Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session R5: EM.1 Detonation II |
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Chair: Carlos Chiquete, Los Alamos National Laboratory Room: Cascade I |
Wednesday, July 10, 2013 3:30PM - 3:45PM |
R5.00001: Experimental Measurement of the Scaling of the Diameter- and Thickness-Effect Curves for Ideal, Insensitive, and Non-Ideal Explosives Scott Jackson, Mark Short Numerous two-dimensional high-explosive slab rate sticks were fielded for explosives that exhibit ideal (PBX 9501), slightly non-ideal (PBX 9502), and highly non-ideal (ANFO) detonation. Detonation velocity versus slab thickness $t$ (thickness-effect curves) are compared to previous diameter-effect measurements obtained by varying the diameter $d$ of cylindrical rate sticks. The scale factors $d/t$ necessary to overlay the diameter- and thickness-effect curves were computed for each explosive formulation. We observe that the scale factor varies with detonation velocity (or level of detonation ``ideality''). The measured scale factors range from 1.89--2.20, 1.41--1.87, and 1.79--1.05 for PBX 9501, PBX 9502, and ANFO formulations, respectively, as detonation velocity varies from the (near failure) critical velocity to the Chapman-Jouget velocity. These results support our previous theoretical prediction that the scale factor relating the diameter- and thickness-effect curves will increasingly deviate from two as the detonation structure becomes increasingly non-ideal. [Preview Abstract] |
Wednesday, July 10, 2013 3:45PM - 4:00PM |
R5.00002: Critical detonation thickness in vapor-deposited hexanitroazobenzene (HNAB) films with different preparation conditions Alexander S. Tappan, Robert Knepper, Michael P. Marquez, J. Patrick Ball, Jill C. Miller At Sandia National Laboratories, we have coined the term ``microenergetics'' to describe sub-millimeter energetic material studies aimed at gaining knowledge of combustion and detonation behavior at the mesoscale. Films of the high explosive hexanitroazobenzene (HNAB) have been deposited through physical vapor deposition. HNAB deposits in an amorphous state that crystallizes over time and modest heating accelerates this crystallization. HNAB films were prepared under different crystallization temperatures, and characterized with surface profilometry and scanning electron microscopy. The critical detonation thickness for HNAB at different crystallization conditions was determined in a configuration where charge width was large compared to film thickness, and thus side losses did not play a role in detonation propagation. The results of these experiments will be discussed in the context of small sample geometry, deposited film morphology, crystal structure, and density. [Preview Abstract] |
Wednesday, July 10, 2013 4:00PM - 4:30PM |
R5.00003: Converging shocks for DSD modelling Invited Speaker: Christophe Matignon Modelling of pyrotechnic systems requires both, a good understanding and precise prediction capabilities of the dynamics of detonation. When using insensitive high explosives IHE (such as TATB-based explosives) the interaction of the detonation front with the confinement can lead to very different detonation velocities. One of the most popular engineering tools used to model this behaviour is the Detonation Shock Dynamics (DSD). In the DSD assumption, the detonation front propagates at a normal shock velocity ($D_n$) which depends only on its local curvature ($\kappa$). For divergent detonations, the DSD limit is very well established both experimentally and theoretically and one can easily propose a model (which obeys the 1D quasi-steady weakly curved detonation theory) to reproduce this behavior. We propose to extend the DSD theory to slightly convergent detonation fronts and to validate it against experimental data. Two series of experiments were carried out. The first series was designed to collect precise information regarding converging detonation. Usually, in such configurations, the detonation is non steady, making precise and simultaneous measurements of velocity and curvature difficult to achieve. The originality of the proposed setup is to drive a self similar convergent detonation at constant speed in an IHE rod by an external explosive tube of greater detonation velocity (allowing an accurate recording of both velocity and curvature). A wide range EOS/reaction rate model (inspired from previous works of Wescott et al.) was then calibrated to reproduce both the strong shock initiation and the newly extended ($D_n$-$\kappa$) law. This model can be used to perform either direct numerical simulation (DNS) on fine resolved mesh grid, or its reduced PZR model (DSD based) on a much coarser grid. This model was then successfully validated against the second series of experiments involving a detonation propagating around an obstacle and exhibiting a non steady converging front while passing the obstacle. Discussions will be focussed on the uniqueness of the ($D_n$-$\kappa$) law on the converging branch ($\kappa<0$) and the ability of DSD to reproduce accelerating detonation fronts through comparisons between DSD and DNS calculations with experimental data. [Preview Abstract] |
Wednesday, July 10, 2013 4:30PM - 4:45PM |
