Publications

Designing products for ~ assembly and disassembly during its entire Iifecycle for purposes including service, field repair, upgrade, and disposal is a process that involves many disciplines. In additiou finding the best solution often involves considering the design as a whole and by considering its intended Iifecycle. DifFerent goals and cortstmints (compared to initial assembly) require us to re-visit the significant fi,mdamental assumptions and methods that underlie current assembly planning techniques. Previous work in this area has been limited to either academic studies of assembly planning or applied studies of lifecycle assembly processes, which give no attention to automatic planning. It is believed that merging these two areas will result in a much greater ability to design for, analyze, and optimize the disassembly and assembly processes.

Abstract not provided.

We describe a general strategy we have found effective for parallelizing solid mechanics simula- tions. Such simulations often have several computationally intensive parts, including finite element integration, detection of material contacts, and particle interaction if smoothed particle hydrody- namics is used to model highly deforming materials. The need to balance all of these computations simultaneously is a difficult challenge that has kept many commercial and government codes from being used effectively on parallel supercomputers with hundreds or thousands of processors. Our strategy is to load-balance each of the significant computations independently with whatever bal- ancing technique is most appropriate. The chief benefit is that each computation can be scalably paraIlelized. The drawback is the data exchange between processors and extra coding that must be written to maintain multiple decompositions in a single code. We discuss these trade-offs and give performance results showing this strategy has led to a parallel implementation of a widely-used solid mechanics code that can now be run efficiently on thousands of processors of the Pentium-based Sandia/Intel TFLOPS machine. We illustrate with several examples the kinds of high-resolution, million-element models that can now be simulated routinely. We also look to the future and dis- cuss what possibilities this new capabUity promises, as well as the new set of challenges it poses in material models, computational techniques, and computing infrastructure.

We propose a multi length scale approach to modeling recrystallization which links a dislocation model, a cell growth model and a macroscopic model. Although this methodology and linking framework will be applied to recrystallization, it is also applicable to other types of phase transformations in bulk and layered materials. Critical processes such as the dislocation structure evolution, nucleation, the evolution of crystal orientations into a preferred texture, and grain size evolution all operate at different length scales. In this paper we focus on incorporating experimental measurements of dislocation substructures, rnisorientation measurements of dislocation boundaries, and dislocation simulations into a mesoscopic model of cell growth. In particular, we show how feeding information from the dislocation model into the cell growth model can create realistic initial microstructure.

A two-phase, Nb-Cr-Ti alloy (bee+ C15 Laves phase) has been developed using several alloy design methodologies. In effort to understand processing-microstructure-property relationships, diffment processing routes were employed. The resulting microstructure and mechanical properties are discussed and compared. Plasma arc-melted samples served to establish baseline, . . . as-cast properties. In addition, a novel processing technique, involving decomposition of a supersaturated and metastable precursor phase during hot isostatic pressing (HIP), was used to produce a refined, equilibrium two-phase microstructure. Quasi-static compression tests as a ~ function of temperature were performed on both alloy types. Different deformation mechanisms were encountered based upon temperature and microstructure.

The generation of surface defects on electron cyclotron resonance (ECR) plasma derived aluminum oxide films has been studied. We find that Cl active O vacancies can be generated using electron and ion irradiation yielding surface concentrations of 3 xl 013 to 1X1014 sites"cm-2. These values correspond to surface defect concentrations of 3 to 10% when compared to ordered, crystalline u-alumina. The vacancies appear to be responsible for increased surface O concentrations when immersed in water. Anodic polarization of irradiated films yields a decrease in the stable pitting potential which correlates with electron dose.

For nearly fifty years the US held a dominant position in research and development in the free world. The situation has changed dramatically in the last decade. Countries around the world realize that to foster sustainable economic growth, they must build and maintain a foundation in science and technology. The time in which a country could base its gross national product solely on extraction of raw materials or on people-intensive manufacturing is drawing to a close. The funding for research and development has been growing in the rest of the world, while US expenditures have not kept pace. In 1961, the United States funded 71 `?40 of the world's R&D. It is estimated that the US contribution to research and development fimding today has reached the 3 3o/0 level, and will drop to 26o/0 of the world's total by 2003.1 In 1981 US government spending per capita on non-defense research and development was nearly fifty percent above our major competitors; by 2002 it is projected to be f@ percent below them.2 This trend has a profound impact on how research and development institutions in the United States plan for their future technical growth. Sandia National Laboratories, as one of the largest US-government tided research establishments, has been watching this trend for some time. %ndi~ focusing on the Laboratories' missions in nuclear weapons and related defense systems, energy security, environmental integrity, and emerging national challenges, is committed to bringing the best in world-class technology to bear on the nation's problems. We realize maintaining our state-of-the-art technolo=~ base requires we look not only to domestic sources in universities, industries and other laboratories, but also to sources overseas. The realization that we must be "worldwide gatherers of technology" has led Sandia National Laboratories to consider the question of international partnering in some detaiI. As a national laboratory with a national security mission we are well aware of the issues that we face in pursuing international collaborations. In order to make the proper decisions, we are interested in understanding the history of such partnerships, when they are appropriate, why we expect them to be important, the risks they present and what we can do to mitigate those risks.

