Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session P6: Reactive Materials II |
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Chair: Willis Mock, Naval Surface Warfare Center Dahlgren Divison Room: Fairmont Orchid Hotel Promenade I/II |
Thursday, June 28, 2007 10:30AM - 10:45AM |
P6.00001: Effect of Aluminum Particle Size on the High Strain Properties of Pressed Aluminized Explosives Chad Rumchik, Jennifer Jordan High strain rate mechanical properties of explosives are important in design as these materials see extreme loading environments. Previous studies have shown that decreasing the particle size of the explosive crystals in a PBX can increase the strength. In this study, pressed explosives (64{\%} explosive, 30{\%} aluminum, and 6{\%} HTPB based binder) were prepared with varying aluminum particle size from 50 nm to 30+ $\mu $m in order to investigate the effect of aluminum particle size and morphology on the compressive stress-strain behavior of the material. The paper will present the experimental results of this study as well as an investigation into potential constitutive models for these materials. [Preview Abstract] |
Thursday, June 28, 2007 10:45AM - 11:00AM |
P6.00002: Detonation Failure Thickness Measurement in an Annular Geometry David B. Mack, Oren E. Petel, Andrew J. Higgins The failure thickness of neat nitromethane in aluminum confinement was measured using a novel experimental technique. The thickness was approximated in an annular geometry by the gap between a concentric aluminum tube and rod. This technique was motivated by the desire to have a periodic boundary condition in the direction orthogonal to the annulus thickness, rather than the free surface that occurs in a typical experiment in a rectangular prism geometry. This results in a two-dimensional charge analogous to previous failure thickness setups but with infinite effective width (i.e. infinite aspect ratio). Detonation propagation or failure was determined by the observation of failure patterns engraved on the aluminum rod by the passing detonation. Analysis of these engraved patterns provides a statistical measurement of the spatial density of failure waves as the failure thickness is approached. The failure thickness was measured to be 0.76 mm +- 0.25 mm, which agrees with previous results, obtained using a rectangular prism geometry. [Preview Abstract] |
Thursday, June 28, 2007 11:00AM - 11:15AM |
P6.00003: Simulation of Particle Size Effect on Dynamic Properties and Fracture of PTFE-W-Al Composites Eric Herbold, Jing Cai, David Benson, Vitali Nesterenko Recent investigations of the dynamic compressive strength of cold isostatically pressed (CIP) composites of polytetrafluoroethylene (PTFE), tungsten and aluminum powders show significant differences depending on the size of metallic particles. PTFE and aluminum mixtures are known to be energetic under dynamic and thermal loading. The addition of tungsten increases density and overall strength of the sample. Multi-material Eulerian and arbitrary Lagrangian-Eulerian methods were used for the investigation due to the complexity of the microstructure, relatively large deformations and the ability to handle the formation of free surfaces in a natural manner. The calculations indicate that the observed dependence of sample strength on particle size is due to the formation of force chains under dynamic loading in samples with small particle sizes even at larger porosity in comparison with samples with large grain size and larger density. [Preview Abstract] |
Thursday, June 28, 2007 11:15AM - 11:30AM |
P6.00004: High-Speed Photography of Detonation Propagation in Dynamically Precompressed Liquid Explosives Oren Petel, Andrew Higgins, Akio Yoshinaka, Fan Zhang The propagation of detonation in shock compressed nitromethane was observed with a high speed framing camera. The test explosive, nitromethane, was compressed by a reverberating shock wave to pressures on the order of 10~GPa prior to being detonated by a secondary detonation event. The pressure and density in the test explosive prior to detonation was determined using two methods: manganin strain gauge measurements and LS-DYNA simulations. The velocity of the detonation front was determined from consecutive frames and correlated to the density of the explosive post-reverberating shock wave and prior to being detonated. Observing detonation propagation under these non-ambient conditions provides data which can be useful in the validation of equation of state models. [Preview Abstract] |
Thursday, June 28, 2007 11:30AM - 11:45AM |
