Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session Y2: Energetic Materials IX |
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Chair: Gerrit Sutherland, Army Research Laboratory Room: Grand Ballroom IV-VI |
Friday, July 1, 2011 9:15AM - 9:30AM |
Y2.00001: A 3-D microstructural level model for analyzing the response of polymer bonded explosives David Hardin, Min Zhou A three-dimensional finite element model is developed to study the microstructural level response of polymer-bonded explosives (PBX) under impact loading. The study focuses on the effect of the morphology and packing of energetic grains on the overall thermomechanical response of the composites. A cohesive finite element method (CFEM) is utilized to account for failure in the form of debonding between the HMX grains and the polymer matrix. Frictional heating along crack faces is tracked through a contact algorithm. Microstructures with cubic and multifaceted three-dimensional polygonal granules with packing densities between 0.42 and 0.74 are generated and used. Both 2D and 3D calculations are carried to analyze the differences between the models. To ensure consistency, the 2D microstructures are sections of the 3D microstructures. In this presentation, we will discuss differences in results from the 2D and 3D calculations, with a particular focus on the progression of damage and heating under impact loading. [Preview Abstract] |
Friday, July 1, 2011 9:30AM - 9:45AM |
Y2.00002: Developments in strong shock wave position tracking Philip Rae, Brain Glover, Lee Perry This poster will highlight several modified techniques to allow the position vs. time to be tracked in strong shock situations (such as detonation). Each is a modification or improvement of existing ideas either making use of advances in specialist materials availability or recent advances in electronics.) Shorting embedded mini-coaxial cable with a standing microwave pattern. This technique is a modified version of an old LANL method of shock position tracking making use of a traveling short imposed in an embedded coaxial cable. A high frequency standing wave (3-8GHz) is present in the cable and the moving short position can be tracked by monitoring the output voltage envelope as a function of time. A diode detector is used to allow the envelope voltage to be monitored on a regular low frequency digitizer significantly reducing the cost. The small and cheap high frequency voltage generators now available allow much greater spatial resolution than possible previously. 2) Very thin shorting resistance track gauges. Parallel tracks of constantan resistance material are etched on a thin dielectric substrate. The gauges are less than 0.2mm thick. The ionized gas present in a detonation front sweeps up the tracks lowering the measured resistance. A potential divider circuit allows the shock position vs. time to be monitored on a regular digitizer after easy calibration. The novel feature is the thin section of the gauge producing minimal perturbation in the detonation front. [Preview Abstract] |
Friday, July 1, 2011 9:45AM - 10:15AM |
Y2.00003: Multi-Shock Experiments and Modeling of PBX 9502 Reactants Invited Speaker: The multi-shock response of PBX 9502 is examined. In particular a set of experiments utilizing multi-component impactors of low density material (TPX) followed by high density material (Ta) are used in a 2-stage gas gun to shock compress PBX 9502 to very high pressures without subsequent chemical reaction. Relevant modeling and computations will be presented for the PBX 9502 reactants equation of state.\\[4pt] Work done in collaboration with Richard Gustavsen, Nathaniel Sanchez, Brian Bartram, and Ralph Menikoff. [Preview Abstract] |
Friday, July 1, 2011 10:15AM - 10:30AM |
Y2.00004: Shock Initiation of Thermally Expanded TATB Roberta Mulford, Damian Swift The plastic-bonded explosive PBX-9502 undergoes unusual hysteretic thermal expansion, or ``ratchet growth'' as a consequence of the uniaxial thermal expansion of the graphitic structure of the major component, TATB explosive. Upon thermal cycling, the density of the material can be reduced by as much as 9\%, resulting in a distinct increase in the shock sensitivity of the solid. Run distances to detonation have been measured in thermally expanded samples of PBX-9502, using embedded particle velocity gauges and shock tracker gauges. Uniaxial shocks were generated using a light gas gun, to provide a repeatable stimulus for initiation of detonation. We have applied a porosity model to adjust standard Pop plot data to the reduced density of our samples, to investigate whether the sensitivity of the PBX 9502 increases ideally with the decreasing density, or whether the microscopically non-uniform expansion that occurs during ``ratchet growth'' leads to abnormal sensitivity, possibly as a result of cracking or debonding from the binder, as observed in micrographs of the sample. [Preview Abstract] |
Friday, July 1, 2011 10:30AM - 10:45AM |
Y2.00005: Modelling Violent Reaction Following Low Speed Impact on Confined Explosives John Curtis, Andrew Jones, Christopher Hughes, John Reaugh To ensure the safe storage and deployment of explosives it is important to understand the mechanisms that give rise to ignition and reaction growth in low speed impacts. The LLNL High Explosive Response to Mechanical Stimulus (HERMES) material model, integrated in LS-DYNA, has been developed to model the progress of the reaction after such an impact. The low speed impact characteristics of an HMX based formulation have been determined in the AWE Steven Test. Axisymmetric simulations have been performed to determine the characteristics of the model. The sensitivity study included looking at the influence of friction, material strength and confinement. By comparing the experimental and calculated results, the key parameters which determine the response in this configuration have been determined. The model qualitatively predicts the point of ignition within the vehicle. Future refinements are discussed. [Preview Abstract] |
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