Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session S2: Energetic and Reactive Materials: Hot Spots and Criticality |
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Chair: Cole Valancius, Sandia National Laboratories Room: Grand Ballroom AB |
Thursday, July 13, 2017 9:15AM - 9:30AM |
S2.00001: A Volumetric Approach to Shock Initiation of Hexanitrostilbene and Pentaerythritol Tetranitrate Mike Bowden A range of analytic shock initiation criteria have been developed, such as those proposed by Walker {\&} Wasley and James. Such criteria allow rapid assessment of whether a particular shock stimulus will result in detonation of explosives. These criteria have been developed for a range of impactors, such as flyers, rods, and spheres, using a single dimension of the impactor, such as diameter. Initiation studies of hexanitrostilbene and pentaerythritol tetranitrate by thin, curved flyers has indicated the need for a three-dimensional shock initiation criteria. A shock initiation criteria, based on the concept of a critical shock volume as a function of shock pressure, has been developed, and shown to describe this data more completely than existing criteria. [Preview Abstract] |
Thursday, July 13, 2017 9:30AM - 9:45AM |
S2.00002: Criticality and Induction Time of Hot Spots in Detonating Heterogeneous Explosives Larry Hill Detonation reaction in physically heterogeneous explosives is--to an extent that depends on multiple material attributes--likewise heterogeneous. Like all heterogeneous reaction, detonation heterogeneous reaction begins at nucleation sites, which, in this case, comprise localized regions of higher-than-average temperature--so-called hot spots. Burning grows at, and then spreads from these nucleation sites, via reactive-thermal (R-T) waves, to consume the interstitial material. Not all hot spots are consequential, but only those that are 1) supercritical, and 2) sufficiently so as to form R-T waves before being consumed by those already emanating from neighboring sites. I explore aspects of these two effects by deriving simple formulae for hot spot criticality and the induction time of supercritical hot spots. These results serve to illustrate the non-intuitive, yet mathematically simplifying, effects of extreme dependence of reaction rate upon temperature. They can play a role in the development of better reactive burn models, for which we seek to homogenize the essentials of heterogeneous detonation reaction without introducing spurious complexity. [Preview Abstract] |
Thursday, July 13, 2017 9:45AM - 10:00AM |
S2.00003: Criticality conditions of heterogeneous energetic materials under shock loading Anas Nassar, Nirmal Kumar Rai, Oishik Sen, H. S. Udaykumar Shock interaction with the microstructural heterogeneities of energetic materials can lead to the formation of locally heated regions known as hot spots. These hot spots are the potential sites where chemical reaction may be initiated. However, the ability of a hot spot to initiate chemical reaction depends on its size, shape and strength (temperature). Previous study by Tarver et al. has shown that there exists a critical size and temperature for a given shape (spherical, cylindrical, and planar) of the hot spot above which reaction initiation is imminent. Tarver et al. assumed a constant temperature variation in the hot spot. However, the meso-scale simulations show that the temperature distribution within a hot spot formed from processes such as void collapse is seldom constant. Also, the shape of a hot spot can be arbitrary. This work is an attempt towards development of a critical hot spot curve which is a function of loading strength, duration and void morphology. To achieve the aforementioned goal, mesoscale simulations are conducted on porous HMX material. The process is repeated for different loading conditions and void sizes. The hot spots formed in the process are examined for criticality depending on whether they will ignite or not. The metamodel is used to obtain criticality curves and is compared with the critical hot spot curve of Tarver et al. [Preview Abstract] |
Thursday, July 13, 2017 10:00AM - 10:15AM |
S2.00004: Towards Understanding the Role of Microstructure in Energetic Material Response: Coarse-Grain Modeling and Simulation John Brennan, Sergei Izvekov, Martin Lisal, James Larentzos Mechanical and thermal loading of energetic material (EM) composites can incite responses over a wide range of spatial and temporal scales due to inherent microscale features. Many energy transfer processes within these materials are atomistically governed, yet the overall material response is manifested at the micro- and mesoscale -- scales beyond those amenable to atomistic simulation techniques. Moreover, continuum level approaches rely on field-based formulations that are empirically based, which lack sufficient fidelity to capture microstructure effects. Particle-based microscale simulation methods that utilize coarse-grain models offer a promising route for extending the attributes of atomistic modeling toward the mesoscale. We have developed such microscale methods based upon the constant-energy dissipative particle dynamics method that includes chemical reactions. Coarse-grain models of EMs have been built using the Multiscale Coarse-Graining approach. Time-resolved depictions of an EM responding to insult has been simulated for a variety of microstructures, including samples with intra- and inter-granular voids of varying shape, size and relative orientation, varying grain shapes and sizes, and polymer binder. A sampling of these results will be presented. [Preview Abstract] |
Thursday, July 13, 2017 10:15AM - 10:30AM |
S2.00005: Morphological effects on sensitivity of heterogeneous energetic materials Sidhartha Roy, Nirmal Rai, Oishik Sen, H.S. Udaykumar The mesoscale physical response under shock loading in heterogeneous energetics is inherently linked to the microstructural characteristics. The current work demonstrates the connection between the microstructural features of porous energetic material and its sensitivity. A unified levelset based framework is developed to characterize the microstructures of a given sample. Several morphological metrics describing the mesoscale geometry of the materials are extracted using the current tool including anisotropy, tortuosity, surface to volume, nearest neighbors, size and curvature distributions. The relevant metrics among the ones extracted are identified and correlated to the mesoscale response of the energetic materials under shock loading. Two classes of problems are considered here: (a) field of idealized voids embedded in the HMX material and (b) real samples of pressed HMX. The effects of stochasticity associated with void arrangements on the sensitivity of the energetic material samples are shown. In summary, this work demonstrates the relationship between the mesoscale morphology and shock response of heterogeneous energetic materials using a levelset based framework. [Preview Abstract] |
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