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The high pressure dynamic response of polymers is important to a wide variety of applications. The details of compressibility and reactivity can have a large effect on overall behaviors of dynamic systems even when polymers are used in small amounts. Polyethylene is of broad interest for a variety of applications, as an ingredient and as a pure material. It is also of significant interest as a model system to understand the correlating effects of polymer dynamics in a material with a relatively simple chemical composition that can have highly varied properties through the alteration of molecular weight and associated crystallinity of the material. Although a variety of Hugoniot and dynamic information is available for polyethylene, it is a challenge to obtain information on the product equation of state at pressures high enough to achieve decomposition. Following recent successes in producing deep release states in compressed epoxy material, a series of plate impact experiments was performed in the same configuration on high density and ultra-high molecular weight polyethylene at pressures where there is only limited Hugoniot data. The experimental wave profiles are presented and the Hugoniot states are compared to previous results. In ongoing work, the release profiles are intended to calibrate a product equation of state.The high pressure dynamic response of polymers is important to a wide variety of applications. The details of compressibility and reactivity can have a large effect on overall behaviors of dynamic systems even when polymers are used in small amounts. Polyethylene is of broad interest for a variety of applications, as an ingredient and as a pure material. It is also of significant interest as a model system to understand the correlating effects of polymer dynamics in a material with a relatively simple chemical composition that can have highly varied properties through the alteration of molecular weight and associated crystallinity of the material. Although a variety of Hugoniot and dynamic information is available for polyethylene, it is a challenge to obtain information on the product equation of state at pressures high enough to achieve decomposition. Following recent successes in producing deep release states in compressed epoxy material, a series of plate impact experiments was performed in the same c... more...

A series of gas-gun experiments was conducted to obtain product isentropes for 70/30 weight percent Epon 828 epoxy resin/Jeffamine T-403 curing agent. Thin epoxy flyers backed by a low-density syntactic foam impacted lithium fluoride (LiF) windows at velocities up to 6.3 km/s, creating stresses in excess of those required for reaction (∼25 GPa). Following this, a rarefaction fan from the back of the thin flyer reduced the pressure in the epoxy products. VISAR and PDV were used to measure the velocity of the epoxy/LiF interface. Numerical simulations using several different treatments for the reactant-to-product transformation were conducted and the results compared with measured wave profiles. The best agreement with experiment was obtained using separate tabular equations of state for the reactants and products and an irreversible transformation to products.A series of gas-gun experiments was conducted to obtain product isentropes for 70/30 weight percent Epon 828 epoxy resin/Jeffamine T-403 curing agent. Thin epoxy flyers backed by a low-density syntactic foam impacted lithium fluoride (LiF) windows at velocities up to 6.3 km/s, creating stresses in excess of those required for reaction (∼25 GPa). Following this, a rarefaction fan from the back of the thin flyer reduced the pressure in the epoxy products. VISAR and PDV were used to measure the velocity of the epoxy/LiF interface. Numerical simulations using several different treatments for the reactant-to-product transformation were conducted and the results compared with measured wave profiles. The best agreement with experiment was obtained using separate tabular equations of state for the reactants and products and an irreversible transformation to products. more...

In this work a methodology for estimating the onset of reaction for porous polymer systems is presented. Shock Hugoniot data for a well-characterized polymer, polyurethane, is used to calibrate a functional relationship that captures the onset of reaction at several initial densities. In doing so, this function is then used to estimate the volume at which reaction is initiated in polyurethane at any initial density. The function is also extended to estimate the onset of reaction in less well-characterized polymer systems, polystyrene and SX358. more...

Experimental data of the principal Hugoniot locus of variable density gas-phase noble and molecular gases are rare. The majority of shock Hugoniot data is either from shock tube experiments on low-pressure gases or from plate impact experiments on cryogenic, liquefied gases. In both cases, physics regarding shock compressibility, thresholds for the on-set of shock-driven ionization, and even dissociation chemistry are difficult to infer for gases at intermediate densities. We have developed an experimental target design for gas gun-driven plate impact experiments on noble gases at initial pressures between 200-1000 psi. Using optical velocimetry, we are able to directly determine both the shock and particle velocities of the gas on the principal Hugoniot locus, as well as clearly differentiate ionization thresholds. The target design also results in multiply shocking the gas in a quasi-isentropic fashion yielding off-Hugoniot compression data. We describe the results of a series of plate impact experiment... more...

The effects of particle morphology and initial density is examined with respect to the shock densification response of initially porous metal (Cu) and metal-oxide (CeO2) materials. Specifically, the ability of a continuum-level compaction model to capture the measured densification trends as a function of initial density and particle morphology are investigated. Particle morphology is observed to have little effect on the densification response of both Cu and CeO2, while initial density appears to have a stronger effect. In terms of continuum-level compaction strength, Cu and CeO2 exhibit dissimilar trends. more...

We are developing a new diagnostic useful for the non-invasive detection of projectile passage in the launch tube of a gas gun. The sensing element consists of one or more turns of single-mode optical fiber that is epoxy-bonded around the external circumference of the launch tube. The hoop strain induced in the launch tube by the passage of the projectile causes a momentary expansion of the fiber loop. This transient change in path length is detected with high sensitivity using a fiber optic-based interferometer developed by the NSTec Special Technologies Laboratory. We have fielded this new diagnostic, along with fiber optic Bragg grating (FBG) strain gauges we previously used for this purpose, on a variety of gas guns used for shock compression studies at Los Alamos and Sandia National Laboratories. We anticipate that, when coupled with a broad-range analog demodulator circuit, the fiber optic interferometer will have improved dynamic range over that of the FBG strain gauge approach. Moreover, in contra... more...