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 E2: Energetic Materials II |
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Chair: Bryce Tappan, Los Alamos National Laboratory Room: Grand Ballroom IV-VI |
Monday, June 27, 2011 4:00PM - 4:30PM |
E2.00001: Dynamic behavior of particulate/porous energetic materials Invited Speaker: Dynamic behavior of particulate/porous energetic materials in a broad range of impact conditions and types of deformation (shock, shear) will be discussed. Samples of these materials were fabricated using Cold Isostatic Pressing, sintering and Hot Isostatic Pressing with and without vacuum encapsulation. The current interest in these materials is due to the combination of their high strength with energy efficiency under critical conditions of mechanical deformation. They may exhibit high compressive and tensile strength with the ability to bulk distributed fracture resulting in a small size reactive fragments and possible reaction on later stages. The results of dynamic deformation and fragmentation of these materials in conditions of low velocity (10 m/s), high energy impact, under localized deformation in single and multiple shear bands generated using explosively driven Thick Walled Cylinder method will be discussed. The mechanical properties of these materials are highly sensitive to mesostructure. For example, a dynamic strength of Al-W composites with fine W particles is significantly larger than the strength of composite with the coarse W particles at the same porosity. Morphology of W inclusions had a strong effect on dynamic strength. Samples with W wires arranged in axial direction with the same volume content of components had a highest dynamic strength. Porosity in these materials can provide a strain hardening mechanism effect due to in situ densification which was observed experimentally for cold isostatically pressed Al and Al-coarse W powders. Experimental results will be compared with available numerical data. [Preview Abstract] |
Monday, June 27, 2011 4:30PM - 4:45PM |
E2.00002: Microstructural effects on ignition sensitivity in Ni/Al systems subjected to high strain rate impacts Robert Reeves, Alexander Mukasyan, Steven Son The effect of microstructural refinement on the sensitivity of the Ni/Al (1:1 at{\%}) system to ignition via high strain rate impacts is investigated. The tested microstructures include compacts of irregularly convoluted lamellar structures with nanometric features created through high-energy ball milling (HEBM) of micron size Ni/Al powders and compacts of nanometric Ni and Al powders. The test materials were subjected to high strain rate impacts through Asay shear experiments powered by a light gas gun. Muzzle velocities up to 1.1 km/s were used. It was found that the nanometric powder exhibited a greater sensitivity to ignition via impact than the HEBM material, despite greater thermal sensitivity of the HEBM. A previously unseen fast reaction mode where the reaction front traveled at the speed of the input stress wave was also observed in the nanometric mixtures at high muzzle energies. This fast mode is considered to be a mechanically induced thermal explosion mode dependent on the magnitude of the traveling stress wave, rather than a self-propagating detonation, since its propagation rate decreases rapidly across the sample. A similar mode is not exhibited by HEBM samples, although local, nonpropagating reaction zones occur in shear bands formed during the impact event. [Preview Abstract] |
Monday, June 27, 2011 4:45PM - 5:00PM |
E2.00003: Enhanced reactivity of mechanically-activated nano-scale gasless reactive materials consolidated via the cold-spray technique Antoine Bacciochini, Matei Radulescu, Onur Meydanoglu, Yannick Charron-Tousignant, Jason Van Dyke, Bertrand Jodoin, Michel Nganbe, Mohamed Yandouzi, Julian J. Lee It has been speculated that gasless reactive systems can sustain supersonic detonations waves, provided the local decomposition rate is sufficiently fast and the initial density is sufficiently close to the theoretical maximal density. The present study presents a novel method to prepare nano-scale energetic materials with high reactivity, vanishing porosity, structural integrity and arbitrary shape. The experiments have focused on the Ni-Al system. To increase the reactivity, an initial mechanical activation was achieved by the technique of ball milling. The consolidation of the materials used the supersonic cold gas spray technique, where the particles are accelerated to high speeds and consolidated via plastic deformation upon impact, forming activated nano-composites in arbitrary shapes with close to zero porosity. This technique permits to retain the micro-structures in the powders and prevents any reactions during the consolidation phase. Deflagration tests of the obtained samples showed an increase in the deflagration rate by up to two orders of magnitude. [Preview Abstract] |
Monday, June 27, 2011 5:00PM - 5:15PM |
E2.00004: The Effect of Gaseous Additives on Dynamic Pressure Output and Ignition Sensitivity of Nanothermites Jan Puszynski, Zac Doorenbos, Ian Walters, Paul Redner, Deepak Kapoor, Jacek Swiatkiewicz This contribution addresses important combustion characteristics of nanothermite systems. In this research the following nanothermites were investigated: a) Al-Bi$_{2}$O$_{3}$, b) Al-Fe$_{2}$O$_{3}$ and c) Al-Bi$_{2}$O$_{3}$-Fe$_{2}$O$_{3. }$The effect of various gasifying additives (such as nitrocellulose (NC) and cellulose acetate butyrate (CAB)) as well as reactant stoichiometry, reactant particle size and shape on processability, ignition delay time and dynamic pressure outputs at different locations in a combustion chamber will be presented. In addition, this contribution will report electrostatic and friction sensitivities of standard and modified nanothermites. [Preview Abstract] |
Monday, June 27, 2011 5:15PM - 5:30PM |
E2.00005: Nano-Al Based Energetics: Rapid Heating Studies and a New Preparation Technique Kyle Sullivan, Josh Kuntz, Alex Gash, Michael Zachariah Nano-Al based thermites have become an attractive alternative to traditional energetic formulations due to their increased energy density and high reactivity. Understanding the intrinsic reaction mechanism has been a difficult task, largely due to the lack of experimental techniques capable of rapidly and uniform heating a sample ($\sim $10$^{4 }$-- 10$^{8}$ K/s). The current work presents several studies on nano-Al based thermites, using rapid heating techniques. A new mechanism termed a Reactive Sintering Mechanism is proposed for nano-Al based thermites. In addition, new experimental techniques for nanocomposite thermite deposition onto thin Pt electrodes will be discussed. This combined technique will offer more precise control of the deposition, and will serve to further our understanding of the intrinsic reaction mechanism of rapidly heated energetic systems. An improved mechanistic understanding will lead to the development of optimized formulations and architectures. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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