms. Our results reveal that the yield stress decreases with temperature and increases with strain rate; whereas the elastic modulus decreases with temperature and is independent of strain rate. Furthermore, incipient plasticity is detected ahead of the yield point at lower temperatures and lower strain rates. Interestingly, the incoherent twin grain boundaries are quite mobile under the uniaxial tensile loading at lower temperatures and lower strain rates. But this mobility decreased at higher temperatures and higher strain rates, thereby, confirming this faceted grain boundary's non-Arrhenius (anti-thermal) migration behavior even under mechanical loading. From a deformation perspective, the incoherent twin facet of the grain boundary served as the major source for stacking fault formation at lower temperatures and higher strain rates. However, with the increase in temperature, the stacking faults became shorter and originated from both the incoherent twin facet and the tips of coherent twin facet. These results are in qualitative agreement with the experimental results documented in the literature.

Unveiling the effect of interface on torsional behavior of crystalline Al-Al90Sm10 metallic glass nanolaminates

ABSTRACT Influence of configurational design of single crystal Al-Al90Sm10 metallic glass nanolaminates on torsion deformation behaviour of Al/Al90Sm10 nanolaminate (Configuration 1) and Al90Sm10/Al nanolaminate (Configuration 2) from a structural evolution aspect have been analysed by employing Molecular Dynamics for a torsion speed of 1/600 revolution/ps. Adaptive common neighbour (a-CNA) analysis, Dislocation extraction algorithm (DXA), atomic shear strain analysis, and Voronoi Polyhedral (VP) analysis have been carried out to reveal the structural evolution in the nanolaminates specimen subjected to torque. As a consequence of dislocation density localisation under torsional loading in Al/Al90Sm10 nanolaminate high atomic strain gradient is developed in the nanolaminate specimen causing torsional buckling of the Al/Al90Sm10 nanolaminate. The localisation of dislocation density rings induces the formation of dislocation substructure in Al/Al90Sm10 nanolaminate. The crystalline/amorphous interface serves as a free surface and encourages the formation of such dislocation substructure. The collective nucleation, coalescence, and growth of shear transformation zones (STZs) leading to the formation of thick shear bands on either end of Al90Sm10/Al nanolaminate inducing an almost homogenous atomic strain gradient across the surface of the nanolaminate specimen thereby averting torsional buckling. The C/A interface serves as a nucleation site for the generation STZs in Al90Sm10/Al nanolaminate. VPs such as <0, 0, 4, 6>, <0, 3, 6, 4>, <0, 3, 6, 5> <0, 2, 8, 2> have the load bearing capacity and are resistant to fragmentation under the subjugation of torsion loading.

Molecular dynamics study of nano-indentation deformation behavior of Al/Al90Sm10 nanolaminate.

Molecular dynamics-based investigation has been carried out to simulate the nano-indentation loading in crystalline Al-amorphous Al90Sm10 metallic glass (MG) with an aim to investigate the effect orientation of crystalline-amorphous (C/A) interface orientation on the nano-indentation behavior of the C/A Al-Al90Sm10 nanolaminate for varying indenter speeds. Post-analysis techniques like adaptive-common neighbor analysis (a-CNA), atomic strain, dislocation extraction algorithm (DXA), and Voronoi polyhedral analysis (VP) have been employed to capture the structural evolution during simulated nano-indentation loading. C/A Al-Al90Sm10 nanolaminate with C/A interface orientated perpendicular to the indenter exhibits the presence of elastic regime followed by plastic curve, whereas load versus depth curve behaves plastically since the beginning in case of C/A Al-Al90Sm10 nanolaminate with C/A interface orientated parallel to the indenter. The dislocation density growth is slower in case of C/A Al-Al90Sm10 nanolaminate with C/A interface orientated perpendicular to the indenter attributed to the sinking of dislocations into MG counterpart of the nanolaminate, thereby triggering shear transformation zone activation. Whereas, the dislocation generation is delayed in case of C/A Al-Al90Sm10 nanolaminate with C/A interface orientated parallel to the indenter by virtue of amorphous Al90Sm10 MG coating on crystalline Al but is extensive and rapid. The disintegration of ICO-like structures and mixed clusters and growth of crystal-like clusters is discernible in C/A Al-Al90Sm10 nanolaminate with C/A interface orientated perpendicular to the indenter. On the other hand, the VP population exhibits cyclic variation in C/A Al-Al90Sm10 nanolaminate with C/A interface orientated parallel to the indenter. A transformation pathway of VPs has been mapped out for C/A Al-Al90Sm10 nanolaminate under nano-indentation loading. The simulations have been carried out by employing Molecular Dynamics using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) platform. Post-analysis techniques like adaptive-common neighbor analysis (a-CNA), atomic strain, dislocation extraction algorithm (DXA), and Voronoi polyhedral analysis (VP) have been employed to capture the structural evolution during simulated nano-indentation loading.

