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One-dimensional shocks can be generated by impacting flyer plates accelerated to terminal velocities by a confined laser-ablated plasma. Over the past few years, we have developed this capability with our facility-size laser, TRIDENT, capable of >=500 Joules at multi-microsecond pulse lengths to accelerate 1-D flyer plates, 8-mm diameter by 0.1–2 mm thick. Plates have been accelerated to terminal velocities of 100 to >=500 m/s, with full recovery of the flyer and target for post mortem metallography. By properly tailoring the laser temporal and spatial profile, the expanding confined plasma accelerates the plate away from the transparent sapphire substrate, and decouples the laser parameters from shock pressure profile resulting from the plate impact on a target. Since the flyer plate is in free flight on impact with the target, minimal collateral damage occurs to either. The experimental method to launch these plates to terminal velocity, ancillary diagnostics, and representative experimental data is presented. [ABSTRACT FROM AUTHOR]

The TRIDENT laser at Los Alamos has been used to drive small plate impact experiments. Flyers are typically 8 mm in diameter and 0.1 to 1.0 mm thick, while the targets are 10 mm in diameters and 0.2 to 2.0 mm thick. One of the sample materials is copper composed of large columnar grains. These samples can reveal information about damage in single crystals and bi-crystals. This work will focus on simulating these experiments to reveal the stress loading histories. A phenomenological single crystal plasticity model in the FLAG hyrdocode will be used. At the time of first negative pressure, calculated stress and strain concentrations occur at regions of high damage seen by metallurgical examination of a recovered sample. These calculated concentrations help to reveal the driving conditions that cause damage formation. [ABSTRACT FROM AUTHOR]

We have applied Transient Imaging Displacement Interferometry (TIDI) to copper targets loaded by laser-launched flyers. TIDI captures the full-field out-of-plane surface displacement map single-shot with the time resolution of the illumination pulses (180 ps). Displacement sensitivity of ∼10 nm with lateral spatial resolution of ∼5 microns is achieved over our ∼1 mm2 field-of-view. A framing camera allows capture of up to eight displacement maps for a single loading event, allowing the evolution of the surface motion to be tracked. Point and line VISARs are used as complementary diagnostics that provide a temporally continuous record of the velocity history of the sample, and also provide time stamps for the TIDI displacement maps. The rich heterogeneity in the surface displacement due to the grain structure of the sample is readily measured. [ABSTRACT FROM AUTHOR]

This paper presents results on the dynamics of damage in copper under incipient spall conditions for multicrystalline specimens. Specimens were annealed from polycrystalline material to reduce the number of grain boundaries the shock wave traverses in passing through the specimen. The specimens incorporated unique fiducials that permit accurate correlation of pre-shot characterization of the grain orientations, grain size etc. with the location of the dynamic diagnostics and with post-shot metallography. The dynamic diagnostics—Transient Imaging Displacement Interferometry (TIDI), point VISAR, line VISAR—were all precisely aligned on the specimen surface to view regions of interest revealed in the pre-shot characterization. Initial analyses demonstrate the wealth of information obtained from this experimental approach. Examples include observation that regions in the surface microstructure most likely to be damaged based on pre-shot characterization show some of the largest displacements during the shock-loading. Post-shot microscopy shows damage in the same places. Another observation is there appears to be localized plastic deformation that occurs during the first compression wave which then remains and evolves through several cycles of compression and release from the spall plane. [ABSTRACT FROM AUTHOR]

Shock waves were induced in single crystals of beryllium, by direct illumination using the TRIDENT laser at Los Alamos. The velocity history at the surface was measured using a line-imaging VISAR, and transient X-ray diffraction (TXD) records were obtained with a. plasma backlighter and X-ray streak cameras. At lower pressures, the VISAR records exhibited an elastic precursor followed by a plastic wave and spall. At higher pressure, the velocity records showed a two-wave structure suggesting a phase change, then at the highest pressure a single broad wave suggesting a shock directly into the high pressure phase. The rocking curves of the crystals were typically about 2 degrees wide, so analysis of the TXD records is complicated by the relatively large amount of blurring. However, the Bragg record of the shocked 0002 peak clearly indicates a smaller lattice parameter at higher pressure. In the shots where polymorphism seemed to appear in the VISAR record, additional lines appeaxed in the Bragg record, and new lines also appeared within the field of view of the Laue camera. These results are consistent with a new quantum mechanical equation of state for beryllium, which suggests that the hexagonal to body-centered cubic transition occurs at ∼40 GPa on the principal Hugoniot. [ABSTRACT FROM AUTHOR]