States

Urban Dispersion Program MSG05 Field Study: Summary of Tracer and Meteorological Measurements (open access)

Urban Dispersion Program MSG05 Field Study: Summary of Tracer and Meteorological Measurements

The Urban Dispersion Program is a multi-year project, funded by the U.S. Department of Homeland Security, to better understand the flow and dispersion of airborne contaminants through and around the deep street canyons of New York City. The first tracer and meteorological field study was a limited study conducted during March 2005 near the Madison Square Garden in midtown Manhattan. Six safe, inert, gaseous perfluorocarbon tracers were released simultaneously at five street-level locations during two experimental days. In addition to collecting tracer data, meteorological data were also collected. Brookhaven National Laboratory conducted the bulk of the tracer and meteorological field efforts with Pacific Northwest National Laboratory and Stevens Institute of Technology assisting by measuring the vertical profile of winds. The Environmental Protection Agency worked with Brookhaven National Laboratory in accomplishing the personal exposure component of the study. This report presents some results from this analysis. In general, different release locations showed vastly different plume footprints for tracer materials, and the situation was made very complex with upwind and/or crosswind transport of tracer near street-level for the different release locations. Overall wind speeds and directions upwind and over the city were generally constant throughout each of the two experimental periods.
Date: August 9, 2006
Creator: Allwine, K Jerry & Flaherty, Julia E.
Object Type: Report
System: The UNT Digital Library
Electrical Conductivity Calculations from the Purgatorio Code (open access)

Electrical Conductivity Calculations from the Purgatorio Code

The Purgatorio code [Wilson et al., JQSRT 99, 658-679 (2006)] is a new implementation of the Inferno model describing a spherically symmetric average atom embedded in a uniform plasma. Bound and continuum electrons are treated using a fully relativistic quantum mechanical description, giving the electron-thermal contribution to the equation of state (EOS). The free-electron density of states can also be used to calculate scattering cross sections for electron transport. Using the extended Ziman formulation, electrical conductivities are then obtained by convolving these transport cross sections with externally-imposed ion-ion structure factors.
Date: January 9, 2006
Creator: Hansen, S B; Isaacs, W A; Sterne, P A; Wilson, B G; Sonnad, V & Young, D A
Object Type: Article
System: The UNT Digital Library
Exploiting Data Parallelism in the Image Content Engine (open access)

Exploiting Data Parallelism in the Image Content Engine

The Image Content Engine (ICE) is a framework of software and underlying mathematical and physical models that enable scientists and analysts to extract features from Terabytes of imagery and search the extracted features for content relevant to their problem domain. The ICE team has developed a set of tools for feature extraction and analysis of image data, primarily based on the image content. The scale and volume of imagery that must be searched presents a formidable computation and data bandwidth challenge, and a search of moderate to large scale imagery quickly becomes intractable without exploiting high degrees of data parallelism in the feature extraction engine. In this paper we describe the software and hardware architecture developed to build a data parallel processing engine for ICE. We discuss our highly tunable parallel process and job scheduling subsystem, remote procedure invocation, parallel I/O strategy, and our experience in running ICE on a 16 node, 32 processing element (CPU) Linux Cluster. We present performance and benchmark results, and describe how we obtain excellent speedup for the imagery searches in our test-bed prototype.
Date: March 9, 2006
Creator: Miller, W M; Garlick, J E; Weinert, G F & Abdulla, G M
Object Type: Article
System: The UNT Digital Library
Computational Fluid Dynamics Simulation of Fluidized Bed Polymerization Reactors (open access)

Computational Fluid Dynamics Simulation of Fluidized Bed Polymerization Reactors

Fluidized beds (FB) reactors are widely used in the polymerization industry due to their superior heat- and mass-transfer characteristics. Nevertheless, problems associated with local overheating of polymer particles and excessive agglomeration leading to FB reactors defluidization still persist and limit the range of operating temperatures that can be safely achieved in plant-scale reactors. Many people have been worked on the modeling of FB polymerization reactors, and quite a few models are available in the open literature, such as the well-mixed model developed by McAuley, Talbot, and Harris (1994), the constant bubble size model (Choi and Ray, 1985) and the heterogeneous three phase model (Fernandes and Lona, 2002). Most these research works focus on the kinetic aspects, but from industrial viewpoint, the behavior of FB reactors should be modeled by considering the particle and fluid dynamics in the reactor. Computational fluid dynamics (CFD) is a powerful tool for understanding the effect of fluid dynamics on chemical reactor performance. For single-phase flows, CFD models for turbulent reacting flows are now well understood and routinely applied to investigate complex flows with detailed chemistry. For multiphase flows, the state-of-the-art in CFD models is changing rapidly and it is now possible to predict reasonably well …
Date: August 9, 2006
Creator: Fan, Rong
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Biomimetic Nanocomposites of Calcium Phosphate and Self-Assembling Triblock and Pentablock Copolymers (open access)

