In-Situ Sampling and Characterization of Naturally Occurring Marine Methane Hydrate Using the D/V JOIDES Resolution (open access)

In-Situ Sampling and Characterization of Naturally Occurring Marine Methane Hydrate Using the D/V JOIDES Resolution

The primary accomplishments of the JOI Cooperative Agreement with DOE/NETL in this quarter were the implementation of a scientific ocean drilling expedition to study marine methane hydrates along the Cascadia margin, in the NE Pacific as part of Integrated Ocean Drilling Program (IODP) Expedition 311 using the R/V JOIDES Resolution and the deployment of all required equipment and personnel to provide the required services during this expedition. IODP Expedition 311 shipboard activities on the JOIDES Resolution began on August 28 and were concluded on October 28, 2005. New ODP Pressure Coring System (PCS) aluminum autoclave chambers were fabricated prior to the expedition. During the expedition, 16 PCS autoclaves containing pressure cores were X-rayed before and after depressurization using a modified Geotek MSCL-P (multi-sensor core logger-pressure) system. These PCS cores were density scanned using the MSCL-V (multi-sensor core logger-vertical) during depressurization to monitor gas evolution. The MSCL-V was set up in a 20-foot-long refrigerated container provided by Texas A&M University through the JOI contract with TAMRF. IODP Expedition 311 was the first time that PCS cores were examined before (using X-ray), during (using MSCL-V gamma density) and after (using X-ray) degassing to determine the actual volume and distribution of sediment and …
Date: December 31, 2005
Creator: Rack, Frank; Schultheiss, Peter & Party, IODP Expedition 311 Scientific
Object Type: Report
System: The UNT Digital Library
Investigation of Efficiency Improvements During CO2 Injection in Hydraulically and Naturally Fractured Reservoirs (open access)

Investigation of Efficiency Improvements During CO2 Injection in Hydraulically and Naturally Fractured Reservoirs

None
Date: December 31, 2005
Creator: Schechter, David S.
Object Type: Report
System: The UNT Digital Library
An Investigation to Resolve the Interaction Between Fuel Cell, Power Conditioning System and Application Loads (open access)

An Investigation to Resolve the Interaction Between Fuel Cell, Power Conditioning System and Application Loads

Development of high-performance and durable solidoxide fuel cells (SOFCs) and a SOFC power-generating system requires knowledge of the feedback effects from the power-conditioning electronics and from application-electrical-power circuits that may pass through or excite the power-electronics subsystem (PES). Therefore, it is important to develop analytical models and methodologies, which can be used to investigate and mitigate the effects of the electrical feedbacks from the PES and the application loads (ALs) on the reliability and performance of SOFC systems for stationary and non-stationary applications. However, any such attempt to resolve the electrical impacts of the PES on the SOFC would be incomplete unless one utilizes a comprehensive analysis, which takes into account the interactions of SOFC, PES, balance-of-plant system (BOPS), and ALs as a whole. SOFCs respond quickly to changes in load and exhibit high part- and full-load efficiencies due to its rapid electrochemistry, which is not true for the thermal and mechanical time constants of the BOPS, where load-following time constants are, typically, several orders of magnitude higher. This dichotomy can affect the lifetime and durability of the SOFCSs and limit the applicability of SOFC systems for load-varying stationary and transportation applications. Furthermore, without validated analytical models and investigative design …
Date: December 31, 2005
Creator: Mazumder, Sudip K.
Object Type: Report
System: The UNT Digital Library
Letter Report: Borehole Flow and Horizontal Hydraulic Conductivity with Depth at Well ER-12-4 (open access)

Letter Report: Borehole Flow and Horizontal Hydraulic Conductivity with Depth at Well ER-12-4

Borehole flow and fluid temperature during pumping were measured at well ER-12-4 at the Nevada Test Site in Nye County, Nevada. This well was constructed to characterize the carbonate aquifer. The well is cased from land surface to the total depth at 1,132 m (3,713 ft bgs) below ground surface (bgs). The screened section of the well consists of alternating sections of slotted well screen and blank casing from 948 to 1,132 m bgs (3,111 to 3,713 ft bgs). Borehole flow velocity (LT-1) with depth was measured with an impeller flowmeter from the top of the screened section to the maximum accessible depth while the well was pumped and under ambient conditions. A complicating factor to data interpretation is that the well was not filter packed and there is upward and downward vertical flow in the open annulus under ambient and pumping conditions. The open annulus in the well casing likely causes the calculated borehole flow rates being highly nonrepresentative of inflow from the formation. Hydraulic conductivities calculated under these conditions would require unsupportable assumptions and would be subject to very large uncertainties. Borehole hydraulic conductivities are not presented under these conditions.
Date: December 31, 2005
Creator: Oberlander, Phil L. & Russell, Charles E.
Object Type: Report
System: The UNT Digital Library
Microturbine Economic Competitiveness: A Study of Two PotentialAdopters (open access)

