Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C23: Materials in Extremes: Energetic Materials - IIIFocus Live
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Sponsoring Units: GSCCM Chair: Kyle Ramos, Los Alamos Natl Lab |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C23.00001: The High-Pressure Equation of State of TATB: Insights on the Monoclinic Phase Transition, Hydrogen Bonding, and Anharmonicity Brad Steele, Elissaios Stavrou, Vitali B. Prakapenka, Matthew Kroonblawd, I-Feng W Kuo The high-pressure equation of state (EOS) of energetic materials (EMs) are important for continuum and mesoscale models of detonation performance and initiation safety. Obtaining a high-fidelity EOS of the insensitive EM 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) has proven difficult due to challenges in experimental characterization at high pressures. In this work, powder x-ray diffraction patterns were fitted using the recently discovered monoclinic I2/a phase above 4 GPa, which shows TATB is less compressible than when indexed with the triclinic P-1 phase. First principles calculations were performed with PBE and PBE0 functionals including thermal effects. PBE0 improves the description of hydrogen bonding and predicts accurate a and b lattice parameters. However, discrepancies are found in the predicted and experimental lattice parameters above 4-10 GPa for the P-1 phase. Layer sliding defects are formed during molecular dynamics simulations which produces an anharmonic effect. The results provide insights into determining high-fidelity EOS parameters of TATB. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C23.00002: Effect of Pore Morphology on Localized Heating from Inert Mesoscale Simulations of PETN Zakary Wilde, Pedro Peralta
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Monday, March 15, 2021 3:24PM - 3:36PM Live |
C23.00003: Development of a New Unreacted Equation of State for LX-17 with a Genetic Algorithm and a Semiparametric Model Reid Ginoza Although the insensitive TATB-based explosive LX-17 is a well-studied energetic material, there is surprisingly little shock data from which to build an accurate unreacted equation of state for use with reactive flow models. In this work, we combine the existing Hugoniot data, including overdriven data, with data points derived from Pop Plots to increase the size of our data set and fit a new equation of state to this expanded data set. A semiparametric approach is used to model the equation of state to allow for more flexibility than traditional parametric equations of state. To find the best fit, a genetic algorithm performs a global search for the optimization and uses a fitness function that both minimizes the residual and respects physical constraints. We finally compare our equation of state to the existing unreacted equations of state by examining their Hugoniot curves, their fit to data, and their performance in simulations of sustained pulse shots and the resulting Pop Plots. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C23.00004: Unsupervised learning-based multiscale model of thermochemistry in 1,3,5-trinitro-1,3,5-triazine (RDX) Michael Sakano, Ahmed Hamed, Edward Kober, Nicolo Grilli, Brenden Hamilton, Md Mahbubul Islam, Marisol Koslowski, Alejandro Strachan The response of high-energy-density materials to thermal or mechanical insults involves complex physical and chemical processes coupling over disparate temporal and spatial scales. Reactive molecular dynamics (MD) simulations can contribute to a predictive understanding of their behavior under dynamical loading; however, computational intensity limits MD to the nanoscale, making it difficult to simulate eventual shock to detonation transition. Therefore, we developed a multiscale model for RDX, where a continuum description is informed by reactive and non-reactive MD simulations to characterize chemical reactions and thermal transport. Coarse graining is done using dimensionality reduction via unsupervised learning to establish a two-step reduced order chemical decomposition model. From homogeneous isothermal and adiabatic simulations, we extract chemical kinetics and heat of reaction parameters. The multiscale approach is validated from hot spot calculations where we find excellent agreement in the hotspot temperature fields. Finally, the continuum model is used to quantify the effects of uncertainties for various materials’ parameters and assess the criticality of hotspots involving scales beyond the reach of atomistic simulations. Approved for unlimited release LA-UR-20-29003. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C23.00005: GnarlyX: a mesoscale hydrocode for the extreme deformation of crystalline materials in high explosives applications Roseanne Cheng, Tariq D Aslam, Darby J Luscher, Christopher C Ticknor We present a new hydrocode, GnarlyX, for investigating shock initiation of plastic bonded explosives (PBX) composed of brittle crystals and polymeric binder. GnarlyX provides a crucial pathway for bridging the microscopic and macroscopic physics of initiation with direct numerical simulations (DNS) of the chemical release and transport at the mesoscale. Our understanding of the behavior of PBX is incomplete because of the lack of experimental support at small scales. GnarlyX is a path to address these shortcomings through a first-principles approach linking deflagration at the microscale to detonation propagation at the macroscale. GnarlyX solves the conservative multi-material hydrodynamic equations, closed with condensed phase equation of states and hyperelastic plastic constitutive models. It has a unique Helmholtz free energy formulation that gives thermodynamically consistent temperature calculations that are essential for high-fidelity reaction. GnarlyX uses robust 3D Eulerian, adaptive mesh refinement for simulating extreme deformation. In this talk, we describe our approach to continuum level modeling at the mesoscale and new computational methods necessary for HE mesoscale DNS. |