Using Molecular Dynamic Simulation to Understand the Deformation Mechanism in Cu, Ni, and Equimolar Cu-Ni Polycrystalline Alloys

The grain boundaries and dislocations play an important role in understanding the deformation behavior in polycrystalline materials. In this paper, the deformation mechanism of Cu, Ni, and equimolar Cu-Ni alloy was investigated using molecular dynamic simulation. The interaction between dislocations and grain boundary motion during the deformation was monitored using the dislocation extraction algorithm. Moreover, the effect of stacking fault formation and atomic band structure on the deformation behavior was discussed. Results indicate that dislocations nucleate around the grain boundary in copper, the deformation in nickel changes from planar slip bands to wavy bands, and high density of dislocation accumulation as well as numerous kink and jog formations were observed for the equimolar Cu-Ni alloy. The highest density of the Shockley dislocation and stacking faults was formed in the equimolar Cu-Ni alloy which results in the appearance of a huge gliding stage in the stress–strain curve. The grain boundaries act as a sinking source for vacancy annihilation in Ni and Cu; however, this effect was not observed in an equimolar Cu-Ni alloy. Finally, radial distribution function was used to evaluate atom segregation in grain boundaries.

Configurational Entropy Effect on Thermal and Mechanical Properties of Pt1Pd1Rh1Co1 and Pt41Pd18Rh5Co32 High‐Entropy Alloys

The configurational entropy effect on thermal and mechanical properties of Pt1Pd1Rh1Co1 and Pt41Pd18Rh5Co32 face‐centered cubic high‐entropy alloys is investigated by the molecular dynamics simulation with the second‐nearest‐neighbor modified embedded‐atom‐method potential. Using the heating process, 3000 and 2375 K are melting temperatures (Tm) of Pt1Pd1Rh1Co1 and Pt41Pd18Rh5Co32. Local structures around Co atoms become more distorted above 2425 K (about 0.81Tm) for Pt1Pd1Rh1Co1 and 1325 K (about 0.56Tm) for Pt41Pd18Rh5Co32. The Arrhenius equation shows that diffusion barriers of all element types in Pt1Pd1Rh1Co1 are about 50–89% higher than those in Pt41Pd18Rh5Co32, and the pre‐exponential factors of Pt1Pd1Rh1Co1 are about one order higher than those of Pt41Pd18Rh5Co32. Using the uniaxial compression simulation, the ultimate and yielding stresses of Pt1Pd1Rh1Co1 are about 88.3% and 53.4% higher than the corresponding values of Pt41Pd18Rh5Co32. For Young's modulus, Pt1Pd1Rh1Co1 is about 34.8% higher than that of Pt41Pd18Rh5Co32. At the yielding strain, the dislocation extraction algorithm results show that no local defected structures appear within Pt1Pd1Rh1Co1, whereas several nanoclusters of defected structures distribute randomly within Pt41Pd18Rh5Co32. At ultimate strain, multiple Shockley partial dislocations nucleate from the free surfaces for Pt1Pd1Rh1Co1, and more nanoclusters of defected structures appear within Pt41Pd18Rh5Co32, where Shockley partial dislocations nucleate.

