J. N. Fritz

Shock compression of tungsten and molybdenum

New high‐pressure shock‐wave data have been obtained for W and Mo. These data have been combined with previous data sets for these materials to extend the range of linear us–up fits for the Hugoniot to 480 GPa for Mo and 680 GPa for W. The shock‐wave data, supplemented by the necessary thermodynamic information, have been used to generate several isotherms (100, 200,...1000 K). Tables of pressure versus relative volume up to 380 GPa suitable for comparison with statically obtained data are given.

Hugoniot data for iron

A definitive set of the Los Alamos Hugoniot data for iron in a pressure regime extending to 442 GPa is given. Earlier standards data, obtained using conventional explosive systems, were thoroughly reprocessed. All original film records were reread. On the basis of more recent experiment and theory, some data were culled because the experimental designs were found to be insufficiently conservative. The analysis was also modified to take into account preheating of the explosively driven flyer plates. Minor clerical errors in transcription of measurements were corrected. An improved algorithm for the flash-gap time correction was incorporated. Higher-pressure data were obtained using a conventional 13-pin target assembly on a two-stage light gas gun. Several polynomial representations of the data are given. A linear fit to the data (Us=3.935+1.578 Up, where the shock velocity Us and the particle velocity Up are in km/s) has a root-mean-square misfit of 62 m/s. The quadratic fit (Us=3.691+1.788 Up−0.038 Up2) ...

The equation of state of polytetrafluoroethylene to 80 GPa

Hugoniot data for polytetrafluoroethylene (PTFE) have been reported. These data can be fitted by two linear us–up Hugoniots which indicate the existence of a phase change. As usual for polymers, a linear low‐pressure us–up fit does not extrapolate to the zero‐pressure bulk sound‐speed. The phase transition occurs at ∼34 GPa and a compression of 0.396. To investigate this high‐pressure phase transition, shock‐recovery experiments were performed. The recovery system used is described. The recovered samples indicate the high‐pressure phase transition is a dissociation reaction into carbon and gaseous fluorocarbons. Release isentropes at various pressures have been measured using the ASM probe. From these measurements, the variation of the Gruneisen parameter was calculated for states both on and off the Hugoniot. The Gruneisen parameter on the Hugoniot monotonically increased from its initial value until the phase transition where it dropped slightly and then continued to increase with further increase in pr...

Overdriven‐detonation and sound‐speed measurements in PBX‐9501 and the ‘‘thermodynamic’’ Chapman–Jouguet pressure

Sound speeds, at pressure, and the overdriven Hugoniot were measured for the plastic‐bonded explosive PBX‐9501. The two curves intersect at the Chapman–Jouguet (CJ) state because of the sonic condition D=c+u. This permitted a novel determination of the ‘‘thermodynamic’’ CJ pressure. A value of 34.8±0.3 GPa was obtained. The data permit a direct experimental determination of the isentropic gamma, γS=−(∂lnP/∂lnV)S, and the Gruneisen parameter, γ=V(∂P/∂E)V, in the overdriven pressure range.

Velocity of sound behind strong shock waves in 2024 A1

Rarefaction waves were produced by impacting a target with a thin plate. An optical technique was used to determine where the rarefaction from the back surface of the impactor overtook the shock wave induced in a step wedge target. Bromoform was placed on the front surface. When the shock reached the liquid it radiated steadily until the rarefaction from the impactor overtakes it. The times when this occurred were used to determine where the rarefaction just overtook the shock in the target, and thus the sound velocity. The leading edge of this rarefaction wave travels at longitudinal sound velocity in solids. This velocity increases smoothly with pressure until shock heating causes the material to melt. The data indicate that melting on the Hugoniot of 2024 Al begins at about 125 GPa and is completed at 150 GPa.

Chapter II : 18 – THE VELOCITY OF SOUND BEHIND STRONG SHOCK WAVES IN 2024 Al*

Rarefaction waves were produced by impacting a target with a thin plate. An optical technique was used to determine where the rarefaction from the back surface of the impactor overtook the shock wave induced in a step wedge target. Bromoform was placed on the front surface. When the shock reached the liquid it radiated steadily until the rarefaction from the impactor overtakes it. The times when this occurred were used to determine where the rarefaction just overtook the shock in the target, and thus the sound velocity. The leading edge of this rarefaction wave travels at longitudinal sound velocity in solids. This velocity increases smoothly with pressure until shock heating causes the material to melt. The data indicate that melting on the Hugoniot of 2024 Al begins at about 125 GPa and is completed at 150 GPa.

Relation of the ’’solid Hugoniot’’ to the ’’fluid Hugoniot’’ for aluminum and coppera)

Strength effects confuse equation‐of‐state data obtained by shock waves. In order to take these effects properly into account in the high‐pressure regime, reduction from uniaxial‐strain experimental shock loci to a mean‐stress curve and from the mean‐stress curve to the ’’fluid Hugoniot’’ curve are derived. Applications to aluminum and copper are given.

Release isentropes of overdriven plastic-bonded explosive PBX-9501

Continuous release isentropes for the plastic-bonded explosive PBX-9501 are obtained from velocity interferometer system for any reflector measurements at a high-explosive/LiF interface. Forward calculations from a tabular representation of the isentropes to the measured u(t) data at the interface are iterated to yield isentropes that give agreement with the data. Curves for the isentropes and for the isentropic gamma, γS=−(∂lnP/∂lnV)S are presented. Because isentropes from different overdriven states differ, a crude estimate of the Gruneisen parameter is obtained. An overall representation of the data is achieved with this Gruneisen parameter and a single isentrope through the Chapman–Jouguet state.

Modeling PBX 9501 overdriven release experiments

We show the failure of the standard Jones-Wilkins-Lee (JWL) equation of state (EOS) in modeling the overdriven release experiments of PBX 9501. The deficiency can be tracked back to inability of the same EOS in matching the shock pressure and the sound speed on the Hugoniot in the hydrodynamic regime above the Chapman-Jouguet pressure. After adding correction terms to the principal isentrope of the standard JWL EOS, we are able to remedy this shortcoming and the simulation is successful.

Release isentropes in overdriven PBX 9502

Experiments have been done to obtain product isentropes of the plastic bonded TATB explosive PBX 9502. A thin aluminum flyer was thrown at an explosive disk so as to generate a state in excess of the Chapman-Jouguet pressure. Because the flyer is thin, the shock wave is followed by a release wave that lowers the pressure in the explosive products. The explosive disk was backed by a LiF tamper/window. Particle velocity at the explosive—window interface was measured with a velocity interferometer (VISAR) and measured particle velocity records were used to construct isentropes. Unexpected behavior is seen in the shape of the isentropes. Experimental details and the resulting isentropes will be presented.