An initial investigation of the sub-microsecond features of dynamic crack propagation in PMMA and the RDX-based explosive PBX 9205

ORAL

Abstract

A dynamic crack propagating in a brittle material releases enough thermal energy to produce visible light. The dynamic fracture of even macroscopically amorphous materials becomes unsteady as the crack propagation velocity approaches the material wave-speeds. The heat generated at a crack-tip, especially as it jumps, may be a mechanism to initiate a self-sustaining reaction in an energetic material. Experiments were conducted in specimens to simulate an infinite plate for 20 $\mu $s. The initial specimens were 152 mm square by 6 mm thick acrylic sheets, and were fabricated to study non-steady near-wave-speed crack propagation. A variant of this specimen embedded a 25 mm x 3 mm PBX 9205 pellet to explore the influence of dynamic Mode-I cracks in these materials. The crack was initiated by up to 0.2 g of Detasheet placed along a precursor 50 mm long notch, with a shield to contain the reaction products and prevent propagation along the fractured surfaces. The crack was studied by means of a streak camera and a Fourier-filter of the light reflecting off the newly minted surfaces. The sub-microsecond behavior of holes initiating, preceding and coalescing with the main crack were observed in the PMMA samples. The embedding and mechanical loading of explosives by this technique did not initiate a self-sustaining reaction in preliminary testing.

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Authors

  • Peter Washabaugh

    University of Michigan

  • A. Rajendran

    DE Division, LANL, Chemistry Division, LANL, University of Cambridge, Sandia National Laboratories, Los Alamos National Laboratory, LLNL, UCSD, Institute of Fluid Physics, CAEP, Institute for High Energy Densities, JIHT RAS, Massachusetts Institute of Technology, Lawrence Livermore National Laboratory, DRDC Suffield, Lockheed Martin Corporation, Laboratoire de Combustion et de D\'etonique (UPR du CNRS n9028), ENSMA, B.P. 40109, 86961 Futuroscope Cedex, France, Wash. State Univ., McGill University, Naval Surface Warfare Center, Dahlgren, Air Force Research Laboratory (AFRL/MNME), Harvard University, Fraunhofer, Ernst-Mach-Institut, Materials and Structures Laboratory, Tokyo Institute of Technology, CEA Valduc, LMPM, ENSMA Poitiers, France, LCD, ENSMA Poitiers, France, Applied Research Associates, Seismological Laboratory MS 252-21, California Institute of Technology, Pasadena, CA 91125, Department of Geological Sciences, Brown University, Providence, RI 02912-1846, Lawrence Livermore National Laboratory, University of California, Department of Aeronautics and Astronautics, Faculty of Engineering, Kyushu University, National Institute of Advanced Industrial Science and Technology, Energetic Materials Technology, NSWC Indian Head, AWE, UK, Los Alamos National Laboratory, Materials Science and Technology Division, Seoul National University, University of Duisburg-Essen, Germany, University of Lund, Sweden, University of Oxford, UK, AWE, Aldermaston, UK, LANL, IHED of JIHT RAS, Dorodnicyn Computing Center RAS, Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, Chinese Academy of Engineering Physics, Mianyang 621900, Materials Science and Engineering, OSU, Columbus, OH, RFNC - VNIIEF, Sarov, Russia, School of Materials Engineering, Purdue University, West Lafayette, IN 47907, Applied Physics Division, Los Alamos National Laboratory, Los Alamos, NM 87545, Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, University of Manchester, AWE, Aldermaston, HCEI, Russian Federal Nuclear Center - VNIIEF, Laboratory for Shock Wave and Detonation Physics Research, Institute of Fluid Physics, P.O.Box 919-102, Mianyang 621900, P. 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