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 1J: Rapid Fire Research CompetitionStudent Symposium
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Room: Anaheim Marriott Platinum 5-6 |
Sunday, July 10, 2022 3:15PM - 3:20PM |
1J.00001: Jointly Embedded Machine Learning Approach for Polymer Combustion Properties Jesse C Hearn High energy density polymeric binders are a class of polymer materials that can be used in lieu of inert binders in high energy density mixtures. By using higher energy binders, the overall internal energy of the mixture can be designed intentionally and proactively. In this presentation, we will showcase our recent efforts to develop a machine learning approach to learn, predict, and design novel energetic polymers. The scarcity of data available for energetic polymers is a particular challenge that we overcome through transfer learning techniques. Generally-speaking, transfer learning is a class of machine learning algorithm that assists the learning of general trends within one dataset using alternate datasets. In our approach, we use a feature transfer learning approach based on low-level physiochemical data that may be obtained for any molecule. We first train the model to learn the form of repeat unit structures using an open synthetic dataset containing 1 million polymer repeat units. Then, the model is trained on a dataset containing <170 polymer repeat units for which thermochemical properties are known. The model is then developed to perform generation functions and new polymers may be proposed with desirable attributes. The resulting machine-learned molecule property estimates are then compared with theoretical thermochemical models. Through the transfer learning approach, we will also address the importance of synthesizability and discuss how the proposed techniques can be used to increase the likelihood of developing synthesizable candidate polymer molecules. |
Sunday, July 10, 2022 3:20PM - 3:25PM |
1J.00002: Many Bodied Mechanochemistry Simulations: Exploring the initial events inside a hotspot Brenden W Hamilton When molecular materials experience high velocity impacts, the resulting shockwave can induce a variety of complex intra-molecular deformations, leading to mechanochemistry. Mechanochemistry can enable novel reaction pathways, lower the thermal energy cost of reactions, and is relevant to thermochemical phenomena such as detonation, with mounting indication that these effects are highly relevant to the initiation of "hotspots" in high explosives. However, these effects are difficult to assess under non-equilibrium and shock loading simulations, and the state-of-the-art simulation techniques for mechanochemistry typically apply linear forces to individual molecules. Therefore, we develop a novel technique of an external biasing potential to apply 'many-bodied steered molecular dynamics' in which we mimic intra-molecular deformations of a shock induced hotspot in TATB. Independent simulations of two different deformation types show different levels of acceleration of reaction kinetics for the applied work and results in different alterations to first-step reaction pathways. We believe these results help to solve the puzzling difference between thermal and shock-loaded kinetics in HEs and provide a more general methodology for assessing mechanochemical effects in bulk, covalent solids. |
Sunday, July 10, 2022 3:25PM - 3:30PM |
1J.00003: Slip competition and rotation suppression in tantalum and copper during dynamic uniaxial compression Patrick G Heighway When dynamically compressed via laser-plasma ablation, a metallic specimen will generally undergo changes to its crystallographic texture due to plasticity-induced rotation. The axis and the extent of the local rotation can provide hints about the combination of plasticity mechanisms activated by the rapid uniaxial compression, thus providing valuable information about the underlying dislocation kinetics that are operative under extreme loading conditions. We present molecular dynamics simulations of shock-induced lattice rotation in three model crystals whose behaviour has previously been characterised in dynamic-compression experiments: tantalum shocked along its [101] direction, and copper shocked along either [001] or [111]. Our simulations indicate that while tantalum loaded along [101] and copper loaded along [001] both show pronounced rotation due to asymmetric multiple slip, the orientation of copper shocked along [111] is stabilised by opposing rotations arising from competing, symmetrically equivalent slip systems. In all three cases, the sense of the reorientation predicted by the simulations is consistent with that measured experimentally using in situ x-ray diffraction. |
Sunday, July 10, 2022 3:30PM - 3:35PM |