Biomimetic Nanocomposites of Calcium Phosphate and Self-Assembling Triblock and Pentablock Copolymers

In an effort to mimic the growth of natural bone, self-assembling, micelle and gel-forming copolymers were used as a template for calcium phosphate precipitation. Because of the cationic characteristics imparted by PDEAEM end group additions to commercially available Pluronic{reg_sign} Fl27, a direct ionic attraction mechanism was utilized and a polymer-brushite nanocomposite spheres were produced. Brushite coated spherical micelles with diameters of {approx}40 nm, and agglomerates of these particles (on the order of 0.5 {mu}m) were obtained. Thickness and durability of the calcium phosphate coating, and the extent of agglomeration were studied. The coating has been shown to be robust enough to retain its integrity even below polymer critical micelle concentration and/or temperature. Calcium phosphate-polymer gel nanocomposites were also prepared. Gel samples appeared as a single phase network of agglomerated spherical micelles, and had a final calcium phosphate concentration of up to 15 wt%. Analysis with x-ray diffraction and NMR indicated a disordered brushite phase with the phosphate groups linking inorganic phase to the polymer.
Date: August 9, 2006
Creator: Enlow, Drew Lenzen
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Field Demonstraton of Existing Microhole Coiled Tubing Rig (MCTR) Technology (open access)

Field Demonstraton of Existing Microhole Coiled Tubing Rig (MCTR) Technology

The performance of an advanced Microhole Coiled Tubing Rig (MCTR) has been measured in the field during the drilling of 25 test wells in the Niobrara formation of Western Kansas and Eastern Colorado. The coiled tubing (CT) rig designed, built and operated by Advanced Drilling Technologies (ADT), was documented in its performance by GTI staff in the course of drilling wells ranging in depth from 500 to nearly 3,000 feet. Access to well sites in the Niobrara for documenting CT rig performance was provided by Rosewood Resources of Arlington, VA. The ADT CT rig was selected for field performance evaluation because it is one of the most advanced commercial CT rig designs that demonstrate a high degree of process integration and ease of set-up and operation. Employing an information collection protocol, data was collected from the ADT CT rig during 25 drilling events that encompassed a wide range of depths and drilling conditions in the Niobrara. Information collected included time-function data, selected parametric information indicating CT rig operational conditions, staffing levels, and field observations of the CT rig in each phase of operation, from rig up to rig down. The data obtained in this field evaluation indicates that the ADT …
Date: May 9, 2006
Creator: Perry, Kent; Batarseh, Samih; Gowelly, Sheriff & Hayes, Thomas
Object Type: Report
System: The UNT Digital Library
An Empirical Study of Block Matching Techniques for the Detection of Moving Objects (open access)

An Empirical Study of Block Matching Techniques for the Detection of Moving Objects

The basis of surveillance, event detection, and tracking applications is the detection of moving objects in complex scenes. Complex scenes are difficult to analyze because of camera noise and lighting conditions. Currently, moving objects are detected primarily using background subtraction. We analyze block matching as an alternative for detecting moving objects. Block matching has been extensively utilized in compression algorithms for motion estimation. Besides detection of moving objects, block matching also provides motion vectors (location of motion) which can aide in tracking objects. Block matching techniques consist of three main components: block determination, search methods, and matching criteria. We compare various options for each of the components with moving object detection as the performance goal. Publicly available sequences of several different traffic and weather conditions are used to evaluate the techniques. A coherence metric and the average magnitude of object motion vector error are used to evaluate block determination approaches and search methods. To compare the matching criteria we use precision-recall curves to evaluate the performance of motion detection. We present an empirical study of the block matching techniques using these metrics of performance as well as process timing. We found the hierarchical block determination approach has an overall higher …
Date: January 9, 2006
Creator: Love, N S & Kamath, C
Object Type: Report
System: The UNT Digital Library
Of extracellular matrix, scaffolds, and signaling: Tissuearchitectureregulates development, homeostasis, and cancer (open access)

Of extracellular matrix, scaffolds, and signaling: Tissuearchitectureregulates development, homeostasis, and cancer

