R. J. Lawrence

Hypervelocity Impact Flash at 6, 11, and 25 KM/S

Impact‐flash phenomenology has been known for decades, and is now being considered for missile‐defense applications, in particular for remote engagement diagnostics. To technically establish this capability, we have conducted a series of experiments at impact velocities of ∼6, ∼11, and ∼25 km/s. Two‐ and three‐stage light‐gas guns were used for the lower two velocities, and magnetically‐driven flyers on the Sandia Z machine achieved the higher velocity. Spectrally‐ and temporally‐resolved flash output addressed data reproducibility, material identification, and target configuration analysis. Usable data were obtained at visible and infrared wavelengths. Standard atomic spectral databases were used to identify strong lines from all principal materials used in the study. The data were unique to the individual materials over the wide range of velocities and conditions examined. The time‐varying nature of the signals offered the potential for correlation of the measurements with various aspects of the target ...

Hypervelocity Impact Flash for Missile- Defense Kill Assessment and Engagement Analysis: Experiments on Z

Kill assessment continues to be a major problem for the nations missile defense program. A potential approach for addressing this issue involves spectral and temporal analysis of the short-time impact flash that occurs when a kill vehicle intercepts and engages a target missile. This can provide identification of the materials involved in the impact event, which will, in turn, yield the data necessary for target identification, engagement analysis, and kill assessment. This report describes the first phases of a project under which we are providing laboratory demonstrations of the feasibility and effectiveness of this approach. We are using two major Sandia facilities, the Z-Pinch accelerator, and the two- and three-stage gas guns at the Shock Thermodynamics and Applied Research (STAR) facility. We have looked at the spectral content of impact flash at velocities up to 25 km/s on the Z-Pinch machine to establish the capability for spectroscopy for these types of events, and are looking at similar experiments at velocities from 6 to 11 km/s on the gas guns to demonstrate a similar capability for a variety of research-oriented and applied materials. The present report describes only the work performed on the Z machine.

Radiation-driven shock and debris propagation down a partitioned pipe

Abstract Two experiments have been performed to measure the effects of pulsed radiation loads on the front of small tubular structures, using as an energy source the X-ray fluence produced by a Z-pinch at the Sandia National Laboratories Z Facility. The project had two major goals: to establish the feasibility of using the Z machine to study the phenomenology associated with debris generation and propagation down tubular structures with partitions; and to use the resultant experimental data to validate numerical hydrocodes (shock physics codes) so that we have confidence in their use in analyzing these types of situations. Two tubular aluminum structures (5 and 10 cm long and 1 cm inside diameter) were prepared, with aluminum partitions located at the front, halfway down the pipe, and at the rear. Interferometry (VISARs) provided multiple velocity histories for all of the partitions. In both experiments, the first barrier, which was exposed directly to the x-ray fluence, was launched into the pipe at a velocity of ∼2 km/s, accelerating to give a mean velocity of ∼2.6 km/s. Loss of plate integrity is inferred from the dispersed launch of the second partition at ∼1 km/s. Wall shocks propagating at 4.5 km/s were inferred. Post-test metallography showed evidence of melting and partial vaporization of the plates, and turbulent mixing with material from the walls. Calculations qualitatively agree with the observed results, but slightly overpredict debris velocity, possibly due to overestimates of total energy fluence. An application for this work is the study of techniques for line-of-sight shock and debris mitigation on high-power pulsed power facilities such as Z and its follow-on machines.

The response of ceramic powders to high-level quasi-isentropic dynamic loads.

The pulsed‐power Z machine, in an isentropic compression experiment (ICE) mode, will allow the dynamic characterization of porous materials—here various ceramic powders, e.g., Al2O3, WC, ZrO2—at roughly half their solid densities. A cylindrical configuration can provide megabar‐level loads on an annulus of the sample material. Data will be provided by velocity interferometers that measure free‐surface (or possibly interface) particle velocities. Differing sample thicknesses using stepped or conical geometries yield experimental efficiency by allowing multiple data records on single shots. With the p/α model for porous materials, the one‐dimensional Lagrangian hydrocode WONDY provides the needed analyses. Based on static data, both power‐law and quadratic crush curves are employed. Within the model constraints, we suggest that the most important parameter for characterizing the material is the crush strength, ps. With adequate sample thicknesses, the planned velocity measurements differentiate among the va...

Multi‐Dimensional Hydrocode Analyses of Penetrating Hypervelocity Impacts

The Eulerian hydrocode, CTH, has been used to study the interaction of hypervelocity flyer plates with thin targets at velocities from 6 to 11 km/s. These penetrating impacts produce debris clouds that are subsequently allowed to stagnate against downstream witness plates. Velocity histories from this latter plate are used to infer the evolution and propagation of the debris cloud. This analysis, which is a companion to a parallel experimental effort, examined both numerical and physics‐based issues. We conclude that numerical resolution and convergence are important in ways we had not anticipated. The calculated release from the extreme states generated by the initial impact shows discrepancies with related experimental observations, and indicates that even for well‐known materials (e.g., aluminum), high‐temperature failure criteria are not well understood, and that non‐equilibrium or rate‐dependent equations of state may be influencing the results.

Multi‐Dimensional Validation Impact Tests on PZT 95/5 and ALOX

Multi‐dimensional impact tests were conducted on the ferroelectric ceramic PZT 95/5 and alumina‐loaded epoxy (ALOX) encapsulants, with the purpose of providing benchmarks for material models in the ALEGRA wavecode. Diagnostics used included line‐imaging VISAR (velocity interferometry), a key diagnostic for such tests. Results from four tests conducted with ALOX cylinders impacted by nonplanar copper projectiles were compared with ALEGRA simulations. The simulation produced approximately correct attenuations and divergence, but somewhat higher wave velocities. Several sets of tests conducted using PZT rods (length:diameter ratio = 5:1) encapsulated in ALOX, and diagnosed with line‐imaging and point VISAR, were modeled as well. Significant improvement in wave arrival times and waveforms agreement for the two‐material multi‐dimensional experiments was achieved by simultaneous multiple parameter optimization on multiple one‐dimensional experiments. Additionally, a variable friction interface was studied in these calculations. We conclude further parameter optimization is required for both material models.