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 B05: Structure and Property EffectsFocus Recordings Available
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Chair: Lee Perry, Los Alamos National Laboratory Room: Anaheim Marriott Platinum 3 |
Monday, July 11, 2022 9:15AM - 9:30AM |
B05.00001: High strain rate properties of Glass/Epoxy composites James Perry, David Williamson Fibre-reinforced composites (FRPs) are strong, light, and resistant to corrosion. However, they are complex and highly anisotropic: They can deform and degrade via a variety of damage and failure modes, and their performance can be affected by macro-, meso- and micro-structural material properties such as fibre architecture – as well as by specimen geometry, loading configuration and environmental conditions. Wider use of FRPs is limited by the need for accurate and reliable predictive modelling, which in turn relies on good experimental data. However, their inherent complexity and structure means they are not necessarily suited to the usual suite of high-rate “materials characterization” tests, as the concept of a wholly bulk-representative specimen may not be applicable. Indeed, we should arguably consider FRPs as structures, rather than materials in the traditional sense. To explore this issue, this talk will consider the effects of variables such as fibre layups, specimen geometry and ageing on small-scale, high-rate laboratory tests, in order to delve deeper into the structure-property relationships of FRPs. |
Monday, July 11, 2022 9:30AM - 9:45AM |
B05.00002: The Evolution of Void Morphology in Pressed TATB with Density and Particle Size Joseph T Mang, Larry G Hill Microstructure plays a significant role in determining the shock sensitivity and performance of pressed high explosives (HEs). This is particularly true for the insensitive high explosive TATB whose corner turning ability is affected by subtle changes in its initial particle size distribution (PSD). This is surprising, as the TATB particles are considerably altered during consolidation. It is likely that the importance of the initial TATB PSD resides in its influence on the final void size size distribution, whose viscous collapse under shock conditions can lead to the formation of hot spots that are known to influence initiation. There is an increasing need for detailed microstructural information such as void size and morphology within pressed parts to support HE production and modeling capabilities. Little is known of the relationship between the initial HE PSD and void size and morphology within a compact. Small-angle scattering techniques were used to study the evolution of this relationship in TATB samples pressed from three distinct PSDs over the density range from 1.55 – 1.89 g/cc. In all samples studied, the void volume is well described as ramified networks of voids. The network size and connectivity will be discussed in terms of the initial TATB PSD and density. |
Monday, July 11, 2022 9:45AM - 10:15AM |
B05.00003: Novel Method to Control Explosive Shock Sensitivity: Formulations, Experiments and Modeling Invited Speaker: Amanda L Duque The microstructure of a heterogeneous high explosive (HE) affects its shock initiation sensitivity and detonation performance. Alteration of the void content and/or void structure (i.e. bulk heating or mechanical damage) therefore changes the shock initiation behavior. Controlling and predicting the change in shock sensitivity after an HE has undergone microstructural changes addresses an important and challenging goal for the design and understanding of novel energetic material formulations. In this study, we aimed to develop HE systems to precisely tune shock sensitivity by a thermal treatment prior to use. Specifically, we incorporated a small fraction (1 wt% or less) of thermally expandable microspheres (TEMs) during the formulation process of various plastic-bonded explosives (PBX). TEMs typically consist of a thermoplastic acrylonitrile shell (10-50 µm diameter), which encapsulates an inert low boiling hydrocarbon. Upon heating, the TEMs expand as the shell softens while the hydrocarbon gasifies, increasing the internal pressure and expanding the particle by as much as 120 vol% (irreversibly). Here, we present our experimental and modeling progress on shock sensitivity comparisons of HE formulations doped with TEMs after heating and expansion. Experiments, using Composition C-4 thermally-cycled to 120 °C, showed a significant increase in shock sensitivity. Mesoscale modeling revealed that the TEM itself does not act as a hotspot, but instead has a secondary effect on the response of nearby voids. We conclude that TEMs indeed do provide a method to tune shock sensitivity. Further, our results emphasize the non-uniformity of shock waves at the mesoscale, and that upstream defects influence the reactivity of downstream defects. |
Monday, July 11, 2022 10:15AM - 10:30AM |
B05.00004: Development of an Expandable HE Formulation for an Explosive Train Interrupter Module Thuy-Ai Nguyen, Amanda L Duque, Bryce C Tappan, Joseph P Lichthardt, Larry G Hill Realization of a reliable interrupter device in an explosive train to prevent unintended detonation is a potentially powerful strategy for enhanced safety in high explosives (HE). We present an interrupter concept that relies on an expandable HE part containing Expancel® microspheres, which are commercially available blowing agents that can expand up to 60 times in volume when heated. These thermally expandable microspheres (TEMs) consist of a thermoplastic shell that encapsulates an inert hydrocarbon that gasifies upon heating, exerting pressure on the softened shell to expand it. We developed and tested a new HE formulation consisting of erythritol-1,3,4-trinitrate-2-acrylate (ETriN A), pentaerythritol tetranitrate (PETN), trimethylolethane trinitrate (TMETN), and TEMs. This formulation remains pliable enough after cast curing to expand dramatically, unlike other formulations that were tested. We present a successful proof of concept for an interrupter module that consists of an unexpanded HE part placed directly below the detonator. In the "inactive" state, an air gap separates the interrupter from the detonator to inhibit shock propagation. In order to complete the explosive train, the HE is expanded to fill the air gap, allowing shock propagation through the expanded HE. |
Monday, July 11, 2022 10:30AM - 10:45AM |
B05.00005: Mesoscopic modelling of the dynamic compaction of a polymeric foam Pierre Pradel, Frédéric Malaise, Isabelle Bertron, David Hebert The use of polymeric foams is widespread in many industrial fields as shock wave mitigators. Indeed, they are lightweight materials with an excellent weight/stiffness ratio and low production costs. One of the applications of interest to the CEA is the protection of structures against mechanical loadings generated by laser irradiation or high velocity impact of small debris. The search for the optimal size and shape of porosities are essential data for improving the mitigation ability of foams. The purpose of this study is to simulate the dynamic behavior of a polyurethane foam subjected to different dynamic loadings at various strain rates, using a mesoscopic model. The foam was modeled in different ways in 2D: first by periodically arranging cylindrical porosities in the polyurethane matrix in a linear manner with boundary conditions, then in a staggered manner, and finally randomly. The matrix was modeled using an equation of state and a constitutive law of dense polyurethane. Comparisons between experiments and calculations were made on velocity profiles obtained by PDV on the rear surface of foam samples. Calculations fairly reproduce experiments and show the influence of the arrangement of porosities on the foam compaction. |
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