Mechanical responses of Al20.4Mo10.5Nb22.4Ta10.1Ti17.8Zr18.8 nanopillar under uniaxial compression

The mechanical responses of crystallographic orientations [001], [110], and [111] of Al 20.4 Mo 10.5 Nb 22.4 Ta 10.1 Ti 17.8 Zr 18.8 refractory high entropy alloy (RHEA) nanopillars under the uniaxial compression are investigated by the MD simulation using 2NN MEAM potential. The [001]-orientated nanopillar shows the widest elastic deformation regime with the yielding strain about 0.075, compared to the other two nanopillars with the yielding strains about 0.03~0.04. The strength of [111]-oriented nanopillar is the highest, which is about 36.3% and 117% higher than those of [001]- and [110]-oriented nanopillars, respectively. After the strain exceeds the ultimate one, the stress gradually declines with the increasing strain, and then displays small flow stress oscillation during plastic deformation, indicating the stresses saturate at the quasi-steady flow stress. For the [001]-orientated nanopillar, the extent of BCC-HCP phase transition is the most significant at strains below the flow stress regime. From strain 0 to the beginning of the flow stress regime, the local structural transition is the main deformation mechanism, and the dislocation slip becomes the dominant deformation mechanism within the flow stress regime. For the [110]-orientated nanopillar, the dislocation nucleates at the strain between the yielding and ultimate strains, and then the dislocation density increases sharply with the increasing strain until the occurrence of the dislocation slip. The dislocation slip and deformation twinning are two main deformation mechanisms for the [110]-orientated nanopillar. For the [111]-orientated nano-pillar, the dislocation nucleates at the strain larger than the ultimate strain when the stress undergoes an abrupt drop. After the dislocation nucleation, the dislocation density shows a distinct increase during the stress drop, leading to the appearance of dislocation lines. In the flow stress regime, the dislocation density gradually decreases from the maximum value about 600.17 10 19 m -2 to zero with the increasing strain. Local shear strain of [110]-oriented Al20.4Mo10.5Nb22.4Ta10.1Ti17.8Zr18.8 nanopillar during the compression • The mechanical responses of crystallographic orientations [001], [110], and [111] of Al 20.4 Mo 10.5 Nb 22.4 Ta 10.1 Ti 17.8 Zr 18.8 refractory high entropy alloy nanopillars under the uniaxial compression • 2NN MEAM potential parametrization process for the Al-Mo-Nb-Ta-Ti-Zr system using DFT calculation data. • Polyhedral template matching (PTM) method for monitoring the local structural transformation. • Atomic local shear strain for observing dislocation slip band growth • dislocation extraction algorithm (DXA) results for dislocation nucleation and evolution

Nanoindentation of a nickel surface with twin boundaries using molecular dynamics simulations

ABSTRACT In this work, nanoindentation on a (110) crystal plane with a spherical indenter and (111) twin boundaries at different distances was simulated using molecular dynamics. In addition, the load–displacement curves and mechanical properties were calculated, and the deformation mechanism of the nickel matrix was analysed using a dislocation extraction algorithm (DXA). The results showed that the load decreased in the load–displacement curve, which was caused by the initial nucleation of the dislocations, and the twinning boundary hindered dislocation propagation. Furthermore, Young’s modulus values near the twin boundary were lower than those farther away, and the maximum shear stress near the twin boundary was lower. Therefore, dislocation activity in the nickel matrix during indentation was mainly in the form of Shockley partial dislocations.

