Molecular dynamics simulations of compression–tension asymmetry in plasticity of Fe nanopillars

Healy, Con; Ackland, Graeme J.

doi:10.1016/j.actamat.2014.02.021

Cited by 85 publications

(68 citation statements)

References 34 publications

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“…3 Mo1-Engineering stress versus engineering strain curves obtained from the experimental test campaign (the average curve is shown for each testing condition): a compression tests at room temperature varying the strain-rate; b tensile tests at room temperature varying the strain-rate; c quasi-static tensile tests varying the temperature; d tensile tests in dynamic loading condition varying the temperature tension, it is possible to notice that the material strength is higher in compression. The same result was found also in [10][11][12][13][14]. As well known, this is the typical behavior expected for BCC metals and it was previously notice precisely on molybdenum.…”

Section: Resultssupporting

confidence: 75%

“…[8,9], also the effect of the irradiation was investigated and modelled. Finally, considering the results reported in [10][11][12][13][14], an asymmetric behavior is expected in compression and tension tests: this was a general characteristic of BCC metals and it was previously noticed on molybdenum. In a lot of the available works, the data were used to calibrate strength models (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Investigation and Mechanical Modelling of Pure Molybdenum at High Strain-Rate and Temperature

Scapin

Peroni

Carra

2016

J. dynamic behavior mater.

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This work shows the results obtained from the investigation of the mechanical behavior of two batches of pure molybdenum specimens (C99.97 % Mo, Mo1 supplied by Plansee and Mo2 supplied by AT&M) under static and dynamic loading conditions at different temperatures, both under tensile and compressive loading conditions. Due to its properties molybdenum has applications in several fields including nuclear. At this moment, it is a good candidate for structural material application for Beam Intercepting Devices of the Large Hadron Collider at CERN, Geneva. The experimental tests in tensile loading condition were performed on small dog-bone specimens. A series of tests at room temperature and a range of strainrates was performed in order to obtain information about the strain-rate sensitivity of the material. A series of tests at different temperatures in both static and high dynamic loading conditions was performed in order to obtain information about the thermal softening of the material. The dynamic tests were performed using the Hopkinson Bar technique, and the heating of the specimen was performed using an induction coil system. The experimental tests in compression were carried out on cylindrical specimens at room temperature and a range of strain-rates. The experimental data were analyzed via a numerical inverse method based on Finite Element numerical simulations.This approach allows to obtain the effective stress versus strain curves, which cannot be derived by using standard relations since instability and necking were present. Moreover, it also allows the non-uniform distribution of strain-rate and temperature inside the specimen to be accounted for. The results obtained from compression tests confirm the data obtained in tension in terms of strainhardening and strain-rate sensitivity, even if the material exhibits a tension-compression asymmetry of the behavior. The analysis of the hardening, temperature and strain-rate sensitivities reveals that a unique standard visco-plastic model could not be defined to reproduce the material strength behavior under different loading conditions, especially over wide range of variation of the variables of interest.Keywords Refractory metal Á High temperature Á High strain-rate Á Hopkinson bar Á Tensile and compression Á Nuclear applications Á Instability Á FE-based numerical inverse approach

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Section: Resultssupporting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Investigation and Mechanical Modelling of Pure Molybdenum at High Strain-Rate and Temperature

Scapin

Peroni

Carra

2016

J. dynamic behavior mater.

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“…Under tensile loading, BCC Fe nanowires oriented in <100>, <112> and <102> axial directions deform predominantly by the twinning mechanism, whereas the full dislocation slip has been observed in <110> and <111> orientations 8 . Further, it has been shown that BCC Fe nanowires exhibit tension-compression asymmetry in deformation mechanisms 8,9 . In contrast to tensile loading, the nanowire with <100> orientation deformed by the dislocation slip, whereas twinning was observed in <110> orientation under compressive loading [8][9][10] .…”

Section: Introductionmentioning

confidence: 99%

“…Further, it has been shown that BCC Fe nanowires exhibit tension-compression asymmetry in deformation mechanisms 8,9 . In contrast to tensile loading, the nanowire with <100> orientation deformed by the dislocation slip, whereas twinning was observed in <110> orientation under compressive loading [8][9][10] . Recently, Wang et al 11 have provided the first experimental evidence of deformation twinning in BCC W nanowires with 15 nm diameter thereby conforming the predictions made using MD simulations.…”

Section: Introductionmentioning

confidence: 99%

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Atomistic simulations on ductile-brittle transition in ⟨111⟩ BCC Fe nanowires