The microenvironment surrounding cells influences gene expression, such that a cell's behavior is largely determined by its interactions with the extracellular matrix, neighboring cells, and soluble cues released locally or by distant tissues. We describe the essential role of context and organ structure in directing mammary gland development and differentiated function, and in determining response to oncogenic insults including mutations. We expand on the concept of 'dynamic reciprocity' to present an integrated view of development, cancer, and aging, and posit that genes are like piano keys: while essential, it is the context that makes the music.
Date: March 9, 2006
Creator: Nelson, Celeste M. & Bissell, Mina J.
Object Type: Article
System: The UNT Digital Library
Surface-Enhanced Raman Scattering (SERS) for Detection in Immunoassays: applications, fundamentals, and optimization (open access)

Surface-Enhanced Raman Scattering (SERS) for Detection in Immunoassays: applications, fundamentals, and optimization

Immunoassays have been utilized for the detection of biological analytes for several decades. Many formats and detection strategies have been explored, each having unique advantages and disadvantages. More recently, surface-enhanced Raman scattering (SERS) has been introduced as a readout method for immunoassays, and has shown great potential to meet many key analytical figures of merit. This technology is in its infancy and this dissertation explores the diversity of this method as well as the mechanism responsible for surface enhancement. Approaches to reduce assay times are also investigated. Implementing the knowledge gained from these studies will lead to a more sensitive immunoassay requiring less time than its predecessors. This dissertation is organized into six sections. The first section includes a literature review of the previous work that led to this dissertation. A general overview of the different approaches to immunoassays is given, outlining the strengths and weaknesses of each. Included is a detailed review of binding kinetics, which is central for decreasing assay times. Next, the theoretical underpinnings of SERS is reviewed at its current level of understanding. Past work has argued that surface plasmon resonance (SPR) of the enhancing substrate influences the SERS signal; therefore, the SPR of the extrinsic …
Date: August 9, 2006
Creator: Driskell, Jeremy Daniel
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Performance Criteria for Residential Zero Energy Windows (open access)

Performance Criteria for Residential Zero Energy Windows

This paper shows that the energy requirements for today's typical efficient window products (i.e. ENERGY STAR{trademark} products) are significant when compared to the needs of Zero Energy Homes (ZEHs). Through the use of whole house energy modeling, typical efficient products are evaluated in five US climates and compared against the requirements for ZEHs. Products which meet these needs are defined as a function of climate. In heating dominated climates, windows with U-factors of 0.10 Btu/hr-ft{sup 2}-F (0.57 W/m{sup 2}-K) will become energy neutral. In mixed heating/cooling climates a low U-factor is not as significant as the ability to modulate from high SHGCs (heating season) to low SHGCs (cooling season).
Date: October 9, 2006
Creator: Arasteh, Dariush; Goudey, Howdy; Huang, Joe; Kohler, Christian & Mitchell, Robin
Object Type: Article
System: The UNT Digital Library
Transient Eddy Current Response Due to a Subsurface Crack in a Conductive Plate (open access)

Transient Eddy Current Response Due to a Subsurface Crack in a Conductive Plate

Eddy current nondestructive evaluation (NDE) is usually carried out by exciting a time harmonic field using an inductive probe. However, a viable alternative is to use transient eddy current NDE in which a current pulse in a driver coil produces a transient .eld in a conductor that decays at a rate dependent on the conductivity and the permeability of the material and the coil configuration. By using transient eddy current, it is possible to estimate the properties of the conductive medium and to locate and size potential .aws from the measured probe response. The fundamental study described in this dissertation seeks to establish a theoretical understanding of the transient eddy current NDE. Compared with the Fourier transform method, the derived analytical formulations are more convenient when the transient eddy current response within a narrow time range is evaluated. The theoretical analysis provides a valuable tool to study the effect of layer thickness, location of defect, crack opening as well as the optimization of probe design. Analytical expressions have been developed to evaluate the transient response due to eddy currents in a conductive plate based on two asymptotic series. One series converges rapidly for a short time regime and the other …
Date: August 9, 2006
Creator: Fu, Fangwei
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Ultrahigh Energy Resolution Gamma-ray Spectrometers for Precision Measurements of Uranium Enrichment (open access)

Ultrahigh Energy Resolution Gamma-ray Spectrometers for Precision Measurements of Uranium Enrichment