A new approach to modelling closed cell nanofoams and analysis of their mechanical properties

A new approach which is based on the discreet element method and can be used for modelling closed cell nanofoams is revealed in this study. Atomistic models of closed cell nanofoams with five different types of porosity are generated with the help of a proposed modelling technique in order to examine the role of the porosity. Following the generation of atomistic models, the mechanical behaviour is investigated by performing molecular dynamic analyses. The findings signify that such mechanical properties as elastic moduli, ultimate and yield stresses rise with decreasing porosity for both loading types. Additionally, dislocation extraction algorithm (DXA) analysis is carried out to observe the evolution of the deformation mechanism of atomistic models. Dislocation analyses show that the Shockley partial dislocation plays a huge role in the deformation mechanism.

Influences of grain size and twin boundary on the tensile properties of nanocrystalline face-centered cubic Cu50Ni50 alloy

ABSTRACT The effects of grain size (GS) and distance between twin boundaries (d) on the tensile properties of nanocrystalline (NC) face-centered cubic Cu50Ni50 alloy are studied using the molecular dynamics simulations. The common neighbour analysis, dislocation extraction algorithm, shear strain, and von Mises stress configurations together with the total dislocation length, stress–strain relation, and tensile strength diagrams are presented to investigate the mechanical characteristics of the NC Cu50Ni50 specimens. The results exhibits that the twin boundaries significantly restrict the formation and propagation of the stacking faults. The integral deformation occurs under a combination of displacement, breakage, and self-destruction of the twin boundary along with the contraction and expansion of the grains. The tensile strength increases as the GS and the d increase, which agrees with the inverse Hall-Petch relation. The tensile strength of the conventional NC is higher than that of the twinned NC for each pair of specimens with the same GS.

Sweep-tracing algorithm: in silico slip crystallography and tension-compression asymmetry in BCC metals

Direct Molecular Dynamics (MD) simulations are being increasingly employed to model dislocation-mediated crystal plasticity with atomic resolution. Thanks to the dislocation extraction algorithm (DXA), dislocation lines can be now accurately detected and positioned in space and their Burgers vector unambiguously identified in silico, while the simulation is being performed. However, DXA extracts static snapshots of dislocation configurations that by themselves present no information on dislocation motion. Referred to as a sweep-tracing algorithm (STA), here we introduce a practical computational method to observe dislocation motion and to accurately quantify its important characteristics such as preferential slip planes (slip crystallography). STA reconnects pairs of successive snapshots extracted by DXA and computes elementary slip facets thus precisely tracing the motion of dislocation segments from one snapshot to the next. As a testbed for our new method, we apply STA to the analysis of dislocation motion in large-scale MD simulations of single crystal plasticity in BCC metals. We observe that, when the crystal is subjected to uniaxial deformation along its [001] axis, dislocation slip predominantly occurs on the {112} maximum resolved shear stress plane under tension, while in compression slip is non-crystallographic (pencil) resulting in asymmetric mechanical response. The marked contrast in the observed slip crystallography is attributed to the twinning/anti-twinning asymmetry of shears in the {112} planes relatively favoring dislocation motion in the twinning sense while hindering dislocations from moving in the anti-twinning directions.

The Influence of Grain Boundaries on Crystal Structure and Tensile Mechanical Properties of Al0.1CoCrFeNi High-Entropy Alloys Studied by Molecular Dynamics Method

The mechanical properties of high-entropy alloys are superior to those of traditional alloys. However, the key problem of finding a strengthening mechanism is still challenging. In this work, the molecular dynamics method is used to calculate the tensile properties of face-centered cubic Al0.1CoCrFeNi high-entropy alloys containing Σ3 grain boundaries and without grain boundary. The atomic model was established by the melting rapid cooling method, then stretched by the static drawing method. The common neighbor analysis and dislocation extraction algorithm are used to analyze the crystal evolution mechanism of Σ3 grain boundaries to improve the material properties of high-entropy alloys during the tensile test. The results show that compared with the mechanical properties Al0.1CoCrFeNi high-entropy alloys without grain boundary, the yield strength and Young’s modulus of a high-entropy alloy containing Σ3 grain boundary are obviously larger than that of high-entropy alloys without grain boundary. Dislocation type includes mainly 1/6&lt;112&gt; Shockley partial dislocations, a small account of 1/6&lt;110&gt; Stair-rod, 1/2&lt;110&gt;perfect dislocation, and 1/3&lt;111&gt; Hirth dislocations. The mechanical properties of high-entropy alloys are improved by dislocation entanglement and accumulation near the grain boundary.

