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Title:Theory and modeling of laser-driven flyer plate experiments to study explosives under a microscope
Author(s):Stekovic, Svjetlana
Director of Research:Stewart, Donald Scott
Doctoral Committee Chair(s):Stewart, Donald Scott
Doctoral Committee Member(s):Dlott, Dana D; Springer, Harry Keo; Glumac, Nick; Krier, Herman
Department / Program:Mechanical Sci & Engineering
Discipline:Theoretical & Applied Mechans
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):explosives
laser-driven flyer impact
nitromethane
shock compression
chemical kinetics
fluid mechanics
Abstract:Studying liquid and solid high-explosive materials requires precise characterization of thermodynamics and chemical kinetics to capture the reactive behavior. Although high explosives have been studied for many decades, there is currently no reactive continuum scale model for characterizing reactive materials in the micrometer length scale and nanosecond time-scale. The Dlott research group at the University of Illinois Urbana-Champaign has developed a novel, tabletop experimental set-up, which has provided high-quality experimental data. In the research described herein, we (1) present a computational framework for modeling and simulating microscopic size, laser-driven flyer impact experiments at 0.5 – 4.5 km/s, (2) identify and develop effective material models for inert and reactive materials, and (3) utilize this framework to present deeper understanding of reactive behavior for a classical reactive material, liquid nitromethane. We present a computational approach using a multi-material, arbitrary Lagrangian-Eulerian code termed ALE3D to model the nanosecond/micrometer dynamics of the launch of 0.5 - 4.5 km/s laser-driven metal flyer plates and the impact with stationary targets of Pyrex and fused silica glasses, and Lexan and Plexiglas polymers, producing pressures in the target in the 5 - 20 GPa range. The simulations are compared to experimental results where the flyer velocity profile and the velocity profile imparted to the target material were measured with high-speed velocimetry. The experimental flyer launch by a high-intensity pulsed laser is modeled by depositing heat into a thin vaporizable layer under the flyer plate. This model produces a flyer plate that has not been exposed to the laser pulse, allowing us to compare the properties of the real flyer to a simulated ideal flyer. Simulations of target impact are in good agreement with experiment except at the highest impact velocities where the shock release process in experiment is slower than in the simulation. In addition, we observe the spallation influence in the metal flyer at these hyper-velocity speeds. We utilize the same computational framework with the multi-physics ALE3D code to model the nanosecond/micrometer dynamics of the 1.60 – 4.30 km/s laser-driven flyer plate and the impact with stationary target containing pure, liquid nitromethane, sandwiched between a metal lid and a transparent Pyrex window. Basically, in this specific case, we extend the inert example above by incorporating a reactive material target to be studied. Shock compressed, nitromethane chemical reactivity is modeled using the CHEETAH, thermochemical code within ALE3D. The reactive model parameters are obtained from past studies in literature, and assessed to capture the reactivity in liquid nitromethane within the experimental time duration. Simulation results show good agreement when compared to experimental data for the incoming PDV velocity profiles and the downstream comparison of velocity profiles at 25 μm, 40 μm, 64 μm, 90 μm, and 170 μm downstream. We also present pressure, density, and temperature results. As part of this research, we developed a novel framework for studying reactive materials at the microscopic scale with fast-time chemical kinetics. We show careful characterization of the inert material behavior at high impact, as well as, the material behavior under shock compressive reactive behavior. This framework can be utilized to studying other liquid and solid materials to further understand the reactive dynamics at the point where physics and chemistry merge together.
Issue Date:2021-07-16
Type:Thesis
URI:http://hdl.handle.net/2142/113060
Rights Information:Copyright 2021 Svjetlana Stekovic
Date Available in IDEALS:2022-01-12
Date Deposited:2021-08


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