Superconducting Gamma-ray detectors offer an order of magnitude higher energy resolution than conventional high-purity germanium detectors. This can significantly increase the precision of non-destructive isotope analysis for nuclear samples where line overlap affects the errors of the measurement. We have developed Gamma-detectors based on superconducting molybdenum-copper sensors and bulk tin absorbers for nuclear science and national security applications. They have, depending on design, an energy resolution between {approx}50 and {approx}150 eV FWHM at {approx}100 keV. Here we apply this detector technology to the measurement of uranium isotope ratios, and discuss the trade-offs between energy resolution and quantum efficiency involved in detector design.
Date: June 9, 2006
Creator: Ali, S; Hau, I D; Niedermayr, T R & Friedrich, S
Object Type: Article
System: The UNT Digital Library
Making and Propagating Elastic Waves: Overview of the new wave propagation code WPP (open access)

Making and Propagating Elastic Waves: Overview of the new wave propagation code WPP

We are developing a new parallel 3D wave propagation code at LLNL called WPP (Wave Propagation Program). WPP is being designed to incorporate the latest developments in embedded boundary and mesh refinement technology for finite difference methods, as well as having an efficient portable implementation to run on the latest supercomputers at LLNL. We are currently exploring seismic wave applications, including a recent effort to compute ground motions for the 1906 Great San Francisco Earthquake. This paper will briefly describe the wave propagation problem, features of our numerical method to model it, implementation of the wave propagation code, and results from the 1906 Great San Francisco Earthquake simulation.
Date: May 9, 2006
Creator: McCandless, K P; Petersson, N A; Nilsson, S; Rodgers, A; Sjogreen, B & Blair, S C
Object Type: Article
System: The UNT Digital Library
Report on coating from Teer (open access)

Report on coating from Teer

A trial coating run has been performed at Teer Coating LTD to assess the use of a barrel coating system as a viable option to coat multilayer spheres. Hollow glass spheres (3M K15) ranging in diameter from 70-120 microns were cleaned in a process using a 0.1 M HCl solution. Comparative photos before and after the cleaning process are shown in figure 1. Approximately, 2 liters of cleaned spheres were sent to Teer for the trial coating in their barrel coater. A picture of barrel coating system is shown in figure 2. The coating process was one layer of titanium followed by one layer of aluminum. The target thickness for each layer is 500 nm, however, no rate runs were performed to calibrate the parameters. Each layer was sputtered for 10 hours, for a total of 20 hours. After the coating process, the coated spheres were sent back to LLNL for SEM analysis. In order to quickly examine the coating in cross-section, the spheres were broken with a spatula. Photos of the broken spheres are shown in Fig 3. One sphere was chosen to look at the uniformity around the sphere. As can be seen in Figure 4, there is …
Date: November 9, 2006
Creator: Florando, J
Object Type: Report
System: The UNT Digital Library
Modeling the Effects of Crevice Former, Partculates, and the Evolving Surface Profile in Crevice Corrsion (open access)

Modeling the Effects of Crevice Former, Partculates, and the Evolving Surface Profile in Crevice Corrsion

Crevice corrosion is an important mode of localized corrosion to be evaluated for the long-term performance of corrosion resistant alloys in high temperature, aqueous environments. This work focuses on the evolution of corrosion damage of Ni-Cr-Mo alloys in hot brines. For the initiation of crevice corrosion, a critical crevice chemistry must develop within the crevice to break down the passive film. The geometry of the crevice and particularly the height of the crevice gap is an important parameter, with tighter crevices being more aggressive. Crevice corrosion models mostly define a smooth walled crevice of uniform gap and do not account for the changing profile after crevice corrosion has initiated. As a complement to the earlier models of the cathodic region, they focus here on the crevice (anodic) region and apply current and potential distribution models to examine the effects of the perturbed surface topography. The analysis focuses on three related issues: (1) the effects surface roughness of the metal and the crevice former, (2) the effects of particulate within the crevice, and (3) the evolution of the crevice profile in the active, anodic region.
Date: June 9, 2006
Creator: Landau, U.; Agarwal, A. S.; Shan, X. & Payer, J. H.
Object Type: Report
System: The UNT Digital Library
Magnetic resonance imaging with an optical atomicmagnetometer (open access)