Microturbine Economic Competitiveness: A Study of Two PotentialAdopters

This project evaluates what $/kW subsidy on microturbines (MT's) makes them economically competitive with natural gas internal combustion engines (ICE's). The Distributed Energy Resources Customer Adoption Model (DER-CAM) is used to determine least cost solutions, including distributed generation (DG) investment and operation, to sites' energy demands. The first site considered is a hospital in New York City. The small hospital (90 beds) has a peak electric load (including cooling) of 1200 kW, with heat loads comparable to electric loads. Consolidated Edison electricity and natural gas tariffs for 2003 are used. A 60% minimum DG system efficiency is imposed on DG operation to avoid the standby tariff, which is less amenable to DG than the parent tariff. The second site considered is the Naval Base Ventura County commissary in Southern California. The commissary has 13,000 m{sup 2} of floor space and contains a large retail store, supermarket, food court, and other small businesses. The site peak electric load (including cooling) is 1050 kW. Electricity and natural gas supply are from direct access contracts, and delivery service is provided by Southern California Edison and Southern California Gas, respectively. 2003 supply and delivery rates are used.
Date: December 31, 2005
Creator: Firestone, Ryan & Marnay, Chris
Object Type: Report
System: The UNT Digital Library
NONLINEAR DYNAMICAL SYSTEMS - Final report (open access)

NONLINEAR DYNAMICAL SYSTEMS - Final report

This document is the final report on the work completed on DE-FG02-95ER25238 since the start of the second renewal period: Jan 1, 2001. It supplements the annual reports submitted in 2001 and 2002. In the renewal proposal I envisaged work in three main areas: Analytical and topological tools for studying flows and maps Low dimensional models of fluid flow Models of animal locomotion and I describe the progess made on each project.
Date: December 31, 2005
Creator: Holmes, Philip
Object Type: Report
System: The UNT Digital Library
Off-Highway Heavy Vehicle Diesel Efficiency Improvement and Emissions Reduction (open access)

Off-Highway Heavy Vehicle Diesel Efficiency Improvement and Emissions Reduction

Cummins Inc. is a world leader in the development and production of diesel engines for on-highway vehicles, off-highway industrial machines, and power generation units. Cummins Inc. diesel products cover a 50-3000 HP range. The power range for this project includes 174-750 HP to achieve EPA's Tier 3 emission levels of 4.0 NOx+NMHC gm/kW-hr and 0.2 PM gm/kWhr and Tier 4 Interim emission levels of 2.0 gm/kW-hr NOx and 0.02 gm/kW-hr PM. Cummins' anticipated product offerings for Tier 4 in this range include the following: QSB6.7, QSC8.3, QSL9, QSM11, QSX15, QSK19. (For reference, numerical values indicate engine displacement in liters, the letter designation ns indicate the product model). A summary of the EPA's mobile off-highway emissions requirements is given in Figure 1.
Date: December 31, 2005
Creator: Rumsey, Jennifer
Object Type: Report
System: The UNT Digital Library
Onboard Plasmatron Hydrogen Production for Improved Vehicles (open access)

Onboard Plasmatron Hydrogen Production for Improved Vehicles

A plasmatron fuel reformer has been developed for onboard hydrogen generation for vehicular applications. These applications include hydrogen addition to spark-ignition internal combustion engines, NOx trap and diesel particulate filter (DPF) regeneration, and emissions reduction from spark ignition internal combustion engines First, a thermal plasmatron fuel reformer was developed. This plasmatron used an electric arc with relatively high power to reform fuels such as gasoline, diesel and biofuels at an oxygen to carbon ratio close to 1. The draw back of this device was that it has a high electric consumption and limited electrode lifetime due to the high temperature electric arc. A second generation plasmatron fuel reformer was developed. It used a low-current high-voltage electric discharge with a completely new electrode continuation. This design uses two cylindrical electrodes with a rotating discharge that produced low temperature volumetric cold plasma., The lifetime of the electrodes was no longer an issue and the device was tested on several fuels such as gasoline, diesel, and biofuels at different flow rates and different oxygen to carbon ratios. Hydrogen concentration and yields were measured for both the thermal and non-thermal plasmatron reformers for homogeneous (non-catalytic) and catalytic reforming of several fuels. The technology was …
Date: December 31, 2005
Creator: Cohn, Daniel R.; Bromberg, Leslie & Hadidi, Kamal
Object Type: Report
System: The UNT Digital Library
Process for Converting Waste Glass Fiber into Value Added Products, Final Report (open access)

