Bulletin of the American Physical Society
22nd Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 67, Number 8
Monday–Friday, July 11–15, 2022; Anaheim, California
Session Z02: Characterization of Reactive and Energetic Materials IIRecordings Available
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Chair: David Damm, Sandia National Laboratories Room: Anaheim Marriott Platinum 6 |
Friday, July 15, 2022 11:00AM - 11:15AM |
Z02.00001: Study of energy localization in shocked PBXs through interface-resolved reactive simulations on imaged profiles of HMX crystal aggregates Shobhan Roy, Belinda P Johnson, Yen t Nguyen, Xuan Zhou, Dana D Dlott, H.S. Udaykumar The formation of hot spots is known to be the primary mechanism for shock to detonation transition in energetic materials such as plastic-bonded explosives (PBXs). However, the mechanistic details of shock initiation are yet to be fully understood and quantified into closure models for energy localization. In recent literature, an experimental procedure was presented to observe hot spots in deconstructed PBX samples of HMX crystals embedded in a polymeric binder, dynamically compressed using laser-launched flyer plates. We present a computational framework to perform mesoscale continuum mechanics simulations for head-to-head comparison with the experimental tests. The crystal profiles were extracted from CT scan images and imported into the computational domain. The computations leveraged interface-resolved reactive simulations using a sharp-interface Eulerian framework, along with vetted reaction and strength models for HMX and binder (Estane). The study assesses the relative importance of several experimentally observed and simulated mechanisms for hot spot initiation in PBXs, such as intra-crystal void collapse, shock-focusing at surface asperities, pores in the binder, delamination zones at crystal-binder interface, and crystal-crystal interactions. |
Friday, July 15, 2022 11:15AM - 11:30AM |
Z02.00002: Effects of Microstructural Void Distribution Relative to Reactive Grains and Polymer Binder on the Detonation Sensitivity of a Heterogeneous Energetic Material Daniel H Olsen, Christopher Coffelt, Christopher Miller, Min Zhou Fully three-dimensional (3D) microstructure-explicit and void-explicit mesoscale simulations of the shock to detonation transition (SDT) in a polymer-bonded explosive (PBX) are performed. The material consists of 75% PETN (pentaerythritol tetranitrate) grains and 25% HTPB (hydroxyl-terminated polybutadiene) polymer binder by volume. The model is 1×1×5 mm and has porosities up to 10% in the form of spherical voids that are 50 µm in diameter. An Arrhenius reactive burn model is used to capture the chemical reaction rate of the PETN grains, resolving the heterogeneous detonation behavior of the PBX. Imposed piston velocities ranging from 800-1500 m/s, result in an applied shock pressures of 3-8 GPa. The quantity of interest is the run distance to detonation (RDD) as it relates to microstructure and porosity. To quantify uncertainties in the behavior arising from the microstructure and void distribution, statistically equivalent microstructure sample sets (SEMSS) are generated, leading to probabilistic formulations for the RDD as functions of shock pressure. The calculations reveal that the location of voids significantly affect the RDD. Understanding void placement and microstructure effects can lead to better designed materials which can be tailored to have specific properties. |
Friday, July 15, 2022 11:30AM - 11:45AM |
Z02.00003: The critical thresold for shock initiation in explosives Neil K Bourne, Peter M Dickson There are a series of observations of explosive response that remain difficult to explain using the present approaches. In particular, consistent explanations for phenomena such as dead pressing, observations of electrical influences on initiation and requirements for an unphysical pressure dependence of the reaction rate in detonation suggest another approach may be necessary. One approach explicitly considers the stress threshold required to shock an explosive so that it runs to full detonation. At present it is assumed that a reaction zone within an explosive is formed of localised burning regions that increase in density as pressure is increased. However, a series of burn rate experiments and shock investigations of the shock response of explosives indicate a critical stress level at which response changes. The stress at which the theoretical shear strength is exceeded is called the Weak Shock Limit and represents the gateway to the strong shock region. It is hypothesised here that there is a change in physical properties above the weak shock limit that allows the reaction to move from localised burning to homogeneous reaction. This work presents this new approach and tests a range of implications that may be tested in further experiments. If explicitly proven, the weak shock limit is a vital quantity to consider for the safe handling of energetic materials. |
Friday, July 15, 2022 11:45AM - 12:00PM |
Z02.00004: Modeling PBX 9501 High Explosive Cylinder Experiments and an Evaluation of WSD and AWSD Parameter Sets Marvin A Zocher, Tariq D Aslam Cylindrical assemblies are often used in experiments aimed at calibrating and validating continuum level models of reactive burn, and of the so-called equation of state model (constitutive model for the spherical part of the Cauchy tensor). Such is the case in work to be discussed here. In particular, work will be described involving the modeling of a series of experiments involving PBX 9501 encased in a copper cylinder. The objective of the work is to test and perhaps refine a set of phenomenological parameters for the Wescott-Stewart-Davis (WSD) and Arrhenius-WSD (AWSD) reactive burn models. The focus of this talk will be on modeling the experiments, which turned out to be non-trivial. Always difficult to handle due to the extremely short reaction zone of PBX 9501, scaling is employed to address issues related to detonation velocity. The modeling is conducted using ALE methodology. |
Friday, July 15, 2022 12:00PM - 12:15PM |
Z02.00005: Development of a new Modified Small-Scale Gap Test Malcolm D Cook, Andrew D Wood, Christopher Stennett Small-scale gap tests are useful when comparing the sensitiveness of compositions where formulation parameters and manufacturing conditions are varied. Such gap tests are very economical in terms of quantity of material, time and effort. |
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