Understanding and Predicting Dynamic Behavior of Materials : Behavior of High Explosives
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Computational Materials Science and Engineering Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Saryu Fensin, Los Alamos National Laboratory; Avinash Dongare, University of Connecticut; Benjamin Morrow, Los Alamos National Laboratory; Marc Meyers, University of California, San Diego; George Gray, Los Alamos National Laboratory
Monday 2:30 PM
February 24, 2020
Room: 5A
Location: San Diego Convention Ctr
Session Chair: John Yeager, Los Alamos National Laboratory
2:30 PM Invited
Dynamic Measurements of Solid Carbon Cluster Growth and Morphology in High Explosives Detonation Products: Dana Dattelbaum1; Erik Watkins1; Kirill Velizhanin1; Rachel Huber1; Rick Gustavsen1; Tariq Aslam1; Millie Firestone1; Bryan Ringstrand1; Trevor Willey and Team2; Nicholas Sinclair3; Paulo Rigg3; 1Los Alamos National Laboratory; 2Lawrence Livermore National Laboratory; 3Washington State University
Carbon clustering behind the detonation front is believed to delay chemical equilibrium at late times in insensitive, carbon-rich explosives. Accurate modeling of both the unreacted and product equations of state is important to predicting the performance of high explosives and an improved description of solid detonation carbon is necessary. Time-resolved small-angle x-ray scattering (TR-SAXS) can provide a in situ measurements of the evolution of solid/fluid detonation products in real time behind the detonation front, including particle size, shape/morphology, and electron density. Here, we will describe the experimental apparatus implemented at the Dynamic Compression Sector at the Advanced Photon Source, and results on several types of explosives including PBX 9502 (TATB/Kel-F 800), PBX 9501 (HMX/Estane), and Composition-B (TNT/RDX). The results will be discussed in the context of reactive flow and hydrodynamic simulation. An analysis of errors will be discussed including how improvements could be made to measuring detonation carbon evolution using x-ray light sources.
3:10 PM
Anisotropic Damage Model for Cyclotrimethylene Trinitramine (RDX) under Impact: Nisha Mohan1; 1Los Alamos National Laboratory
Dynamic, high strain rate experiments on oriented single crystals of the explosive cyclotrimethylene trinitramine (RDX) have demonstrated the effects of elastic and plastic anisotropy on its deformation processes. We have developed a brittle, discrete fracture model that takes into account material and stress state anisotropy.Material anisotropy is represented through three effects, the elastic and plastic anisotropic stiffness and the anisotropic surface energies obtained from atomistic simulations.Crack growth mechanics is developed from Griffith’s theory of elliptical cracks. The energetic dependence on the inelastic part of deformation is added in terms of plastic dissipation potential to the Griffith criterion.Inelastic hardening effects in the vicinity of crack-tip were included by hardening the moduli as a function of the plasticity.Fracture planes were deduced from the directional form of the criterion.The ability to derive the right fracture angles and crack lengths were assessed against recent split Hopkinson pressure bar experiments on single crystals.
3:30 PM
Controlled Fragment Impact Experiments for Initiation Response of PBXs: Patrick Bowden1; Andrew Schmalzer1; John Yeager1; Joseph Lichthardt1; Alexander Mueller1; 1Los Alamos National Laboratory
Fragment initiation of explosives is an important area of research for safety and explosive response scenarios. Experiments range from single, large, slow moving flyers to multiple, microscopic, fast moving particles. Determining the initiation criteria for target plastic-bonded explosive (PBX) materials is difficult because the interplay between fragment size/shape, incident angle and velocity create a highly complex variable set. To attempt to simplify this problem (and enable new hydrocode simulations), experiments were undertaken to design and parameterize a flyer system capable of launching multiple small flyers of a standardized size and shape. By creating a uniform fragment field, multi-wave interactions were probed. Additionally, with the large stochastic dataset in hand, insight into elucidating a James-type criterion for initiation was gained for various PBXs. Simulations using the CTH hydrocode were also performed to guide the experimental design and help analyze ignition criteria.
