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 ambient pressure thermodynamic parameters, have been used to formulate an equation of state based on the Helmholtz free energy, which was shown to adequately represent the dynamic response of the polymer to ∼5 GPa.
The shock response of poly[methyl methacrylate] (PMMA) acquired from two providers, Spartech and Rohm & Haas, has been measured to investigate the shock response variations related to material pedigree. These measurements have also been used to examine the effects of viscoelasticity on Spartech PMMA. Measurements of the Hugoniot curves, release wave speeds, and index of refraction have been acquired up to previously unexplored stresses, ∼10.7 GPa, for Spartech PMMA. In-situ, time-resolved particle velocity wave profiles, as a function of time and depth, were obtained using twelve separate electromagnetic gauge elements embedded at different depths in the PMMA. A comparison of the new data to the shock response data for Rohm and Haas PMMA, used as a “standard” material in shock compression studies, shows that there are no significant differences in shock response for the two materials. From the index of refraction measurements, the apparent particle velocity correction for a PMMA window exhibits an interesting oscillation, increasing at up = 0.3 km/s after decreasing up to that point. The results are generalized into guidelines for sourcing PMMA for use in shock studies.
The effect of grain size and moisture content on the dynamic macroscopic response of granular geological materials was explored by performing uniaxial planar impact experiments on high purity, Oklahoma #1, sand samples composed of either fine (75–150 μm) or coarse (425–500 μm) grain sizes in either dry or fully water-saturated conditions. Oklahoma #1 sand was chosen for its smooth, quasi-spherical grain shapes, narrow grain size distributions, and nearly pure SiO2 composition (99.8 wt. %). The water-saturated samples were completely saturated ensuring a two-phase mixture with roughly 65% sand and 35% water. Sand samples were dynamically loaded to pressures between 1 and 11 GPa. Three-dimensional meso-scale simulations using an Eulerian hydrocode, CTH, were created to model the response of each sand sample. Multi-phase equations of state were used for both silicon dioxide, which comprised individual sand grains, and water, which surrounded individual grains. Particle velocity profiles measured from the rear surface of the sand, both experimentally and computationally, reveal that fine grain samples have steeper rise characteristics than coarse grain samples and water-saturated samples have an overall much stiffer response than dry samples. The experimentally determined particle velocity vs. shock velocity response of dry sand was linear over this pressure range, with little difference between the two grain sizes investigated. The experimental response for the water saturated sand exhibited a piecewise continuous response with a transition region between particle velocities of 0.6 km s−1 and 0.8 km s−1 and a pressure of 4.5–6 GPa. Hypotheses for the cause of this transition region are drawn based on results of the meso-scale simulations.
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