Robert G. McQueen

Compression of Solids by Strong Shock Waves

Publisher Summary For most solids, shock wave pressures in the range extending from 100 kilobars to 400 kilobars are attained easily. Pressures in excess of 1000 kilobars can be obtained by the slight modification of the simple in contact explosive–solid geometry. The task of determining the associated pressure–compression data derives part of its appeal from the fact that precise static compressibility studies have been limited to pressures below 100 kilobars. The experimental approaches to the problem of determining the pressure–compression states behind shock waves are reviewed and a summary of the published experimental data for solids is given in the chapter. The experimental data that consist of a known pressure P, volume V, energy E locus for each material are extended to a complete thermodynamic description of states neighboring the experimental curves. These calculations are based upon the Mie–Gruneisen equation of state and the Dugdale–MacDonald relation, the latter being used to determine the volume dependence of the Gruneisen ratio. The Dugdale–MacDonald relation is tested at zero pressure, where sufficient thermodynamic data exist to permit the comparison with Gruneisens ratio as calculated from the usual thermodynamic relations.

Equation of State for Nineteen Metallic Elements from Shock‐Wave Measurements to Two Megabars

Plane‐wave explosive systems were used to accelerate thin metal plates to high velocities. Shock pressures resulting from the collision of these driver plates with a stationary target plate are approximately three times greater than the original shock pressure in the driver plate. The photographic flash‐gap technique was used to record velocities associated with the shock waves. The new experimental data extend the Hugoniot loci into the one‐to two‐megabar region for 19 metallic elements: Ag, Au, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sn, Th, Ti, Tl, V, W, Zn, Bi, Fe, Sb.The Hugoniot P, V, E data have been extended to a more complete P, V, E, T equation of state by use of the Mie‐Gruneisen theory. The thermodynamic variable, γ=V(∂P/∂E)v, necessary for this extension, was obtained by solving the Dugdale‐MacDonald relation.

Shock-Wave Compression and X-Ray Studies of Titanium Dioxide

The Hugoniot of the rutile phase of titanium dioxide has been determined to 1.25 megabars, and data show the existence of a phase change at about 0.33 megabar. The volume decrease associated with this transformation appears to be quite large (approximately 21 percent). Rutile, when recovered from shockloading in excess of the transformation pressure, is found to be irreversibly transformed to the orthorhombic lead dioxide structure (a distortion of the fluorite structure) with parameters a, 4.529; b, 5.464; and c, 4.905 angstroms and a calculated density of 4.374 grams per cubic centimeter. The new phase reverts to rutile at temperatures above 450�C. It is suggested that the new phase may be another diagnostic indicator of meteorite impact on the earths surface.

Hugoniot equation of state of the lanthanides

Abstract Shock wave studies of the lanthanide series show the existence of a very high pressure phase transition in all members of the series. The data show that this transformation is of necessity to a more incompressible phase and has been identified with melting. Thermodynamic considerations allow calculation of the solid-liquid phase boundary from these data; the results indicate that all the rare earths melt anomalously at sufficiently high pressures. This can be understood in the context of a “two-fluid” theory, in which the composition of the liquid along the phase boundary changes continuously with pressure due to the degree of pressure-induced electronic transition present in the liquid. Hence, at sufficiently high pressure, the density of the liquid becomes greater than the density of the contiguous solid and dP dT becomes negative.

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.

MACH DISC FORMATION IN CYLINDRICAL RECOVERY SYSTEMS

Cylindrical recovery systems have been used to shock-load polymers to pressures exceeding 50 GPa. In order to determine the pressures generated in these recovery systems the formation of the Mach disc on axis and its approach to steady state was monitored. The relation of the Mach disc diameter to the lateral dimension of the high explosive used to compress the polymer samples was also investigated.

RESULTS ON RICHTMYER – MESHKOV INSTABILITIES IN CONDENSED FLUIDS (1)

We report experimental and theoretical results on the motion of a shock-accelerated, perturbed interface between liquids of different densities. The growth of the impulsively-driven perturbations, known as a Richtmyer-Meshkov instability, is observed in our calculation using the hydrodynamics code PETRA. Our experiments examine the evolution of a shock wave as it passes from a high-density fluid, through a rippled interface, into a lower-density fluid. We observe that the shock front remains planar but the flow in the shock-compressed, lower-density fluid is complex. The complex flow is dominated by coherent structures having the same spatial period as the rippled interface. In a related experiment, we produced a rippled shock front in the higher-density fluid and observed that the interface remains specular after the passage of the rippled shock.