Computational study of 3-D hot-spot initiation in shocked insensitive high-explosive

Najjar, Fady; Howard, William A.; Fried, Laurence E.; Manaa, M. Riad; Nichols, Albert L.; Levesque, George

doi:10.1063/1.3686267

Cited by 13 publications

(12 citation statements)

References 4 publications

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“…Figure 3 shows the time evolution of the spatial extent of the dynamically formed hotspots for different pore sizes by tracking the amount of material in the simulation cell above 1700 K. In all cases studied there is an initial sudden rise in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 the hot spot area due to the collision of the ejected material with the downstream wall of the pore. The overall behavior described thus far is fairly consistent with current understanding of hot spot formation from continuum modelling and experiments 13,15,23,24,36,[39][40][41] . An important distinction is the initial temperature spike and local non-equilibrium state at short times, which continuum models suppress through limited resolution, artificial viscosity and equilibrated equations of state.…”

Section: Dynamical Hot Spot Formationsupporting

confidence: 81%

“…Such defects are presumed to be the dominant initiation sites in this class of materials and most initiation models include some ad hoc representation of their physical response [9][10][11] . Continuum models have been used to analyze the hot spot initiation process, but these necessarily make assumptions regarding reaction kinetics, local equilibration and materials properties that are not well-known under the conditions of interest 7,[12][13][14][15]36,[39][40][41] .…”

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confidence: 99%

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Ultrafast Chemistry under Nonequilibrium Conditions and the Shock to Deflagration Transition at the Nanoscale

et al. 2015

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We use molecular dynamics simulations to describe the chemical reactions following shockinduced collapse of cylindrical pores in the high-energy density material RDX. For shocks with particle velocities of 2km/s we find that the collapse of a 40nm diameter pore leads to a deflagration wave. Molecular collisions during the collapse lead to ultra-fast, multi-step chemical reactions that occur under non-equilibrium conditions. Exothermic products formed during these first few picoseconds prevent the nanoscale hotspot from quenching. Within 30ps, a local deflagration wave develops; it propagates at 0.25km/s and consists of an ultra-thin reaction zone of only ~5nm, thus involving large temperature and composition gradients. Contrary to the assumptions in current models, a static thermal hotspot matching the dynamical one in size and thermodynamic conditions fails to produce a deflagration wave indicating the importance of nonequilibrium loading in the criticality of nanoscale hot spots. These results provide insight into the initiation of reactive decomposition. TOC GRAPHICS

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Section: Dynamical Hot Spot Formationsupporting

confidence: 81%

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confidence: 99%

Ultrafast Chemistry under Nonequilibrium Conditions and the Shock to Deflagration Transition at the Nanoscale

et al. 2015

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Section: A Nalysismentioning

confidence: 99%

“…In prior work, we have simulated pore collapse using ah ighly-parallelized arbitrary-Lagrangian/Eulerian multiphysics hydrocode, ALE3D, in combination with the thermochemical code, CHEETAH, which supplies equation of state information at every time step to the multiphysics hydrocode [12,22,23] Keywords: Pore collapse · Microscale simulation · Explosive initiation · Pore shape of axisymmetric pores, with nanometer-scale refinement, of differing morphologies but identical volumes. All pores are subjected to shock pressures, P s ,o f1 0GPa in triaminotrinitrobenzene (TATB) material, which is simulated as having ac onstant viscosity of 4.6 Pa ·s [24].W hile chemical kinetics for TATB decomposition are available, [25] the explosive is treated as inert to understand the effect of pore morphology on the unreacted material.…”

