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in creator/contributor: "Stolken, J S"

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The Importance of Geometric Nonlinearity in Finite Element Studies of Yielding in Trabecular Bone

No Description Available.

Date: February 14, 2005

Creator: Kinney, J H & Stolken, J S

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Derivation and Solution of Multifrequency Radiation Diffusion Equations for Homogeneous Refractive Lossy Media

Starting from the radiation transport equation for homogeneous, refractive lossy media, we derive the corresponding time-dependent multifrequency diffusion equations. Zeroth and first moments of the transport equation couple the energy density, flux and pressure tensor. The system is closed by neglecting the temporal derivative of the flux and replacing the pressure tensor by its diagonal analogue. The system is coupled to a diffusion equation for the matter temperature. We are interested in mo… more

Date: January 5, 2010

Creator: Shestakov, A I; Vignes, R M & Stolken, J S

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Effects of Grain Boundary Constraint on the Constitutive Response of Tantalum Bicrystals

The role of grain boundary constraint in strain localization, slip system activation, slip transmission, and the concomitant constitutive response was examined performing a series of uniaxial compression tests on tantalum bicrystals. Tantalum single crystals were diffusion bonded to form a (011) twist boundary and compressed along the [011] direction. The resulting three-dimensional deformation was analyzed via volume reconstruction. With this, both, the effective states of stress and strain ov… more

Date: April 8, 2003

Creator: Ziegler, A; Campbell, G H; Kumar, M & Stolken, J S

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Simulation of Infrared Laser Heating of Silica Using Heat Conduction and Multifrequency Radiation Diffusion Equations Adapted for Homogeneous Refractive Lossy Media

Localized, transient heating of materials using micro-scale, highly absorbing laser light has been used in many industries to anneal, melt and ablate material with high precision. Accurate modeling of the relative contributions of conductive, convective and radiative losses as a function of laser parameters is essential to optimizing micro-scale laser processing of materials. In bulk semi-transparent materials such as silicate glass melts, radiation transport is known to play a significantly la… more

Date: October 28, 2010

Creator: Shestakov, A I; Matthews, M J; Vignes, R M & Stolken, J S

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Densification and residual stress induced by CO2 laser-based mitigation of SiO2 surfaces

Knowing the ultimate surface morphology resulting from CO{sub 2} laser mitigation of induced laser damage is important both for determining adequate treatment protocols, and for preventing deleterious intensification upon subsequent illumination of downstream optics. Physical effects such as evaporation, viscous flow and densification can strongly affect the final morphology of the treated site. Evaporation is a strong function of temperature and will play a leading role in determining pit shap… more

Date: October 21, 2010

Creator: Feit, M D; Matthews, M J; Soules, T F & Stolken, J S

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Silica Molecular Dynamic Force Fields- A Practical Assessment

No Description Available.

Date: August 30, 2010

Creator: Soules, T; Gilmer, G H; Matthews, M J; Stolken, J S & Feit, M D

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

An Assessment of Molecular Dynamic Force Fields for Silica for Use in Simulating Laser Damage Mitigation

We compare force fields (FF's) that have been used in molecular dynamic (MD) simulations of silica in order to assess their applicability for use in simulating IR-laser damage mitigation. Although pairwise FF?s obtained by fitting quantum mechanical calculations such as the BKS and CHIK potentials have been shown to reproduce many of the properties of silica including the stability of silica polymorphs and the densification of the liquid, we show that melting temperatures and fictive temperatur… more

Date: October 21, 2010

Creator: Soules, T F; Gilmer, G H; Matthews, M J; Stolken, J S & Feit, M D

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Structural Modifications in Fused Silica Due to Laser Damage Induced Shock Compression

High power laser pulses can produce damage in high quality fused silica optics that can lead to its eventual obscuration and failure. Current models suggest the initiation of a plasma detonation due to absorbing initiators and defects, leading to the formation of shock waves. Recent experiments have found a densified layer at the bottom of damage sites, as evidence of the laser-damage model. We have studied the propagation of shock waves through fused silica using molecular dynamics. These simu… more

Date: December 5, 2001

Creator: Kubota, A; Davila, L; Caturla, M J; Stolken, J S; Sadigh, B; Quong, A et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Shear Localization and Failure in Shocked Metals Final Report

The goal of the project was to understand the effect of shocks on the subsequent mechanical response of metals. The framework revolves around the sequence and timing of events during shock loading. A shock will transmit through a solid at speed of several mm per {micro}s. The result of the shock passage is a step change in the velocity of the material. This subsequent velocity will cause deformation in the material that could extend in time to several 10s or 100s of {micro}s after the passage o… more

Date: February 13, 2004

Creator: Garaizar, F X; Trebotich, D P; McNaney, J M; Kumar, M; Stolken, J S & Campbell, G H

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Dislocation Dynamics using Anisotropic Elasticity: Methodology and Analysis

A numerical methodology to incorporate anisotropic elasticity into three-dimensional dislocation dynamics codes has been developed, employing theorems derived by Lothe (1967), Brown (1967), Indenbom and Orlov (1968) and Asaro and Barnett (1976). The formalism is based on the stress field solution for a straight dislocation segment of arbitrqq orientation in 3-dimensional space. The general solution is given in a complicated closed integral form. To reduce the computation complexity, look-up tab… more

Date: June 15, 2000

Creator: Rhee, M; Stolken, J S; Bulatov, V V; Diaz de la Rubia, T; Zbib, H M & Hirth, J P

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Experimental assessment of gradient plasticity

Classical plasticity theories generally assume that the stress at a point is a function of strain at that point only. However, when gradients in strain become significant, this localization assumption is no longer valid. A common factor in the failure of these conventional models is that, since they do not account for the strain gradients, they do not display a size effect. This effect is seen experimentally when the scale of the phenomenon of interest is on the order of several microns. At thi… more