Monday, March 15, 2021 4:00PM - 4:12PM Live |
C23.00006: Local shock viscosity measurements at the interface of cyclotetramethylene-tetranitramine crystal and hydroxyl-terminated polybutadiene binder Abhijeet Dhiman, Ayotomi Olokun, Nolan Simon Lewis, Vikas Tomar In a heterogeneous microstructure such as plastic bonded explosives, the microscale shock behavior of different phases and the interface between the phases is crucial to correlate with the macroscale behavior of the material. The shock propagation between the different phases of material could be affected by delamination under shock pressure, temperature rise due to different dissipation mechanisms or chemical reactions. In this article, we investigated the shock propagation between hydroxyl-terminated polybutadiene (HTPB) binder and cyclotetramethylene-tetranitramine (HMX) crystal under shock loading by characterizing local shock viscosity at the interface. The shock was created at strain rates higher than 106/s by the impact of the planar disk of aluminum foil accelerated by laser-based setup. The local measurements at the interface were done using time-resolved Raman spectroscopy by combining a streak camera to obtain 1ns time resolution. The change in the Raman shift in the time domain was analyzed to extract information about local stress and shock stress rise time at the interface. The results show different rise times at the interface compared to a bulk HTPB binder and HMX crystal providing insight into the time-dependent local behavior and dissipation mechanisms. |
Monday, March 15, 2021 4:12PM - 4:24PM Live |
C23.00007: High Pressure Vibrational Spectra of Molecules via Molecular Dynamics Simulations Darryl Wilson, Jordan Penner, Jacob Alan Spooner, Noham Weinberg Pressure has a profound effect on intermolecular interactions and thus vibrational frequencies of molecular species in the condensed phase. Although a significant amount of experimental data on pressure dependences of vibrational frequencies has been obtained by now using high-pressure Raman and infra-red spectroscopy, theoretical studies of these effects are limited to a few recent publications utilizing a newly developed quantum mechanical technique based on specially adapted self-consistent reaction field model.1 In this work, we apply an alternative approach, based on the use of constant pressure molecular dynamics simulations, to compute high-pressure vibrational spectra for a number of simple molecular systems. |
Monday, March 15, 2021 4:24PM - 4:36PM Live |
C23.00008: Experimental and theoretical study on polymorphism and phase transitions of hydrazine nitrate under high temperature and high pressure Yangyang Zeng, Zhaoyang Zheng, Sha Bai, Yanqiang Yang Hydrazine Nitrate (HN) N2H4HNO3 is one of the promising solid propellants for replacing ammonium perchlorate (AP) with low signature and low pollution. It can also be used as liquid high explosive (HE) and lead-free primary HE in commercial detonators. Although detonation and other physical chemical properties of HN have been investigated. Effects of pressure and temperature on structural stabilities are unknown. We carried out experiments of isobaric heating and isothermal compressing, using thermal stage at ambient pressure, diamond anvil cells (DAC) at high pressure and micro-Raman spectroscopy. Density functional theory and analysis of weak interactions were also employed for HN. Phase transitions triggered by temperature and pressure were observed. The present results provide phase diagram of HN to 8 GPa and 200oC. |
Monday, March 15, 2021 4:36PM - 4:48PM Live |
C23.00009: High-order methods for reactive dynamics in condensed phases with interfaces Chukwudubem Okafor, Nirmal K Rai, H. S. Udaykumar Heterogenous energetic materials (HE) are central functional components in munitions, fuzes and triggers. HE such as plastic bonded explosive (PBX) and pressed explosives contain void spaces and interfaces. The sensitivity of HEs depends on shock interactions at crystal-crystal, crystal-binder interfaces and at voids/defects. Spatial resolution requirements to accurately calculate reactive dynamics localized at the complex interfaces in both PBX and pressed explosives are very stringent. 3rd-order accurate schemes used in previous works require very fine meshes to resolve interfaces, shocks and reactive fronts and to capture reactive dynamics in a grid-independent manner. High-order methods offer a way out. Small error magnitudes can be achieved using much coarser meshes. In this work, a WENO5 scheme is used to study the response of condensed phase materials under shock loading. This study is done through interface resolved simulations using a sharp interface Eulerian framework. The high-order scheme is combined with levelset tracking and ghost-fluid methods to delineate and apply boundary conditions on embedded interfaces. Test problems involving shocks, reactive flows and interfaces are used to evaluate the accuracy, computational cost, and performance of high-order methods. |
