Micro-scale fatigue mechanisms in metals: Insights gained from small-scale experiments and discrete dislocation dynamics simulations

Lavenstein, Steven; El‐Awady, Jaafar A.

doi:10.1016/j.cossms.2019.07.004

Cited by 40 publications

(17 citation statements)

References 168 publications

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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%

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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Section: Conclusion and Final Remarksmentioning

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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“…Even small stresses below the technical yield point can cause dislocation glide. This results in dislocation intersections, source activation and other irreversible mechanisms [5][6][7]. The summation of those small irreversible deformations leads to fatigue failure.…”

Section: Introductionmentioning

confidence: 99%

A new method for microscale cyclic crack growth characterization from notched microcantilevers and application to single crystalline tungsten and a metallic glass

Gabel

Merle

Bitzek

et al. 2022

Journal of Materials Research

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The lifetime of most metals is limited by cyclic loads, ending in fatigue failure. The progressive growth of cracks ends up in catastrophic failure. An advanced method is presented for the determination of cyclic crack growth on the microscale using a nanoindenter, which allows the characterization of > 10,000 loading cycles. It uses focused ion beam fabricated notched microcantilevers. The method has been validated by cyclic bending metallic glass and tungsten microcantilevers. The experiments reveal a stable crack growth during the lifetime of both samples. The metallic glass shows less plasticity due to the absence of dislocations, but shows shearing caused by the deformation. The crack growth rates determined in the tests follow Paris’ power law relationship. The results are reliable, reproducible and comparable with macroscopic setups. Due to the flexibility of the method, it is suitable for the characterization of specific microstructural features, like single phases, grain boundaries or different grain orientations. Graphical abstract

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“…It is recognized that the strength of micro/submicron crystals depends not only on the material itself but also the sample/grain size. Many efforts have been made to study the size effects of crystal materials at the micro/submicron scale in order to improve material performance for highquality products [8][9][10][11]. The size effect is induced by many physical mechanisms, such as dislocation motion, nucleation, and starvation [12,13].…”

Section: Introductionmentioning

confidence: 99%

“…Computational simulation methodologies have been continuously developed to predict material deformation behaviors. According to the difference in simulation scale, the main simulation methods can be broadly classified into the finite element method (FEM) [14,15], crystal plasticity finite element methods (CPFEMs) [16,17], discrete dislocation dynamics (DDD) [8,18,19], and molecular dynamics (MD) [20]. Based on empirical constitutive equations, the FEM shows a great advantage in dealing with various complex boundary problems at the macroscale.…”

Section: Introductionmentioning

confidence: 99%

Development of the Concurrent Multiscale Discrete-Continuum Model and Its Application in Plasticity Size Effect

2022

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A concurrent multiscale model coupling discrete dislocation dynamics to the finite element method is developed to investigate the plastic mechanism of materials at micron/submicron length scales. In this model, the plastic strain is computed in discrete dislocation dynamics (DDD) and transferred to the finite element method (FEM) to participate in the constitutive law calculation, while the FEM solves the complex boundary problem for DDD simulation. The implementation of the whole coupling scheme takes advantage of user subroutines in the software ABAQUS. The data structures used for information transferring are introduced in detail. Moreover, a FE mesh-based regularization method is proposed to localize the discrete plastic strain to continuum material points. Uniaxial compression tests of single crystal micropillars are performed to validate the developed model. The results indicate the apparent dependence of yield stress on sample size, and its underlying mechanisms are also analyzed.

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Micro-scale fatigue mechanisms in metals: Insights gained from small-scale experiments and discrete dislocation dynamics simulations

Cited by 40 publications

References 168 publications

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

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

A new method for microscale cyclic crack growth characterization from notched microcantilevers and application to single crystalline tungsten and a metallic glass

Development of the Concurrent Multiscale Discrete-Continuum Model and Its Application in Plasticity Size Effect

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