Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D03: Materials in Extremes: Multiscale Models of Energetic MaterialsFocus
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Sponsoring Units: GSCCM Chair: Mitchell Wood, Sandia National Laboratories Room: 107 |
Monday, March 2, 2020 2:30PM - 3:06PM |
D03.00001: Understanding the Role of Microstructure in Energetic Materials Using a Predictive Hierarchical Multiscale Simulation Approach Invited Speaker: James P. Larentzos Composite energetic materials contain microstructural heterogeneities (i.e., crystal defects, voids, interfaces, etc.), where the community consensus is that this microstructure plays a critical role in the energetic material response. However, an understanding and characterization of its precise role for system design is lacking. This is due in part to the significant experimental challenges caused by the extreme conditions occurring at short time and length scales. Modeling and simulation are not hampered by these conditions; rather, limitations are due to the approximations made in the models and the available computational resources. |
Monday, March 2, 2020 3:06PM - 3:18PM |
D03.00002: Microstructure-informed, statistical approach for shock to detonation transition modelling in high explosives Ahmed Hamed, Marisol Koslowski Shock to detonation transition phenomenon (STDT) is a synergistic effect of different underlying mechanical, chemical, and thermal processes, where the racing between different modes of energy production and dissipation is the key factor. Accurate prediction of these far-from-thermodynamic-equilibrium phenomena dictates careful consideration of different entropic fluxes associated with various inelastic processes, along with their characteristic modes of transport. Hot-spot formation and initiation is the main paradigm to tackle STDT, which, in turn, is known to be heterogeneous in nature. Accordingly, mean-field approaches, which employ averaged-measures of microstructural properties, predict critical parameters for STDT regime that can deviate significantly from experiment. In the present study, we seek a statistical approach to represent the heterogeneity in the microstructure of polymer-bonded explosives, which better captures the sensitivity of hot-spot initiation to local variation in the microstructure. The reactive flow system of equations is solved in Lagrangian framework, within finite strain formalism. In addition, this thermo-mechanical-chemical model is supplemented by the Hugoniot equation of state for closure purposes and solved using finite-element technique. |
Monday, March 2, 2020 3:18PM - 3:30PM |
D03.00003: Mesoscale modeling of explosive mixtures containing TNT and HMX H. Keo Springer, Sorin Bastea, Craig M Tarver Different energetic constituents can be combined to achieve desired explosive mixture properties. One example of an explosive mixture is Octol which is comprised of a less ideal constituent, TNT, and a more ideal constituent, HMX. Changes to HMX content in this mixture can alter its shock sensitivity and performance. However, the microscale reaction mechanisms underlying such changes are not well understood. In this study we perform mesoscale simulations to investigate different TNT-HMX mixtures. Simulations are performed with the multi-physics code, ALE3D. A coupled thermochemical code provides equation-of-state and chemical kinetic properties. Simulations are performed for TNT-HMX weight ratios of 25-75, 40-60, and 70-30 with 2 and 5% porosity. A range of shock pressures are considered. Non-reactive studies examining changes to the p-v response and temperature distribution will be discussed with comparisons to common mixture rules. Trends for the mixture reaction rate with varying HMX content and porosity will also be discussed. These studies are important for developing mixture reactive flow models when the constituents are mixed at length-scales below the reaction zone size. |
Monday, March 2, 2020 3:30PM - 3:42PM |
D03.00004: Mesoscale Dynamic Damage Visualization and Simulation of Energetic Materials under Impact Jonathan Drake, Weinong Chen, Marisol Koslowski, Kamel Fezzaa Energetic materials may be subjected to impact. Under such loading conditions, local stress or strain concentrations may lead to the formation of hot spots and unintended reaction. To visualize the dynamic damage and reaction processes in polymer bonded energetic crystals under dynamic compressive loading, a high-speed X-ray phase contrast imaging setup was synchronized with a Kolsky bar and a light gas gun. Controlled compressive loading was applied on PBX specimens with a single or multiple energetic crystal particles and impact-induced, time-resolved damage and reaction processes were captured using the high-speed X-ray PCI. Numerical simulation models were built based on the experimental results and used to investigate the impact damage in PBX over a wider range of parameter variations. |
Monday, March 2, 2020 3:42PM - 4:18PM |
D03.00005: Developing and validating thermomechanics models for explosives with experiments on commensurate scales Invited Speaker: Kyle Ramos In both manufacturing and dynamic loading, the interplay between deviatoric stress, plastic strain, and heat generation at the mesoscale dictate the responses of plastic bonded explosives (PBX). In situ mesoscale insights are needed to quantify structure-property relationships, inform theory, and enable simulations. We have attempted such an effort and will present an overview of our progress so far. |
Monday, March 2, 2020 4:18PM - 4:30PM |
