Nanoscale Modeling of Shock-Induced Deformation of Diamond
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AA7.7.1
Nanoscale Modeling of Shock-Induced Deformation of Diamond S. V. Zybin1, I. I. Oleinik2, M. L. Elert3, C. T. White4 1
The George Washington University, Washington D.C. 20052 University of South Florida, Tampa, FL 33620 3 U.S. Naval Academy, Annapolis, MD, 21402 4 Naval Research Laboratory, Washington D.C. 20375 2
ABSTRACT Molecular dynamics (MD) simulations of shock-induced deformations in diamond were performed using a reactive bond order (REBO) potential. A splitting of shock wave structure into elastic and crystal deformation fronts was observed in the [110] and [111] crystallographic directions above piston velocity thresholds of up ≈ 1.8 and 2.5 km/s, respectively. The crystal lattice response in a split two-wave regime consists of the relative movement of {111} planes in the diamond crystal and has different structural character for [110] and [111] shock waves. The strain produced by a [110] shock wave occurs only along one of the transverse crystalline directions, whereas in the [111] case crystal deformation involves the movement of the atoms in both transverse directions. To gain insight into the atomistic mechanisms of orientational dependence of shock compression of crystals, we have investigated in detail the constitutive stress-strain relationships under static uniaxial compression. The REBO potential gives a reasonably good description of stresses and energetics under moderate uniaxial compressions corresponding to an elastic shock wave regime. However, under compressions higher than 10% ([110] case) and 20% ([111] case) the REBO potential shows deficiencies in the quantitative description of stress response that might affect the MD picture of shock wave deformations in diamond. INTRODUCTION Microscopic study of the orientational dependence of shock-induced transformations of crystal lattices and splitting of shock wave fronts in solids is of paramount importance for understanding materials response under shock compression at the nanoscale. Such structural transformations are dependent on the crystallographic orientation of shock wave propagation as well as the details of interatomic interactions that govern the energetics and dynamics of the underlying atomic scale processes. To elucidate the internal structure of shock-compressed crystals and to develop robust constitutive models, a better understanding of atomic scale mechanisms is highly desirable. Molecular dynamics (MD) simulations of shock waves in solids at the atomistic level have been successfully applied to study plastic deformations [1-3], melting [4,5], amorphization [6], and shock wave splitting due to phase transitions [7,8]. The interatomic potentials are at the heart of MD simulations and their ability to describe quantitatively the fundamental physics and chemistry at the atomic scale is the key to achieving reliable and meaningful results. Simple Lennard-Jones (LJ) pairwise interatomic potentials have already revealed complex mechanisms of shock-induced lattice transformation, such as emission of stacking fault arrays and
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