Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session D2: ERM: Sensitivity, Safety, and Initiation |
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Chair: Su Peiris Room: Grand Ballroom II |
Monday, June 17, 2019 2:00PM - 2:15PM |
D2.00001: A comparison of Gaussian Process Classification to classical statistical methods in sensitivity tests Alex Casey, Nick Cummock, Ilias Bilionis, Steven Son The input at which there is 50\% probability of a `go' in a binary outcome test -- also known as the L50 -- is a commonly used safety metric when evaluating the sensitivity of energetic materials to impact and shock. The L50 of a given material is typically determined using the Neyer Sensitivity Test or the Bruceton Test. These tests can provide a framework for a sequential design of experiments in order to choose the subsequent input given the observed data. In the present work, Gaussian Process Classification (GPC) is similarly applied to sensitivity test data to estimate a material's L50 and design sequential experiments. The GPC model defines a probability distribution over function space which provides a rich representation of the underpinning function. The function space can be constrained to those with a physically-based rationale. Additionally, the GPC model is easily extensible to experiments with multivariate inputs. A comparison of the Neyer and GPC statistical methods is presented alongside their implementation on a multivariate input gap-test experiment involving PBX 9501 pellets of varying porosities. [Preview Abstract] |
Monday, June 17, 2019 2:15PM - 2:30PM |
D2.00002: TNT Equivalency Testing for Energetic Materials Kevin M. Jaansalu, Christelle Collet, Ernest L. Baker, Martijn M. van der Voort TNT equivalency is commonly used to quantify the explosive effects of energetic materials and munitions. For blast lethality calculations, we need a set of accurate TNT equivalence values for the effects we are considering and, if relevant, at different distances. For safety purposes on the other hand, we need conservative, but reasonable values, and if possible, standardized ones. For standardized safety calculations, TNT equivalence methodology is not only applied to high explosives, but to all energetic materials including propellants and pyrotechnics. Although explosive blast testing methods for TNT equivalence characterization tends to be fairly similar, there is surprisingly little standardization. For propellants and pyrotechnics, there is no standardization at all. A review of blast testing methods and data reduction for TNT characterization was conducted for high explosives, propellants and pyrotechnics. Very large differences in results are noted with many factors affecting the results. Some of these factors include initiation or ignition method, munition confinement, testing geometry and data reduction methodology. The various testing methods are reviewed, resulting in conclusions and recommendations. [Preview Abstract] |
Monday, June 17, 2019 2:30PM - 2:45PM |
D2.00003: Modeling the Response of Steven Tests Elisha Rejovitzky, Yehuda Partom, Roman Kositski, Alon Malka-Markovitz Steven test was introduced for studying low velocity impact initiation of explosives. The original diagnostic of Steven test was blast gauges at a distance of about 10m. Trying to use this diagnostic to characterize the response of the explosive after its ignition, we realized that it's not reliable and not informative enough. We therefore replaced the blast gauges by interferometric velocity gauges looking at the free surface of the back plate. Our explosive was similar to LX07, and we performed several tests with impact velocities from 30 to 122m/s. The velocity histories we obtained from the gauges show the following: 1) there's a rather long delay between impact and ignition (or gauge response), 50\textmu s for the highest impact velocity and around 350\textmu s for 36m/s; 2) there's no ignition for an impact velocity of 30m/s; and 3) gauge velocity histories rise gradually to a maximum and then continue with elastic oscillations. We model the response of the explosive assuming that it reacts through \underline {shear initiation}. The projectile impact causes shear flow in the explosive, which leads to strain localization and formation of shear bands. The shear bands heat up and reach ignition temperature, and deflagration fronts expand out of them, similar to deflagration fronts out of hot spots for shock initiation. Shear initiation reaction rate is rather slow, and it depends on pressure and not on reactant temperature. Here we use this pressure dependent reactive flow model to reproduce our Steven test data. We get good agreement with delay times and amplitudes of the velocity gage data. [Preview Abstract] |
Monday, June 17, 2019 2:45PM - 3:00PM |
D2.00004: Modeling of TATB-Based HE Cook-off for Safety Analysis Jason Moore, Matthew McClelland, Peter Hsu, Evan Kahl We investigate and model the cook-off behavior of LX-17 to understand the response of explosive systems in abnormal thermal environments. Decomposition has been explored via conventional ODTX (One-Dimensional Time-to-eXplosion), PODTX (ODTX with pressure-measurement), TGA, and DSC experiments under isothermal and ramped temperature profiles. The data were used to fit reaction rate parameters for proposed schemes in an ALE3D computational model. This model includes chemical reactions, thermo- and hydro-dynamics, and material properties, including thermal expansion, compressibility, and strength. These parameterizations were carried out utilizing a Python evolutionary optimization method on LLNL's high-performance computing clusters. Additional experiments will be conducted to further elucidate decomposition intermediates to improve the model. Once experimentally validated, this model will be scalable to several applications involving LX-17 and can be used to develop more sophisticated experimental methods. Furthermore, the optimization methodology developed herein should be applicable to other high explosive materials. LLNL-ABS-768048 [Preview Abstract] |
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