Chapter 7 The Influence of Formulation Variation and Thermal Boundary Conditions on the Near-Resonant Thermomechanics of Mock Explosives Allison R. Range, Nicole R. McMindes, Jaylon B. Tucker, and Jeffrey F. Rhoads Abstract The thermomechanics of energetic and inert particulate composite materials are of pronounced interest in the defense community. This work seeks to further characterize the macroscale, thermal and mechanical response of these materials under various near-resonant mechanical excitations. The fabrication of mock energetic samples based on the PBXN-109 formulation, comprised of hydroxyl-terminated polybutadiene (HTPB) binder with 85% solids loading and varying additive content (0%, 15%, and 30%) of sucrose and/or spherical aluminum crystals, enabled a systematic investigation into the effect of formulation variation on the thermal and mechanical response. Experiments were also performed on insulated plate samples of identical composition to examine the effect of varying thermal boundary conditions. In each of these experiments, the samples were mechanically excited using an electrodynamic shaker, while their thermal and mechanical responses were recorded using an infrared camera and scanning laser Doppler vibrometer, respectively. The investigation of these responses aids in the effort to characterize and understand the behavior of polymer-bonded explosives under mechanical excitation. Keywords Energetic materials • Explosives • Thermomechanics • Vibration • Viscoelastic materials 7.1 Introduction Energetic and inert particulate composite materials are of pronounced interest in the defense community due to their prevalent use in improvised explosive devices and munitions systems, which must be properly detected or handled to ensure public safety and national security. These materials present unique challenges in regards to their thermomechanical behavior. For example, the combination of solid particles with elastic binder results in phenomenon such as hot spot formation and particle de-bonding at the crystal-binder interface [1]. It has also been observed that these polymer-bonded materials exhibit stiffening as their age increases [2], an effect not accounted for in classic behavioral models. The materials also exhibit dramatically varying bulk thermal and mechanical moduli with particle/binder ratio and can rapidly decompose, both thermally and mechanically, under comparatively weak external loads [3–6]. Although mechanically-induced heat generation is a well-studied effect for pure materials and alternative composites, there exists an appreciable literature gap related to the influence of mechanical vibrations on particulate composite materials such as polymer-bonded explosives. The works of Loginov [7, 8] provide useful insight into the phenomenological nature of the vibration-induced heating of energetic materials. Initial investigations by this investigator and collaborators sought A.R. Range • N.R. McMindes Ray W. Herrick Laboratories, Purdue University, 47907, West Lafayette, IN, USA School of Mechanical Engineering, Purdue University, 47907, West Lafayette, IN, USA J.B. Tucker School of Mechanical Engineering, Purdue University, 47907, West Lafayette, IN, USA J.F. Rhoads ( ) Ray W. Herrick Laboratories, Purdue University, 47907, West Lafayette, IN, USA School of Mechanical Engineering, Purdue University, 47907, West Lafayette, IN, USA Birck Nanotechnology Center, Purdue University, 47907, West Lafayette, IN, USA e-mail: jfrhoads@purdue.edu © The Society for Experimental Mechanics, Inc. 2018 J. Carroll et al. (eds.), Fracture, Fatigue, Failure and Damage Evolution, Volume 7, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-62831-8_7 47
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