Atomistic modeling of fracture

Andric, P; Curtin, W A

doi:10.1088/1361-651x/aae40c

Cited by 66 publications

(46 citation statements)

References 84 publications

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“…From this uniaxial strain loading one can derive a traction-separation law for continuum fracture simulations under mode I loding and plane strain conditions. In this case, a triaxial stress state is expected at the crack tip, which corresponds well to the stress occuring in the ab initio tensile test without lateral contraction [ 17 , 22 , 23 ].…”

Section: Methodssupporting

confidence: 55%

Hydrogen Embrittlement at Cleavage Planes and Grain Boundaries in Bcc Iron—Revisiting the First-Principles Cohesive Zone Model

et al. 2020

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Hydrogen embrittlement, which severely affects structural materials such as steel, comprises several mechanisms at the atomic level. One of them is hydrogen enhanced decohesion (HEDE), the phenomenon of H accumulation between cleavage planes, where it reduces the interplanar cohesion. Grain boundaries are expected to play a significant role for HEDE, since they act as trapping sites for hydrogen. To elucidate this mechanism, we present the results of first-principles studies of the H effect on the cohesive strength of α-Fe single crystal (001) and (111) cleavage planes, as well as on the Σ5(310)[001] and Σ3(112)[11¯0] symmetrical tilt grain boundaries. The calculated results show that, within the studied range of concentrations, the single crystal cleavage planes are much more sensitive to a change in H concentration than the grain boundaries. Since there are two main types of procedures to perform ab initio tensile tests, different in whether or not to allow the relaxation of atomic positions, which can affect the quantitative and qualitative results, these methods are revisited to determine their effect on the predicted cohesive strength of segregated interfaces.

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Section: Methodssupporting

confidence: 55%

Hydrogen Embrittlement at Cleavage Planes and Grain Boundaries in Bcc Iron—Revisiting the First-Principles Cohesive Zone Model

et al. 2020

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“…Creation of traction free atomically sharp cracks can be somehow problematic when dealing with atomic systems because of the longrange interaction between atoms. A detailed discussion of crack modeling is out of the scope of the current work, but these problems and possible solutions are addressed by Andric et al [13].…”

Section: Molecular Statistics Simulations Geometries and Mechanicalmentioning

confidence: 99%

“…The cohesive force to separate the bonds was then supposed to be dependent on interatomic force-displacement relationships, i.e., interatomic potential, and later associated with the surface energy per unit area. However, it has been only recently that those concepts have been addressed systematically, due to important advancements of in-situ observation of mechanical behavior at small scales [2][3][4][5][6][7][8][9][10][11] and developments of computational techniques such as molecular dynamics supported by improvement in computational power [12][13][14]. Sumigawa et al.…”

Section: Introductionmentioning

confidence: 99%

Strain energy density approach for brittle fracture from nano to macroscale and breakdown of continuum theory

Gallo

Hagiwara

Shimada

et al. 2019

Theoretical and Applied Fracture Mechanics

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In contrast to the great success at the macroscale, fracture mechanics theory fails to describe the fracture at a critical size of several nanometers due to the emerging effect of atomic discreteness with decreasing material size. Here, we propose a novel formulation for brittle fracture, from macro-to even atomic scales, based on extended strain energy density, and give an insight into the breakdown of continuum theory. Numerical experiments based on molecular statistics (MS) simulations are conducted on single-edge cracked samples made of silicon while varying the size until few nanometers, and loaded under mode I. The strain energy density is then defined as a function of the interatomic potential and averaged over the fracture process zone. Finally, by using an attenuation function, the atomic strain energy density gradient is homogenized to allow a comparison between the continuum and discrete formulation. Results show that the fracture process zone is scale independent, confirming that the ideal brittle fracture is ultimately governed by atomic bond-breaking. A singular stress field according to continuum fracture mechanics is still also present. However, when the singular stress field length (distance from the crack tip at which the stress deviates 5% from the theoretical field of r 0.5) is in the range of 4-5 times the fracture process zone, continuum fracture mechanics fails to describe the fracture, i.e., the breakdown of continuum theory. The new formulation, instead, goes well beyond that limit.

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“…10 comprised a block of height and length ≈ 15 nm, i.e. consistent with the threshold system size suggested by Andric and Curtin (2019). The crack with a crack plane (110) and crack front direction [1 a 10] was generated by removing 6 half-planes 2 of atoms and subjecting the system to mode-I tensile loading.…”

mentioning

confidence: 60%

Hydrogen induced fast-fracture

Shishvan

Csänyi

Deshpande

2020

Journal of the Mechanics and Physics of Solids

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One of the recurring anomalies in the hydrogen induced fracture of high strength steels is the apparent disconnect between their toughness and uniaxial tensile strength in identical hydrogen environments. Here we propose, supported by detailed atomistic and continuum calculations, that unlike macroscopic toughness, hydrogen-mediated tensile failure is a result of a fastfracture mechanism. Specifically, we show that failure originates from the fast propagation of cleavage cracks that initiate from cavities that form around inclusions such as carbide particles. The failure process occurs in two stages. In stage-A, hydrides rapidly form around the roots of stressed notches on the cavity surfaces with hydrogen fed from the hydrogen gas within the cavity. These hydrides promote cleavage fracture with the cracks propagating at > 100 ms '( until the hydrogen gas in the cavity is exhausted. Predictions of this hydrogen-assisted crack growth mechanism are supported by atomistic calculations of binding energies, mobility barriers and molecular dynamics calculations of the fracture process. Typically, cracks grow by less than 1 µm via this hydrogen-assisted mechanism and thus insufficient to cause macroscopic fracture of the specimen. However, this stage is then followed by a stage-B process where these fast propagating cracks can continue to grow, now in the absence of hydrogen supply, given an appropriate level of remote tensile stress. This is surprising because the fracture energy is now that of Fe in the absence of H and cleavage fracture requires opening tractions on the order of 15 GPa to be generated. Thus, fracture is usually precluded due to plasticity around the crack-tip. Here we show via macroscopic continuum crack growth calculations in a rate dependent elastic-plastic solid with fracture modelled using a cohesive zone that cleavage is possible if the crack propagates fast enough. This is because strain-rates at the tips of fast propagating cracks are sufficiently high for the drag on the motion of dislocations resulting from phonon scattering to limit plasticity. This combined atomistic/continuum model is used to explain a host of well-established experimental observations including (but not limited to): (i) insensitivity of the strength to the concentration of trapped hydrogen; (ii) the extensive microcracking in addition to the final cleavage fracture event and (iii) the higher susceptibility of high strength steels to hydrogen embrittlement. Importantly, we also show that the stage-A hydrogen-assisted fracture process only occurs in certain crystallographic orientations with crack-tip plasticity processes, such as twinning, blunting cracks in other orientations. This inhibits the fast-fracture mechanism in a macroscopic toughness on a polycrystalline material and thus explains the apparent contradiction between the hydrogen-assisted macroscopic toughness and tensile strength of steels.

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Atomistic modeling of fracture

Cited by 66 publications

References 84 publications

Hydrogen Embrittlement at Cleavage Planes and Grain Boundaries in Bcc Iron—Revisiting the First-Principles Cohesive Zone Model

Hydrogen Embrittlement at Cleavage Planes and Grain Boundaries in Bcc Iron—Revisiting the First-Principles Cohesive Zone Model

Strain energy density approach for brittle fracture from nano to macroscale and breakdown of continuum theory

Hydrogen induced fast-fracture

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