P6.00005: Shock-induced reaction in Ti-Si powder mixtures Julian Lee, Fan Zhang The reactive properties of shocked powders consisting of a mixture of titanium and silicon have been investigated experimentally in cylindrical charges initiated by high explosives. Selected tests using a flyer plate for initiation were also performed for comparison. Although titanium and silicon are known to deflagrate and produce high-temperature solid products, shock-initiated reactions are not yet understood. In the present work, fine powders 1-5 $\mu$m in size are thoroughly mixed and packed into cylindrical containers with varying degrees of confinement. The packing density was varied between 30\% and 50\% TMD. Upon shock impact, a rapidly decaying supersonic reactive wave was observed through both optical and piezo-electric time-of- arrival gauges. The decay rate of the wave was found to depend very weakly on strength of confinement, but more strongly on packing density. Traditional detonation mechanisms such as volume expansion and front curvature may consequently not be applicable in systems with solid reactants and products. Post- test examination of the charges showed nearly complete reaction of the powder in most cases, indicating a sustained reaction in spite of the decay of the supersonic part of the reaction. [Preview Abstract] |
Thursday, June 28, 2007 11:45AM - 12:00PM |
P6.00006: Mechanical and Microstructural Properties of PTFE/Al/W Composite Jing Cai, Fengchun Jiang, Kenneth Vecchio, Marc Meyers, Vitali Nesterenko Mechanical and microstructural properties of PTFE/Al/W composites with a density up to 7.1 g/cc fabricated by cold isostatic pressing with identical weight ratios of constituents (PTFE serving as the matrix) were investigated using quasi-static and Hopkinson Bar compression tests. The ultimate compressive strengths of the PTFE/Al/W composite (7.1 g/cc) with coarse W particles was $\sim $18 MPa (quasistatic loading) and $\sim $24 MPa (dynamic loading), while more porous PTFE/Al/W composite with fine W particles (5.9 g/cc) had flow stress 24 MPa (quasistatic) and 44 MPa (dynamic). Critical strains to failure for both composites are 4-5{\%}. We attribute this unusual behavior to force chains created by small tungsten particles. Environmental scanning electron microscope revealed that the PTFE matrix was populated by a homogeneous distribution of nano-cracks and nanofibers of PTFE were observed after dropweight tests. [Preview Abstract] |
Thursday, June 28, 2007 12:00PM - 12:15PM |
P6.00007: Impact Initiation of Rods of Pressed Polytetrafluoroethylene (PTFE) and Aluminum Powders Willis Mock, Jr., Jason T. Drotar A gas gun has been used to investigate the impact initiation of rods consisting of a mixture of 72 wt{\%} PTFE (28 $\mu $m particle size) and 28 wt{\%} aluminum (95 micron particle size) powders. The rods were 7.6 mm in diameter by 51 mm long, and were fabricated from material that had been pressed and sintered to a full density of 2.27 gm/cm$^{ 3}$. They were sabot-launched into steel anvils at impact velocities ranging from 468 to 970 m/sec. This corresponds to calculated initial impact stresses of 25 to 64 kbar, respectively. A framing camera was used to observe the time sequence of events. These include change in rod shape, fracture, and the initiation and evolution of the reaction phenomena. The time of observation of first light after impact was taken as the initiation time. Initiation occurred at discrete locations in the impacted material. At the lowest impact stress of 25 kbar no light was observed; this value was taken as the initiation threshold stress for this material. Above the initiation threshold, the initiation time dropped abruptly from 74 $\mu $s just above threshold to 14 $\mu $s at the highest impact velocity of 970 m/s. These results are compared with rod impact experiments for a similar material [1] in which the only major difference is a smaller aluminum particle size (9 micron). [1] W. Mock, Jr. and W. H. Holt, in Proc. APS Shock Compression of Condensed Matter--2005, p.1097. [Preview Abstract] |
Thursday, June 28, 2007 12:15PM - 12:30PM |
P6.00008: Reaction of Titanium and Zirconium Particles in Cylindrical Explosive Charges David Frost, Malcolm Cairns, Samuel Goroshin, Fan Zhang The critical conditions for the reaction of high melting-point metallic particles (Ti, Zr) dispersed during the detonation of long cylindrical explosive charges have been investigated experimentally. The charges consisted of packed beds of either spherical titanium particles (with diameters of 35, 90, or 215 $\mu $m; AP{\&}C, Inc.) or nonspherical zirconium particles (250 -- 500 $\mu $m or 500 -- 600 $\mu $m, Atlantic Equipment Eng., NJ) saturated with sensitized liquid nitromethane. For the titanium particles, a threshold particle diameter exists, above which self-sustained particle reaction is not observed, although some particle reaction occurs immediately behind the detonation front then rapidly quenches. For the smallest particles, the proportion of the conical particle cloud that reacts increases with charge diameter, suggesting that the reaction initiation is a competition between particle heating and expansion cooling of the products. For zirconium particles, no critical conditions exist; particle ignition was observed for all particle and charge diameters tested. In this case, interaction of the high pressure detonation wave with the particles is sufficient to initiate reaction at the particle surface after a delay time ($\sim $ 10's $\mu $s), which is much less than the time required for thermal equilibration of the particles. [Preview Abstract] |
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