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Show 272 Joseph R. Peterson DEFLAGRATION AND DETONATION IN ENERGETIC MATERIALS: NEW MODELING EFFORTS Joseph R. Peterson (Charles A. Wight) Department of Chemistry University of Utah honors college spring 2012 High energetic materials are commonly used as rocket propellants and rocket warheads in the form of plastic bonded explosives (PBXs). Plastics play the dual role of both a dampener to reduce sensitiv-ity of the explosive to both mechanical and thermal insult, and a binder to bond smooth explosive crystals together. With age, these mixtures undergo chemical change that affect the sensitivity of explosive devices. Such processes include thermal deconsolidation of binder and explosive, Ostwald ripening of explosive grains, and reduced binder elasticity. As the United States stockpile ages it be-comes desirable to understand the dangers associated with these chemical changes both cheaply and accurately. Modeling efforts have found great favor among explosives experts for their cost effective-ness and safety relative to experimentation. Of importance is the deflagration to detonation transition (DDT) in explosives where a semi-violent ex-plosion transitions to an extremely violent explosion due to inertial confinement, material damage or shock induced hot-spot formation. DDT models have traditionally been formulated as direct numeri-cal solutions on length scales too small for large accident scenarios. Three explosive reaction regimes can be seen in explosions. These are, in order of increasing violence, conductive burning, convective burning and detonation. In an effort to bring the DDT to a scale feasible for modeling real scenarios, validated combustion (WSB) and detonation (JWL++) models were combined with realistic material damage models and thresholds partitioning reaction regimes. An experimentally inspired threshold between conductive and convective burning is based on the average length-scale of the damage (cracks, porosity, etc.) in the explosive. A threshold between convective burning and detonation is based on a critical pressure designed to mimic the necessary shock strength to raise the energy in the explosive beyond the activation threshold for bulk reaction. The model, known as DDT1, was implemented in the Uintah Computational Framework (UCF) and vali-dated against run distance to detonation data, convective burning data, cylinder test data, explosive size effect data and semi-violent "Steven test" data with good agreement. Current work is on validat-ing the model against convective burning data and DDT behavior in bulk granular materials, with new efforts focused on mesoscale modeling of granular compaction and resulting DDT designed to validate the larger bulk models. In addition, the model is being used to study explosion violence as a function of heating rate and device size in slow cook-off scenarios. 1 http://www.uintah.utah.edu Charles A. Wight SlowCookOff.jpeg: The calculated temperature 48 microseconds after detonation of a 25 mm diameter cylindrical explosive confined in 5 mm thick steel. The device was heated slowly until the point of self-ignition for the explosive after which it quickly transitioned to detonation withing 45 microseconds. The color scale is represents temperature in Kel-vin and the gray regions indicate steel material rapidly accelerating outwards. GranularCompaction.jpeg A 12.7 mm long by 4 mm wide sample of granular HMX packed initially to 69% volume fraction impacted by a steel projectile at 280 m/s. The shock front, labeled A, can be seen to outrun the compaction front, labeled B. Also, plastic flow behind the compaction front, labeled C, reduces stress while diverting energy from deformation to bulk heating. |