Irreversible Deformation Mechanisms for 1,3,5-Triamino-2,4,6-Trinitrobenzene Single Crystal through Molecular Dynamics Simulations

Abstract

The plastic behavior of the insensitive energetic molecular crystal 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is investigated through molecular dynamics simulations.A recent method, built to follow any prescribed deformation path, is used to apply directional shear and compressive deformations to a TATB single crystal, leading to the tridimensional characterization of its nucleation von Mises stresses σ v (θ, φ), where θ and φ are the two angles (latitude and longitude, respectively) that define the loading direction. Furthermore, the local computation of the deformation gradient tensor helps to identify the mechanisms of the irreversible deformation. Two main types of plasticity mechanisms have been identified for the TATB single crystal: first, molecular dynamics simulations predict the existence of dislocations with an unusual local through-plane dilatancy process. Various slip systems among four different non-basal planes have been identified, namely ( 101), (101), (0 11) and (011) planes. Secondly, every deformation containing a basal-plane compressive component involves buckling deformation. A deformation path allowing a perfect twinning of the TATB triclinic cell has been found. This structure has been verified through molecular dynamics (MD) simulations. In order to understand the buckling mechanism, the TATB single crystal behavior under compression along its basal plane is studied in detail.

Tandem Molecular Dynamics and Continuum Studies of Shock‐Induced Pore Collapse in TATB

“…These results are consistent with the results of recent MD simulations of controlled uniaxial strain and strain-rate deformation [60] and 1.0 km s À 1 shock-wave simulations [73] of TATB, both performed for the case of no pre-existing defects and using essentially the same force field as here.…”

“…Practically, this dictates that defects which nucleate and grow to more than approximately two crystallographic unit‐cells extent along the thin direction will either be blocked or fill the sample at an unrealistic density along the shock direction, due to geometric constraints imposed by the periodic boundary conditions. However, we think the salient features of the collapse studied here would be preserved for cylindrical collapse in fully 3D simulation domains: Prior to shock arrival at the upstream pore surface, the present simulations yield deformation mechanisms that are qualitatively similar to those reported for controlled‐strain, controlled strain‐rate, rigid‐molecule MD simulations of initially defect‐free TATB as well as all‐atom MD simulations of explicit shocks in oriented, initially defect‐free 3D (as opposed to quasi‐2D) samples .…”

“…The crystal is triclinic with two molecules per unit cell. The structure of the crystal is strongly anisotropic and this is reflected in pronounced anisotropy for many of the thermal [39][40][41][42][43][44][45][46][47][48][49][50], mechanical [51][52][53][54][55][56][57][58][59][60], and optical properties [61].…”

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)

“…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.…”