Process for Converting Waste Glass Fiber into Value Added Products, Final Report

Nature of the Event: Technology demonstration. The project successfully met all of its technical objectives. Albacem has signed an exclusive licensing agreement with Vitro Minerals Inc., a specialty minerals company, to commercialize the Albacem technology (website: www.vitrominerals.com). Location: The basic research for the project was conducted in Peoria, Illinois, and Atlanta, Georgia, with third-party laboratory verification carried out in Ontario, Canada. Pilot-scale trials (multi-ton) were conducted at a facility in South Carolina. Full-scale manufacturing facilities have been designed and are scheduled for construction by Vitro Minerals during 2006 at a location in the Georgia, North Carolina, and South Carolina tri-state area. The Technology: This technology consists of a process to eliminate solid wastes generated at glass fiber manufacturing facilities by converting them to value-added materials (VCAS Pozzolans) suitable for use in cement and concrete applications. This technology will help divert up to 250,000 tpy of discarded glass fiber manufacturing wastes into beneficial use applications in the concrete construction industry. This technology can also be used for processing glass fiber waste materials reclaimed from monofills at manufacturing facilities. The addition of take-back materials and reclamation from landfills can help supply over 500,000 tpy of glass fiber waste for processing into value …
Date: December 31, 2005
Creator: Hemmings, Raymond T.
Object Type: Report
System: The UNT Digital Library
Production Well Performance Enhancement using Sonication Technology (open access)

Production Well Performance Enhancement using Sonication Technology

The objective of this project was to develop a sonic well performance enhancement technology that focused on near wellbore formation damage. In order to successfully achieve this objective, a three-year project was defined. The entire project was broken into four tasks. The overall objective of all this was to foster a better understanding of the mechanisms involved in sonic energy interactions with fluid flow in porous media and adapt such knowledge for field applications. The fours tasks are: • Laboratory studies • Mathematical modeling • Sonic tool design and development • Field demonstration The project was designed to be completed in three years; however, due to budget cuts, support was only provided for the first year, and hence the full objective of the project could not be accomplished. This report summarizes what was accomplished with the support provided by the US Department of Energy. Experiments performed focused on determining the inception of cavitation, studying thermal dissipation under cavitation conditions, investigating sonic energy interactions with glass beads and oil, and studying the effects of sonication on crude oil properties. Our findings show that the voltage threshold for onset of cavitation is independent of transducer-hydrophone separation distance. In addition, thermal dissipation under …
Date: December 31, 2005
Creator: Adewumi, Michael A.; Ityokumbul, M. Thaddeus; Watson, Robert W.; Eltohami, Eltohami; Farias, Mario; Heckman, Glenn et al.
Object Type: Report
System: The UNT Digital Library
REALTIME MONITORING OF PIPELINES FOR THIRD-PARTY CONTACT (open access)

REALTIME MONITORING OF PIPELINES FOR THIRD-PARTY CONTACT

Third-party contact with pipelines (typically caused by contact with a digging or drilling device) can result in mechanical damage to the pipe, in addition to coating damage that can initiate corrosion. Because this type of damage often goes unreported and can lead to eventual catastrophic failure of the pipe, a reliable, cost-effective method is needed for monitoring the pipeline and reporting third-party contact events. The impressed alternating cycle current (IACC) pipeline monitoring method developed by Southwest Research Institute (SwRI) consists of impressing electrical signals on the pipe by generating a time-varying voltage between the pipe and the soil. The signal voltage between the pipe and ground is monitored continuously at receiving stations located some distance away. Third-party contact to the pipe that breaks through the coating (thus resulting in a signal path to ground) changes the signal received at the receiving stations. The IACC method was shown to be a viable method that can be used to continuously monitor pipelines for third-party contact. Electrical connections to the pipeline can be made through existing cathodic protection (CP) test points without the need to dig up the pipe. The instrumentation is relatively simple, consisting of (1) a transmitting station with a frequency-stable …
Date: December 31, 2005
Creator: Burkhardt, Gary L.
Object Type: Report
System: The UNT Digital Library
RECENT REFERENCES: JANUARY 1, 2005 TO DECEMBER 31, 2005 (open access)

