Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session V3: PM-2: Particulate Mechanics |
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Chair: R. Kraus, Harvard University Room: Hermitage C |
Thursday, July 2, 2009 1:30PM - 2:00PM |
V3.00001: The Configurationally-dependent Mechanochemical Behavior of Reactive Powder Mixtures Invited Speaker: In reactive powder mixtures, the initiation of shock-induced chemical reactions is dependent upon the micromechanical processes (deformation, mass flow, and mixing) that occur during void collapse and the crush-up to full density. The specific modes of these processes are in turn affected by the intrinsic and extrinsic properties of the components, i.e. strength, density, particle size and morphology. For example, variations in particle size (micrometer to nanometer) and morphology (spherical to flake) in Ni+Al powder mixtures result in a wide range of crush-strengths, from 0.5 to 6 GPa, and varying chemical response, i.e. inert vs. reactive. Such a link between powder properties and reaction response has resulted from years of experimental, numerical, and theoretical work. In this talk, we will first review the key experiments that have supplied much of the evidence for shock-induced chemical reactions in powder mixtures. Next, we will discuss the results of numerical simulations to help describe the micromechanical processes that occur during crush-up. Finally, we will present a conceptual framework for shock-induced reactions, that may be used to guide development of energetic systems with tailored chemical response. [Preview Abstract] |
Thursday, July 2, 2009 2:00PM - 2:15PM |
V3.00002: Meso-Scale Heating Predictions for Weak Impact of Granular Energetic Solids Rohan Panchadhar, Keith Gonthier An explicit, 2-D, Lagrangian finite and discrete element technique is used to computationally characterize meso-scale fluctuations in thermomechanical fields within piston supported low pressure deformation waves propagating through particulate energetic solids. The numerical technique combines conservation principles with a plane strain, thermoelastic-viscoplastic and friction constitutive theory, and an energy consistent, penalty based contact interaction model, to describe deformation and motion of individual particles. Emphasis is placed on characterizing the relative importance of plastic and friction work as heating mechanisms which may cause bulk ignition of these materials. Predictions indicate that, in addition to low speed impact ($< 200$ m/s), friction work is an important heating mechanism at higher impact speeds. The variation in spatial partitioning of energy within the spatial deformation wave structure, and its variation with piston speed (50-500 m/s) and particle size distribution, is demonstrated. [Preview Abstract] |
Thursday, July 2, 2009 2:15PM - 2:30PM |
V3.00003: ABSTRACT WITHDRAWN |
Thursday, July 2, 2009 2:30PM - 2:45PM |
V3.00004: The Effect of Particle Size and Separation upon PBX Yield Stress Daniel Drodge, William Proud A Hall-Petch-like relationship between yield stress and particle size has previously been documented for some monomodal PBX compositions loaded in uniaxial compression. However, due to the fixed fill-fraction of these materials, the particle separation was proportional to particle size, thus either or both parameters could be responsible for the relationship. A set of inert monomodal composites have been produced to resolve this ambiguity and supply modellers with validation scenarios for their PBX codes. So far, uniaxial compression response has been measured at quasi-static and dynamic ($10^3~s^{-1}$) strain rates. This presentation summarises the findings to date and outlines the future direction of this project. [Preview Abstract] |
Thursday, July 2, 2009 2:45PM - 3:00PM |
V3.00005: Static and Dynamic Compaction of CL-20 Powders Marcia Cooper, Aaron Brundage, Evan Dudley Hexanitrohexaazaisowurtzitane (CL-20) powders were compacted under quasi-static and dynamic loading conditions. A uniaxial compression apparatus quasi-statically compressed the powders to 90{\%} theoretical maximum density with applied stresses up to 0.5 GPa. Dynamic compaction measurements using low-density pressings (62-70{\%} theoretical maximum density) were obtained in a single-stage gas gun at impact velocities between 0.17-0.70 km/s. Experiments were conducted in a reverse ballistic arrangement in which the CL-20 ladened projectile impacted a target consisting of an aluminized window. VISAR-measured particle velocities at the explosive-window interface determined the shock Hugoniot states for pressures up to 0.9 GPa. The powder compaction behavior is found to be stiffer under dynamic loading than under quasi-static loading. Additional gas gun tests were conducted in which the low-density CL-20 pressings were confined within a target cup by the aluminized window. This arrangement enabled temporal measurement of the transmitted wave profiles in which elastic wave precursors were observed. [Preview Abstract] |
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