D03.00006: Non-Schmid effect of pressure on plasticdeformation in molecular crystal HMX Anirban Pal, Catalin Picu The energetic molecular crystal HMX is a key constituent in common plastic bonded explosives. Its plastic deformation under shock conditions is important in reaction initiation and detonation. Here, we study the effect of high pressureon dislocation slip using isothermal-isobaric atomistic simulations. We consider 2 slip planes, (011) and (101), that are reported to be most active under ambient conditions. For all slip systems considered, the effect of pressure is to increase the critical resolved shear stress for dislocation slip. Pressure may fully inhibit dislocation-based plasticity if the resolved shear stress is not increased in proportion. On the other hand, at sufficiently high shear stresses, the crystal loses shear stability. Therefore, in a broad range of shock conditions, plastic deformation takes place by a combination of dislocation glide in some slip systems and localization in some other systems, with dislocation activity being gradually inhibited as the shock pressure increases. |
Monday, March 2, 2020 4:30PM - 4:42PM |
D03.00007: Atomistic mechanisms in the plasticity of energetic crystal HMX Mohammad Khan, Anirban Pal, Catalin Picu The energetic molecular crystal cyclotetramethylene tetranitramine (HMX) is a key constituent in common plastic bonded explosives. Its plastic deformation under shock conditions is important in reaction initiation and detonation. In this work we identify, using atomistic simulations, the slip systems in b-HMX and compute the critical resolved shear stresses for dislocation motion. We also evaluate the mobility of dislocations in various slip systems and the likelihood of cross-slip. The implications of these results for the overall physical picture of plasticity in HMX are discussed. |
Monday, March 2, 2020 4:42PM - 4:54PM |
D03.00008: Anisotropic Thermal Conductivity and Elasticity of RDX Using Impulsive Stimulated Thermal Scattering John Lazarz, Shawn David McGrane, Romain Perriot, Cynthia Bolme, Marc Cawkwell, Kyle Ramos Anisotropy of single crystals plays an integral role in meso-scale behavior of materials. In energetic materials, the anisotropy of thermal conductivity and elasticity plays a key role in hot spot generation during dynamic loading, potentially leading to deflagration or detonation. Precise measurements are needed to validate predictive models of these materials during accident scenarios. Toward these goals, we are investigating single crystal orthorhombic 1,3,5- trinitroperhydro-1,3,5-triazine (RDX) using impulsive stimulated thermal scattering (ISTS). Here we present results of the experimentally determined thermal diffusivity and its comparison with the anisotropic values predicted by atomistic simulations, as well as experimentally measured anisotropic acoustic velocities. |
Monday, March 2, 2020 4:54PM - 5:06PM |
D03.00009: Dynamic fracture and frictional temperature rise in HMX-Sylgard microstructures under impact and vibration Akshay Dandekar, Marisol Koslowski Polymer bonded explosives are sensitive to impact and vibrations and can form critical hot-spots under certain conditions leading to ignition. Thus, understanding the behavior of PBXs under mechanical loading is crucial to avoid accidents during manufacturing, handling, and transport of these materials. In this study, the response of HMX-Sylgard samples is numerically studied using a finite element approach that includes dynamic damage coupled with temperature evolution due to frictional heat. At impact velocities close to 100 m/s several cracks develop and grow. Consequently, critical hot spots are observed in agreement with PBX. The maximum frictional temperature rise is found at particle polymer interfaces. The effect of crystal orientation of the particles including plasticity and orientation and cleavage planes is analyzed under vibration and impact in 3D simulations. |
Monday, March 2, 2020 5:06PM - 5:18PM |
D03.00010: Temperature- and pressure-dependent lattice constants of CL-20 polymorphs from ab initio molecular dynamics simulations Igor Schweigert, Benjamin Datko Hexanitrohexaazaisowurtizane (CL-20) is a high-density nitramine compound with several known polymorphs. We're interested in using density functional theory (DFT) to predict the thermodynamic stabilities of various polymorphs at elevated temperatures and pressures. This presentation will describe DFT-based molecular dynamics simulations of temperature- and pressure-dependent lattice constants for the epsilon and zeta polymorphs and compare the results to available experimental data. |
Monday, March 2, 2020 5:18PM - 5:30PM |
D03.00011: Material Diffusion and Combustion Process Modeling Using a Stochastic Particle-Based Framework Nikolai Petsev, Xia Ma, Bryan Henson, Brad Edwin Clements We describe a novel mesoscale particle-based computational strategy for modeling non-isothermal reaction-diffusion problems. Importantly, this simulation framework gives the foundation for investigating the deflagration-to-detonation transition (DDT) in combustion, where the material transitions from burning at a rapid subsonic pace (deflagration) to the emergence of a shockwave (detonation). The basis for this approach is "smoothed dissipative particle dynamics" (SDPD), a stochastic thermodynamically-consistent approach for solving the fluctuating hydrodynamic equations of Landau and Lifshitz. Presently our new approach incorporates heat and mass transfer driven by conduction and diffusion, exchange of heat and chemical species due to thermal fluctuations, and source terms arising from the chemical reaction. In future work, this will be coupled to the fluctuating momentum equation, or included in multiscale molecular-continuum simulations, opening the possibility for simulations studying DDT in energetic materials, in addition to a broad range of other applications involving chemical reactions and concurrent mass and heat transfer. |
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