David B. Stahl

Equation of state and high pressure properties of a fluorinated terpolymer: THV 500

We present the results of an investigation of the static compressive and dynamic (shock) responses of a fluorinated terpolymer of tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (Dyneon THV 500), in an effort to further understand its behavior under static and dynamic high pressures, and elucidate its equation of state properties. Fluorinated polymers, and, in particular, their copolymers, have garnered increasing attention by the static high pressure and shock wave communities, due to their widespread use in engineering applications, and formulation into energetic materials as binders. Shock wave compression experiments performed at two laboratories showed good consistency, and provide the first Hugoniot data for this fluorinated terpolymer. The Hugoniot of THV 500 is in general agreement with that of the related fluoropolymers polytetrafluoroethylene and poly(chlorotrifluoroethylene-co-vinylidene fluoride), reported previously. The static compressive data, combined with measurement of the am...

Laser-driven MiniFlyer induced gold spall

A laser-launched miniature flyer system (MiniFlyer) is being used to study the dynamic properties of materials. A 3-mm diameter and 0.05-mm thick flyer plate is accelerated by a laser-pulse-induced plasma contained between a clear window substrate and the flyer plate. The substrate is coated with carbon, aluminum oxide, and aluminum to enhance the plasma formation process. The flyer impacts a gold target plate of 0.10 or 0.26 mm thickness, producing a shock. The shock pulse interacts with the free surface and reflects as a rarefaction wave, producing tension in the foil. Dynamic measurements of the free surface particle velocity were made using VISAR (Velocity Interferometer System for Any Reflector). Cross-sections of the gold targets exhibit spall planes at the expected locations.

EQUATION OF STATE OF AMMONIUM NITRATE

Ammonium nitrate (AN) is a widely used fertilizer and mining explosive. AN is commonly used in ammonium nitrate‐fuel oil (ANFO), which is a mixture of explosive‐grade AN prills and fuel oil in a 94:6 ratio by weight. ANFO is a non‐ideal explosive with measured detonation velocities around 4 km/s. The equation of state properties and known initiation behavior of neat AN are limited. We present the results of a series of gas gun‐driven plate impact experiments on pressed neat ammonium nitrate at 1.72 g/cm3. No evidence of initiation was observed under shock loading to 22 GPa. High pressure x‐ray diffraction experiments in diamond anvil cells provided insight into the high pressure phase behavior over the same pressure range (to 25 GPa), as well as a static isotherm at ambient temperature. From the isotherm and thermodynamic properties at ambient conditions, a preliminary unreacted equation of state (EOS) has been developed based on the Murnaghan isotherm and Helmholtz formalism [1], which compares favorably...

High Pressure Hugoniot and Reaction Rate Measurements in PBX9501

Single‐stage and two‐stage gas gun experiments have been completed to measure the unreacted Hugoniot of PBX9501 high explosive (HE). Two types of experiments were done: 1) PBX9501 was impacted with a higher impedance projectile and the interface particle velocity history was measured using a magnetic gauge glued to the HE front; 2) a PBX9501 disc was mounted in the front of a projectile that impacted a LiF window and velocity interferometers (VISAR) were used to measure the impact interface particle velocity history. Inputs to the PBX9501 ranged from 3 to 15 GPa in these experiments. Particle velocity waveforms show an induction time followed by a particle velocity change (the nature of the change depends on the type of experiment) corresponding to shock‐induced reaction in the PBX9501. The induction part of the waveform provided unreacted Hugoniot information so several new high‐pressure Hugoniot points were generated. These data do not indicate a softening in the unreacted Hugoniot at high pressures; more experiments will be necessary to determine this. By using an estimate for the reaction product EOS, it was possible to estimate the average PBX9501 initial reaction rate for each experiment. The induction time decreases with pressure and the reaction rate increases with pressure.Single‐stage and two‐stage gas gun experiments have been completed to measure the unreacted Hugoniot of PBX9501 high explosive (HE). Two types of experiments were done: 1) PBX9501 was impacted with a higher impedance projectile and the interface particle velocity history was measured using a magnetic gauge glued to the HE front; 2) a PBX9501 disc was mounted in the front of a projectile that impacted a LiF window and velocity interferometers (VISAR) were used to measure the impact interface particle velocity history. Inputs to the PBX9501 ranged from 3 to 15 GPa in these experiments. Particle velocity waveforms show an induction time followed by a particle velocity change (the nature of the change depends on the type of experiment) corresponding to shock‐induced reaction in the PBX9501. The induction part of the waveform provided unreacted Hugoniot information so several new high‐pressure Hugoniot points were generated. These data do not indicate a softening in the unreacted Hugoniot at high pressures; mo...