Glide Mobility of a-Type Edge Dislocations in Aluminum Nitride by Molecular Dynamics Simulation.

Classical molecular dynamics simulations are performed to investigate the motion of a-type edge dislocations in wurtzite aluminum nitride (AlN). The nucleation and propagation of kinks are observed via the dislocation extraction algorithm. Our simulation results show that the nucleation energy of the kink pair in AlN is 1.2 eV and that the migration energy is 2.8 eV. The Peierls stress of the 1/3⟨112̅0⟩{101̅0} edge dislocation at 0 K is 15.9 GPa. The viscous motion of dislocations occurs when τ > τp, and the dislocation velocity is inversely proportional to the temperature and directly proportional to the applied stress. Below room temperature, the value of the critical resolved shear stress (CRSS) on the prismatic plane is the lowest, which suggests that the dislocation mobility on the prismatic plane is the easiest. The CRSS on the pyramidal plane is always the highest at all temperatures, which suggests that pyramidal slip is the hardest among these three slip systems.

Comparative analysis of mechanical properties for mono and poly-crystalline copper under nanoindentation – Insights from molecular dynamics simulations

Crystallographic orientation and grain size for monocrystalline and polycrystalline materials respectively play a critical role in defining their mechanical behaviour under nanoindentation. To understand their effects on mechanical properties, molecular dynamics (MD) simulations help in revealing the underlying physical phenomena governing the nanoindentation behaviour. This paper attempts to comparatively analyse and study the effects of crystallographic orientations of monocrystalline copper {(100), (110) and (111)} and critical grain size of polycrystalline copper on the nanoindentation response using MD simulations. The results obtained for indentation load vs. depth curve, hardness, dislocations, and elastic recovery were analysed for comparison. Cu(111) exhibited an average hardness of 12.62 GPa, which is 18.27% more than that of Cupoly. The pile-ups of 8 Å size were observed in Cupoly; and this was higher than any of copper system studied here. The dislocation extraction algorithm (DXA) analysis revealed that the total dislocations in Cu(111) was 34.23% and 153.8% lower than that of Cu(110) and Cupoly, respectively. Cu(111) comprised of highest Stair-rod dislocation along with LC and Hirth locks. Furthermore, a prismatic loop comprised of sessile dislocations also appeared in Cu(111). The elastic depth recovery rate for Cu(100) was 52.75%, 41.60% and 40.66% higher than that of Cu(110), Cu(111) and Cupoly, respectively. This study revealed that the nanoindentation based mechanical performances of monocrystalline copper systems, specifically Cu(111) were superior to any other copper systems.

Recent Advances in Copper Polycrystal Film’s Grain Boundaries Behavior and Its Influence in Properties with Molecular Dynamic Simulation

.Copper polycrystal film(CPF) is accepted as a promising material for electroplated film in semiconductor devices for its outstanding conductivity and ductility as well as the good resistance to elector-migration. However, the film material attains a rapid failure in the working environment, and hence the failure mechanism and the fabrication methods require more exploration. In previous studies, it is convinced that grain boundaries(GBs) movement and its interaction with twining boundaries(TBs) and dislocations have a great influence on the failure process. In this study, the applications of Molecular Dynamic(MD) Simulation in the research of CPF have been introduced. The GBs behaviour including deformation of the GBs and the interaction between GBs and TBs that is observed by dislocation extraction algorithm(DXA) has been summarized, and its relation to the properties such as yield strength and the roughness of growth has been discussed. And the best condition to construct a CPF with magnetron sputtering method is concluded to have substrates in 700K as well as low misorientation with grains under incident atoms of large enough kinetic energy and vertical incident angle.

