Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session S2: Energetic and Reactive Materials IX: Microstructural Effects |
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Chair: Laura Smilowitz, Los Alamos National Laboratory, Fan Zhang, Defence R&D Canada-Suffield Room: Grand F |
Thursday, June 18, 2015 9:15AM - 9:30AM |
S2.00001: Study of void collapse leading to shock initiation and ignition in heterogeneous energetic material Nirmal Kumar Rai, Sushilkumar Prabu Koundinyan, H.S. Udaykumar In heterogeneous energetic materials like PBX, porosity plays an important role in shock initiation and ignition. This is because the collapse of voids leads to the formation of local high temperature regions termed as hot spots under the application of shock loading. The formation of hot spots can take place because of several mechanisms such as plastic deformation of voids, hydrodynamic impact on voids leading to the formation of high speed material jets etc. Once these hot spots are formed, they can lead to reaction and ignition in the explosive material. However, diffusive phenomenon like heat conduction can play an important role in shock initiation because depending on the size and intensity of void collapse hot spots, local ignition conditions can be smeared out. In the current work, void collapse leading to shock initiation and ignition in HMX has been studied using a massively parallel Eulerian code, SCIMITAR3D. The chemical kinetics of HMX decomposition and reaction has been modeled using the Henson-Smilowitz multi-step mechanism. Based on the current framework an ignition criterion has been established for single void collapse analysis for various shock strengths. Furthermore, the effects of void-void interactions have been analyzed demonstrating the important role of the combination of void fraction, reaction chemistry and heat conduction in determining the ignition threshold. [Preview Abstract] |
Thursday, June 18, 2015 9:30AM - 9:45AM |
S2.00002: Study of void sizes and loading configurations effects on shock initiation due to void collapse in heterogeneous energetic materials Sidhartha Roy, Nirmal Rai, H.S. Udaykumar In heterogeneous energetic materials, presence of porosity has been seen to increase its sensitivity towards shock initiation and ignition. Under the application of shock load, the viscoplastic deformation of voids and its collapse leads to the formation of local high temperature regions known as hot spots. The chemical reaction triggers at the hot spot depending on the local temperature and grows eventually leading to ignition and formation of detonation waves in the material. The temperature of the hot spot depends on various factors such as shock strength, void size, void arrangements, loading configuration etc. Hence, to gain deeper understanding on shock initiation and ignition study due to void collapse, a parametric study involving various factors which can affect the hot spot temperature is desired. In the current work, effects of void sizes, shock strength and loading configurations has been studied for shock initiation in HMX using massively parallel Eulerian code, SCIMITAR3D. The chemical reaction and decomposition for HMX has been modeled using Henson-Smilowitz multi step mechanism. The effect of heat conduction has also been taken into consideration. Ignition threshold criterion has been established for various factors as mentioned. The critical hot spot temperature and its size which can lead to ignition has been obtained from numerical experiments. [Preview Abstract] |
Thursday, June 18, 2015 9:45AM - 10:00AM |
S2.00003: Development of numerical framework to study microstructural effects on shock initiation in heterogeneous energetic materials Martin Schmidt, Nirmal Rai, H.S. Udaykumar Heterogeneous energetic materials like plastic bonded explosives (PBX) have very detailed and non-uniform microstructure. The heterogeneity is mainly because of presence of HMX crystals embedded in a polymer binder matrix. Also, manufacturing defects often creates pores and cracks in the material. Shock interaction with these heterogeneities leads to local heated regions known as hot spots. It is widely accepted that these hot spots are predominantly the cause of triggering reaction and eventually ignition in these energetic materials. There are various physical phenomenon through which hot spot can be created such as pore collapse, inter-granular friction in HMX crystals, shock heating of HMX crystals and binder etc. Hence, microstructural heterogeneity can play a vital role for shock initiation in PBX. In the current work, a general framework has been established for performing mesoscale simulations on heterogeneous energetic material. In order to get an accurate representation of the microstructure, image processing algorithms have been employed on XCMT images of PBX microstructure. The image processing framework has been built up with massively parallel Eulerian code, SCIMITAR3D. Shock simulation on PBX microstructures has been performed and the effect of microstructure geometry has been studied for different shock strengths case. The simulation results have been shown to resolve hot spots created due to various heterogeneities present in the microstructure. [Preview Abstract] |