Section: A Nalysismentioning

confidence: 99%

The Effect of Pore Morphology on Hot Spot Temperature

Levesque

Vitello

2014

Propellants Explo Pyrotec

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Insensitive explosives are intentionally initiated by transmitting as hock wave. This shock wave heats the explosive composite, but not enough for thermal decomposition on its own. The mechanism of initiation is attributed to localized heating sites (referred to as hot spots), to which there are many attributed mechanisms including:( a) hydrodynamic pore collapse ,( e) mach stems and more [5].T hermal energy calculations suggested that collapsing pores are the most effective mechanism [6]. In addition, experiment has shown that composites with more porosity are more sensitive to shock initiation [7].A s ar esult, hot spot nucleation has been mainly attributed to pore collapse.Analysis on pore collapse is not hard to find [8,9].F or small pores in materials of high viscosity,t here are simplified axisymmetric partial differential equations to analyze the amount of heat generated post-collapse [3,6,10,11]. There are computational analyses in continuum hydrodynamics of pore collapse on the microscale of varying resolution and complexity [12] and in molecular dynamics simulations of pore collapse (which are limited by domain size) [13][14][15][16].T here are also analyses of fields of pores to examine interaction during collapse [17] and ambitiousm icroscale simulations for the run-to-detonation evolution [18]. Despite all this analysis, the only articles to explore an onspherical pore collapse is in Ref. [19],w here as phere and at riangle are analyzed and more recently,p erturbed shapes have been investigated in Ref. [20].While as phere might be the average of all pore shapes about their centroids, pores are not commonly spherical. In an explosive crystal, ap ore could be of any geometry of missing molecules in al attice. In the synthesis of explosive composites, rough explosive crystal grains are coated with plasticized binder materials forming prills. These prills are pressed under high pressure and vacuum to generate ah igh density part. Even if ap rill formed with as pherical bubble, it is unlikely to remain spherical in the pressing process [21].A dditionally,e ven if the average shape was spherical, this does not necessarily mean that the average shape will generate an average amount of thermal energy when compared to the full range of pore shapes. Researchers have still gravitated to the spherical pore for the bulk of their analyses. Herein, differences in thermal energy as af unction of pore morphology are analyzed and discussed. 2A nalysisIn prior work, we have simulated pore collapse using ah ighly-parallelized arbitrary-Lagrangian/Eulerian multiphysics hydrocode, ALE3D, in combination with the thermochemical code, CHEETAH, which supplies equation of state information at every time step to the multiphysics hydrocode [12,22,23]

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“…Over the past several years, numerous hydrodynamic simulations [14][15][16][17][18][19][20][21][22][23][24] at the continuum scale have been conducted to derive valuable clues regarding spherical void collapse and hot spot formation in shocked HEs. For example, by using a spherical void model, Tran, and Udaykumar [16,17] simulated void collapse for both reactive and inert materials possessing mechanical properties similar to those of HMX crystals.…”

Section: Introductionmentioning

confidence: 99%

Influence of Void Configurations on Hot Spot Temperature in PBXs under Impact Loading

Duan

et al. 2021

Propellants Explo Pyrotec

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In this study, similarity analysis and mesoscale simulations were performed to investigate hot spot temperatures in triangular voids inside polymer-bonded explosives (PBXs). We found that there are two different void collapse modes, namely single and double hydrodynamic jet modes. The hot spot temperatures achieved in the double hydrodynamic jet mode are much higher than previous predictions, such as predictions based on circular voids, which agrees with recent experimental observations. Additionally, we verified that void configuration (position and shape) plays a significant role in increasing hot spot tem-peratures, implying that when establishing a mesoscale reaction rate model, it is insufficient to use void volume alone to characterize the impact sensitivity of PBXs. Finally, two semi-empirical analytical expressions are proposed to represent the dependence of hot spot temperature on both the void configuration and shock intensity. The resulting theoretical predictions are in good agreement with the numerically simulated results. Such mesoscale analytical expressions can be used for establishing theoretical mesoscale hot spot ignition rate models in the future.

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Computational study of 3-D hot-spot initiation in shocked insensitive high-explosive

Cited by 13 publications

References 4 publications

Ultrafast Chemistry under Nonequilibrium Conditions and the Shock to Deflagration Transition at the Nanoscale

Ultrafast Chemistry under Nonequilibrium Conditions and the Shock to Deflagration Transition at the Nanoscale

The Effect of Pore Morphology on Hot Spot Temperature

Influence of Void Configurations on Hot Spot Temperature in PBXs under Impact Loading

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