Shear deformation mechanical performance of Ni–Co alloy nanoplate by molecular dynamics simulation

Ni–Co alloy has great advantages in the fields of micro-electromechanical systems and aerospace, however, the lack of micro-deformation mechanism restricts its industrial application. Herein, the deformation mechanism and microstructure evolution of Ni–Co alloy nanoplate under shear loading are investigated by MD. The yield strength increases gradually with the increase of the velocity, and the highest shear modulus is 111.43 GPa. The stress concentration leads to the nucleation and expansion of the dislocation, and the stacking fault expands with the dislocation motion, swallowing most of the disordered atoms. By Dislocation Extraction Algorithm (DXA), it is found that Shockley and Perfect dislocations make a major role, and the interactions between dislocations are responsible for the high mechanical properties. As the temperature increases, the yield strength decreases significantly, the stress fluctuations in the plastic phase at 100 K and 200 K are greater compared to other temperatures. Meanwhile, the coherence of the dislocations motion decreases, and the atoms in the stacking faults are scattered, leading to the decreasing of area. The above results are helpful for the design and control of nanoelectronic facilities and provide a significant guide for the industrial applications of Ni–Co alloy nanoplate.

Defect dynamics and uniaxial tensile deformation of equi and non-equi-atomic configuration of multi-elemental alloys

In this article, molecular dynamics and statics-based simulations were carried out to study the effect of equi-atomic and non-equi-atomic compositions of multi-elemental alloys on defect dynamics and tensile deformation. High and medium entropy alloy configurations were subjected to uni-axial tensile loading, and deformation governing mechanism was identified with the help of dislocation extraction algorithm and common neighbour analysis. Due to low or negative stacking fault energy, phase transformation from FCC to HCP in conjunction with solid solution hardening was identified as the governing mechanism for the plastic deformation in most of the multi-elemental alloys. Atomistic snapshots of simulation box containing deformed configurations of medium and high entropy alloys also show heterogenous nucleation, pinning of dislocations, cross channelling of twin boundaries. It was predicted that in alloys with higher Cr content twinning and stacking fault is prominent mode of deformation. Nudged elastic band algorithm was used to predict the vacancy migration energies in each of the atomistic configurations. The results presented in the article are in qualitatively in agreement with the experimental results, and higher fidelity simulations helps in developing better understanding about the plastic deformation in equi and non-equi-atomic composition of multi-elemental alloys.

Simulation of interaction behavior between dislocation and graphene during nanoindentation of graphene/aluminum matrix nanocomposites

Graphene has been thought to be an ideal reinforcement material for metal matrix composite due to its superior mechanical properties and unique two-dimensional geometry. However, the deformation mechanism of graphene/aluminum matrix composite is still unclear. In this paper, molecular dynamics simulation is used to elucidate the evolution details of the dislocation microstructure and the underlying interaction behavior between dislocation and graphene during nanoindentation of the graphene/aluminum matrix composite with various graphene orientations. To this end, four different cases, i.e. the pure aluminum and the graphene/aluminum matrix composite with the graphene orientation of 90°, 45° and 0° are examined, respectively. Based on the force-indentation depth curve, the interaction behavior between dislocation and graphene and its effect on the plastic zone are analyzed. The results indicate that the graphene can act as an effective dislocation motion barrier, and the elastic deformation of graphene can occur locally along the direction of dislocation slip. Using the visualization technique of dislocation extraction algorithm, the nucleation and propagation of dislocation are investigated. The results show that the differences in interaction behavior between dislocation and graphene with various orientations affect the spreading trend of the plastic zone and the blocking strength of graphene to dislocation. For the composite with the graphene orientations of 45° and 0°, the interaction between graphene and dislocation causes the number of dislocations to increase. Additionally, the plastic zone of the composite with the graphene orientation of 45° is tangent to two symmetrical graphene sheets. For the composite with the graphene orientation of 90°, the interaction between graphene and dislocation shortens the total length of the dislocation line, and the volume shrinkage of plastic zone is most significant after indenter retraction. Here, the hardness is also calculated to quantitatively evaluate the influence of graphene orientation on the mechanical properties of graphene/aluminum matrix composite. The hardness of the composite with the graphene orientation of 45° is highest, which is due to the decrease of the volume of the plastic zone and the increase of dislocation number. The decrease of the hardness of the composite with the graphene orientation of 90° is attributed to the reduction of dislocation number in the plastic zone. However, for the composite with the graphene orientation of 0°, the interaction between graphene and dislocation results in the softening effect, because of a wide range of elastic deformation in the graphene plane. The study can provide a certain theoretical guidance for designing and preparing the high-performance graphene/metal matrix composites.

