Dislocation Core Structure at Finite Temperature Inferred by Molecular Dynamics Simulations for 1,3,5-Triamino-2,4,6-trinitrobenzene Single Crystal

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. ABSTRACT: The dislocation core structures and elastic properties of the insensitive energetic molecular crystal 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) are investigated as a function of pressure and temperature. A new method is proposed to compute the generalized stacking fault surfaces (noted γ-surfaces) and the complete second-order elastic tensor at finite temperature through molecular dynamics (MD) simulations. The energy landscapes in the two glide planes are shown to be similar between 0 and 300 K, thus leading to almost no modification on the dislocation evolution. A spreading of the dislocation cores over a hundred Burgers vectors is observed along the [100] and [010] directions for the edge and screw dislocations at 0 and 300 K, showing that dislocations should exhibit a very low friction for these glide systems at ambient pressure. For pressures varying between 0 and 10 GPa, the γ-surfaces' energy barriers that drive the width of partial dislocations follow the increase of shear elastic constants within the considered glide planes, thus limiting the changes of the dislocation core structure.

Strongly Anisotropic Thermomechanical Response to Shock Wave Loading in Oriented Samples of the Triclinic Molecular Crystal 1,3,5-Triamino-2,4,6-Trinitrobenzene (TATB)

“…Finally, compression behind the shock significantly increases barriers to homogeneous dislocation nucleation and glide. 24,25 These factors, combined with dynamic structural imperfections-whether relatively long lived (e.g., sliding defects) or induced transiently behind the shock-all tend to hinder or disrupt smooth dislocation glide. Several of these factors are present in flexible molecules but not rigid ones, or are likely behind explicit shock waves but not (or less so) for homogeneous, isothermal deformations.…”

“…21 A monoclinic polymorph, also layered, has been reported recently at room temperature for pressures greater than 4 GPa. 22 The high degree of structural anisotropy leads to significant anisotropy in the mechanical, [23][24][25][26][27][28][29][30][31][32][33][34] thermal, [35][36][37][38][39][40][41][42][43][44][45][46][47] and spectroscopic 21 properties of the substance. See Figure 1 for a view of a TATB crystal and additional information pertinent to the shock simulation geometry and crystal orientations studied here (detailed below).…”

“…Atomic-based studies of the non-shock mechanical response of TATB have also been reported. 22,[24][25][26]28,29,[67][68][69] Because of the nature of the crystal packing, plasticity involving slip between basal planes in TATB (the crystal exhibits two inequivalent basal planes) is expected to occur with much lower barriers to dislocation glide (i.e., stacking-fault energies), 70 in a fashion somewhat analogous to that in graphite, 71 compared to slip that occurs within a given molecular layer or that involves dislocation glide across multiple basal planes (both of which involve disrupting the intermolecular hydrogen-bonding network that exists within the layers). Indeed, using MD, very low stacking fault energies, and thus easy dislocation glide, were predicted for slip between adjacent basal planes both at zero kelvin 24 and at finite temperature.…”

“…Indeed, using MD, very low stacking fault energies, and thus easy dislocation glide, were predicted for slip between adjacent basal planes both at zero kelvin 24 and at finite temperature. 25 In a study that is particularly relevant to the present one, Lafourcade et al 29 used all-atom but rigid-molecule MD in conjunction with the reaction field 72 -74 approximation for electrostatic interactions to characterize plastic deformation mechanisms and energetics in crystalline TATB for a variety of different strain-and strain-rate loading paths. Of particular note is that Lafourcade et al provided a molecular-based definition of the deformation-gradient tensor, which enables imposition of a generalized prescribed strain, and constant strain rate, in the simulations.…”

Strongly Anisotropic Thermomechanical Response to Shock Wave Loading in Oriented Samples of the Triclinic Molecular Crystal 1,3,5-Triamino-2,4,6-Trinitrobenzene (TATB)

“…Atomic-based studies of the non-shock mechanical response of TATB have also been reported. 22,[24][25][26]28,29,[67][68][69] Because of the nature of the crystal packing, plasticity involving slip between basal planes in TATB (the crystal exhibits two inequivalent basal planes) is expected to occur with much 8 lower barriers to dislocation glide (i.e., stacking-fault energies), 70 in a fashion somewhat analogous to that in graphite, 71 compared to slip that occurs within a given molecular layer or that involves dislocation glide across multiple basal planes (both of which involve disrupting the intermolecular hydrogen-bonding network that exists within the layers). Indeed, using MD, very low stacking fault energies, and thus easy dislocation glide, were predicted for slip between adjacent basal planes both at zero kelvin 24 and at finite temperature.…”