RECENT REFERENCES: JANUARY 1, 2005 TO DECEMBER 31, 2005

This document lists experimental references added to Nuclear Science References (NSR) during the period January 1, 2005 to December 31, 2005. The first section lists keynumbers and keywords sorted by mass and nuclide. The second section lists all references, ordered by keynumber.
Date: December 31, 2005
Creator: WINCHELL, D.F.
Object Type: Report
System: The UNT Digital Library
RECENT REFERENCES: OCTOBER 1, 2005 TO DECEMBER 31, 2005 (open access)

RECENT REFERENCES: OCTOBER 1, 2005 TO DECEMBER 31, 2005

This document lists experimental references added to Nuclear Science References (NSR) during the period October 1, 2005 to December 31, 2005. The first section lists keynumbers and keywords sorted by mass and nuclide. The second section lists all references, ordered by keynumber.
Date: December 31, 2005
Creator: WINCHELL, D.F.
Object Type: Report
System: The UNT Digital Library
Reducing Barriers To The Use of High-Efficiency Lighting Systems (open access)

Reducing Barriers To The Use of High-Efficiency Lighting Systems

With funding from the U.S. Department of Energy (DOE), the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute completed the four-year research project, Reducing Barriers to the Use of High-Efficiency Lighting Systems. The initial objectives were: (1) identifying barriers to widespread penetration of lighting controls in commercial/industrial (C/I) applications that employ fluorescent lamp technologies, and (2) making recommendations to overcome these barriers. The addition of a fourth year expanded the original project objectives to include an examination of the impact on fluorescent lamps from dimming utilizing different lamp electrode heating and dimming ratios. The scope of the project was narrowed to identify barriers to the penetration of lighting controls into commercial-industrial (C/I) applications that employ fluorescent lamp technologies, and to recommend means for overcoming these barriers. Working with lighting manufacturers, specifiers, and installers, the project identified technological and marketing barriers to the widespread use of lighting controls, specifically automatic-off controls, occupancy sensors, photosensors, dimming systems, communication protocols and load-shedding ballasts. The primary barriers identified include cost effectiveness of lighting controls to the building owner, lack of standard communication protocols to allow different part of the control system to communicate effectively, and installation and commissioning issues. Overcoming the identified barriers requires …
Date: December 31, 2005
Creator: Morante, Peter
Object Type: Report
System: The UNT Digital Library
Rhodium-105 Bombesin Analogs for Prostate Cancer Radiotherapy (open access)

Rhodium-105 Bombesin Analogs for Prostate Cancer Radiotherapy

Over the period of this grant (11/01/2001 to 12/31/2005), the consistent and reproducible production of Rh-105, synthesis and evaluation of three new chelate systems based on hydroxymethyl phosphines, development of a new non-hydroxymethyl phosphine N{sub 2}P{sub 2} chelate system, conjugation of two of the chelates to the bombesin peptide analog BBN[7-14]NH{sub 2}, evaluation of the bombesin conjugates and their Rh-105 complexes for stability, cell binding affinity, and in vivo biodistribution in normal mice has been developed. The BBN analogs bind to GRP receptors that are overexpressed on PC-3 prostate tumor cells. A dedicated glove box is used for the separation and isolation of {sup 105}Rh from the target ({sup 104}Ru). All tubing/connections/valves from the point of the Cl{sub 2} tank are made of Teflon to minimize/eliminate the introduction of any metal into the process (e.g., iron from stainless steel corrosion). The separation of {sup 105}Rh produced from the enriched {sup 104}Ru target involves oxidation of the enriched {sup 104}Ru metal target to ruthenium tetroxide with chlorine gas and sodium hydroxide solution to generate hypochlorite in situ. The RuO4 is removed by distillation and the {sup 105}Rh remaining in the reaction vial is converted into {sup 105}Rh-chloride by acidification with hydrochloric …
Date: December 31, 2005
Creator: Silvia S. Jurisson, PhD
Object Type: Report
System: The UNT Digital Library
A Sea Floor Survey of the Sleipner Field to Monitor CO2 Migration (open access)

