Multiscale modeling of shock wave localization in porous energetic material

All‐atom molecular dynamics (MD) and Eulerian continuum simulations, performed using the LAMMPS and SCIMITAR3D codes, respectively, were used to study thermo‐mechanical aspects of the shock‐induced collapse of an initially cylindrical 50 nm diameter pore in single crystals of 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB). Three impact speeds, 0.5 km s−1, 1.0 km s−1 and 2.0 km s−1, were used to generate the shocks. These impact conditions are expected to yield collapse mechanisms ranging from predominantly visco‐plastic to hydrodynamic. For the MD studies, three crystal orientations (relative to shock‐propagation direction) were examined that span the limiting cases with respect to the crystalline anisotropy in TATB. An isotropic constitutive model was used for the continuum simulations, thus crystal anisotropy is absent. The evolution of spatiotemporally resolved quantities during collapse is reported including local pressure, temperature, pore size and shape, and material flow. Multiple models for the melting curve and specific heat were studied. Within the isotropic elastic/perfectly plastic continuum framework and for the range of impact conditions studied, the specific heat and melting curve sub‐models are shown to have modest effects on the continuum hotspot predictions in the present inert calculation. Treating the MD predictions as ‘ground truth’, albeit with a classical rather than quantum‐like heat capacity, it is clear that – at a minimum – an extension of the constitutive model to account for crystal plasticity and anisotropic strength will be required for a high‐fidelity continuum description.

Section: Resultssupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

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

Zhao

Lee

Sewell

et al. 2020

“…To analyze the data with different void diameters and impact velocities, a characteristic time

τ = D / U_{s}

is defined following the work of Woods et al . . This time represents the time it takes the shock to travel the void diameter.…”

Section: Resultsmentioning

confidence: 99%

“…For comparison the molecular dynamics and continuum simulations of Wood et al . in HNS are also included.…”

Section: Resultsmentioning

confidence: 99%

Void Collapse in Shocked ‐HMX Single Crystals: Simulations and Experiments

Duarte

Hamed

Drake

et al. 2020

Heat generation in the vicinity of a void during shock compression plays a key role in the initiation of energetic materials. The shock response of a single β ‐HMX crystal with a single void is studied with simulations that include plasticity and heat transport. The numerical results are validated with an experiment in which a 500 μ m void is machined in an HMX single crystal and impacted. Experiments and simulations of the dynamical evolution of the morphology of the void during the collapse and the rate of the area are in very good agreement for weak shocks.

“…Comparison studies are also given to show the relative importance of the number density of hot spots, the microstructure of the crystalline pack, and other numerical parameters. In addition, Wood et al [18] examined the role that the constitutive model plays in a mesoscale calculation by using the atomistic code, LAMMPS, to train a strain ratedependent SGL viscoplastic strength model. Two mesoscale simulations were then run with and without the SGL model turned on (i. e., hydrodynamic only), where it was found that an increase in the shocked temperature distribution occurs at lower impact velocities (less than~1 km/s) if the SGL model is in use.…”

Section: Introductionmentioning

confidence: 99%

Prediction of Probabilistic Detonation Threshold via Millimeter‐Scale Microstructure‐Explicit and Void‐Explicit Simulations

Miller

Kittell

Yarrington

et al. 2019

We present an approach and relevant models for predicting the probabilistic shock‐to‐detonation transition (SDT) behavior and Pop plot (PP) of heterogeneous energetic materials (HEM) via mesoscopic microstructure‐explicit (ME) and void explicit (VE) simulations at the millimeter (mm) sample size scale. Although the framework here is general, the particular material considered in this paper is pressed Octahydro‐1,3,5,7‐tetranitro‐1,2,3,5‐tetrazocine (HMX). To systematically delineate the effects of material heterogeneities, four material cases are considered. These cases are homogeneous material, material with granular microstructure but no voids, homogeneous material with voids, and material with both granular microstructure and voids. Statistically equivalent microstructure sample sets (SEMSS) are generated and used. Eulerian hydrocode simulations explicitly resolve the material heterogeneities, voids, and the coupled mechanical‐thermal‐chemical processes. In particular, it is found that both microstructure and voids strongly influence the SDT behavior and PP. The effects of different combinations of microstructure heterogeneity and voids on the SDT process and PP are quantified and rank‐ordered. The overall framework uses the Mie–Grüneisen equation of state and a history variable reactive burn model (HVRB). A novel probabilistic representation for quantifying the PP is developed, allowing the calculation of (1) the probability of observing SDT at a given combination of shock pressure and run distance, (2) the run‐distance to detonation under a given combination of shock pressure and prescribed probability, and (3) the shock pressure required for achieving SDT at a given run distance with a prescribed probability. The results are in agreement with general trends in experimental data in the literature.