Discrete dislocation plasticity HELPs understand hydrogen effects in bcc materials

Yu, Haiyang; Cocks, A.C.F.; Tarleton, Edmund

doi:10.1016/j.jmps.2018.08.020

Cited by 60 publications

(36 citation statements)

References 70 publications

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“…This includes studies of solute strengthening (see for instance [24,46]) where the Kanzaki force model of the dislocation core may be employed alongside the Kanzaki force model of the solute in the matrix to model their respective interactions more accurately. The same core Kanzaki forces may also improve diffusion models of atomic species such as hydrogen about the dislocation core via the additional hydrostatic pressure field [47,80,81]. Other applications in this area would include the study of dislocation-precipitate interactions in the near field [45].…”

Section: Discussionmentioning

confidence: 99%

Elastic models of dislocations based on atomistic Kanzaki forces

Gurrutxaga-Lerma

Verschueren

2018

Phys. Rev. B

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This paper studies the relationship between the atomistic representation of crystalline dislocations as Kanzaki forces and the continuum representation of dislocations as Burridge-Knopoff (BK) force distributions. We first derive a complete theory of the BK force representation of dislocations in an anisotropic linear elastic continuum, showcasing a number of fundamental features found when dislocations are represented as distributions of body forces in defect-free continuum media. We then build, within the harmonic approximation, the Kanzaki force representation of dislocations in atomistic lattice models. We rigorously show that in the long-wave limit, the Kanzaki force representation converges to the continuum BK representation. We therefore justify employing the Kanzaki forces as source terms in continuum theories of dislocations. We do this by establishing a methodology to compute the Kanzaki forces of dislocations via the force constant matrix of the material's perfect lattice. We use it to study a model of a screw dislocation in bcc tungsten, where we show the existence of two distinct Kanzaki force terms: the slip Kanzaki forces, which we show directly correspond with the BK forces implied by a Volterra dislocation; and the core Kanzaki forces, which are computed from the relaxed dislocation structure, and serve to model all core effects not captured by the Volterra dislocation. We build a multipolar field expansion of both the core and the slip Kanzaki forces, showing that the dislocation core is agreeable to correction via the multipolar field expansion of the core Kanzaki forces.

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Section: Discussionmentioning

confidence: 99%

Elastic models of dislocations based on atomistic Kanzaki forces

Gurrutxaga-Lerma

Verschueren

2018

Phys. Rev. B

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“…Hydrogen influences dislocation plasticity by exerting elastic shielding, core force shielding and modifying the dislocation mobility. Long-range hydrogen elastic shielding and a hydrogen dependent mobility law were implemented by Yu et al (2019a). However, the model was not able to capture the effect of hydrogen on dislocation junction formation, due to the short-range and quasi static nature of the process.…”

Section: Ddd Simulation With Hydrogen Core Forcementioning

confidence: 99%

Influence of hydrogen core force shielding on dislocation junctions in iron

Katzarov

Paxton

et al. 2020

Phys. Rev. Materials

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The influence of hydrogen on dislocation junctions was analysed by incorporating a hydrogen dependent core force into nodal based discrete dislocation dynamics. Hydrogen reduces the core energy of dislocations, which reduces the magnitude of the dislocation core force. We refer to this as hydrogen core force shielding, as it is analogous to hydrogen elastic shielding but occurs at much lower hydrogen concentrations. The dislocation core energy change due to hydrogen was calibrated at the atomic scale accounting for the nonlinear inter-atomic interactions at the dislocation core, giving the model a sound physical basis. Hydrogen was found to strengthen binary junctions and promote the nucleation of dislocations from triple junctions. Simulations of microcantilever bend tests with hydrogen core force shielding showed an increase in the junction density and subsequent hardening. These simulations were performed at a small hydrogen concentration realistic for bcc iron.

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“…This method expands on a previous three-dimensional model for solutes in an infinite medium with dislocation fields only (Gu and El-Awady 2018). The developed model can be incorporated into two-dimensional or three-dimensional discrete dislocation dynamics simulations (Gu and El-Awady 2018;Yu et al 2019a;Yu et al 2019b;El-Awady et al 2016;Lavenstein and El-Awady 2019), continuum dislocation dynamics simulations (Zhu and Xiang 2015), or crystal plasticity simulations (Castelluccio and McDowell 2017;Castelluccio et al 2018). For instance, in the crystal plasticity model developed by Castelluccio et al (2018), the flow rule can be improved by introducing a weighted average of edge and screw dislocation densities since the solute effects are dependent on the dislocation character.…”

Section: Conclusion and Final Remarksmentioning

confidence: 99%

“…Cai et al (2014) and developed a three-dimensional (3D) formulation for the solute-induced stresses in an infinite medium to quantify the effect of hydrogen on dislocation dynamics in 3D (Gu and El-Awady 2018). This was then extended by Yu et al to a finite boundary value problem via the superposition principle (Yu et al 2019a), which enabled the study of the influence of H on junction formation (Yu et al 2019;Yu et al 2019b).…”

Section: Introductionmentioning

confidence: 99%

Theoretical framework for predicting solute concentrations and solute-induced stresses in finite volumes with arbitrary elastic fields

El‐Awady

2020

Mater Theory

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A theoretical model for computing the interstitial solute concentration and the interstitial solute-induced stress field in a three-dimensional finite medium with any arbitrary elastic fields was developed. This model can be directly incorporated into two-dimensional or three-dimensional discrete dislocation dynamics simulations, continuum dislocation dynamics simulations, or crystal plasticity simulations. Using this model, it is shown that a nano-hydride can form in the tensile region below a dissociated edge dislocation at hydrogen concentration as low as χ 0 = 5 × 10 −5 , and its formation induces a localized hydrogen elastic shielding effect that leads to a lower stacking fault width for the edge dislocation. Additionally, the model also predicts the segregation of hydrogen at 109(13 7 0)/33.4 • symmetric tilt grain boundary dislocations. This segregation strongly alters the magnitude of the shear stresses at the grain boundary, which can subsequently alter dislocation-grain boundary interactions and dislocation slip transmissions across the grain boundary. Moreover, the model also predicts that the hydrogen concentration at a mode-I central crack tip increases with increasing external loading, higher intrinsic hydrogen concentration, and/or larger crack lengths. Finally, linearized approximate closed-form solutions for the solute concentration and the interstitial solute-induced stress field were also developed. These approximate solutions can effectively reduce the computation cost to assess the concentration and stress field in the presence of solutes. These approximate solutions are also shown to be a good approximation when the positions of interest are several nanometers away (i.e. long-ranged elastic interactions) from stress singularities (e.g. dislocation core and crack tip), for low solute concentrations, and/or at high temperatures.

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Discrete dislocation plasticity HELPs understand hydrogen effects in bcc materials

Cited by 60 publications

References 70 publications

Elastic models of dislocations based on atomistic Kanzaki forces

Elastic models of dislocations based on atomistic Kanzaki forces

Influence of hydrogen core force shielding on dislocation junctions in iron

Theoretical framework for predicting solute concentrations and solute-induced stresses in finite volumes with arbitrary elastic fields

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