Accelerating dislocations to transonic and supersonic speeds in anisotropic metals

Abstract

The dynamics of stress-accelerated dislocations in copper is investigated using molecular dynamics simulations. The structure and motion of dissociated edge dislocations are analyzed using the common neighborhood parameter and local stresses. Dislocations are accelerated by high shear stresses and reach stable velocities in the two transonic regimes. Supersonic dislocations are generated but are transient, as they require high stresses, which trigger nucleation of multiple dislocation dipoles. A velocity plateau in the first transonic regime indicates a radiation-free state in agreement with theoretical predictions.

Dynamic Discrete Dislocation Plasticity

“…As far as the authors know, experimental evidence of dislocations moving above the transverse speed barrier is still lacking, other than for two-dimensional plasma crystals (Nosenko, Zhdanov, & Morfill, 2007). However, since 1999 a great number of MD simulations have shown transonic dislocations for a wide number of materials (Li & Shi, 2002;Marian & Caro, 2006;Olmsted, Hector, Curtin, & Clifton, 2005;Tsuzuki, Branicio, & Rino, 2008).…”

Simulations of copper single crystals subjected to rapid shear

“…We will use a simple fit to the data of Tsuzuki et al for edge dislocation velocities in Mishin Cu. 26 However, we may consider these steady state dislocation mobilities to be inappropriate for the study of a highly dynamic process, especially considering that previous studies have shown dislocations can take over 10 ps to reach these steady state velocities; a time comparable to our dynamic studies. 23 Therefore, in addition to fits to the steady state data, we also determine dislocation velocities from a dynamic simulation.…”

“…Previous MD simulations of plastic flow have largely concentrated either on shock compression [18][19][20][21] or on the steady state properties of plasticity; typically then being run at constant temperature and shear stress. [22][23][24][25][26][27][28][29] Although this has produced a wealth of information used to inform multi-scale modeling 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 approaches, it has left the field of plastic heating during high strain rate ramped compression (relevant to quasi-isentropic compression) largely unexplored.…”

Equation of motion and subsonic-transonic transitions of rectilinear edge dislocations: A collective-variable approach

“…Another immediate perspective consists in extending the present EoM to anisotropic elasticity, 33 to exploit the wealth of available simulation data on anisotropic materials. 5,6,8,69 .…”

“…In the last decade, high-velocity dislocation motion in crystals has been the subject of many two-dimensional (2D) studies by molecular dynamics, [1][2][3][4][5][6][7][8][9] or via direct measurements in a plasma crystal slab. 11,12 From these studies, a wealth of data has been collected, either in the form of time-velocity curves, 5 or of terminal velocity-versus-applied stress plots.…”