Date: December 14, 2000

Creator: Barney, M M; Campbell, G H; Stolken, J S; Schwartz, A J; Plitzko, J; King, W E et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Orientation imaging microscopy investigation of the compression deformation of a [011] ta single crystal

High-purity tantalum single crystal cylinders oriented with [110] parallel to the cylinder axis were deformed 10, 20, and 30 percent in compression. The samples were subsequently sectioned for characterization using Orientation Imaging Microscopy (O&I) along two orthogonal sectioning planes: one in the plane containing [001] and [110] (longitudinal) and the other in the plane containing [1{anti 1}0] and[110] (transverse). To examine local lattice rotations, the Euler angles relative to a refere… more

Date: January 8, 1999

Creator: Adams, B L; Campbell, G H; King, W E; Lassila, D H; Stolken, J S; Sun, S et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Analysis of compression behavior of a [011] Ta single crystal with orientation imaging microscopy and crystal plasticity

High-purity tantalum single crystal cylinders oriented with [011] parallel to the cylinder axis were deformed 10, 20, and 30 percent in compression. The engineering stress-strain curve exhibited an up-turn at strains greater than {approximately}20% while the samples took on an ellipsoidal shape during testing, elongated along the [100] direction with almost no dimensional change along [0{bar 1}1]. Two orthogonal planes were selected for characterization using Orientation Imaging Microscopy (OIM… more

Date: February 3, 1999

Creator: Adams, B. L.; Campbell, G. H.; King, W. E.; Lassila, D. H.; Stolken, J. S.; Sun, S. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

DIRECT OBSERVATION OF THE ALPHA-EPSILON TRANSITION IN SHOCKED SINGLE CRYSTAL IRON

In-situ x-ray diffraction was used to study the response of single crystal iron under shock conditions. Measurements of the response of [001] iron showed a uniaxial compression of the initially bcc lattice along the shock direction by up to 6% at 13 GPa. Above this pressure, the lattice responded with a further collapse of the lattice by 15-18% and a transformation to a hcp structure. The in-situ measurements are discussed and results summarized.

Date: August 23, 2005

Creator: Kalantar, D H; Collins, G W; Colvin, J D; Davies, H M; Eggert, J H; Hawreliak, J et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

An Analysis of the X-Ray Diffraction Signal for the (alpha) - (epsilon) Transition in Shock-Compressed Iron: Simulation and Experiment

Recent published work has shown that the phase change of shock compressed iron along the [001] direction does transform to the {epsilon} (HCP) phase similar to the case for static measurements. This article provides an indepth analysis of the experiment and NEMD simulations, using x-ray diffraction in both cases to study the crystal structure upon transition. Both simulation and experiment are consistent with a compression and shuffle mechanism responsible for the phase change from BCC to HCP. … more

Date: April 10, 2006

Creator: Hawreliak, J; Colvin, J D; Kalantar, D H; Lorenzana, H E; Stolken, J S; Davies, H M et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Shock Induced (Alpha)-(Epsilon) Phase Change in Iron: Analysis of MD Simulations and Experiment

Multimillion atom non-equilibrium molecular dynamics simulations for shock compressed iron are analyzed using Fourier methods to determine the long scale ordering of the crystal. By analyzing the location of the maxima in k-space we can determine the crystal structure and compression due to the shock. This report presents results from a 19.6 GPa simulated shock in single crystal iron and compare them to recent experimental results of shock compressed iron where the crystal structure was determi… more

Date: August 25, 2005

Creator: Hawreliak, J.; Rosolankova, K.; Belak, J. F.; Collins, G.; Colvin, J.; Davies, H. M. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Direct Observation of the alpha-epsilon Transition in Shock-compressed Iron via Nanosecond X-ray Diffraction

In-situ x-ray diffraction studies of iron under shock conditions confirm unambiguously a phase change from the bcc ({alpha}) to hcp ({var_epsilon}) structure. Previous identification of this transition in shock-loaded iron has been inferred from the correlation between shock wave-profile analyses and static high-pressure x-ray measurements. This correlation is intrinsically limited because dynamic loading can markedly affect the structural modifications of solids. The in-situ measurements are c… more

Date: March 21, 2005

Creator: Kalantar, D. H.; Belak, J. F.; Collins, G. W.; Colvin, J. D.; Davies, H. M.; Eggert, J. H. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Picosecond X-Ray Diffraction From Laser-Shocked Copper and Iron

In situ X-ray diffraction allows the determination of the structure of transient states of matter. We have used laser-plasma generated X-rays to study how single crystals of metals (copper and iron) react to uniaxial shock compression. We find that copper, as a face-centered-cubic material, allows rapid generation and motion of dislocations, allowing close to hydrostatic conditions to be achieved on sub-nanosecond timescales. Detailed molecular dynamics calculations provide novel information ab… more

Date: August 23, 2005

Creator: Wark, J. S.; Belak, J. F.; Collins, G. W.; Colvin, J. D.; Davies, H. M.; Duchaineau, M. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

FY06 Engineering Research and Technology Report

This report summarizes the core research, development, and technology accomplishments in Lawrence Livermore National Laboratory's Engineering Directorate for FY2006. These efforts exemplify Engineering's more than 50-year history of developing and applying the technologies needed to support the Laboratory's national security missions. A partner in every major program and project at the Laboratory throughout its existence, Engineering has prepared for this role with a skilled workforce and techn… more

Date: January 22, 2007

Creator: Minichino, C.; Alves, S. W.; Anderson, A. T.; Bennett, C. V.; Brown, C. G.; Brown, W. D. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department