Coarse-grained elastodynamics of fast moving dislocations

Journal of Computational Physics

Xiong

et al. 2018

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Progress in the development of coupled atomistic-continuum methods for simulations of critical dynamic material behavior has been hampered by a spurious wave reflection problem at the atomistic-continuum interface. This problem is mainly caused by the difference in material descriptions between the atomistic and continuum models, which results in a mismatch in phonon dispersion relations. In this work, we introduce a new method based on atomistic dynamics of lattice coupled with a concurrent atomistic-continuum method to enable a full phonon representation in the continuum description. This then permits the passage of short-wavelength, high-frequency phonon waves from the atomistic to continuum regions. The benchmark examples presented in this work demonstrate that the new scheme enables the passage of all allowable phonons through the atomistic-continuum interface; it also preserves the wave coherency and energy conservation after phonons transport across multiple atomistic-continuum interfaces. This work is the first step towards developing a concurrent atomistic-continuum simulation tool for non-equilibrium phononmediated thermal transport in materials with microstructural complexity.

Section: The Cac Methods and Wave Reflections At The A-c Interfacementioning

confidence: 99%

Passing waves from atomistic to continuum

Chen

Journal of Computational Physics

Xiong

et al. 2018

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“…For monoatomic face-centred cubic (FCC) crystals, three options are shown in figure 2 with each containing only one atom and having the same volume. They are (a) the Wigner-Seitz cell which is the primitive unit cell widely used in solid-state physics, (b) the rhombohedral shaped unit cell which is the primitive unit cell primarily used in the concurrent atomistic-continuum (CAC) method for modelling of FCC crystals [55][56][57][58][59][60][61][62][63] and the rectangular prism which is the only unit cell for FCC crystals whose faces are mutually orthogonal. Recall that the stress tensor defined by Cauchy is the 'the force per unit area on three given rectangular planes' [19].…”

Section: Numerical Methods For Local Stress Calculationmentioning

confidence: 99%

Asymmetry of the atomic-level stress tensor in homogeneous and inhomogeneous materials

et al. 2018

Proc. R. Soc. A.

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The stress tensor is described as a symmetric tensor in all classical continuum mechanics theories and in most existing statistical mechanics formulations. In this work, we examine the theoretical origins of the symmetry of the stress tensor and identify the assumptions and misinterpretations that lead to its symmetric property. We then make a direct measurement of the stress tensor in molecular dynamics simulations of four different material systems using the physical definition of stress as force per unit area acting on surface elements. Simulation results demonstrate that the stress tensor is asymmetric near dislocation cores, phase boundaries, holes and even in homogeneous material under a shear loading. In addition, the atomic virial stress and Hardy stress formulae are shown to significantly underestimate the stress tensor in regions of stress concentration.

“…The CAC method can be used to complement MD to provide this information. A verification study of the CAC method in modeling fast moving dislocations has been reported 74 . One of our recent works has presented a phonon pulse propagation in crystalline materials with a fast moving dislocation and dislocation array while studying the effect of phonons on dislocation mobility 75 .…”

Section: Phonons Scattering By Moving Dislocationsmentioning

confidence: 99%

Recent progress in the concurrent atomistic-continuum method and its application in phonon transport

Chen

et al. 2017

MRS Communications

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This work presents recent the progress in the development of the Concurrent Atomistic-Continuum (CAC) method for coarse-grained space-and time-resolved atomistic simulations of phonon transport. Application examples, including heat pulses propagating across grain boundaries and phase interfaces, as well as the interactions between phonons and moving dislocations, are provided to demonstrate the capabilities of CAC. The simulation results provide visual evidence and reveal the underlying physics of a variety of phenomena including: phonon focusing, wave interference, dislocation drag, interfacial Kapitza resistance caused by quasi-ballistic phonon transport, etc. A new method to quantify fluxes in transient transport processes is also introduced.