We present a set of high explosive driven Rayleigh-Taylor strength experiments for beryllium to produce data to distinguish predictions by various strength models. Design simulations using existing strength model parameterizations from Steinberg-Lund and Preston-Tonks-Wallace (PTW) suggested an optimal design that would delineate between not just different strength models, but different parameters sets of the PTW model. Application of the models to the post-shot results, however, suggests growth consistent with little material strength. We focus mostly on efforts to simulate the data using published strength models as well as the more recent RING relaxation model developed at VNIIEF. The results of the strength experiments indicate weak influence of strength in mitigating the growth with the RING model coming closest to predicting the material behavior. Finally, we present shock and ramp-loading recovery experiments.

A basic tenet of material science is that the flow stress of a metal increases as its grain size decreases, an effect described by the Hall-Petch relation. This relation is used extensively in material design to optimize the hardness, durability, survivability, and ductility of structural metals. This Letter reports experimental results in a new regime of high pressures and strain rates that challenge this basic tenet of mechanical metallurgy. We report measurements of the plastic flow of the model body-centered-cubic metal tantalum made under conditions of high pressure (>100  GPa) and strain rate (∼10(7)  s(-1)) achieved by using the Omega laser. Under these unique plastic deformation ("flow") conditions, the effect of grain size is found to be negligible for grain sizes >0.25  μm sizes. A multiscale model of the plastic flow suggests that pressure and strain rate hardening dominate over the grain-size effects. Theoretical estimates, based on grain compatibility and geometrically necessary dislocations, corroborate this conclusion.

The Laser Inertial Fusion-based Energy (LIFE) engine design builds upon on going progress at the National Ignition Facility (NIF) and offers a near-term pathway to commercial fusion. Fusion technologies that are critical to success are reflected in the design of the first wall, blanket and tritium separation subsystems. The present work describes the LIFE engine-related components and technologies. LIFE utilizes a thermally robust indirect-drive target and a chamber fill gas. Coolant selection and a large chamber solid-angle coverage provide ample tritium breeding margin and high blanket gain. Target material selection eliminates the need for aggressive chamber clearing, while enabling recycling. Demonstrated tritium separation and storage technologies limit the site tritium inventory to attractive levels. These key technologies, along with the maintenance and advanced materials qualification program have been integrated into the LIFE delivery plan. This describes the development of components and subsystems, through prototyping and integration into a First Of A Kind power plant.

We report on nanosecond resolution lattice measurements of shock-compressed Mg in the hcp and bcc phases between 12 and 45 GPa. X-ray diffraction signals consistent with a compressed bcc lattice were captured above a shock pressure of 26.2 +/- 1.3 GPa. Our results are in agreement with the phase boundary calculated by Moriarty and Althoff using the generalized pseudopotential theory in the pressure and temperature region intersected by the principal shock Hugoniot.

Single crystal zinc particles, 1–2 μm in diameter, were observed in situ with transmission electron microscopy during sublimation. The rate of sublimation is strongly dependent on the presence of a surface oxide layer. Near 375 °C, minimally oxidized Zn surfaces sublime in tens of seconds, consistent with a model in which the particle behaves similarly to an isolated microscale effusion cell. By contrast, zinc particles fully enclosed by oxide sublime less than one-tenth as quickly. These results provide new insight into the synthesis mechanisms of hollow ZnO microspheres and related structures formed from metallic zinc at elevated temperatures.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

We report on a focusing x-ray diffraction geometry capable of high-resolution in situ lattice probing from dynamically loaded polycrystalline and amorphous materials. The Seeman-Bohlin-type camera presented here is ideally suited for time-resolved x-ray diffraction measurements performed on high energy multibeam laser platforms. Diffraction from several lattice planes of ablatively shock-loaded 25 mum thick Cu foils was recorded on a focusing circle of diameter D=100 mm with exceptional angular resolution limited only by the spectral broadening of the x-ray source. Excellent agreement was found between the density measured using x-ray diffraction and that inferred from Doppler velocimetry and the known shock Hugoniot of Cu. In addition, x-ray diffraction signal was captured from an amorphous material under static conditions.

