Pressure‐dependent Elastic Coefficients of β‐HMX from Molecular Simulations

Mathew, Nithin; Sewell, Tommy

doi:10.1002/prep.201700286

Cited by 36 publications

(30 citation statements)

References 31 publications

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“…These deviations are partly derived from the absence of anharmonic softening with temperature. Previous molecular dynamics studies have shown the SOECs of β ‐HMX at 300 K are in accordance well with experiments, reflecting that such temperature softening effects are significant to determine the SOECs of energetic materials accurately. Furthermore, the bulk modulus ( B = 12.80 GPa) and shear modulus ( G = 7.45 GPa) are calculated within Voigt–Reuss–Hill approximations .…”

Section: Resultssupporting

confidence: 79%

The pressure effects and vibrational properties of energetic material: Hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (α‐RDX)

Fan

Zheng

et al. 2019

J Raman Spectroscopy

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Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a secondary high-explosive material with thermal stability and high-detonation velocity. It has been widely utilized for military and civilian purposes. Using systematic first-principle calculations, we comprehensively explore structural, mechanical, electronic, and vibrational properties of α-RDX modulated by pressure loading. The evolutions of structure, elastic modulus, and band gap are examined. A near-linear pressure response and strong anisotropy are shown preliminarily. Further, pressure response and strong anisotropy are exhibited by Raman spectra analysis under hydrostatic and uniaxial compressions. Calculated Raman spectrum is well in accordance with experimental data at ambient conditions. Under uniaxial compression, the anisotropic vibration properties of α-RDX in different lattice directions are presented. The discontinuity in b axis and red shift along c axis, which is related to the modification of the strength of noncovalent interactions, is highlighted. Our results exhibit the comprehensive pressure responses and anisotropy of α-RDX on the atomic level.

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Section: Resultssupporting

confidence: 79%

The pressure effects and vibrational properties of energetic material: Hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (α‐RDX)

Fan

Zheng

et al. 2019

J Raman Spectroscopy

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“…The MD simulations were performed using LAMMPS Plimpton (1995) in conjunction with a modified version of the all-atom, fully flexible, non-reactive force field originally developed for HMX by Smith and Bharadwaj (S-B). Smith and Bharadwaj (1999); Bedrov et al (2000); Kroonblawd et al (2016); Mathew and Sewell (2018); Chitsazi et al (2020) Intramolecular interactions in the S-B force field are modeled using harmonic functions for covalent bonds, three-center angles, and improper dihedral ("wag") angles; and truncated cosine expansions for proper dihedrals. Intermolecular non-bonded interactions between atoms separated by three or more covalent bonds (i.e., 1-4 and more distant intramolecular atom pairs) are modeled using Buckingham-plus-charge (exponential-6-1) pair terms.…”

Section: Force Fieldmentioning

confidence: 99%

MD-inferred neural network monoclinic finite-strain hyperelasticity models for $β$-HMX: Sobolev training and validation against physical constraints

Vlassis¹,

Zhao²,

Ma³

et al. 2021

Preprint

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We present a machine learning framework to train and validate neural networks to predict the anisotropic elastic response of the monoclinic organic molecular crystal β-HMX in the geometrical nonlinear regime. A filtered molecular dynamic (MD) simulations database is used to train the neural networks with a Sobolev norm that uses the stress measure and a reference configuration to deduce the elastic stored energy functional. To improve the accuracy of the elasticity tangent predictions originating from the learned stored energy, a transfer learning technique is used to introduce additional tangential constraints from the data while necessary conditions (e.g. strong ellipticity, crystallographic symmetry) for the correctness of the model are either introduced as additional physical constraints or incorporated in the validation tests. Assessment of the neural networks is based on (1) the accuracy with which they reproduce the bottom-line constitutive responses predicted by MD, (2) detailed examination of their stability and uniqueness, and (3) admissibility of the predicted responses with respect to continuum mechanics theory in the finite-deformation regime. We compare the neural networks' training efficiency under different Sobolev constraints and assess the models' accuracy and robustness against MD benchmarks for β-HMX.

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“…The stiffness matrix of β-HMX has a moderate anisotropy that changes with pressure. Experimental measurements obtained by stimulated thermal pulse scattering [36] and molecular dynamics simulations [37] were used to complement and study their pressure dependence [18,38]. A thirdorder polynomial interpolation provides the elastic coefficients for a pressure of 800 MPa (Table 1).…”

Section: Numerical and Theoretical Frameworkmentioning

confidence: 99%

“…β-HMX elastic coefficients at 298 K and 0 MPa from [36]. Data (in GPa) at 800 MPa have been extracted from [14,38]. (0.00,0.00,1.0 meshing software, GMSH [44], is used to generate a 200 μm side mesh cube.…”

Section: Numerical and Theoretical Frameworkmentioning

confidence: 99%

Plastic Dissipation and Hot‐Spot Formation in HMX‐Based PBXs Subjected to Low Velocity Impact

Drouet

Picart

Bailly

et al. 2020

Propellants Explo Pyrotec

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Low-velocity, shock-free impact is one of the accidental loads that can lead to a thermal explosion, the latter being the consequence of a chain of mechanisms depending on the microstructure of the material. To investigate the causes, the predictive capability of numerical tools depends on the physics embedded in the models. While a consensus has developed around the concept of hot spots, the exact nature of the thermo-mechanical heat-generating processes that preceded them remains to be clarified. We are studying a composition similar to the PBX 9501. HMX crystals are mixed with a few percent of a polymer binder. Recent experiments (reverse edge-on impact test) have revealed the influence of the plasticity of HMX grains even at low strain rates and low confinement. The heat released by the plastic dissipation has been identified as a potential candidate for the formation of hot spots. In this study, a numerical representation based on a polycrystalline β-HMX material subjected to intense shear is presented. Due to the high pressure generated by the impact, the intergranular slip is ignored. Emphasis is placed on the heterogeneity resulting from the micro-structural characteristics and the interaction between the anisotropic single crystals. The behavior of the binder and the influence of other heterogeneities such as friction or micro cracks are set aside. Finally, the mechanical dissipation is calculated in the models and the maximum temperature is deduced.

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Pressure‐dependent Elastic Coefficients of β‐HMX from Molecular Simulations

Cited by 36 publications

References 31 publications

The pressure effects and vibrational properties of energetic material: Hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (α‐RDX)

The pressure effects and vibrational properties of energetic material: Hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (α‐RDX)

MD-inferred neural network monoclinic finite-strain hyperelasticity models for $β$-HMX: Sobolev training and validation against physical constraints

Plastic Dissipation and Hot‐Spot Formation in HMX‐Based PBXs Subjected to Low Velocity Impact

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