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 Q6: Explosives/Mechanical Response II |
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Chair: David Williamson, Cambridge University Room: Fairmont Orchid Hotel Promenade I/II |
Thursday, June 28, 2007 1:45PM - 2:15PM |
Q6.00001: Dislocations and Dynamic Yield of RDX Single Crystals Invited Speaker: To further understand the role of dislocations in the dynamic yield point and shock initiation of single crystals of explosives, shock wave loading experiments were performed on the (100), (210), and (111) planes of RDX at impact stresses of about 1GPa. Defect content in the crystals and the surface polishing technique were varied and the resulting materials were characterized by polarized light, differential interference contrast, and scanning probe microscopy. In previous experiments on (100) oriented crystals, multiple elastic peaks were thought to be due to cracks in specific directions introduced during experiment assembly; experiments were performed to try to reproduce these features on other crystal orientations by deliberately choosing crystals with voids and poorer surface finish. The multiple elastic steps are discrete events potentially caused by one or more defects that eventually lead to a disperse elastic-plastic transition as observed in randomly oriented powders or perhaps sufficiently defective single crystals. To understand the relative importance of discrete crystal plasticity we have begun nano-indentation experiments on the crystals demonstrating plastic yielding without fracture in RDX, a technique tested using the simulant sucrose. [Preview Abstract] |
Thursday, June 28, 2007 2:15PM - 2:30PM |
Q6.00002: A Study of the Shock Sensitivity of PBX 9501 Damaged by Compressive Loading Darla Thompson, Richard Gustavsen, Daniel Hooks, Paul Peterson, Racci DeLuca, David Stahl, Stephanie Hagelberg, Robert Alcon We have studied the effects of damage caused by compressive loading on the shock sensitivity of the plastic bonded explosive PBX 9501. PBX 9501 consists of 95 wt. {\%} HMX (C4H8N8O8) and 5 wt. {\%} Nitroplasticized Estane binder. The binder is a mixture of 49 wt. {\%} Estane$^{\mbox{{\textregistered}}}$5703 (BF Goodrich), 49 wt. {\%} Nitroplasticizer (a 50/50 eutectic mixture of bis(2,2-dinitropropyl)formal and bis(2,2 dinitropropyl)acetal), and 2 wt. {\%} Irganox$^{\mbox{{\textregistered}}}$ 1010 stabilizer. PBX 9501 cubes, 25.4 mm on a side, were subjected to various uniaxial compressive loads in an Instron machine. After loading, 3.5 mm thick slices were taken from the center of each cube. These slices were then subjected to nearly identical 35 kbar shocks. Transmitted shock wave profiles were measured using interface velocimetry (VISAR). Comparison of shock wave growth is a measure of shock sensitivity. Results on four specimens are being analyzed relative to previous baseline data on PBX 9501 at various pressed densities, to determine if the response of damaged material is due to factors other than simple density changes. \textit{(LA-UR 07-1206)} [Preview Abstract] |
Thursday, June 28, 2007 2:30PM - 2:45PM |
Q6.00003: High Strain, Strain Rate Behavior of PTFE/Al/W John Addiss, Jing Cai, Steve Walley, William Proud, Vitali Nesterenko Conventional dropweight technique was modified to accommodate low amplitude signals from low strength, cold isostatically pressed energetic ``heavy'' composites of polytetrafluoroethylene (PTFE)/AL/W.~ The fracture strength, strain and post-critical behaviour of fractured samples were measured for samples of different porosity and W grain size (the masses of each component being the same in each case).~ Unusual phenomenon of significantly higher strength (55 MPa) of porous composites (density 5.9 g/cc) with small tungsten particles (1 micron) in comparison with strength (32 MPa) of dense composites (7.1 g/cc) with larger tungsten particles (20 micron) was observed.~ This is attributed to force chains created by a network of small tungsten particles. Interrupted tests at the different level of strains revealed mechanism of fracture under dynamic compression. [Preview Abstract] |
Thursday, June 28, 2007 2:45PM - 3:15PM |
Q6.00004: Shear Induced Reaction Localizations and Mechanisms of Energy Dissipation in PBX Subjected to Strong Shock Invited Speaker: Paper addresses two emerging topics: how reaction initiation arises when PBX is subjected to shock and how detonation wave becomes oscillating. We apply the 96-channel optical analyzer for simultaneous measurements of radiation from the reaction spots surface and stress field caused by shock or detonation reaction zone in multi-layer optical monitor. This metrology allows meso-scale probing of the 3-D structure of shock- or detonation- reaction-zone as well as revealing mechanisms of its formation at different initiation scenarios. The dominant role of the shear driven plastic deformation in initiation scenario is disclosed in all tested PBX-s (including simulants of PBXN-110, PBAN-128, PBXN-109, 111, 121 and B-2208), in wide range of PBX sample sizes: from 1 mm$^{3}$ (single crystal within the binder) up to few cm$^{3}$. This research is complementing a separate, longer running, theoretical effort by Dr. Steve Coffey that examines the solid state--quantum physics responsible for initiation of explosive crystals subjected to shock or impact. Finally, this represents a novel research effort to relate plastic deformation, energy dissipation and localization in crystals to shear and shear deformation. The accompanying experimental results strongly support Coffey's theoretical prediction that initiation is due to shear driven plastic deformation and is not due solely to uniform shock pressure. Finally, we will present and discuss the recently revealed phenomenon of the thermal precursor origination caused by the reaction front radiation. The role of this earlier unknown energy localization mechanism, at Shock-to-Detonation transition in PBX, will be shown as a function of HMX particle sizes and the PBX porosity. [Preview Abstract] |
Thursday, June 28, 2007 3:15PM - 3:30PM |
Q6.00005: A Viscoelastic Fracture Model for Simulation of Solid Propellant Impacts Erik R. Matheson A viscoelastic kinetics (VEK) model for deformation and damage in solid rocket propellant has been previously developed and correlated to an extensive set of experiments to determine mechanical properties. Ultimately, VEK will be extended to perform coupled damage and reaction modeling of XDT during propellant impacts. There are two types of damage considered in VEK: 1) decohesion at particle/binder interfaces, and 2) scission of the binder. The first type of damage leads to formation of essentially spherical voids around the decohered particles, and development of a model for the surface area that supports combustion is rather straightforward. The second type of damage leads to formation of propellant rubble, and the fineness depends on the impact stresses. Thus, a kinetic fracture model describing surface area generation due to scission damage has been added to the VEK model. To obtain data on the surface area generated, 25 mm $L/D$=1 propellant samples were fired into steel target plates at various velocities, and the resultant fragments were collected and burned in a combustion bomb. The total surface area generated was then estimated for each impacted sample. The upgraded VEK model is used to simulate the 25 mm impact experiments and is correlated to the combustion bomb data. [Preview Abstract] |
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