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 U6: Shock Initiation II |
Hide Abstracts |
Chair: Steven Chidester, Lawrence Livermore National Laboratory Room: Fairmont Orchid Hotel Promenade I/II |
Friday, June 29, 2007 8:00AM - 8:30AM |
U6.00001: The Puzzle of Explosive Response to Shock: Complexity to Simplicity by Changing the Observational Scale. Invited Speaker: At the mesoscale the shock interaction with a heterogeneous explosive is a complex mix of wave interactions with density discontinuities, localized heating, transient chemical reactions and multiphase flows. However, the macroscopic response can often be described in terms of simple phenomenological models. Those describing initiation thresholds and the onset of detonation have long been known and are widely used. This paper shows that simplicity at the continuum level is observed over a much larger range of explosive responses; from the parallel behaviours of the different markers present during reaction growth, to the simple rules for scaling in-material gauge results. The transition from complex trigger to simple response currently provides one of the great challenges for understanding explosive behaviour, and aspects of this transition will be explored and discussed. [Preview Abstract] |
Friday, June 29, 2007 8:30AM - 8:45AM |
U6.00002: Effect of Transverse Electric Field on Sensitivity of an 88{\%} by Weight HMX Based Energetic Material Richard Lee, Jerry Forbes, Edward Palermo, William Wilson Thresholds for shock sensitivity were determined for explosive samples with and without applied fields using a variation of the Navy's modified gap test. Rectangular charges (76 mm wide x 12.7 mm long x 5 mm thick) confined on two sides by 50.8 mm thick bars of Teflon were shock loaded using the Navy's standard large scale gap test donor system. Free surface velocity at the opposite end of the sample (12.7 mm from input surface) was measured using a high-speed camera. Velocity versus input pressure plots highlight thresholds for first reaction, deflagration, and detonation. In addition the use of an intensified high-speed electronic camera provided a clear differentiation of when the products were self-luminous, directly confirming initiation. Electric fields were applied transverse to the shock direction via thin foil electrodes. These electrodes were held in place by the Teflon insulation. The data shows that this energetic material requires less input pressure to ignite the reaction with voltages of 5 kV applied across the 5 mm thick sample as compared to results without a field. [Preview Abstract] |
Friday, June 29, 2007 8:45AM - 9:00AM |
U6.00003: Shock Initiation Thresholds for Insensitive High Explosives Hugh James Work with conventional high explosives shows that the initiation thresholds for a variety of projectile types can be mapped onto a single curve in a space defined by the pressure or particle velocity of the initial shock, and the time of the maximum non-divergent shock volume generated in the explosive by the initial impact. This curve is distinct from, although parallel to, the Pop Plot curve, where the time is defined as the time to detonation. In contrast for an insensitive high explosive, the location of the initiation thresholds in the above space appear divided between those forming a distinct threshold curve and those which appear to be a continuation of the Pop Plot. Projectile diameters larger than the failure diameter still form a distinct threshold, but smaller projectile diameters lie on the Pop Plot curve. An examination of the data indicates that impacts lying on the threshold curve produce non-divergent detonations. These detonations appear likely to remain non-divergent or even fade. The initial conditions need to be enhanced so that the impact lies on, or just above, the Pop Plot before divergence takes place. Those initial conditions that lie on the Pop Plot only need sufficient run distance in the explosive before a diverging detonation is achieved. [Preview Abstract] |
Friday, June 29, 2007 9:00AM - 9:15AM |