BC13, with addition of Nz, Ar or Hz, is found to provide smooth anisotropic pattern transfer in GaAs, GaN, GaP, GaSb and AIGriAs under Inductively Coupled Plasma conditions, Maxima in the etch rates for these materials are observed at 33% N2 or 87$'40 Hz (by flow) addition to BC13, whereas Ar addition does not show this behavior. Maximum etch rates are typically much higher for GaAs, Gap, GaSb and AIGaAs (-1,2 @rein) than for GaN (-0.3 ymu'min) due to the higher bond energies of the iatter. The rates decrease at higher pressure, saturate with source power (ion flux) and tend to show maxima with chuck power (ion energy). The etched surfaces remain stoichiometric over abroad range of plasma conditions.

We develop a general model that describes the electrical responses of thickness shear mode resonators subject to a variety of surface loadkgs. The model incorporates a physically diverse set of single component loadings, including rigid solids, viscoelastic media and fluids (Newtonian or Maxwellian). The model allows any number of these components to be combined in any configuration. Such multiple loadings are representative of a variety of physical situations encountered in electrochemical and other liquid phase applications, as well as gas phase applications. In the general case, the response of the composite is not a linear combination of the individual component responses. We discuss application of the model in a qualitative diagnostic fashion, to gain insight into the nature of the interracial structure, and in a quantitative fashion, to extract appropriate physical parameters, such as liquid viscosity and density and polymer shear moduli.

Electronic structure calculations frequently invoke periodic boundary conditions to solve for electrostatic potentials. For systems that are electronically charged, or contain dipole (or higher) moments, this artifice introduces spurious potentials due to the interactions between the system and multipole moments of its periodic images in aperiodic directions. I describe a method to properly handle the multipole moments of the electron density in electronic structure calculations using periodic boundary conditions. The density for which an electrostatic potential is to be evaluated is divided into two pieces. A local density is constructed that matches the desired moments of the full density, and its potential computed treating this density as isolated. With the density of this local moment countercharge removed from the full density, the remainder density lacks the troublesome moments and its electrostatic potential can be evaluated accurately using periodic boundary conditions.

In organometallic vapor phase epitaxial growth of Gail on sapphire, the role of the low- temperature-deposited interlayers inserted between high-temperature-grown GaN layers was investigated by in situ stress measurement, X-ray diffraction, and transmission electron microscopy. Insertion of a series of low temperature GaN interlayers reduces the density of threading dislocations while simultaneously increasing the tensile stress during growth, ultimately resulting in cracking of the GaN film. Low temperature AIN interlayers were found to be effective in suppressing cracking by reducing tensile stress. The intedayer approach permits tailoring of the film stress to optimize film structure and properties.

In this work, we report the realization of a series of silicon 3D photonic crystals operating in the infrared (IR), mid-IR and most importantly the near-IR (k= 1 -2pm) wavelengths. The structure maintains its crystal symmetry throughout the entire 6-inches wafer and holds a complete photonic bandgap.

The Waste Isolation Pilot Plant is a mined, geologic repository designed for permanent disposal of transuranic waste. The facility is owned by the United States Department of Energy, and licensed for operations by the Environmental Protection Agency. Compliance with license requirements dictates that the repository must comply with regulatory stipulations that performance assessment calculations include the effects of resource exploitation on probable releases. Scenarios for these releases incorporate inadvertent penetration of the repository by an exploratory drilling operation. This paper presents the scenarios and models used to predict releases from the repository to the biosphere during. an inadvertent intrusion into the waste disposal regions. A summary of model results and conclusions is also presented.

