Date of Award
2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Chemistry
Department
Chemistry
First Advisor
Jimmie C. Oxley
Second Advisor
James L. Smith
Abstract
A wide range of shock physics experiments require a high pressure, 2D-planar shock with pressure and temporal uniformity. Researchers, traditionally, would utilize a gas gun facility or high explosive plane wave lens. These techniques have several limitations. Gun facilities have high facility cost and long experiment times. Legacy fast-slow explosive lenses require labor intensive and high risk, high precision pressed or casted and, subsequently, machined explosives. Any design changes made with the explosives in such traditional lenses leads to significant increases in cost and time. Previous groups demonstrated that inert waveguides can generate a planar shock using only a single explosive formulation. These inert or Fritz plane wave lenses also have significantly lower net explosive weight and can be printed in parallel as opposed to single machining operations. By utilizing 3D printing and hydrodynamic modeling, a wide design space was explored experimentally and computationally to optimize the pressure and temporal uniformity of lenses. Statistical design of experiments was used to visualize and interpret an extensive set of simulations to inform experimental geometries. Using a cast cure explosive formulation, 3D printed lenses were fabricated at the 1” and 2” diameter scale. Lenses were evaluated using streak photography and photon Doppler velocimetry. Results of simulations and experiments illustrate key design parameters including the waveguide contour radius and explosive formulation composition. After calibration and geometry optimization, lenses had a temporal and pressure uniformity of < 50 ns and < 3 GPa respectively.
Simulations and experiments were conducted to control the shock-to-detonation transition by energy trapping in localized regions of nitromethane that contained arrays of embedded dense particles (tantalum rods). The localizations were additively manufactured and designed. with simulations carried out with ALE3D, that used the ignition and growth reactive flow model for the explosive. Modelling demonstrated enhanced reactivity when the tantalum rods were present, leading to a detonation that otherwise did not occur for the same strength shock without rods. Experiments that confirmed predictions of the simulation were conducted using Fritz plane wave lenses to drive various input shocks into the system. Photon doppler velocimetry was the primary diagnostic used to measure shock input and reaction progression. These results suggest that it is possible design explosives to localize sensitivity to shock loading within an insensitive material increasing the overall safety of fielded energetic materials.
Simulations and experiments were conducted to control energy released during explosive corner turning within localized regions of nitromethane. These localized geometries were additively manufactured and tuned based on simulations carried out in ALE3D. High explosive ignition and growth reactive flow modeling identified specific high impedance inclusion geometries for given donor-acceptor charge geometries that would induce corner turning when present. Synthetic, pressure-dependent streak camera images were generated in simulations to inform experimental results. Experiments were conducted using Fritz plane wave lenses to drive planar input shocks into the system. Ultra-high-speed framing and streak camera imaging was used to view shock time of arrivals within manufactured metamaterials. Framing camera images revealed localized instabilities within the nitromethane that were not present in untuned experiments. Streak camera imaging was used to measure corner turning time of arrival at the boundaries of the experimental geometry. Corner turning did not occur in simulations or experiments that did not include the tuned inclusions. These results suggest that it is possible to localize sensitivity to detonation within an insensitive material increasing the overall safety of fielded energetic materials.
To date plastic bonded explosives used in commercial, military, and research have been largely formulated using slurry coating. There are ongoing initiatives to replace per- and polyfluorinated substances. The question is how to replace these in various energetic formulations without sacrificing safety and performance. Spray drying is an alternative processing technique that can provide several advantages to slurry coating. Unlike some forms of slurry coating, spray drying does not require a fluorinated working fluid. Spray drying does not require the use of water and is easily adapted to processing under inert atmospheres, allowing for a wider range of compatibility for additives. Cyclotetramethylene tetranitramine (HMX) was spray dried with Viton A-100 and with Estane-5703 to serve as direct comparisons to PBXN-5 and LX-14, respectively. The resultant molding powders were tested for impact, electrostatic discharge, and friction sensitivity. Spray-dried formulations were found to be less impact sensitive than commercially obtained PBXN-5 and LX-14. Electrostatic discharge and friction sensitivity were found to be sufficiently low to classify molding powders as secondary explosives. The disk acceleration experiment was conducted on pressed samples to measure detonation velocity and CJ-pressure. Results are compared to commercially obtained PBXN-5 and LX-14 pressed to similar densities.
A small detonation chamber was designed, manufactured, and tested to facilitate near field imaging of detonation driven experiments. The chamber was constructed from 0.50” thick mild steel and has feedthroughs for both fiber optic instrumentation and high voltage cables. The chamber was equipped with viewing ports on the front, top, left, and right side for ultra-high-speed imaging and illumination. Qualification testing was conducted to rate the chamber to a working mass of 5 grams of trinitrotoluene. Thick and thin flyer plates were found to minimally damage the interior of the chamber. Blast overpressure testing found no damage to the chamber and optical viewports and minimal damage to feed throughs. Explosive spall damage was investigated due to unintentional contact with the chamber walls and found to induce moderate damage with potential equipment damage if not protected against.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Recommended Citation
Ichiyama, Robert, "DIAGNOSTICS DEVELOPMENT FOR AND STUDY OF ENERGETIC MATERIALS SUBJECT TO SHOCK LOADING" (2024). Open Access Dissertations. Paper 1684.
https://digitalcommons.uri.edu/oa_diss/1684