A Sea Floor Survey of the Sleipner Field to Monitor CO2 Migration

In the North Sea natural gas production field at Sleipner, CO{sub 2} is being separated from natural gas and injected into an underground saline aquifer, known as the Utsira formation, for environmental purposes. In this study, gravity measurements were made over the Sleipner CO{sub 2} injection site in 2002 and again in 2005 on top of 30 concrete benchmarks on the seafloor to study the behavior and physical properties of the injected CO{sub 2}. As the gas is injected, pore space water is replaced by gas, altering the bulk density of the formation. This results in a change in gravitational acceleration observed on the overlying sea floor. Our gravity measurements show a repeatability of 4.3 {micro}Gal for 2003 and 3.5 {micro}Gal for 2005. Forward models of the gravity change are calculated based on both 3-D seismic data and reservoir simulation models from other studies. These forward models indicate that the magnitude of maximum gravity change is primarily related to CO{sub 2} density rather than flow geometry. The time-lapse gravity observations best fit a high temperature forward model based on the seismically determined CO{sub 2} geometry, suggesting that the 3-D reflection seismics are imaging the geometry of the injected CO{sub 2}, …
Date: December 31, 2005
Creator: Zumberge, Mark A.
Object Type: Report
System: The UNT Digital Library
Speciation and Attenuation of Arsenic and Selenium at Coal Combustion By-Product Management Facilities (open access)

Speciation and Attenuation of Arsenic and Selenium at Coal Combustion By-Product Management Facilities

The overall objective of this project was to evaluate the impact of key constituents captured from power plant air streams (principally arsenic and selenium) on the disposal and utilization of coal combustion products (CCPs). Specific objectives of the project were: (1) to develop a comprehensive database of field leachate concentrations at a wide range of CCP management sites, including speciation of arsenic and selenium, and low-detection limit analyses for mercury; (2) to perform detailed evaluations of the release and attenuation of arsenic species at three CCP sites; and (3) to perform detailed evaluations of the release and attenuation of selenium species at three CCP sites. Each of these objectives was accomplished using a combination of field sampling and laboratory analysis and experimentation. All of the methods used and results obtained are contained in this report. For ease of use, the report is subdivided into three parts. Volume 1 contains methods and results for the field leachate characterization. Volume 2 contains methods and results for arsenic adsorption. Volume 3 contains methods and results for selenium adsorption.
Date: December 31, 2005
Creator: Ladwig, K.
Object Type: Report
System: The UNT Digital Library
A Strong Hot Spot Theorem (open access)

A Strong Hot Spot Theorem

A real number alpha is said to be b-normal if every m-long string of digits appears in the base-b expansion of alpha with limiting frequency b-m. We prove that alpha is b-normal if and only if it possesses no base-b ''hot spot''. In other words, alpha is b-normal if and only if there is no real number y such that smaller and smaller neighborhoods of y are visited by the successive shifts of the base-b expansion of alpha with larger and larger frequencies, relative to the lengths of these neighborhoods
Date: December 31, 2005
Creator: Bailey, David H. & Misiurewicz, Michal
Object Type: Article
System: The UNT Digital Library
Supported, Alkali-Promoted Cobalt Oxide Catalysts for NOx Removal from Coal Combustion Flue Gases (open access)

Supported, Alkali-Promoted Cobalt Oxide Catalysts for NOx Removal from Coal Combustion Flue Gases

A series of cobalt oxide catalysts supported on alumina ({gamma}-Al{sub 2}O{sub 3}) were synthesized with varying contents of cobalt and of added alkali metals, including lithium, sodium, potassium, rubidium, and cesium. Unsupported cobalt oxide catalysts and several cobalt oxide catalysts supported ceria (CeO{sub 2}) with varying contents of cobalt with added potassium were also prepared. The catalysts were characterized with UV-visible spectroscopy and were examined for NO{sub x} decomposition activity. The CoO{sub x}/Al{sub 2}O{sub 3} catalysts and particularly the CoO{sub x}/CeO{sub 2} catalysts show N{sub 2}O decomposition activity, but none of the catalysts (unsupported Co{sub 3}O{sub 4} or those supported on ceria or alumina) displayed significant, sustained NO decomposition activity. For the Al{sub 2}O{sub 3}-supported catalysts, N{sub 2}O decomposition activity was observed over a range of reaction temperatures beginning about 723 K, but significant (>50%) conversions of N{sub 2}O were observed only for reaction temperatures >900 K, which are too high for practical commercial use. However, the CeO{sub 2}-supported catalysts display N{sub 2}O decomposition rates similar to the Al{sub 2}O{sub 3}-supported catalysts at much lower reaction temperatures, with activity beginning at {approx}573 K. Conversions of >90% were achieved at 773 K for the best catalysts. Catalytic rates per cobalt atom …
Date: December 31, 2005
Creator: Argyle, Morris D.
Object Type: Report
System: The UNT Digital Library
The Tapestry of Life: Lateral Transfers of Heritable Elements - Scientific Meeting (open access)

