The Effect of Pore Morphology on Hot Spot Temperature

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]

Microscopic evidence of stishovite generated in low‐pressure shock experiments on porous sandstone: Constraints on its genesis

“…We conclude therefore that the temperatures were heterogeneously distributed with hot spots, where local peak strain upon shock compression caused frictional heating and melting (Kieffer 1971;Grady 1980;Tan and Ahrens 1990). This hypothesis is also supported by numerical calculations on porous materials (Frey 1986;Heider and Kenkmann 2003;Levesque and Vitello 2015). Experimental evidence is, however, only rarely reported, that is, for shockcollapsed pores in the related field of explosive materials (Bourne and Milne 2003).…”

Modeling The Effects of Shock Pressure and Pore Morphology on Hot Spot Mechanisms in HMX

“…While not the focus of this study, multiple crystal simulations are an important part of multi-scale modeling strategies, as they provide information on heterogeneous hot spots distributions and improved understanding of microstructureproperty relationships [10][11][12][13]. Previous pore collapse studies in a single HMX crystal have examined the effect of pore size, shape, orientation, spacing of multiple pores, and a range of pressures [14][15][16][17][18][19][20][21][22]. However, these studies are limited to interior pores rather than pores on the crystal surface.…”

Molecular Dynamics Simulations of the Collapse of a Cylindrical Pore in the Energetic Material α-RDX

“…Most simulations of pore collapse consider idealized spherical pores in 3-D or cylindrical pores with the cylinder axis oriented normal to the shock direction in 2-D. However, Levesque and Vitello [28] analyzed temperature maps obtained from continuum simulations of shocked-induced pore collapse in TATB containing other pore morphologies and determined that higher temperatures are achieved for certain oriented non-spherical pore shapes including elliptical, cylindrical, and conical.…”