Thursday, June 18, 2015 10:00AM - 10:15AM |
S2.00004: Subscale Testing of Prompt Agent Defeat Formulations Christopher Milby, Demitrios Stamatis, Amber Daniels, Forrest Svingala, Jim Lightstone, Kendra Miller, Misty Bensman, Matthew Bohmke There is a need to improve the current bioagent defeat systems with formulations that produce lower peak pressure, impulse, sustained high temperatures, and release of biocidal species for prompt defeat applications. In this work, explosive charge configurations similar to fuel-air explosives were detonated in a semi-enclosed chamber configuration. Binder type and fuel-to-oxidizer ratios were varied to observe the effects on combustion performance. Thermocouple measurements and high-speed video were used to monitor the combustion of the dispersed formulation. The down-selected formulations were then tested in a sub-scale vented agent defeat system developed to evaluate performance of formulations against aerosolized Bacillus thuringiensis (BT) spores. Diagnostics such as thermocouples, piezoelectric pressure gauges, and pyrometry were utilized to characterize the detonation event. Biological sampling with surface coupons, liquid impingement, and filters of the post detonation environment were utilized to determine spore survivability and rank the relative effectiveness of each formulation. Distribution Statement A: Approved for Public Release; Distribution is Unlimited [Preview Abstract] |
Thursday, June 18, 2015 10:15AM - 10:30AM |
S2.00005: Radio-frequency electromagnetic emissions from materials under high-frequency mechanical excitation Christian Sorensen, David Moore Direct contact piezoelectric transducers were used to excite compacted polycrystalline dielectric material samples with high amplitude but short duration ultrasound through a frequency range of 50 kHz to 10 MHz, while near field RF emissions were measured in 12 frequency bands from 18 to 750 GHz using a suite of detectors. Emissions were observed only in three detectors, covering the 40-75 GHz, 110-170 GHz, and 170-260 GHz frequency ranges. Emission amplitudes appear to rise nonlinearly with applied ultrasound amplitude, and the emission amplitudes versus ultrasound frequency are different than the thermal responses of these samples. Data comparing thermal responses and electromagnetic emissions versus ultrasound frequency and amplitude for several sample types (oxidizers and energetic materials) will be presented. [Preview Abstract] |
Thursday, June 18, 2015 10:30AM - 10:45AM |
S2.00006: Effect of Pellet Coatings on PETN Porosity and Slapper Detonator Efficacy Kathryn Brown, Erik Haroz, Geoff Brown, Deirdre Monroe PETN is well known to have a high vapor pressure and tends to sublime when heated. Preliminary experiments suggest that this phenomenon results in increased porosity and may decrease sensitivity to shock initiation by a chip slapper detonator. In this study, PETN pellets were coated on the flyer impact surface with various materials. The pellets were subjected to heating over several days, and the surfaces were analyzed for porosity and recrystallization. We attempted to shock initiate each using a chip slapper detonator, and the timing and voltages required were noted. [Preview Abstract] |
Thursday, June 18, 2015 10:45AM - 11:00AM |
S2.00007: Shock initiation of the {TATB} based explosive {PBX} 9502 heated to $\sim$ 76$^{\circ}${C} Richard Gustavsen, Russell Gehr, Scott Bucholtz, Adam Pacheco, Brian Bartram Recently we reported on shock initiation of PBX 9502 (95 wt.\% tri-amino-trinitro-benzene, 5 wt.\% Kel-F800 binder) cooled to -55$^{\circ}$C (J. Appl. Phys., 112, 74909 (2012)) and to 77K (J. Phys.: Conf. Ser. 500, 182014 (2014)) Shock waves were generated by gas-gun driven plate impacts and reactive flow in the cooled PBX 9502 was measured with embedded electromagnetic gauges. Here we use similar methods to warm the explosive to $\sim$ 76$^{\circ}$C. The explosive sample is heated by warm air flowing through channels in an aluminum sample mounting plate and a copper tubing coil surrounding the sample. Temperature in the sample is monitored using six type-E thermocouples. Results show increased shock sensitivity; time and distance to detonation onset vs. initial shock pressure are shorter than when the sample is initially at ambient temperature. Our results are consistent with those reported by Dallman \& Wackerle (10$^{th}$ Int. Det. Symp., 130 (1993)). Particle velocity wave profiles were also obtained during the shock-to-detonation transition and will be presented. [Preview Abstract] |
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