The National Ignition Facility (NIF) will allow scientists to prove the feasibility of inertial confinement fusion (ICF). The success of ICF experiments at NIF will critically depend on the availability of robust targets. Guided by computer simulations, we generated a new target design that takes advantage of the extreme atomic density of synthetic diamond, and developed a process that allows us to produce large quantities of these ultrahigh precision diamond targets via a low-cost batch process. Computer simulations were used to assess the performance and the robustness of these diamond targets. The results demonstrate that diamond has the potential to outperform other target materials in terms of energy efficiency and implosion stability, thus making successful ignition more likely.

Extract HTML view is not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button. Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

Thermal expansion induced spontaneous microcracking in large-grained polycrystalline alumina was analyzed using experimental techniques as well as numerical simulations. A microstructure-based finite-element model (object oriented finite-element analysis) was used to simulate the accumulation of microcrack damage upon cooling, taking the measured real crystallographic orientations of the grains into account. Crack initiation and propagation were simulated using a Griffith-type fracture criterion. The computed evolution of Young's modulus as a function of temperature and grain size was compared with the corresponding experimental results.

We report on tensile tests performed on thin sheet samples of tantalum that have a nearcolumnar structure. By annealing sheet of approximately 1 mm thickness at high temperatures, a columnar structure is generated with grain boundaries nearly perpendicular to the flat surfaces. The purpose of the experiments is to investigate the mechanical behavior in terms of crystal plasticity in a geometry that is readily amenable to both experimental characterization and computer simulation. Automated electron backscatter diffraction (EBSD) has been used to obtain orientation maps both before and after deformation. For the small strains used in this study (<10%), the grains deform rather uniformly with little evidence of cell formation. Analysis of the lattice rotations shows considerable scatter in the rotation axis and demonstrates significant disagreement with polycrystal plasticity calculations.

Many issues in forming are influenced to some degree by the internal structure of the material which is commonly referred to by the materials science community as microstructure. Although the term microstructure is commonly only thought of in the context of grain size, it more properly encompasses all relevant aspects of internal material structure. For the purposes of forming, the most relevant features are the crystallographic orientations of the grains ("texture") and the locations of the grain boundaries, or, equivalently, the size, topology and shape of the grains. In order to perform realistic simulations one needs to specify the initial state of the material, e.g. on a finite element mesh, with sufficient detail that all these features are reproduced. Measuring microstructure at the scale of individual grains is possible in the synchrotron but scarcely practicable for an analyst. Cross-sections or surfaces are easily evaluated through automated diffraction in the scanning electron microscope (SEM), however. Therefore this paper describes a set of methods for generating statistically representative 3D microstructures based on microscopy input for both single-phase and two-phase materials. Examples are given of application of the technique for generating input structures for recrystallization simulation, dynamic deformation and finite element modeling.

Recrystallization kinetics of hot rolled aluminum alloy is analyzed from the indirect method of micro-hardness test and direct method of microstructural evolution using Electron Back Scattered Diffraction (EBSD) in an SEM. Isothermally annealed samples of hot rolled aluminum alloy were studied using JMAK type analysis to see if there exists any correlation between the two methods on analysis, differing in the scale of observation. A good agreement between the two methods is clearly indicated by similar numerical values of kinetics parameters from the two methods.

Application of electron backscattering diffraction methods to recover estimates of the geometrically necessary dislocation density is described. The limitations of the method arising from the opacity of crystalline materials and the spatial and angular resolution limits are discussed.

Experimental results on grain boundary properties and grain growth that are obtained from Electron Backscattered Diffraction (EBSD) technique are compared with the Finite Element simulation results of an Al-foil with a columnar grain structure. The starting microstructure and grain boundary properties are implemented as an input for the three-dimensional grain growth simulation. In the computational model, minimization of the interface energy is the driving force for the grain boundary motion. The computed evolved microstructure is compared with the final experimental microstructure, after annealing at 550 degreesC. Good agreement is observed between the experimentally obtained microstructure and the simulated microstructure. The constitutive description of the grain boundary properties was based on a 1-parameter characterization of the variation in mobility with misorientation angle.