FLYER VELOCITY CHARACTERISTICS OF THE LASER-DRIVEN MINIFLYER SYSTEM

The laser-driven MiniFlyer system is used to launch a small, thin flyer plate for impact on a target. Consequently, it is an indirect drive technique that de-couples the shock from the laser beam profile. The flyer velocity can be controlled by adjustment of the laser energy. The upper limits on the flyer velocity involve the ability of the substrate window to transmit the laser light without absorbing, reflecting, etc.; i.e., a maximum amount of laser energy is directly converted into kinetic energy of the flyer plate. We have investigated the use of sapphire, quartz, and BK-7 glass as substrate windows. In the past, a particular type of sapphire has been used for nearly all MiniFlyer experiments. Results of this study in terms of the performance of these window materials, based on flyer velocity are discussed.

EXPERIMENTAL MEASUREMENTS OF THE CHEMICAL REACTION ZONE OF DETONATING LIQUID EXPLOSIVES

We have a joint project between CEA‐DAM Le Ripault and Los Alamos National Laboratory (LANL) to study the chemical reaction zone in detonating high explosives using several different laser velocimetry techniques. The short temporal duration of the von Neumann spike and early part of the reaction zone make these measurements difficult. Here, we report results obtained from detonation experiments using VISAR (velocity interferometer system for any reflector) and PDV (photon Doppler velocimetry) methods to measure the particle velocity history at a detonating nitromethane/PMMA interface. Experiments done at CEA were high‐explosive‐plane‐wave initiated and those at LANL were gas‐gun‐projectile initiated with a detonation run of about 6 charge diameters in all experiments. The experiments had either glass or brass confinement. Excellent agreement of the interface particle velocity measurements at both Laboratories were obtained even though the initiation methods and the velocimetry systems were somewhat differ...

Shock‐Induced Chemical Reaction in Organic and Silicon Based Liquids

Shock‐induced chemical reactions remain an area in shock physics that needs further investigation, particularly for determining the influence of pressure, temperature, and chemical structure on reactivity. Several studies have been done in the past that indicate dimerization, polymerization, and decomposition take place in different shock‐produced pressure and temperature regimes depending on chemical functionality. We present results obtained from single‐shock experiments in which liquids were studied using embedded multiple magnetic gauges to make in‐situ measurements of the particle velocity profiles at up to ten Lagrangian positions in the liquid. One of the liquids was organic (tert‐butylacetylene) and the other was a closely related silicon‐based material (ethynyltrimethylsilane). Multiple wave structures were measured in each liquid when the input pressure was above a certain threshold. Here, the reactivity of these materials are compared.

Interferometry, streak photography, and stereo photography of laser-driven miniature flying plates

Optical diagnostics to evaluate the velocity, acceleration profiles, planarity, and integrity of miniature (≤5 μm thick x ≤600 μm diam) plates of aluminum and other metals will be reported. By correlating various optical techniques and collected data, a complete understanding of the flying plate can be determined. Velocity interferometer system for any reflector (VISAR), with ≤120 ps resolution per data point, is used to record plate acceleration and terminal velocity. Electronic-streak and pulsed-laser stereo photography can determine planarity and integrity. Flyer-plate performance data are related to the properties of the laser beam that accelerates the plate. Laser parameters, such as energy density, power density, and spatial profile, affect the flying-plate performance parameters, i.e., planarity, acceleration, and velocity. Flying-plate accelerations of ≥10 10 G and terminal velocities of ≥6 mm/μs have been recorded, via a 10-ns-Nd:YAG laser pulse delivered to a tamped, 5-μm-aluminum plate.

IN‐SITU MEASUREMENT OF SHOCK‐INDUCED REACTIVE FLOW IN A SERIES OF RELATED HYDROCARBONS

Understanding of the chemistry that occurs under extreme, high‐pressure, high‐temperature shock environments poses both a significant scientific challenge, due to the difficulty of direct experimental observations, and an opportunity for discovery of new materials and bonding constructs. The combined high pressure, high temperature conditions induced by shock loading results in prompt reactions that may include dynamic bond breaking, dimerization and polymerization, and dissociation to small molecules. Understanding of the evolution of different reaction pathways as a function of shock input remains a significant challenge, due to both the very short shock timescales, and difficulty in measurement of reaction intermediates and products. We have used in‐situ multiple magnetic gauges to measure changes in mechanical variables (such as particle velocity waveforms) resulting from the shock‐induced chemistry. This allows us to gain some understanding of the shock input conditions necessary to start chemical re...

Interferometry And High Speed Photography Of Laser-Driven Flyer Plates

Laser-driven thin (2-10-1 thick) plates of aluminum and copper are accelerated to velocities ≥5 km/s by a 1.06-11 wavelength Nd:YAG 8-10 ns FWHM laser pulse at power densities 0.7-4.0 GW/cm2. Accelerations ≥109 km/s2 have been achieved. The acceleration and velocity of these 0.4-1.0-mm-diameter plates are experimentally recorded by velocity interferometry (VISAR)1 and the planarity of impact by streak photography.2