U6.00004: A Study of SDT in an Ammonium Nitrate (NH$_{4}$ NO$_{3})$ Based Granular Explosive Malcolm Burns, Peter Taylor In order to study the SDT process in a granular non ideal explosive (NIE) an experimental technique has been developed that allows the granular explosive to be shock initiated at a well controlled ``tap density''. The granular NIE was contained in a PMMA cone and a planar shock was delivered to the explosive through buffer plates of varying material. A combination of piezoelectric probes, ionization pins, PVDF stress gauges and a high speed framing camera were used to measure the input shock pressure and shock and detonation wave positions in the explosive. Four trials were performed to characterize the run to detonation distance versus pressure relationship (Pop plot) of the granular NH$_{4}$ NO$_{3}$ explosive. Input pressures ranged from close to the 4GPa predicted CJ pressure of the granular explosive down to 1.4 GPa, giving run distances up to 14mm for the lowest pressure. The data indicates a steady acceleration of the input shock to the detonation velocity, implying significant reaction growth at the shock front. This is in contrast to the behaviour of most high density pressed PBXs which show little growth in shock front velocity before transit to detonation. The experimentally observed initiation behaviour is compared to that predicted by a simple JWL++ reactive burn model for the granular NH$_{4}$ NO$_{3}$ explosive which has been fitted to other detonics experiments on this material. [Preview Abstract] |
Friday, June 29, 2007 9:15AM - 9:30AM |
U6.00005: Shock Reactivity Study on Standard and Reduced Sensitivity RDX of Different Particle Size Distributions Nicholas McGregor, Allen Lindfors Embedded gauge experiments have been performed using a three inch high velocity powder gun to assess the effects of RDX particle size and crystal quality on shock induced reactivity in support of the Combat Safe Insensitive Munitions (CSIM) program. Four monomodal experimental compositions containing 73{\%} solids loading by weight and 27{\%} HTPB binder were tested. The compositions were made using either standard or reduced sensitivity grades of RDX in Class 5 or Class 1 150-300 micron sieve cut particle size classes. Results have shown marked changes in the mode of reaction between the two particle size classes. Both RDX grades at the Class 1 sieve cut particle size distribution showed significant reaction at the shock front as well as behind the front. The Class 5 RDX compositions however showed little reaction at the shock front with rapid growth behind the front. Similar input pressures resulted in a full detonation in a similar distance for like RDX grades. Reaction modes were similar but occurring at greater input pressures for the reduced sensitivity grade of RDX compared to the corresponding particle size distribution standard grade RDX counterpart. [Preview Abstract] |
Friday, June 29, 2007 9:30AM - 9:45AM |
U6.00006: Initiation of Explosives From the Bow Shock of a Supersonic Penetrator Eric N. Ferm An analytic and computational study of supersonic penetration of an explosive is presented. The goal is the development of an initiation criterion relating projectile diameter and threshold projectile velocity determined by fundamental material and explosive parameters. The basis of the initiation criterion is an examination of the steady flow structure around a supersonic penetrator in the unreacted materials, yielding the states along the bow shock and the size and sonic character of the flow structure. The state is used to determine the time scale of the reacting explosive using initiation experiment results (Pop Plot). The size of the subsonic region is compared to the failure diameter to examine the viability of the initiation. The results are compared with experimental initiation criterion. [Preview Abstract] |
Friday, June 29, 2007 9:45AM - 10:00AM |
U6.00007: Coherency for the Critical Condition of DDT and SDT in Energetic Materials Huan Shi, Tan Xiangqian Most of the past research for the energetic materials focused on the SDT for explosives and DDT for solid propellants. Since the difference between the explosive and solid propellant decreases with the increase of the energy density in the solid propellant, the study of SDT for the solid propellant is needed. In this paper, two-dimensional SDT experiments and thin wall copper DDT experiments have been carried out for two types explosives[E1(95{\%} RDX), E2(95{\%} HMX)] and two types solid propellants[P1(55{\%} RDX), P2(55{\%} HMX)] to investigate the coherency for the critical conditions of SDT and DDT for the same energetic materials. The results show that E1 has the highest sensitivity in both the SDT and DDT tests followed by E2, P1 and P2. Although such rules cannot be generalized to all high energetic materials, it is obvious that a relationship exists between SDT and DDT sensitivity. The relationship between the deflagration hazard in SDT and the combustion hazard in DDT is critical in this study. The measured critical conditions and parameters such as the increase velocity of combustion peak, the highest scope and the movement velocity in SDT indicated that coherency exists between the SDT and DDT. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700