Sainath

Choudhary

2017

Journal of Applied Physics

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Molecular dynamics simulations have been performed to understand the influence of temperature on the tensile deformation and fracture behavior of <111> BCC Fe nanowires. The simulations have been carried out at different temperatures in the range 10-1000 K employing a constant strain rate of 1× 10 8 s −1 . The results indicate that at low temperatures (10-375 K), the nanowires yield through the nucleation of a sharp crack and fails in brittle manner. On the other hand, nucleation of multiple 1/2<111> dislocations at yielding followed by significant plastic deformation leading to ductile failure has been observed at high temperatures in the range 450-1000 K. At the intermediate temperature of 400 K, the nanowire yields through nucleation of crack associated with many mobile 1/2<111> and immobile <100> dislocations at the crack tip and fails in ductile manner. The ductile-brittle transition observed in <111> BCC Fe nanowires is appropriately reflected in the stress-strain behavior and plastic strain at failure. The ductile-brittle transition increases with increasing nanowire size. The change in fracture behavior has been discussed in terms of the relative variations in yield and fracture stresses and change in slip behavior with respect to temperature. Further, the dislocation multiplication mechanism assisted by the kink nucleation from the nanowire surface observed at high temperatures has been presented.

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Interface Driven Pseudo‐Elasticity in a‐Fe Nanowires

Yang

Ding

et al. 2015

Adv Funct Materials

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wileyonlinelibrary.comwill specify exactly the conditions under which the formation of nanostructures is reversible after bending the nanowire.Reversibility is typically related to the shape memory effect and pseudo-elasticity in shape memory alloys (SMAs). [5][6][7] The shape recovery is achieved by thermoelastic martensitic phase transformations and domain switching. The driving force for the shape recovery arises from the free energy difference between the martensite and parent phase. This effect is strongly size-dependent and it is not obvious how SMAs operate in thin wires. [ 8,9 ] The fundamental question is whether a different shape memory effect exists at the nanoscale and if so by which mechanism. This is important because many traditional SMAs fail under nanoscale bending and it becomes important to search for alternative functional materials to replace the traditional SMAs for such nanoscale applications. We show by molecular dynamics simulations that α-Fe, which is not a shape memory alloy, also shows shape recovery (or pseudo-elasticity) after bending. Large bending in α-Fe occurs via the formation of interfaces between domains of different orientation and twinning. The deformed nanowire completely recovers under unloading. The mechanism is shown to be very different from the classic pseudo-elasticity, and is related to high-energy interfaces in the nanowire and not the martensite-austenite phase transformation. This result has implications more widely for shape-dependent SMAs that are used in microelectromechanical systems (MEMS) technology. This is also an example of the emerging fi eld of domain boundary engineering where functionality (namely the shape recovery) is linked to domain boundaries and interfaces, but not to bulk properties (such as the martensite-austenite phase transformation). [10][11][12] Previous molecular dynamics (MD) simulations have identifi ed a class of metallic nanowires with both face-centered cubic (fcc) and body-centered cubic (bcc) structures that show pseudo-elasticity and shape memory effects. [13][14][15][16][17][18][19] This pseudoelastic behavior was achieved under uniaxial tension while little is known whether such unique behavior can still exist when a wire is bent. Under tension, the shape recovery relates to the reversibility of conventional twinning. The driving force for the recoverable deformation stems from the minimization of the surface energy. [ 14,15,17,18 ] The total recoverable strain is very large and can exceed 40%. A large inelastic deformation mediated by conventional twinning has been confi rmed experimentally in fcc palladium and bcc tungsten. [ 20,21 ] Here we also show that the shape recovery effect under bending in α -Fe relates to the formation of nonconventional interfaces between domains of different orientations. Unlike conventional <111>/{112}-type Interface Driven Pseudo-Elasticity in α-Fe Nanowires Yang Yang , Suzhi Li , * Xiangdong Ding , * Jun Sun , and Ekhard K. H. Salje * Molecular dynamics simulations of bent [100] α-Fe nanowires...

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Molecular dynamics simulations of compression–tension asymmetry in plasticity of Fe nanopillars

Cited by 85 publications

References 34 publications

Investigation and Mechanical Modelling of Pure Molybdenum at High Strain-Rate and Temperature

Investigation and Mechanical Modelling of Pure Molybdenum at High Strain-Rate and Temperature

Atomistic simulations on ductile-brittle transition in ⟨111⟩ BCC Fe nanowires

Interface Driven Pseudo‐Elasticity in a‐Fe Nanowires

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