Title page for ETD etd-10082012-132131

Type of Document Master's Thesis
Author Gilbert, John
Author's Email Address johng12@vt.edu
URN etd-10082012-132131
Title Characterizing Impact Induced Hot-Spot Morphology in Granular Solid Explosive
Degree Master of Science in Mechanical Engineering (M.S.M.E.)
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Gonthier, Keith Alan Committee Chair
Martin, Michael James Committee Member
Schoegl, Ingmar Committee Member
  • hot-spot formation
  • impact
  • energetic solids
Date of Defense 2012-08-16
Availability unrestricted
Deformation induced ignition of heterogeneous solid explosives is believed to originate at hot-spots within the material which are local regions of elevated temperature resulting from dissipative mechanisms such as plastic deformation and inter-particle friction. Inert meso-scale modeling of these materials can principally account for hot-spot formation enabling the characterization of hot-spot size and temperature distributions which are important for ignition but are dicult to experimentally resolve.

The focus of this study is to characterize hot-spot morphology, as well as the distribution of hot-spots, behind quasi-steady compaction waves computed from predicted temperature fields resulting from numerical simulations of rigid planar piston impact on randomly packed, granular HMX (C4H8N8O8). Hot-spots are analyzed from the inert heating predictions of four meso-structures, composed of hexagonal and/or circular shaped particles having average initial solid volume fractions in the range 0.57 to 0.84. Predictions

indicate that hot-spot temperature distributions are largely insensitive to changes in piston speeds between 300 m/s to 500 m/s, or initial solid volume fraction. Higher piston speed and lower initial solid volume fraction resulted in larger hot-spot sizes. Hot-spot number density, volume fraction, and specific surface area, were shown to be sensitive to variations in initial solid volume fraction and are predicted to grow

exponentially with piston speed over the ranges considered in this study.

Combustion implications are examined by combining inert heating predictions for uniaxial waves with thermal explosion data and analysis to estimate ignition time distributions and local fractions of ignited mass. These are important first steps in establishing a general statistical theory for early time ignition in heterogeneous solid explosives. Preliminary results indicate number density and size of hot-spots are the major factors which influence the impact and shock sensitivity of these materials over the range of impact speeds considered.

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