In the last ten years, since the break-up of the Soviet Union, remarkable progress in arms control and disarmament has occurred. The Nuclear Non-Proliferation Treaty (NPT), the completion of the Comprehensive Test Ban Treaty (CTBT), and the Chemical Weapons Treaty (CWC) are indicative of the great strides made in the non- proliferation arena. Simultaneously, the Intermediate Nuclear Forces Treaty (INF), the Conventional Forces Treaty in Europe (CFE), and the Strategic Arms Reduction Treaties (START), all associated with US-Soviet Union (now Russia) relations have assisted in redefining European relations and the security landscape. Finally, it now appears that progress is in the offing in developing enhanced compliance measures for the Biological and Toxin Weapons Convention (BTWC). In sum, all of these achievements have set the stage for the next round of arms control activities, which may lead to a much broader, and perhaps more diffused multilateral agenda. In this new and somewhat unpredictable international setting, arms control and disarmament issues will require solutions that are both more creative and innovative than heretofore.

We report the results of recent experiments on thermally degraded HMX and HMX/binder materials. Small-scale samples were heated confined in either constant-volume or load- controlled configurations. A main emphasis of the work reported here is developing an understanding of the complex coupling of the mechanical and chemical responses during thermal degradation.

We report magneto-transport measurements including Hall, Rxy, longitudinal, Rxx, and vertical, Rzz, magnetoresistance on nearly 3-dimensional (3D) 200 layer GaAs/AlGaAs quantum well structures. Although the interlayer band-width is nearly 20% of the Fermi energy, we still observe complete quantization of the Hall resistance for the 3D quantum Hall state. The temperature dependence of the Rxx minimum shows two unusual features: initially, at higher temperatures 1 K where the quantum Hall state develops, a gap with an activation energy much smaller than the Landau gap is observed; in the low temperature limit 0.030 K a variable range hopping behavior takes over with a residual resistivity limit. Independent measurements of Gzz (in 3D ≈ 1/Rzz) where the chiral edge states dominate the vertical transport show the same temperature dependence. © 1998 Published by Elsevier Science B.V. All rights reserved.

The Simdarion Infranet (S1) is a term which is being used to dcscribc one element of a multidisciplinary distributed and distance computing initiative known as DisCom2 at Sandia National Laboratory (http ct al. 1998). The Simulation Intranet is an architecture for satisfying Sandia's long term goal of providing an end- to-end set of scrviccs for high fidelity full physics simu- lations in a high performance, distributed, and distance computing environment. The Intranet Architecture group was formed to apply current distributed object technologies to this problcm. For the hardware architec- tures and software models involved with the current simulation process, a CORBA-based architecture is best suited to meet Sandia's needs. This paper presents the initial desi-a and implementation of this Intranct based on a three-tier Network Computing Architecture(NCA). The major parts of the architecture include: the Web Cli- ent, the Business Objects, and Data Persistence.

A parametric study of etch rates and surface morphologies of In-containing compound semiconductors (InP, InGaAs, InGaAsP, InAs and AlInAs) obtained by BClj-based Inductively Coupled Plasmas is reported. Etch rates in the range 1,500-3,000 &min. are obtained for all the materials at moderate source powers (500 W), with the rates being a strong function of discharge composition, rf chuck power and pressure. Typical root-mean-square surface roughness of-5 nm were obtained for InP, which is worse than the values obtained for Ga-based materials under the same conditions (-1 run). The near surface of etched samples is typically slightly deficient in the group V element, but the depth of this deficiency is small (a few tens of angstroms).

This process combines the best features of bulk and surface micromachining. It enables the production of stress free, thick, virtually arbitrarily shaped structures with well defined, thick or thin sacrificial layers, high sacrificial layer selectivity and large undercuts using IC compatible, processes. The basis of this approach is the use of readily available {111} oriented substrates, anisotropic Si trench etching, SiN masking and KOH etching.

The conditions of particle injection into the side of plasma jets play an important role in determining the microstructure and properties of sprayed deposits. However, few investigations have been carried out on this topic. The current work presents the results of an experimental and computational study of the influence of injector geometry and gas mass flow rate on particle dynamics at injector exit and in the plasma jet. Two injector geometries were tested : a straight tube and a curved tube with various radii of curvature. Zirconia powders with different particle size range and morphology were used. A possible size segregation effect in the injector was analyzed from the space distribution of particles collected on a stick tape. The spray pattern in the plasma jet was monitored from the thermal radiation emitted by particles. An analysis of the particle behavior in the injector and mixing of the carrier-gas flow with the plasma jet was carried out using a 3-D computational fluids dynamics code.

