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

Abstract

Molecular dynamics simulations were used to study the shock-induced collapse of cylindrical pores in oriented single crystals of the energetic material a-1,3,5-trinitroperhydro-1,3,5-triazine (a-RDX). The shock propagation direction was parallel to the [100] crystal direction and the cylinder axis of the initially 35.0 nm diameter pore was parallel to [010]. Features of the collapse were studied for Rankine-Hugoniot shock pressures P s = 9.71, 24.00, and 42.48 GPa. Pore collapse for the weak shock is dominated by visco-plastic deformation in which the pore pinches shut without jet formation and with little penetration of the upstream material into the downstream pore wall. For the strong shock the collapse is hydrodynamiclike and results in the formation of a jet that penetrates significantly into the downstream pore wall. Material flow during collapse was characterized by examining the spread and mixing of sets of initially contiguous molecules and evolution of local velocity fields. Local disorder during collapse was assessed using time autocorrelation functions for molecular rotation. Energy deposition and localization was studied using spatial maps of temperature and pressure calculated as functions of time.

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

“…The vortical flow ‘rolls up’ the hotspot in the regions of the sidelobes. While this rollup and concentration of the high temperatures in the vortex cores have been observed in MD calculations as well , in the present study the strong anisotropy appears to disrupt the formation of concentrated vortical structures. Despite these differences, the overall locations of the incident shock wave, the blast wave emanating from the collapse site, and the location of the Mach stem and triple points all appear to be in fairly good agreement between the MD and continuum predictions.…”

“…Specific equations used to compute the various other properties used for the MD analysis are described elsewhere [72][73][74][75].…”

Celebrating 75 Years of the Society for Experimental Mechanics and the Study of Dynamic Behavior of Materials

“…The journal is highly international, publishing experimental and theoretical studies of metals [57], polymers [58], glasses [59], composites [60], granular materials [61], explosives [62], biological materials [63], geological materials [64], phase transitions [65], and structural response [66]. The journal includes application and development of techniques including split Hopkinson pressure bar/Kolsky bar [67], plate impact with light gas guns and powder guns [68], Taylor Anvil [69], Dynamic-TensileExtrusion [70], spectroscopy-and pyrometry-based shock temperature measurements [71], optical and X-ray imaging methods [72], interferometry and velocimetry techniques [73], dynamic fracture [74], laser based dynamic drivers [75], penetration and ballistics [76], equation of state [77], and spall failure [78].…”

Embedded Manganin Gauge Measurements and Modeling of Shock Initiation in HMX‐Based PBX Explosives with Different Particle Sizes and Porosities

“…It has been suggested that the pore collapse (e. g., the viscoplastic deformation, the hydrodynamic micro jetting, the compression of gas in cavities and the shear bandings) is a dominant hot-spot generation mechanism for the shock initiation in pressed solid explosives [6][7][8][9][10]. Numerous researches have investigated the pore collapse hot-spot ignition mechanism via experiments (the voids in mm-scale) [11][12][13], molecular dynamics (MD) simulations [14,15] and mesoscale simulations [16,17], suggesting that the initial size and shape of the pore, the material viscosity, and the shock pressure have noticeable effects on the hot spot formation. These studies have permitted a closer micro-mechanical description and accurate prediction of the pore collapse hot spot formation mechanisms.…”