1J.00004: Modeling Multi-dimensional Shock-to-Detonation Transition of Pressed HMX Using a Meso-informed Ignition and Growth Model Pradeep Kumar Seshadri In previous works we have demonstrated that traditional semi-empirical ignition and growth model that relies on parameters fit to empirical data can be successfully replaced by a meso-aware energy deposition model trained using ensembles of reactive void collapse simulations to predict the shock-to-detonation transition at the macro-scale. While quasi-1D studies have been successfully validated against the experimental results, here we extend the framework to a multi-dimensional setting. In this work, we perform shock-to-detonation transition (SDT) simulations of pressed HMXs to predict corner turning behavior. The Enhanced Corner Turning (ECOT) test provides a measure of pressure initiation sensitivity of an energetic material. As the detonation wave moves around a sharp corner, the wave dynamics and accompanying pressure field can lead to a failure in sustaining the detonation. The porosity of the material, size and shape of the voids and cracks, and shock loading all play a crucial role in this corner turning behavior. We use the meso-informed ignition and growth model (MES-IG) based multi-scale framework to study the detonation initiation and propagation regimes in an ECOT simulation. We also study the sensitivity of the corner turning behavior to variations in overall porosity and void diameter. |
Sunday, July 10, 2022 3:35PM - 3:40PM |
1J.00005: Thin Pulse Experiments Performed At -55°C On TATB-Based Explosives Emily N Weerakkody Experiments were performed at -55°C to measure the thin pulse shock initiation of TATB-based explosive formulations to build on previous experiments at ambient temperature. A thin stainless steel flyer plate backed by a low-density foam was used to generate the thin pulse, and the experiments were performed in a pressure regime where the thin pulse input was high enough to cause a transition to detonation at ambient temperature. This process entailed a redesign of previous hardware utilized to perform similar experiments to minimize material usage and prevent damage to the test chamber, as well as validation of temperature profiles within the target using thermocouples embedded in manganin gauges. Information about temperature-based kinetics of TATB can be gleaned from these tests, and data obtained can be used to inform computational models in development. A discussion of this work will include the experimental parameters, data analysis, run-distance-to-detonation comparisons to prior ambient temperature results, possible comparisons to modelling and simulation results, as well as detail on potential future experiments. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. |
Sunday, July 10, 2022 3:40PM - 3:45PM |
1J.00006: Spall strength of polycarbonate measured using laser-driven micro-flyer impact experiments Jacob M Diamond Polymers play an increasingly large role in application areas involving extreme loadings, from polymer-bonded explosives to personnel and vehicular protection systems. However, there remain substantial gaps in our knowledge of polymer mechanics at very high strain rates, especially regarding spall strength and dynamic void growth. Further, the underlying micromechanisms that control dynamic void growth and spall in polymers are not fully understood. Here we present experimental results on the spall strength of a model amorphous thermoplastic, polycarbonate, measured using laser driven micro-flyer (LDMF) plate impact and photonic Doppler velocimetry (PDV). Our experimental method enables high-throughput testing, such that we can collect an order of magnitude more data points than traditional gas gun spall experiments. This large volume of tests allows us to generate spall strength statistics, and to correlate spall response with material characteristics. The results presented here will serve as a basis for future efforts in modeling dynamic void growth and spall in amorphous polymers. |
Sunday, July 10, 2022 3:45PM - 3:50PM |
1J.00007: Inelastic Deformations in Shock Compressed Diamond Jonathan T Willman Understanding diamond response to shock compression at megabar pressures is of critical importance for design of instability-free inertial confinement fusion implosions of diamond ablation capsules. Recent shock experiments using single crystal diamond have uncovered strong orientational dependent response in split elastic-inelastic shock wave regime. However, underlying mechanisms of crystalline anisotropy of shock response are currently unknown. In this work, large-scale molecular dynamic simulations of shock compression on diamond are performed using quantum accurate SNAP machine learning potential for carbon to provide atomic scale insights into the mechanisms of inelastic deformations in shocked diamond. The MD simulations of shock propagation along three crystallographic directions and a wide range of shock intensities uncover unusual persistence of anisotropic effects at very high pressures up to complete melting along diamond shock Hugoniot. |
Sunday, July 10, 2022 3:50PM - 4:00PM |
1J.00008: Break III
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