Dislocation emission from a crack under mixed mode loading studied by molecular statics

Gouriet, Karine; Tanguy, D.

doi:10.1080/14786435.2012.657704

Cited by 6 publications

(12 citation statements)

References 17 publications

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“…On the contrary, it was found that at high H concentrations, the stacking would reconstruct and that it would prevent sliding [19]. An additional motivation for the present study, that will be detailed in a forthcoming paper [20], is the evaluation of the effect of sub-surface hydrogen on, in plane, Shockley partial emission at a crack tip loaded in mixed mode I plus II [21]. In this crack-dislocation configuration, the stress intensity factor is simply related to the lowest local maximum of the GSF (the unstable stacking energy g us ), by the relation: k IIe (k I ) = 2mg us (Du z )/(1 − n) .…”

Section: Introductionmentioning

confidence: 86%

“…The corresponding rigid shear is (Du y = b = 1/6 112 ), where b is the Burgers vector of a Shockley partial (Figure 1). As mentioned in the introduction, the GSF is sensitive to transverse stresses which can be high, for example when considering dislocation emission at crack tips [21,23]. This is taken into account by introducing a displacement Du z normal to the glide plane (the z-direction is along [111]).…”

Section: Methods and Computational Setupmentioning

confidence: 99%

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Site stability and pipe diffusion of hydrogen under localised shear in aluminium

Wang

Connétable

Tanguy

2019

Philosophical Magazine

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This paper studies the effect of a plastic shear on the tetrahedral vs. octahedral site stability for hydrogen, in aluminium. Based on Density Functional Theory calculations, it is shown that the tetrahedral site remains the most stable site. It transforms into the octahedral site of the local hexagonal compact structure of the intrinsic stacking fault. The imperfect stacking is slightly attractive with respect to a regular lattice site. It is also shown that the shearing process involves a significant decrease of the energetic barrier for hydrogen jumps, at half the value of the Shockley partial Burgers vector, but not in the intrinsic stacking fault. These jumps involve a displacement component perpendicular to the shearing direction which favours an enhancement of hydrogen diffusion along edge dislocation cores (pipe diffusion). The magnitude of the boost in the jump rate in the direction of the dislocation line, according to Transition State Theory and taking into account the zero point energy correction, is of the order of a factor 50, at room temperature. First Passage Time Analysis is used to evaluate the effect on diffusion which is significant, by only at the nanoscale. Indeed, the common dislocation densities are too small for these effects (trapping, or pipe diffusion) to have a signature at the macroscopic level. The observed drop of the effective diffusion coefficient could therefore be attributed to the production of debris during plastic straining, as proposed in the literature.

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Section: Introductionmentioning

confidence: 86%

Section: Methods and Computational Setupmentioning

confidence: 99%

Site stability and pipe diffusion of hydrogen under localised shear in aluminium

Wang

Connétable

Tanguy

2019

Philosophical Magazine

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“…where μ and ν are the shear modulus and Poisson ratio of the material. Mode I can be taken into account [25,26] provided the proper transverse opening Du z is included in the calculation of g us . Furthermore, including H in the GSF increases the complexity of the calculation because the neighbourhood of the H atom needs to be relaxed, while the GSF is calculated by rigidly sliding two crystal blocks one on top of the other.…”

Section: Simulation and Modelling Detailsmentioning

confidence: 99%

“…A small mode I is superimposed. k IIe (k I , C H ) values are extracted from the stress maps calculated at the atomic scale by a fit to the elastic solutions [26]. They are used as references.…”

Section: Simulation and Modelling Detailsmentioning

confidence: 99%

Effect of sub-surface hydrogen on intrinsic crack tip plasticity in aluminium

Wang

Connétable

Tanguy

2019

Philosophical Magazine

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The effects of sub-surface hydrogen and mixed mode loading on dislocation emission in aluminium are studied using a combination of techniques including crack simulations with an empirical interatomic potential, generalised stacking fault energy (GSF) calculations, with empirical interactions and Density Functional Theory, and the model by Rice which links the critical stress intensity factor to the unstable stacking energy. The crack orientation is {1 1 1}〈1 1 2〉 and the loading is composed of a moderate traction along 〈1 1 1〉 and a shear along 〈1 1 2〉, such that Shockley partials are emitted along the crack plane. The role of the relaxations around the H atoms and of the concentration of H in the glide plane, in the GSF calculation, is revealed by comparing Rice's model to the results of brute force simulations. The enhanced GSF is then calculated ab initio. The conclusion is a large decrease of the critical load to emit a dislocation, due to the displacement transverse to the glide direction. The effect of sub-surface hydrogen is negligible with respect to the mechanical one.

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“…Evidently, a comprehensive understanding of these processes must involve some degree of atomistic modeling (for example, Refs. [22][23][24] yielded important results pertaining to embryonic dislocation loop emission and crack blunting), last but not least to reconcile continuum models with results of atomistic modeling. Nevertheless, atomistic modeling necessitates an underlying interatomic potential that reproduces the necessary material parameters, dislocation cores, fracture properties, etc., accurately.…”

Section: Introductionmentioning

confidence: 97%

Ductile and brittle crack-tip response in equimolar refractory high-entropy alloys

Irving

et al. 2020

Acta Materialia

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Understanding the strengthening and deformation mechanisms in refractory high-entropy alloys (HEAs), proposed as new high-temperature material, is required for improving their typically insufficient room-temperature ductility. Here, density-functional theory simulations and a continuum mechanics analysis were conducted to systematically investigate the competition between cleavage decohesion and dislocation emission from a crack tip in the body-centered cubic refractory HEAs HfNbTiZr, MoNbTaVW, MoNbTaW, MoNbTiV, and NbTiVZr. This crack-tip competition is evaluated for tensile loading and a totality of 15 crack configurations and slip systems. Our results predict that dislocation plasticity at the crack tip is generally unfavorable -although the competition is close for some crack orientations, suggesting intrinsic brittleness and low crack-tip fracture toughness in these five HEAs at zero temperature. Fluctuations in local alloy composition, investigated for HfNbTiZr, can locally reduce the resistance to dislocation emission for a slip system relative to the configuration average of that slip system, but do not change the dominant cracktip response. In the case of single-crystal MoNbTaW, where an experimental, room-temperature fracture-toughness value is available for a crack on a {100} plane, theoretical and experimental results agree favorably. Factors that may limit the agreement are discussed. We survey the effect of material anisotropy on preferred crack tip orientations, which are found to be alloy specific. Mixedmode loadings are found to shift the competition in favor of cleavage or dislocation nucleation, depending on crack configuration and amplified by the effect of material anisotropy on crack tip stresses.

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Dislocation emission from a crack under mixed mode loading studied by molecular statics

Cited by 6 publications

References 17 publications

Site stability and pipe diffusion of hydrogen under localised shear in aluminium

Site stability and pipe diffusion of hydrogen under localised shear in aluminium

Effect of sub-surface hydrogen on intrinsic crack tip plasticity in aluminium

Ductile and brittle crack-tip response in equimolar refractory high-entropy alloys

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