Magnetic resonance imaging with an optical atomicmagnetometer

Magnetic resonance imaging (MRI) is a noninvasive andversatile methodology that has been applied in many disciplines1,2. Thedetection sensitivity of conventional Faraday detection of MRI depends onthe strength of the static magnetic field and the sample "fillingfactor." Under circumstances where only low magnetic fields can be used,and for samples with low spin density or filling factor, the conventionaldetection sensitivity is compromised. Alternative detection methods withhigh sensitivity in low magnetic fields are thus required. Here we showthe first use of a laser-based atomic magnetometer for MRI detection inlow fields. Our technique also employs remote detection which physicallyseparates the encoding and detection steps3-5, to improve the fillingfactor of the sample. Potentially inexpensive and using a compactapparatus, our technique provides a novel alternative for MRI detectionwith substantially enhanced sensitivity and time resolution whileavoiding the need for cryogenics.
Date: May 9, 2006
Creator: Xu, Shoujun; Yashchuk, Valeriy V.; Donaldson, Marcus H.; Rochester, Simon M.; Budker, Dmitry & Pines, Alexander
Object Type: Article
System: The UNT Digital Library
A Consistent Prescription for the Production Involving MassiveQuarks in Hadron Collisions (open access)

A Consistent Prescription for the Production Involving MassiveQuarks in Hadron Collisions

This paper addresses the issue of production of charm orbottom quarks in association with a high pT process in hadron hadroncollision. These quarks can be produced either as part of the hardscattering process or as a remnant from the structure functions. Thelatter sums terms of the type (alpha_s log(pT/mq))n. If structurefunctions of charm or bottom quarks are used together with a hard processwhich also allows production of these quarks double counting occurs. Thispaper describes the correct procedure and provides two examples of itsimplimentation in single top and Drell-Yan at the LHC.
Date: March 9, 2006
Creator: Kersevan, Borut Paul & Hinchliffe, Ian
Object Type: Article
System: The UNT Digital Library
Effect of Soaking in Hot Saline Solution and Humid Atmosphere on the Passive Film Behavior of a Ni-Cr-Mo Alloy (open access)

Effect of Soaking in Hot Saline Solution and Humid Atmosphere on the Passive Film Behavior of a Ni-Cr-Mo Alloy

Alloy 22, a Ni-Cr-Mo alloy, is the candidate material for fabrication of canisters for disposal of high-level and spent nuclear fuel waste in the proposed Yucca Mountain repository in Nevada. This paper investigated the passive film behavior and corrosion properties on Alloy 22 as a function of soaking in hot, saline environments and in hot, humid atmospheres. Environmental parameters include potential, temperature, pH in chloride and multi-species solutions. Hot, humid exposures are planned for temperatures up to 300 C. Soaking times are planned to extend for up to 1000 hours. This work is part of a multi-investigator study to determine the durability of passive films and localized corrosion processes in metal exposed to moist particulate and deposits. Of particular interest are the long-term stability of the passive film and the effects of soaking in aqueous solutions or hot, humid atmospheres. A combination of electrochemical methods measure changes in passive film properties, and a combination of surface analysis techniques are used to characterize the film composition and structure. Electrochemical methods include Potentiodynamic Polarization tests for the general corrosion behavior; along with Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky (M-S) analysis for electronic properties of the passive films. Alterations in the chemical composition …
Date: June 9, 2006
Creator: Pharkya, P. & Payer, J.H.
Object Type: Report
System: The UNT Digital Library
FY05 LDRD Final Report Coupled Turbulenc/Transport Model for Edge-Plasmas (open access)

FY05 LDRD Final Report Coupled Turbulenc/Transport Model for Edge-Plasmas

An edge-plasma simulation for tokamak fusion devices is developed that couples 3D turbulence and 2D transport, including detailed sources and sinks, to determine self-consistent steady-state plasma profiles. Relaxed iterative coupling is shown to be effective when edge turbulence is partially suppressed, for example, by shear E x B shear flow as occurs during the favorable H-mode region. Unsuppressed turbulence is found to lead to large, intermittent edge transport events where the coupling procedure can lead to substantial inaccuracies in describing the true time-averaged plasma behavior.
Date: February 9, 2006
Creator: Rognlien, T.; Cohen, R.; LoDestro, L.; Palasek, R.; Umansky, M. & Xu, X.
Object Type: Report
System: The UNT Digital Library
Economic Implementation and Optimization of Secondary Oil Recovery (open access)

