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 V05: Structure, Performance, and Sensitivity RelationshipsRecordings Available
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Chair: Michael Armstrong, Lawrence Livermore Natl Lab Room: Anaheim Marriott Platinum 3 |
Thursday, July 14, 2022 2:00PM - 2:15PM |
V05.00001: Modeling of the Dihedral Shear Compression Test for Studying Non-Shock Ignition in High Explosives Bradley W White, John E Reaugh, Christopher Miller, Aaron J Ruch, Kevin S Vandersall Understanding the conditions that lead to ignition in high explosives under non-shock loading scenarios is a challenging area in the field of energetic materials. This is in part due to a limited number of test results for high explosives at low and moderate impact speeds (10-100 m/s). We have developed the Dihedral Shear Compression (DiSCo) test to place high explosives under shear and compressive loads that lead to ignition. This test produces complementary ignition thresholds to those that occur in the Steven test, which allows us to constrain our High Explosive Response to Mechanical Stimuli (HERMES) shear ignition sub-model and better predict the likelihood of an explosive to ignite under non-shock load scenarios [1]. The DiSCo test will be introduced along with results of HERMES modeling of an HMX-based explosive. Where possible, comparisons between the DiSCo and Steven tests will also be drawn. |
Thursday, July 14, 2022 2:15PM - 2:30PM |
V05.00002: Model for explosive sensitivity using enthalpy of explosion and effective trigger linkage kinetics Marc J Cawkwell, Jack Davis, Nicholas Lease, Frank Marrs, Alexandra Burch, Suyana Ferreira, Virginia W Manner A simple and physically transparent model for the origin of explosive sensitivity has been developed from gas-phase enthalpies of explosion and the kinetics of trigger linkage rupture. These properties parameterize an Arrhenius rate law that connects energy release and bond strengths to the stability of explosive molecules. The effective trigger linkage kinetics are computed using gas-phase reactive molecular dynamics simulations that rapidly and automatically sample all possible decomposition pathways on the potential energy surface of each molecule. The model is parameterized to the results of drop weight impact testing, where H50 is the height from which a 2.5 kg mass is dropped onto small, 40 mg samples such that they react with 50% probability, for a set of 24 primary, conventional, and insensitive explosives from a number of distinct chemical families with sensitivities that span H50 = 0.7 cm to greater than 320 cm. Our results indicate that insensitive explosives (those with high H50 values) generally derive their properties from a combination of strong trigger linkages and a small enthalpy of explosion while the most sensitive explosives (with small H50 values) exhibit both weak trigger linkages and large enthalpies of explosion. |
Thursday, July 14, 2022 2:30PM - 2:45PM |
V05.00003: Synthetic Functionalization and Reaction Kinetics of Pentaerythritol Tetranitrate (PETN) Derivatives Virginia W Manner, Nicholas Lease, Marc J Cawkwell The handling sensitivity of explosives is influenced by a number of fundamental chemical properties, with contributions from both kinetics (reaction rates) and thermodynamics (heat of explosion). In order to evaluate the interplay of these parameters, we have designed a series of derivatives of pentaerythritol tetranitrate (PETN) by substituting nitrate ester functional groups with inert hydroxy groups. The four explosives have similar chemical properties but exhibit wildly different handling sensitivities when tested for sub-shock sensitivity using the drop-weight impact test. The thermal stability of each PETN derivative has been evaluated via its reaction kinetics using molecular dynamics simulations to determine time to explosion or trigger linkage rupture for each derivative over a range of temperatures. In general, it is expected that the first energetic bond to break (i.e. the "trigger linkage") is critical in influencing the sensitivity of an explosive. Our preliminary results suggest while all four explosives have the same trigger linkages – the nitrate ester – the relatively small specific heats of explosion of the mono-nitrate and di-nitrate derivatives result in lower impact sensitivity values. Ongoing experiments with more advanced diagnostics will also be discussed. |
Thursday, July 14, 2022 2:45PM - 3:00PM |
V05.00004: Halogen substitution on PETN framework: An energetic material sensitivity study Nicholas Lease, Marc J Cawkwell, Virginia W Manner Evaluating explosives for safety properties is critical in order to develop safe handling, transport, and storage requirements. Literature reports have provided evidence that many factors can influence sensitivity, including chemical effects such as functional groups, bond connectivity, and thermal decomposition. Additionally, macroscale effects such as crystal structure, hydrogen bonding, electrostatic effects and co-crystallization can play important roles. Herein we describe work in which the explosive PETN (pentaerythritol tetranitrate) has been modified though systematic substitution of the nitrate ester groups with halogens (Cl, Br, I). All PETN derivatives with a single halogen substitution exhibited similar explosive sensitivities, despite differences in their crystal packing properties. Results from these experiments suggest that when dealing with sensitive explosives, i.e. nitrate esters, chemical structure and bond connectivity are more important in determining properties than secondary effects such as crystal packing. Both the presence and quantity of the weakest bond, in this case the O-NO2 “trigger linkage,” can be the most important factor in determining the ability of the explosive to generate and sustain a measurable reaction in small-scale sensitivity testing. |
Thursday, July 14, 2022 3:00PM - 3:15PM |
V05.00005: A Bond Centered Approach to Energetic Performance and Sensitivity Jack Davis, Frank Marrs, Alexandra Burch, Nicholas Lease, Suyana Ferreira, Marc J Cawkwell, Virginia W Manner Handling sensitivity, as measured by the drop-weight impact apparatus, is frequently |
Thursday, July 14, 2022 3:15PM - 3:30PM |
V05.00006: Investigating correlations between explosive impact sensitivity and mechanical properties using nanoindentation Alexandra Burch, Hugh P Grennan, David F Bahr, John D Yeager, Marc J Cawkwell, Virginia W Manner Handling sensitivity is the first parameter that must be evaluated in order to work safely with explosive samples. This can be measured using a variety of tests, including drop-weight impact sensitivity. In addition to safety, there is is a longstanding scientific interest in the explosives community to connect, if possible, chemical, physical, and mechanical properties to impact sensitivity. Although the physical and mechanical properties of explosives have been studied for many decades, systematic efforts investigating their relationship to handling sensitivity are rare. Most mechanical characterization of explosives has historically been done on plastic-bonded composites containing conventional explosives, but recently nanoindentation has been used to probe the mechanical response of pure explosive single crystals. In this study, we employ nanoindentation techniques to measure hardness and elastic modulus of a variety of explosives in order to search for correlations to drop-weight impact sensitivity. Both primary and secondary explosives are studied, along with mechanical behavior and sensitivity trends. |
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