Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session U1: Energetic Materials VIII |
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Chair: Jared Gump, Naval Surface Warfare Center -- Indian Head Room: Grand Ballroom II-III |
Thursday, June 30, 2011 2:00PM - 2:15PM |
U1.00001: Detailed Characterization of PBX Morphology for Mesoscale Simulations Scott Bardenhagen, Huiyang Luo, Hongbing Lu, Ronald Armstrong Plastic-Bonded Explosives (PBXs) are composed of energetic grains embedded in a polymeric binder. The heterogeneity at this material scale serves to localize energy during deformation, determining damage and hot spot development leading to reaction. Accurate determination of PBX morphology is needed to characterize and understand these materials, and is essential input for mesoscale simulations. X-ray microtomography was used to determine the three-dimensional x-ray cross-section of a mock explosive for which all formulation details are known. Specialized image processing routines were used to identify individual features (voids, grains, binder). Mass fractions, void content, and grain size statistics were compared with the formulation. The quantity of material needed to accurately represent the mesostructure in simulations, i.e. representative volume element size, was determined, as well as grain on grain contact density, which may correlate with sensitivity. Preliminary results from computations using these mesostructures will be reported. [Preview Abstract] |
Thursday, June 30, 2011 2:15PM - 2:30PM |
U1.00002: Hot-spot ignition in a layer of widely-spaced HMX powders subjected to a falling weight impact Fenglei Huang, Yanqing Wu A micromechanics approach based on heating equations, the kinematic and deformation description for a thin layer of HMX energetic powders under drop-weight impact is presented. The work focuses on the thermal and mechanical processes that act to transfer the input kinetic energy into the localized high-temperature ignition sites. By considering contact plastic work, frictional heating, fragmentation energy, chemical reaction, and melting at a single particle level, localized deformation and temperature can be predicted. Effects of drop height and particle size on the ignition process are analyzed. The analyses of localized dissipated energy rate as well as radial expansion help to understand the physical process that leads to ignition. In the case of non-ignition, no sudden rise occurs in the dissipated energy rate until the end of the impact loading. Two sharp decreases in pressure appear due to breakage and melting at contact zone with impact loading proceeds. [Preview Abstract] |
Thursday, June 30, 2011 2:30PM - 2:45PM |
U1.00003: Sonocrystallization as a tool for controlling crystalline explosive morphology and inclusion content Chad Stoltz, Bryan Mason, Colin Roberts, Steven Hira, Geoffrey Strouse It is well known that reduced-sensitivity versions of cyclotrimethylene trinitramine (RDX) powder have been reported such that the resulting plastic-bonded explosive (PBX) formulations containing this RDX become less sensitive to shock initiation than those formulated with standard RDX. While the reasons for the reduction in shock sensitivity are debated in the energetic materials community, we have recently reported correlations between PBX shock sensitivity and RDX void content by Small Angle Neutron Scattering (SANS). The obvious next step in understanding the effects of crystalline explosive microstructure is to control defect type and quantity, as well as particle size and morphology during energetic material crystallization. To this end, uniform crystallite morphology, narrow particle size distribution, and tailored inclusion content have been achieved for RDX explosive recrystallization by a combination of simple ultrasonic agitation and solvent evaporation. Optical and confocal microscopy imaging show significantly reduced inclusion content in crystallites grown using sonocrystallization with slow solvent evaporation while particle size distributions are considerably narrower using sonocrystallization with any evaporation rate. [Preview Abstract] |
Thursday, June 30, 2011 2:45PM - 3:00PM |
U1.00004: Defect characterization and the effect of pre-existing and shock-induced defects on the shock response of single crystal explosives Kyle Ramos, Marc Cawkwell, Daniel Hooks Defects in single crystal materials have been shown to influence shock response. In single crystals of organic molecular explosives, it has proven difficult to perform quantitative characterization of samples prior to shock experiments, so many previous experiments relied on simple techniques and experience to ensure sample consistency. This has made interpretation of some previous results difficult. Several types of defect characterization have been performed both statically and dynamically to determine the influence of defects. Additionally, with guidance from molecular dynamics simulations, continuum observations have been correlated with changes in deformation mechanisms in cyclotrimethylene trinitramine (RDX) across a range of loading pressures. Recent examples will be discussed. [Preview Abstract] |
Thursday, June 30, 2011 3:00PM - 3:15PM |
U1.00005: A Study of Energy Partitioning Using A Set of Related Explosive Formulations Mark Lieber, Joseph C. Foster, Jr., D. Scott Stewart Condensed phase high explosives convert potential energy stored in the electro-magnetic field structure of complex molecules to kinetic energy during the detonation process. This energy is manifest in the internal thermodynamic energy and the translational flow of the products. Historically, the explosive design problem has focused on intramolecular stoichiometry providing prompt reactions based on transport physics at the molecular scale. Modern material design has evolved to approaches that employee intermolecular ingredients to alter the spatial and temporal distribution of energy release. CHEETA has been used to produce data for a set of fictitious explosive formulations based on C-4 to study the partitioning of the available energy between internal and flow energy in the detonation. The equation of state information from CHEETA has been used in ALE3D to develop an understanding of the relationship between variations in the formulation parameters and the internal energy cycle in the products. [Preview Abstract] |
Thursday, June 30, 2011 3:15PM - 3:30PM |
U1.00006: Analysis of the Requirements on Modern Energetics and Their Impact on Materials Design Joseph C. Foster, Jr., Nick Glumac, D. Scott Stewart We have characterized the ``design'' of explosive materials as represented by the complete suite of engineering specifications on ingredients and processes used in the manufacture of specific components used in various application. The detonation of explosive materials and the associated high power density of this process has historically been an essential element of the design. Evolving requirements such as the desire for insensitive munitions and broadened demands on the control of the power output are producing a new class on energetic materials whose thermo-chemical response to specific intentional trigger mechanisms result in reactive behavior far removed the classical detonation modeling represented by the physics and chemistry of Chapman-Jouguet [CJ] or Zel'dovich, VonNeuman, Doering [ZND] detonation model. Experimental studies of representative designs and analysis of the role of processes controlled by the mesostructure suggest functional paths to establishing the desired output. [Preview Abstract] |
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