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 F2: Energetic and Reactive Materials: Cook-Off I |
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Chair: Pamela Bowlan, Los Alamos National Laboratory Room: Grand Ballroom AB |
Monday, July 10, 2017 5:00PM - 5:15PM |
F2.00001: Improved Cook-off Modeling of Multi-component Cast Explosives Albert Nichols In order to understand the hazards associated with energetic materials, it is important to understand their behavior in adverse thermal environments. These processes have been relatively well understood for solid explosives, however, the same cannot be said for multi-component melt-cast explosives. Here we describe the continued development of ALE3D, a coupled thermal/chemical/mechanical code, to improve its description of fluid explosives. The improved physics models include: 1) Chemical potential driven species segregation. This model allows us to model the complex flow fields associated with the melting and decomposing Comp-B, where the denser RDX tends to settle and the decomposing gasses rise, 2) Automatically scaled stream-wise diffusion model for thermal, species, and momentum diffusion. These models add sufficient numerical diffusion in the direction of flow to maintain numerical stability when the system is under resolved, as occurs for large systems. And 3) a slurry viscosity model, required to properly define the flow characteristics of the multi-component fluidized system. These models will be demonstrated on a simple Comp-B system. [Preview Abstract] |
Monday, July 10, 2017 5:15PM - 5:30PM |
F2.00002: One-Dimensional Thermal Violence Cook-Off Test. Malcolm Cook, Christopher Stennett The One-Dimensional Thermal Violence (ODTV) test is designed to quantify and rank the violence of HE charges when heated to elevated temperatures. The test design consists of a central spherical explosive pellet encased in two aluminium barrel shaped halves, fitted with a copper sealing ring, encased by two aluminium locking rings placed over them from either end. The outer surface of the capsule is heated uniformly by placing in a pre-heated molten solder bath. This allows the time-to-explosion to be recorded for different initial bath temperatures. The ODTV capsule can hold samples up to 30mm in diameter. Diagnostics include both thermocouples and Photon Dopler Velocimetry (PDV). A series of live firings have been carried out on a range of bespoke HMX/HTPB explosives. These include HMX/HTPB mix ratios of 95/5, 92/8, 90/10, 88/12 and 85/15. These tests showed that the ODTV capsule had sufficient confinement and size that it could capture the spectrum of events expected from these formulations. It has been demonstrated that the deformation of the heater cup (that houses the molten solder) can be used as an additional violence metric along with the fragmentation and PDV wall velocities of the aluminium ODTV capsule. [Preview Abstract] |
Monday, July 10, 2017 5:30PM - 5:45PM |
F2.00003: 4D Imaging in Thermally Damaged Polymer-bonded Explosives Gary Parker, Neil Bourne, David Eastwood, Simon Jacques, Peter Dickson, Ian Lopez-Pulliam, Eric Heatwole, Matt Holmes, Laura Smilowitz, Christoph Rau PBXs are composites in which explosive crystallites are bound by compliant polymers. There are safety benefits derived from compliant binders; e.g. they mitigate some effects of mechanical insult. However, during elevated thermal insult, degradation of binder and HE crystallites can modify the morphology in ways that can reduce safety margins by increasing post-ignition reaction violence. The response of thermally damaged PBXs, before and following self-ignition has safety implications and it is desirable to understand the fundamental physics controlling the rate of pre-ignition thermal runaway and the post-ignition flame propagation in thermal accident scenarios. Coupled with this there is an ongoing effort to make in situ, time-resolved, measurements of the size, nature and extent of micro-porosity in PBX 9501 during thermal decomposition. We report on PBX heating experiments conducted at the Diamond synchrotron with both PBX 9501 and an inert mock. During heating, CT radiography was conducted in order to observe void production and interconnectivity of gas flow pathways, as well as to monitor phase changes within the crystals. We explore the variation of behavior as a function of heating rate, soak temperature, soak time and confinement. [Preview Abstract] |
Monday, July 10, 2017 5:45PM - 6:00PM |
F2.00004: Live Imaging and Heating of Confined RDX and HMX Crystals Until Reaction Using the Dual Windowed Test Vehicle Chris Stennett, Malcolm Cook, Philip Cheese, Andrew Wood, Nathan White, Tom Reeves A high fidelity live camera feed recording RDX and HMX crystals, measuring 1 mm thick and 15 mm in diameter, decomposing while heavily confined and subjected to various heating rates until a reaction occurs has been analysed. Video records reveal unexpected behaviour in both RDX and HMX crystals prior to ignition. Three distinct stages can be observed: phase changes and melting; slow, flameless decomposition with production of gaseous intermediates; and finally burning with a luminous flame of the gaseous intermediates. Tests with pure RDX and HMX crystals reveal pockets of gaseous materials forming above the molten and bubbling nitramine, before a flame appears at one side then burns inwards in an apparent conductive manner at a few metres per second. This causes the remaining bubbling nitramine to be compressed. Violent reaction appears to occur via a bubble collapse mechanism. The violence of this event is dependent on the loss of confinement; if it fails in the first or second phase the reaction is less violent than if the third phase is reached. The third phase burning reaction has associated pressure waves, which is presumed oscillation of the flame front, leading to wave interactions, pressure spikes and ultimately a violent reaction. [Preview Abstract] |
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