Economic Implementation and Optimization of Secondary Oil Recovery

The St Mary West Barker Sand Unit (SMWBSU or Unit) located in Lafayette County, Arkansas was unitized for secondary recovery operations in 2002 followed by installation of a pilot injection system in the fall of 2003. A second downdip water injection well was added to the pilot project in 2005 and 450,000 barrels of saltwater has been injected into the reservoir sand to date. Daily injection rates have been improved over initial volumes by hydraulic fracture stimulation of the reservoir sand in the injection wells. Modifications to the injection facilities are currently being designed to increase water injection rates for the pilot flood. A fracture treatment on one of the production wells resulted in a seven-fold increase of oil production. Recent water production and increased oil production in a producer closest to the pilot project indicates possible response to the water injection. The reservoir and wellbore injection performance data obtained during the pilot project will be important to the secondary recovery optimization study for which the DOE grant was awarded. The reservoir characterization portion of the modeling and simulation study is in progress by Strand Energy project staff under the guidance of University of Houston Department of Geosciences professor Dr. …
Date: January 9, 2006
Creator: Brock, Cary D.
Object Type: Report
System: The UNT Digital Library
Entangled Solid-State Circuits (open access)

Entangled Solid-State Circuits

None
Date: August 9, 2006
Creator: Siddiqi, Irfan & Clarke, John
Object Type: Article
System: The UNT Digital Library
QUARKONIUM AT FINITE TEMPERATURE. (open access)

QUARKONIUM AT FINITE TEMPERATURE.

Lattice QCD studies on charmonium at finite temperature are presented After a discussion about problems for the Maximum Entropy Method applied to finite temperature lattice QCD, I show several results on charmonium spectral functions. The 'wave function' of charmonium is also discussed to study the spatial correlation between quark and anti-quark in deconfinement phase.
Date: June 9, 2006
Creator: UMEDA, T.
Object Type: Article
System: The UNT Digital Library
AMMA 2005 Dakar International Conference to be Held November 28-December 2, 2005 (open access)

AMMA 2005 Dakar International Conference to be Held November 28-December 2, 2005

Consistent with the original proposal (dated April 14, 2005), the grant supported the participation in the above conference of a number of West African meteorologists, the majority of whom will be supporting the ARM Mobile Facility deployment in Niamey in various ways during 2006. The following seven individuals were fully funded (complete airfare, accommodation, registration, meals) to participate in the Conference –Yerima Ladan (Head, ASECNA Forecast Office, Niamey Airport); Dr. Ousmane Manga Adamou (University of Niamey); Abdou Adam Abdoul-Aziz Abebe (Forecasater, ASECNA Forecast Office, Niamey Airport); Hassane Abdou (Forecaster, ASECNA Forecast Office, Niamey Airport); Saley Diori (Forecaster, ASECNA Forecast Office, Niamey Airport); Alhassane Diallo (Meteorological Engineer, Burkina Faso Weather Service). The following three individuals were partly funded (for some of their airfare, accommodation, registration, meals) to participate in the Conference – Katiellou Lawan (International Relations, Niger Weather Service); Mamoutou Kouressy (Institute of Rural Economics, Niger Department of Agriculture); and Francis Dide (Benin Weather Service). I am confident that the participation of the above individuals in the Conference will facilitate both the smooth operation of the ARM Mobile Facility in Niamey during 2006 and the involvement of University of Niamey scientists in analysis of the data collected. We appreciate greatly this …
Date: May 9, 2006
Creator: Lamb, Peter
Object Type: Report
System: The UNT Digital Library
Substrate Creep on The Fatigue Life of A Model Dental Multilayer Structure (open access)

Substrate Creep on The Fatigue Life of A Model Dental Multilayer Structure

In this paper, we investigated the effects of substrate creep on the fatigue behavior of a model dental multilayer structure, in which a top glass layer was bonded to a polycarbonate substrate through a dental adhesive. The top glass layers were ground using 120 grit or 600 grit sand papers before bonding to create different sub-surface crack sizes and morphologies. The multilayer structures were tested under cyclic Hertzian contact loading to study crack growth and obtain fatigue life curves. The experiment results showed that the fatigue lives of the multilayer structures were impaired by increasing crack sizes in the sub-surfaces. They were also significantly reduced by the substrate creep when tested at relatively low load levels i.e. P{sub m} < 60 N (Pm is the maximum magnitude of cyclic load). But at relatively high load levels i.e. P{sub m} > 65 N, slow crack growth (SCG) was the major failure mechanisms. A modeling study was then carried out to explore the possible failure mechanisms over a range of load levels. It is found that fatigue life at relatively low load levels can be better estimated by considering the substrate creep effect (SCE).
Date: October 9, 2006
Creator: Zhou, J; Huang, M; Niu, X & soboyejo, W
Object Type: Article
System: The UNT Digital Library