The Tapestry of Life: Lateral Transfers of Heritable Elements - Scientific Meeting

The Sackler Colloquium The Tapestry of Life: Lateral Transfers of Heritable Elements was held on December 12-13, 2005. What Darwin saw as a tree of life descending in a linear fashion, is now more accurately seen as a tapestry of life, an anastomosing network, with important lateral transfers of heritable elements among parallel lines of descent These transfers range in complexity from small insertion sequences, to whole genes, gene islands, and portions of whole genomes which may be combined in symbiogenesis. The colloquium brought together researchers, empirical and theoretical, working at all levels on genomics, comparative genomics, and metagenomics to identify common and differentiating features of lateral gene transfer and to examine their implications for science and for human concerns.
Date: December 31, 2005
Creator: Fraser, Claire M.
Object Type: Report
System: The UNT Digital Library
Time-Lapse Modeling and Inversion of CO2 Saturation for Sequestration and Enhanced Oil Recovery (open access)

Time-Lapse Modeling and Inversion of CO2 Saturation for Sequestration and Enhanced Oil Recovery

None
Date: December 31, 2005
Creator: Meadows, Mark A.
Object Type: Report
System: The UNT Digital Library
Underground Coal Gasification Test Project (open access)

Underground Coal Gasification Test Project

None
Date: December 31, 2005
Creator: Dennis, D. Steve
Object Type: Report
System: The UNT Digital Library
Use of the GranuFlow Process in Coal Preparation Plants to Improve Energy Recovery and Reduce Coal Processing Wastes (open access)

Use of the GranuFlow Process in Coal Preparation Plants to Improve Energy Recovery and Reduce Coal Processing Wastes

With the increasing use of screen-bowl centrifuges in today's fine coal cleaning circuits, a significant amount of low-ash, high-Btu coal can be lost during the dewatering step due to the difficulty in capturing coal of this size consist (< 100 mesh or 0.15mm). The GranuFlow{trademark} technology, developed and patented by an in-house research group at DOE-NETL, involves the addition of an emulsified mixture of high-molecular-weight hydrocarbons to a slurry of finesized coal before cleaning and/or mechanical dewatering. The binder selectively agglomerates the coal, but not the clays or other mineral matter. In practice, the binder is applied so as to contact the finest possible size fraction first (for example, froth flotation product) as agglomeration of this fraction produces the best result for a given concentration of binder. Increasing the size consist of the fine-sized coal stream reduces the loss of coal solids to the waste effluent streams from the screen bowl centrifuge circuit. In addition, the agglomerated coal dewaters better and is less dusty. The binder can also serve as a flotation conditioner and may provide freeze protection. The overall objective of the project is to generate all necessary information and data required to commercialize the GranuFlow{trademark} Technology. The technology …
Date: December 31, 2005
Creator: Shirey, Glenn A. & Akers, David J.
Object Type: Report
System: The UNT Digital Library
Void Coalescence Processes Quantified through Atomistic and Multiscale Simulation (open access)

Void Coalescence Processes Quantified through Atomistic and Multiscale Simulation

Simulation of ductile fracture at the atomic scale reveals many aspects of the fracture process including specific mechanisms associated with void nucleation and growth as a precursor to fracture and the plastic deformation of the material surrounding the voids and cracks. Recently we have studied void coalescence in ductile metals using large-scale atomistic and continuum simulations. Here we review that work and present some related investigations. The atomistic simulations involve three-dimensional strain-controlled multi-million atom molecular dynamics simulations of copper. The correlated growth of two voids during the coalescence process leading to fracture is investigated, both in terms of its onset and the ensuing dynamical interactions. Void interactions are quantified through the rate of reduction of the distance between the voids, through the correlated directional growth of the voids, and through correlated shape evolution of the voids. The critical inter-void ligament distance marking the onset of coalescence is shown to be approximately one void radius based on the quantification measurements used, independent of the initial separation distance between the voids and the strain-rate of the expansion of the system. No pronounced shear flow is found in the coalescence process.
Date: December 31, 2005
Creator: Rudd, R E; Seppala, E T; Dupuy, L M & Belak, J
Object Type: Article
System: The UNT Digital Library