Study on micro-crack propagation behavior of single-crystal α-Ti under shear stress based on molecular dynamics

In order to reveal the micro-crack behavior of single-crystal titanium under nanoscale shear stress conditions, a molecular dynamics model of single-crystal titanium was constructed. Shear force is applied to the single-crystal titanium model on 000112¯10 crystal orientation and 1¯0101¯21¯0 crystal orientation, respectively. The crystal structure is analyzed by Common Neighbor Analysis (CNA) method and Dislocation Extraction Algorithm (DXA) to identify defects and dislocations which reveal the microstructure evolution mechanism of single-crystal titanium. The results show that under the action of shear stress, the dislocation of single-crystal titanium is mainly formed in the crack area and the dislocation moves completely along the direction of the shear force. When the shear force is applied on 000112¯10 crystal orientation, the formation of dislocations is accompanied by a largescale phase change and the proliferation mode of dislocation is single point Frank-Read source. When the shear force is applied on 1¯0101¯21¯0 crystal orientation, the crystal dislocation is first generated in the crack region, and the proliferation mode of dislocation is dynamic proliferation mechanism. Then dislocation occurs at the corner of the material and continuous slip occurs in the atomic layer, which seriously affects the shear resistance of the single-crystal α-Ti.

High Velocity and Temperature Effects on the Bending Behavior of Nickel Nanowire: A Large-Scale Molecular Dynamics Simulation Study

Abstract We performed classical molecular dynamics (MD) simulation of bending of large-size nickel nanowire (NW) of size 28a (x-axis) by 284a (y-axis) by 28a (z-axis) comprising of 925,965 atoms (where a = 3.52 Å). Embedded atom method potential is used for modeling the interactions between nickel atoms. Bending studies have been carried out at temperatures in the range of 300 K–1,500 K. A rigid diamond tip is used to apply force on the NW at a velocity of 100 m/s along z-direction [0 0 −1]. The load time results show that as the temperature increases the yield load decreases as expected and is more significant at temperatures higher than 900 K. The structural studies are carried out by centro-symmetry parameter (CSP) and radial distribution function (RDF) analysis. The CSP analysis reveals the formation of stacking faults in the NW regions below the indenter tip, indicating localized plastic deformation. The RDF analysis reveals that with an increase in temperature the regions in the NW below the indenter tip become disordered. Dislocation extraction algorithm analysis carried out for understanding the plastic deformation mechanism reveals that the deformation mechanism is by slip by Shockley partial dislocations. We also observed twins in a few regions of the NW. The fracture features of the NW suggest ductile nature.

Mechanical response of nanoporous nickel investigated using molecular dynamics simulations.

The effect of pore size on the deformation mechanism and mechanical properties of nanoporous Ni under tension and compression tests is studied using molecular dynamic simulations in terms of atomic trajectories, dislocation extraction algorithm, and the stress-strain curve. The simulation results show that samples have a longer elastic deformation period during tension compared to that during compression. Dislocations nucleate at pore surfaces and propagate until they are terminated by neighboring pores. Samples under tension have lower ultimate stress and higher strain at ultimate stress compared to those of samples under compression. Samples with smaller pore diameter have more transformation from face-centered cubic to hexagonal close-packed structures due to more dislocation activity. The ultimate stress of samples significantly decreases with increasing pore diameter.