Using both wet and plasma etching, we have fabricated micro-channels in silicon substrates suitable for use as gas chromatography (GC) columns. Micro-channel dimensions range from 10 to 80 μm wide, 200 to 400 μm deep, and 10 cm to 100 cm long. Micro-channels 100 cm long take up as little as 1 cm2 on the substrate when fabricated with a high aspect ratio silicon etch (HARSE) process. Channels are sealed by anodically bonding Pyrex lids to the Si substrates. We have studied micro-channel flow characteristics to establish model parameters for system optimization. We have also coated these micro-channels with stationary phases and demonstrated GC separations. We believe separation performance can be improved by increasing stationary phase coating uniformity through micro-channel surface treatment prior to stationary phase deposition. To this end, we have developed microfabrication techniques to etch through silicon wafers using the HARSE process. Etching completely through the Si substrate facilitates the treatment and characterization of the micro-channel sidewalls, which dominate the GC physico-chemical interaction. With this approach, we separately treat the Pyrex lid surfaces that form the top and bottom surfaces of the GC flow channel.

The conflicting demands for finer features and increased production rates in integrated circuit manufacturing have emphasized the need for improved wafer positioning technology. In this paper we present operational test results from a magnetically levitated platen with structurally integrated piezoelectric actuators. The strain based actuators provide active damping of the platen's flexible body modes, enabling increased bandwidth on the mag-lev positioning system. Test results reveal a dramatic reduction in steady state positioning error and settling time through implementation of active vibration control.

Record-high impact speeds achieved using the Sandia Hyper Velocity Launcher have permitted a systematic study of shock-induced full vaporization of zinc. Pressures up to 5.5 Mbar and temperatures as high as 39000 K (∼3.4 eV) are induced in a thin zinc plate by impacting it with a tantalum flier at speeds up to 10.1 km/s. Such high pressures produce essentially full vaporization of the zinc because the thermodynamic release isentropes pass into the vapor dome near the critical point. To characterize vapor flow, the velocity history produced by stagnation of the zinc expansion products against a witness plate is measured with velocity interferometry. For each experiment, the time-resolved experimental interferometer record is compared with wave-code calculations using an analytical equation of state, called ANEOS, that is known to have performed quite well at lower impact speeds (less than -7 km/s) where vaporization is negligible. Significant discrepancies between experiment and calculation are shown to exist under conditions of the more recent higher impact speeds in excess of 7 km/s where the release isentrope appears to pass near the critical point.

Mixed Metal Phospho-Sulfates were prepared and evaluated for use as acid catalysts via 2-methyl-2-pentene isomerization and o-xylene isomerization. Particular members of this class of materials exhibit greater levels of activity than sulfated zirconia as well as lower rates and magnitudes of deactivation. 31P MAS NMR has been used to examine the role of phosphorous in contributing to the activity and deactivation behavior of these materials, while powder X-ray diffraction, BET surface area, IR, and elemental analysis were used to characterize the bulk catalysts.

The oxidative dehydrogenation (ODH) reactions for the formation of two important organic feedstocks ethylene and propylene are of great interest because of the potential in capital and energy savings associated with these reactions. Theoretically, ODH can achieve high conversions of the starting materials (ethane and propane) at lower temperatures than conventional dehydrogenation reactions. The important focus in our study of ODH catalysts is the development of a structure-property relationship for catalyst with respect to selectivity, so as to avoid the more thermodynamically favorable combustion reaction. Catalysts for the ODH reaction generally consist of mixed metal oxides. Since for the most selective catalyst lattice oxygen is known to participate in the reaction, catalysts are sought with surface oxygen atoms that are labile enough to perform dehydrogenation, but not so plentiful or weakly bound as to promote complete combustion. Also, catalysts must be able to replenish surface oxygen by transport from the bulk. Perovskite materials are candidates to fulfill these requirements. We are studying BaCeO3 perovskites doped with elements such as Ca, Mg, and Sr. During the ODH of the alkanes at high temperatures, the perovskite structure is not retained and a mixture of carbonates and oxides is formed, as revealed by XRD. While the Ca doped materials showed enhanced total combustion activity below 600°C, they only showed enhanced alkene production at 700°C. Bulk structural and surface changes, as monitored by powder X-ray diffraction, and X-ray photoelectron spectroscopy are being correlated with activity in order to understand the factors affecting catalyst performance, and to modify catalyst formulations to improve conversion and selectivity.