3:50 PM
Experiments and Modeling to Explore Dynamic Behavior of Materials via Kolsky Bar at Equilibrium and Beyond: Benjamin Morrow1; Francis Addessio1; Christopher Meredith2; Kyle Ramos1; Cheng Liu1; Carl Cady1; Clarissa Yablinsky1; 1Los Alamos National Laboratory; 2U.S. Army Research Laboratory
Kolsky bar (or split-Hopkinson pressure bar, SHPB) is a commonly used technique to probe dynamic materials behavior at intermediate strain rates (on the order of 1000 /s). However, the technique relies on several key assumptions to achieve a “valid” test. In the present study, a miniaturized Kolsky bar setup was used to test RDX single crystals at higher rates than are usually achieved on a standard-sized setup. The increased rates, combined with brittle samples, push testing to the very edge of the equilibrium assumption, requiring advanced simulations to interpret results. Additional diagnostics, including high-speed imaging, help bridge gaps between measured strain gage signals and simulations. A comparison of experimental and computational results will be presented, along with a case study for using the synergy of simulation and experiment to enable more complex test setups than current convention. A discussion of experimental error for the miniaturized system will also be presented.
4:10 PM Break
4:30 PM
One Dimensional Shock Initiation of the HMX- based Explosive PBX-9012: Malcolm Burns1; 1Los Alamos National Laboratory
Five one dimensional shock initiation experiments have been carried out on the HMX-based polymer bonded explosive PBX-9012. This explosive comprises of 90% HMX and 10 % Viton A. The experiments delivered sustained pulses of shock pressures ranging from 2.0 to 4.4 GPa. This resulted in a turn over to detonation ranging from 4.9 to 20 mm from the impact plane. Reactive growth wave-profiles have been measured in up to eleven Legrangian locations using the electromagnetic embedded gauge technique at the Los Alamos National Laboratory gas gun facility. In addition, the evolution of the shock to detonation transition has been tracked using the embedded shock tracker gauge comprising of up to 118 measurement locations. These data have been used to determine the relative shock sensitivity and the unreacted Equation of State for PBX-9012.
4:50 PM
Multiscale Modeling to Study Effects of Microstructure in Shocked Hexanitrostilbene: Judith Brown1; David Kittell1; Mitchell Wood1; Aidan Thompson1; Dan Bolintineanu1; 1Sandia National Laboratories
Energetic materials can release large amounts of stored chemical energy through exothermic, fast reactions. When exposed to shock environments, mechanical energy interacts with microstructure heterogeneities such as pores, crystal grain boundaries, and defects, that can result in hot spot formation and possible transition to detonation. To better understand microstructure dependence in the shock to detonation transition, we present a multiscale modeling study of pressed hexanitrostilbene (HNS). The continuum hydrocode CTH is used to model the shock response for an ensemble of microstructure realizations using an ab initio derived crystalline equation of state for HNS in conjunction with a rate and temperature-dependent plasticity constitutive model and temperature-dependent chemical reaction kinetics. The hydrocode simulations are directly compared to molecular dynamics (MD) simulations with a fully reactive interatomic potential to provide mechanistic detail on the local processes driving hot spot formation and insight into plastic flow mechanisms.
5:10 PM
Single Crystal Plasticity for the High Rate Deformation of an HMX-based Plastic Bonded Explosive: Milovan Zecevic1; Marc Cawkwell1; Kyle Ramos1; Darby Luscher1; 1Los Alamos National Laboratory
A dislocation-based continuum model has been developed for β-cyclotetramethylene tetranitramine (β-HMX). The relation between Green-Lagrange elastic strain and 2nd Piola-Kirchoff stress is derived from Taylor expansion of free energy around the reference state, containing the contribution from equation of state. The inelastic deformation is modeled with contributions from dislocation-based slip and deformation twinning. The temperature evolution in the model is derived from an energy balance and includes heat generation due to mechanical dissipation. The model parameters for β-HMX have been calibrated against plate impact experiments. The simulation results are used to gain insight into set of active slip systems in β-HMX. The calibrated material model is applied in finite element simulations of weak shock impacts of β-HMX based plastic bonded explosives (PBX). The simulation results are discussed from physical and modeling perspective.