Analysis of microstructure-dependent shock dissipation and hot-spot formation in granular metalized explosive

• Published in: Journal of applied physics Vol. 120; no. 2
• Main Authors: Chakravarthy, Sunada, Gonthier, Keith A.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 14.07.2016
• Subjects: Aluminum; Applied physics; Deformation; Explosives; HMX; Microstructure; Packing density; Porosity; Spatial distribution
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4956302

Variations in the microstructure of granular explosives (i.e., particle packing density, size, shape, and composition) can affect their shock sensitivity by altering thermomechanical fields at the particle-scale during pore collapse within shocks. If the deformation rate is fast, hot-spots can form, ignite, and interact, resulting in burn at the macro-scale. In this study, a two-dimensional finite and discrete element technique is used to simulate and examine shock-induced dissipation and hot-spot formation within low density explosives (68%–84% theoretical maximum density (TMD)) consisting of large ensembles of HMX (C4H8N8O8) and aluminum (Al) particles (size ∼ 60 –360 μm). Emphasis is placed on identifying how the inclusion of Al influences effective shock dissipation and hot-spot fields relative to equivalent ensembles of neat/pure HMX for shocks that are sufficiently strong to eliminate porosity. Spatially distributed hot-spot fields are characterized by their number density and area fraction enabling their dynamics to be described in terms of nucleation, growth, and agglomeration-dominated phases with increasing shock strength. For fixed shock particle speed, predictions indicate that decreasing packing density enhances shock dissipation and hot-spot formation, and that the inclusion of Al increases dissipation relative to neat HMX by pressure enhanced compaction resulting in fewer but larger HMX hot-spots. Ensembles having bimodal particle sizes are shown to significantly affect hot-spot dynamics by altering the spatial distribution of hot-spots behind shocks.