R5.00004: Modelling an IHE Experiment with a Suite of DSD Models Alexander Hodgson At the 2011 APS conference, Terrones, Burkett and Morris published an experiment primarily designed to allow examination of the propagation of a detonation front in a 3-dimensional charge of PBX9502 insensitive high explosive. The charge is confined by a cylindrical steel shell, has an elliptical tin liner, and is line-initiated along its length. The detonation wave must propagate around the inner hollow region and converge on the opposite side. The Detonation Shock Dynamics (DSD) model allows for the calculation of detonation propagation in a region of explosive using a selection of material input parameters, amongst which is the D-K relation that governs how the local detonation velocity varies as a function of wave curvature. In this paper, experimental data are compared to calculations using the newly-developed 3D DSD code at AWE with a variety of D-K relations. The effects of D-K variation through different calibration methods, material lot and initial density are investigated. [Preview Abstract] |
Wednesday, July 10, 2013 4:45PM - 5:00PM |
R5.00005: Detonation performance of high-dense BTF charges Alexander Dolgoborodov, Michael Brazhnikov, Michael Makhov, Sergey Gubin, Irina Maklasova New experimental data on detonation wave parameters and explosive performance for benzotrifuroxan (BTF) are presented. Optical pyrometry was applied in order to measure the temperature and pressure of BTF detonation products. Chapman-Jouguet pressure and temperature were obtained as following: 33.8 GPa and 3990 K; 34.5 GPa and 4170 K (initial charge densities 1.82 and 1.84 g/cc respectively), the polytropic exponent was estimated as 2.8. The heat of explosion and acceleration ability were measured also. The results of calorimetric measurements performed in bomb calorimeter indicate that BTF slightly surpasses HMX in the heat of explosion. However BTF is inferior to HMX in the acceleration ability, measured by the method of copper casing expansion. It is also considered the hypothesis of formation of nanocarbon particles in detonation products directly behind the detonation front and influence of this processes on the temperature-time history in detonation products. The results of calculations with in view of formation of liquid nanocarbon in products of a detonation also are presented. [Preview Abstract] |
Wednesday, July 10, 2013 5:00PM - 5:15PM |
R5.00006: Effects of confinement conditions on the detonation properties of vapor-deposited hexanitroazobenzene films Robert Knepper, Michael Marquez, Alexander Tappan It is well known that confining an explosive with a high-density inert material can cause substantial changes in its detonation properties. However, the thickness of confinement needed and the magnitude of the effect on quantities such as detonation velocity and critical thickness are largely unknown. In this work, we present vapor-deposited hexanitroazobenzene (HNAB) and copper films as a model system to study the effects of confinement on the detonation properties of secondary explosives. HNAB is chosen for the reproducibility of both its microstructure and detonation velocity when vapor-deposited, as well as for its small critical thickness and the low surface roughness of the deposited films. Both the HNAB and copper confinement layers are vapor-deposited to promote intimate contact between the explosive and confinement and to provide precise control over both layer thicknesses and microstructure. Confinement thickness is varied to determine the minimum necessary to behave as though the confinement was effectively infinite, and the effects on detonation properties are quantified. These experiments may also provide insight into the structure of the detonation reaction zone by using the infinite confinement conditions (thickness and shock speed) to give an indirect measure of the reaction zone length. [Preview Abstract] |
Wednesday, July 10, 2013 5:15PM - 5:30PM |
R5.00007: On the Partially Reacted Boundary Layer in Rate Sticks Yehuda Partom Using our reactive flow model TDRR to simulate detonation in a rate stick, we observe that a partially reacted layer (PRL) is formed near the boundary. We are not aware that such a PRL has been observed in tests, and this is why we regarded it in the past as a numerical artifact. Assuming that such an artifact may be caused by the finite rise time of the detonation shock, we showed in [1] how it can be eliminated by delaying the outward boundary motion for a length of time comparable with the shock rise time. Here we revisit the PRL problem. First we show that it is not a numerical artifact but a real phenomenon. We do this by repeating the reactive flow run with a finer resolution. By looking at the PRL structure, we see doubling the resolution affects the PRL only slightly. We then conjecture that the PRL formation has to do with the finite duration of the reaction process (or the finite extent of the reaction zone). By the time the boundary rarefaction reaches a cell near the boundary, it is only partially reacted, and its reaction is cut off. To strengthen our conjecture we also show how the PRL structure changes with the reaction duration. \\[4pt] [1] Yehuda Partom, Reactive Flow calculation near a Free Boundary, SCCM, 405-408 (2007). [Preview Abstract] |
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