Monday, March 15, 2021 4:48PM - 5:00PM Live |
C23.00010: Structure-property-performance linkages for heterogeneous energetic materials using deep-learning generated synthetic microstructures Pradeep Kumar Seshadri, Yen Nguyen, Sidhartha Roy, Oishik Sen, H.S. Kumar This work investigates the shock sensitivity of synthetic microstructures generated using a deep neural network specifically Transfer Learning based approach. The structure-property linkages obtained from synthetic microstructures are compared with that of real microstructures obtained from SEM images of pressed HMX materials belonging to three classes (Class-3, Class-5 and FEM). We show that they closely mimic the global and local morphologies (quantified in terms of void sizes, shapes and orientations) of the real microstructures. To investigate energy localization (quantified in terms of hotspot ignition and growth rates), direct numerical simulations are performed on synthetic microstructures. We show that they perform realistically both qualitatively and quantitatively when compared to real microstructures. The ability to generate synthetic stochastic microstructures for ensemble simulations provides a route for energetic material designers to perform in silico experiments on synthetic microstructures and manipulate microstructural characteristics to achieve performance design outcomes. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C23.00011: Evaluation of the importance of void shapes in predictive meso-informed ignition and growth surrogate models for heterogeneous energetic materials Yen Nguyen, Pradeep Kumar Seshadri, Oishik Sen, David Hardin, H. S. Udaykumar The void collapse behavior of a heterogeneous energetic material at the mesoscale, leading to energy localization, is dependent on void geometrical features. In MES-IG, a meso-informed ignition and growth model, the surrogate reaction rate is taken as a function of shock loading as well as void morphometry. In this paper, we focus on the effects of void shapes on the performance of MES-IG. A large void collection of arbitrary shapes is extracted from SEM images of real, pressed HMX samples and classified into groups based on similarity in their shapes. Reactive void collapse direct numerical simulation (DNS) is performed using SCIMITAR3D code. The reaction rates obtained from DNS are compared with their counterpart MES-IG values for voids within each group and across groups. It is found that overall, the parameterization of complex void morphometry using orientation and aspect ratio gives fairly good agreement between DNS and MES-IG in reaction rate prediction. The intricate details of highly complex void shapes, however, do impact their hotspot characteristics to a significant extend. This work suggests possible improvements for the prediction of reaction rate in energetic microstructure by adopting a more detailed shape analysis, which points to future work. |
Monday, March 15, 2021 5:12PM - 5:24PM Live |
C23.00012: Void collapse simulations using a molecular-dynamics-informed rate-dependent elastoplastic model for HMX Dylan Walters, Pratik Das, Puhan Zhao, Tommy Sewell, H. S. Udaykumar A predictive computational model for detonation initiation in EMs must encapsulate physical mechanisms across length-scales ranging from molecular through microstructural to macroscale. A Molecular Dynamics model (MD) or an anisotropic rate-dependent crystal plasticity model may be able to capture mechanisms of energy localization at the different length scales. However, these models are computationally expensive and impractical for real-life problems. Isotropic rate-independent strength models are popular; however, they miss important physics (e.g. rate-dependent features such as shear localization). In this work, an MD informed rate-dependent J2-plasticity model is developed that captures the salient mechanism of energy localization in HMX. The model produces results in agreement with MD calculations for 1D shock passage through an HMX block, and for cylindrical pore collapse in HMX. It also performs well under a wide range of strain rates. It is shown that an MD-calibrated isotropic rate-dependent strength model produces similar results as MD calculations but at a much lower computational cost. This makes it feasible to predict the detonation-initiation of practical-size explosive samples of HMX. |
Monday, March 15, 2021 5:24PM - 6:00PM On Demand |
C23.00013: Understanding the Role of Microstructure in Energetic Materials Using a Predictive Hierarchical Multiscale Simulation Approach Invited Speaker: James 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. |
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