Density functional theory calculations of anisotropic constitutive relationships in alpha-cyclotrimethylenetrinitramine

Abstract

Constitutive relationships in the crystalline energetic material ␣-cyclotrimethylenetrinitramine ͑␣-RDX͒ have been investigated using first-principles density functional theory. The equilibrium properties of ␣-RDX including unit cell parameters and bulk modulus, as well as the hydrostatic equation of state ͑EOS͒, have been obtained and compared with available experimental data. The isotropic EOS has been extended to include the anisotropic response of ␣-RDX by performing uniaxial compressions normal to several low-index planes, ͕100͖, ͕010͖, ͕001͖, ͕110͖, ͕101͖, ͕011͖, and ͕111͖, in the Pbca space group. The uniaxial-compression data exhibit a considerable anisotropy in the principal stresses, changes in energy, band gaps, and shear stresses, which might play a role in the anisotropic behavior of ␣-RDX under shock loading.

Density Functional Theory Calculations of Solid Nitromethane under Hydrostatic and Uniaxial Compressions with Empirical van der Waals Correction

“…The percent error for the lattice constants using DFT alone is approximately 2-6%, which is slightly greater than the error in our calculations of the zero-pressure structure of PETN, 42 HMX, 43 and RDX. 44 The vdW-corrected calculations significantly improve the agreement with experiment, reducing the error in the lattice parameters and unit-cell volume to less than 1% each.…”

Simulations of High-Pressure Phases in RDX

“…The direct experimental investigation of shear-induced kinetic structural response of RDX can be accomplished by exploiting such surface effects such as those through indentation . Simulations have also investigated RDX in the context of directional loading of the crystal. − , This also produces local crystal shear that can promote bulk kinetic effects such as phase transitions. Common in these approaches are imposed or generated nontrivial components to the deviatoric stress tensor.…”

An Anisotropic Elastoviscoplasticity Model of Thermomechanical Responses of Shocked β‐HMX and α‐RDX Single Crystals

“…In this work, we choose the nine elastic coefficients obtained from resonant ultrasound [53] and temperature and pressure derivatives obtained from molecular dynamics simulations [54] (Table 7). The bulk modulus and its pressure derivatives for Birch-Murnaghan EOS are taken from Conroy et al [55] ( Table 8).…”

“…À 0.019 À 0.01 À 0.005 À 0.012 À 0.018 À 0.014 À 0.006 0.002 À 0.007 Table 8. RDX physical properties and EOS parameters [55].…”