Abstract
It is well known that energy can be spatially localized when explosives are mechanically deformed; however, the heat generation mechanisms associated with this localization process are not fully understood. In this work, mesoscale hot spot formation in ultrasonically-excited energetic materials has been imaged in real-time. More specifically, periodic, mechanical excitation has been applied to Dow Corning Sylgard® 184/octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) composite materials using contact piezoelectric transducers resulting in heating at various crystal locations. A thermally-induced phase transition from a β to δ non-centrosymmetric crystal structure for HMX results in the frequency doubling of incident laser radiation and can be used as a temperature proxy. In light of this, a high-repetition-rate 1064 nm Nd:YAG laser has been used to illuminate discrete HMX crystals, and a 532 nm filter has been applied to capture only the light emitted from δ-phase second harmonic generation (SHG). The visualization of δ-phase initiation and growth is useful for determining both heat generation mechanisms and heating rates at crystal/crystal and/or crystal/binder interfaces and contributes to the understanding and prediction of hot spots.
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Acknowledgments
This work was made possible by support from the U. S. Air Force Office of Scientific Research through award no. FA9550-15-1-0102 and the project’s Program Manager Dr. Jennifer Jordan. The author J. O. Mares would like to express gratitude to the National Science Foundation Graduate Research Fellowship Program under grant no. DGE-1333468.
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Roberts, Z.A., Mares, J.O., Miller, J.K., Gunduz, I.E., Son, S.F., Rhoads, J.F. (2017). Phase Changes in Embedded HMX in Response to Periodic Mechanical Excitation. In: Antoun, B., et al. Challenges in Mechanics of Time Dependent Materials, Volume 2. Conference Proceedings of the Society for Experimental Mechanics Series. Springer, Cham. https://doi.org/10.1007/978-3-319-41543-7_10
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DOI: https://doi.org/10.1007/978-3-319-41543-7_10
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