Mesoscale Thermo-Mechanical Response of Traditionally and Additively Manufactured Energetic Materials to Dynamic Loading

By Keyhani, Amirreza

Georgia Institute of Technology

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Advisors: Min Zhou, Richard W Neu, Antonia Antoniou, Shuman Xia, Julian J Rimoli

The thermo-mechanical responses of traditionally manufactured polymer-bonded explosives (PBXs) and an additively manufactured energetic material (AMEM) simulant under dynamic loading are studied. The performance of energetic materials subjected to dynamic loading significantly depends on their micro- and meso-scale structural morphology. The geometric versatility offered by additive manufacturing opens new pathways to tailor the performance of these materials. Additively manufactured energetic materials (AMEMs) have a wide range of structural characteristics with a hierarchy of length scales and process-inherent heterogeneities which are hitherto difficult to precisely control. Therefore, it is essential to understand how these features affect AMEMs' response under dynamic/shock in order to tailor these materials for applications, improve performance, and minimize uncertainties. To analyze the thermo-mechanical response and ignition behavior of PBXs, a cohesive finite element framework is used. The framework explicitly accounts for finite-strain elastic-viscoplastic deformation, arbitrary crack initiation and propagation, contact between internal surfaces, post-contact friction, heat generation resulting from inelastic bulk deformation and friction, and heat conduction. The analyses focus on material behavior at various levels of constituent friction and plasticity, and load intensity. The time to ignition is analyzed and quantified, providing explicit expressions for the ignition probability as a function of load intensity, load duration, and constituent properties. The AMEM simulant analyzed is unidirectionally printed using direct ink writing (DIW) of a high solid-loaded photopolymer and cured under UV-light exposure. To study the thermo-mechanical response of the AMEM simulant, quasi-static mechanical tests, intermediate strain rate Split-Hopkinson pressure bar (SHPB) experiments integrated with simultaneous high-speed visible and thermal imaging, and high strain rate x-ray phase-contrast imaging (PCI) experiments are performed. The experiments capture deformation modes and corresponding temperature signatures in the AMEM simulant. However, the effects of microstructural attributes and energy dissipation cannot be quantified experimentally due to limitations of available diagnostics. Therefore, experimentally-informed finite element computations are also performed to gain the quantification. The microstructural attributes are found to significantly affect the development of the hotspots in the AMEM simulant. The computations establish trends in and quantification of the relations between structure and response of a class of additively manufactured photopolymer-particulate composites.

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Researchers should cite this work as follows:

  • Keyhani, Amirreza (2021), "Mesoscale Thermo-Mechanical Response of Traditionally and Additively Manufactured Energetic Materials to Dynamic Loading,"

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