No abstract

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]

High explosive performance and sensitivity is strongly related to the mesoscale defect densities. Bracketing the population of mesoscale hot spots that are active in the shocked ignition of explosives is important for the development of predictive reactive flow models. By coupling a multiphysics-capable hydrodynamics code (ale3d) with a chemical kinetics solver (cheetah), we can parametrically analyze different pore sizes undergoing collapse in high pressure shock conditions with evolving physical parameter fields. Implementing first-principles based decomposition kinetics, burning hot spots are monitored, and the regimes of pore sizes that contribute significantly to burnt mass faction and those that survive thermal conduction on the time scales of ignition are elucidated. Comparisons are drawn between the thermal explosion theory and the multiphysics models for the determination of nominal pore sizes that burn significantly during ignition for the explosive 1,3,5-triamino-2,4,6-trinitrobenzene.

International Journal of Solids and Structures 47 (2010) 2543-2553. doi:10.1016/j.ijsolstr.2010.05.018Received by publisher: 2010-01-17Harvest Date: 2016-01-04 12:19:58DOI: 10.1016/j.ijsolstr.2010.05.018Page Range: 2543-255

Abstract. High-explosive (HE) material consists of large-sized grains with micron-sized embedded impurities and pores. Under various mechanical/thermal insults, these pores collapse generating hightemperature regions leading to ignition. A hydrodynamic study has been performed to investigate the mechanisms of pore collapse and hot spot initiation in TATB crystals, employing a multiphysics code, ALE3D, coupled to the chemistry module, Cheetah. This computational study includes reactive dynamics. Two-dimensional high-resolution large-scale meso-scale simulations have been performed. The parameter space is systematically studied by considering various shock strengths, pore diameters and multiple pore configurations. Preliminary 3-D simulations are undertaken to quantify the 3-D dynamics.