A molecular dynamics study of dislocation density generation and plastic relaxation during shock of single crystal Cu

Sichani, Mehrdad M.; Spearot, Douglas E.

doi:10.1063/1.4959075

Cited by 37 publications

(11 citation statements)

References 42 publications

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“…It is also possible that the repulsive stress of dislocation‐dislocation interactions begins to saturate and balance the stress from the shock wave. It is worth noting that similar results have been observed in molecular dynamics simulations of dislocation development during the shock of copper single crystals (Sichani & Spearot, 2016). Copper crystals shocked parallel to {100} and {110} illustrate a large increase in dislocation density between 20 and 40 GPa shock pressure.…”

Section: Discussionsupporting

confidence: 81%

Dislocation Generation in Experimentally Shocked Olivine Crystals

et al. 2022

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During shock metamorphism, crystals in planetary bodies are exposed to extreme conditions of stress, pressure, and temperature, resulting in the development of a range of shock‐induced defects, including dislocations. To investigate the shock‐induced development of dislocations in olivine, one of the most common minerals found in meteorites and other planetary samples, a series of shock experiments were carried out on olivine single crystals. Olivine crystals were shocked to peak reverberation pressures ranging from 21.3 to 58.7 GPa in a flat‐plate accelerator. The crystals were characterized using electron backscatter diffraction (EBSD), Raman spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, and electron microprobe. EBSD analyses reveal that geometrically necessary dislocations form on all common slip systems. Raman spectroscopy reveals that the full width at half height of characteristic peaks increases linearly as a function of shock pressure. Dislocation loops with the Burgers vector b = [001] have higher densities near fractures as revealed by TEM analyses, whereas dislocations away from fractures are more dependent on the crystal orientation relative to impact direction. The type and density of dislocations that form during shock are largely independent of the starting hydrogen content of crystals. Calculations that incorporate post‐shock cooling rates of meteorites ejected from planetary surfaces, dislocation annihilation rates in olivine, and dislocation densities measured in shocked olivine suggest that shock‐induced dislocations are preserved in olivine in meteorites ejected from planetary bodies and therefore give insight into the conditions of ancient impact events in the solar system.

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Section: Discussionsupporting

confidence: 81%

Dislocation Generation in Experimentally Shocked Olivine Crystals

et al. 2022

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“…The most naive approach to calculating the dislocation density would be to compute the total length of dislocation lines in a simulation box and divide by the box Accepted in Computational Materials Science [8] volume. This method was previously adapted in MD simulations [25] but a significant drawback of this approach is that one can only obtain a single value evolving with time, assuming the dislocation structure is homogeneous throughout the specimens. All local features are hence lost in the conversion process.…”

Section: Discrete To Continuum (D2c)mentioning

confidence: 99%

“…On the other hand, dislocation-based continuum models of plasticity are not restricted to the particular details of each dislocation, as they describe dislocations as continuous fields on different slip planes with some physical rules from length scales below the averaging volume size. In most cases, the way the continuum is related to the atomic scale is by transforming individual dislocations from the MD simulations into a total dislocation density field [9,25].…”

Section: Introductionmentioning

confidence: 99%

Shear relaxation behind the shock front in 110 molybdenum – From the atomic scale to continuous dislocation fields

Kositski

Steinberger

Sandfeld

et al. 2018

Computational Materials Science

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In this work we study shock-induced plasticity in Mo single crystals, impacted along the <110> crystal orientation. In particular, the shear relaxation behind the shock front is quantitatively inspected. Molecular dynamics (MD) simulations are employed to simulate the deformation during shock, followed by post-processing to identify and quantify the dislocation lines nucleated behind the shock front. The information on the dislocation lines is ensemble averaged inside slabs of the simulation box and over different realizations of the MD simulations, from which continuous dislocation fields are extracted using the Discrete-to-Continuous method. The continuous dislocation fields are correlated with the stress and strain fields obtained from the MD simulations. Based on this analysis, we show that the elastic precursor overshoots the shear stress, after which dislocations on a specific group of slip planes are nucleated, slightly lagging behind the elastic front. Consequently, the resolved shear stress is relaxed, but the principal lateral stress increases. The latter leads to an increase in the resolved shear stress on a plane parallel to the shock wave, resulting in an additional retarded front of dislocation nucleation on planes parallel to the shock front. Finally, the twostage process of plasticity results in an isotropic stress state in the plane parallel to the shock wave. The MD simulation results are employed to calculate the dislocation densities on specific slip planes and the plastic deformation behind the shock, bridging the gap between the information on the atomic scale and the continuum level.

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“…Complex phenomena can also arise; for example, a void can lead to highpressure phase transformation [4], and the barrierless melt nucleation will arise for some energetic nitramine [5]. However, numerous molecular dynamics (MD) simulations have demonstrated that the dislocation density will go up with the increase of impact pressure, while the nucleation and motion of dislocations still dominate the plastic deformation of the material under the high strain rate condition [6][7][8][9]. For example, when the strain rate is below 2.77 × 10 8 /s −1 and temperature is over 50 K, the plasticity is dislocation-mediated in the body-centered-cubic (BCC) metal tantalum [10].…”

Section: Introductionmentioning

confidence: 99%

Elastodynamics Field of Non-Uniformly Moving Dislocation: From 3D to 2D

Luo

Cui

2022

Crystals

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Molecular dynamics (MD) and experiments indicate that the high-speed dislocations dominate the plasticity properties of crystal materials under high strain rate. New physical features arise accompanied with the increase in dislocation speed, such as the “Lorentz contraction” effect of moving screw dislocation, anomalous nucleation, and annihilation in dislocation interaction. The static description of the dislocation is no longer applicable. The elastodynamics fields of non-uniformly moving dislocation are significantly temporal and spatially coupled. The corresponding mathematical formulas of the stress fields of three-dimensional (3D) and two-dimensional (2D) dislocations look quite different. To clarify these differences, we disclose the physical origin of their connections, which is inherently associated with different temporal and spatial decoupling strategies through the 2D and 3D elastodynamics Green tensor. In this work, the fundamental relationship between 2D and 3D dislocation elastodynamics is established, which has enlightening significance for establishing general high-speed dislocation theory, developing a numerical calculation method based on dislocation elastodynamics, and revealing more influences of dislocation on the macroscopic properties of materials.

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A molecular dynamics study of dislocation density generation and plastic relaxation during shock of single crystal Cu

Cited by 37 publications

References 42 publications

Dislocation Generation in Experimentally Shocked Olivine Crystals

Dislocation Generation in Experimentally Shocked Olivine Crystals

Shear relaxation behind the shock front in 110 molybdenum – From the atomic scale to continuous dislocation fields

Elastodynamics Field of Non-Uniformly Moving Dislocation: From 3D to 2D

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