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Articles 9091 - 9120 of 11510

Full-Text Articles in Engineering

Experimentation And Analysis Of Composite Scarf Joint, Benjamin M. Cook Mar 2005

Experimentation And Analysis Of Composite Scarf Joint, Benjamin M. Cook

Theses and Dissertations

Composite bonded scarf repairs were examined by experimentally measuring and analytically predicting the residual curing strains and strains due to mechanical loading. To accomplish this a three prong approach was used: a full strain field through a repaired laminate's thickness was measured for both a loaded specimen and a specimen with the residual strain released, models were developed for comparison to both states, and data was collected for large tensile test specimens at various stages of being scarf repaired. A ~14:1 straight scarfed one-inch wide specimen was used to collect Moire interferometry data to calculate a full strain field due …

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Creep-Rupture Behavior Of An Oxide/Oxide Ceramic Matrix Composite At Elevated Temperatures In Air And Steam Environments, Lee B. Harlen Mar 2005

Creep-Rupture Behavior Of An Oxide/Oxide Ceramic Matrix Composite At Elevated Temperatures In Air And Steam Environments, Lee B. Harlen

Theses and Dissertations

Oxide/oxide ceramic matrix composites (CMCs) are being considered for applications such as jet engine combustion chambers and afterburner flaps. Nextel™ 720/A (N720/A), an oxide/oxide CMC with an alumina matrix and no interphase at the fiber-matrix interface, was developed specifically to provide improved long-term properties and performance at 1200°C. This study focused on experimental investigation of creep behavior of N720/A [0/90] at elevated temperatures in laboratory air and in 100% steam environment. Monotonic tensile tests to failure were performed at 23, 1200, and 1330°C. Ultimate tensile strength (UTS) values were established and monotonic stress-strain curves were produced. Creep-rupture tests at 1200°C …

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A Systems Architectural Model For Man-Packable/Operable Intelligence, Surveillance, And Reconnaissance Mini/Micro Aerial Vehicles, Cory A. Cooper, Matthew L. Ewoldt, Steaven A. Meyer, Edward W. Talley Mar 2005

A Systems Architectural Model For Man-Packable/Operable Intelligence, Surveillance, And Reconnaissance Mini/Micro Aerial Vehicles, Cory A. Cooper, Matthew L. Ewoldt, Steaven A. Meyer, Edward W. Talley

Theses and Dissertations

With the increase in both technology push and operational pull of mini/micro aerial vehicles (MAVs) within DoD organizations, an understanding of their interactions and capabilities is necessary. Many MAVs have already been developed for a specific usage and much speculation has been made on their future uses. Despite the growth of MAVs, there is currently no overarching systems architecture which would envelop and guide the DoD's MAV development efforts. The goal of this thesis is to apply sound systems engineering principals to develop a MAV architectural model describing their use in three separate but closely related mission areas: Over-the-Hill-Reconnaissance, Battle …

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Modeling And Simulation Of Commercial Satellite Imagery Processes, David A. Shultz Mar 2005

Modeling And Simulation Of Commercial Satellite Imagery Processes, David A. Shultz

Theses and Dissertations

The purpose of this research was to develop a general, statistical model of order-to-delivery times for commercial satellite imagery. The research looked at the current four satellite providers with 3-meter or better imagers in the context of a generalized model of commercial imaging satellite operations. Existing methods use orbit analysis tools to determine the imaging time of a specified target based on defined satellite position and times, but can only develop shortest and longest times to an imaging opportunity. To address the general question of the time it takes to deliver an image for non-specific targets, this research develops a …

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Timing Of Increasing Electron Counts From Geosynchronous Orbit To Low Earth Orbit, Kirk M. Olson Mar 2005

Timing Of Increasing Electron Counts From Geosynchronous Orbit To Low Earth Orbit, Kirk M. Olson

Theses and Dissertations

Under certain conditions, high energy electron fluxes can increase over short periods of time in the outer radiation belt and diffuse to low altitudes. Sudden increases of high energy electron densities at low altitudes can drastically damage unsuspecting low-earth-orbit satellites. The progression of electron flux increases from a geosynchronous orbit to low-earth orbit during an electron event is somewhat unknown. If the beginning of electron flux increases at low-earth-orbits could be anticipated, warnings could be issued to space system operators allowing time to take proper measures to protect and minimize satellite damage extending satellite lifetimes and space mission operations. The …

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Electro-Optic Beam Steering Using Domain Engineered Lithium Tantalate, Daren J. Chauvin Mar 2005

Electro-Optic Beam Steering Using Domain Engineered Lithium Tantalate, Daren J. Chauvin

Theses and Dissertations

The operation of a 14-channel five stage electro-optic beam steering device was studied. Beam deflection scanned from 0° to 10.1° was demonstrated. The maximum angle is within 0.3% of design. Many laser systems in operation today implement mechanical beam steering methods that are often expensive in terms of cost, weight and power. They are slow and subject to wear and vibration. A non-inertial beam scanning mechanism, such as one based on the device studied in this research could enhance the performance of these systems. The device studied here is fabricated in LiTaO3 using micro-patterned domain reversal. The 14 channels …

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Detection Of Residual Stress In Sic Mems Using Μ-Raman Spectroscopy, John C. Zingarelli Mar 2005

Detection Of Residual Stress In Sic Mems Using Μ-Raman Spectroscopy, John C. Zingarelli

Theses and Dissertations

Micro-Raman (µ-Raman) spectroscopy is used to measure residual stress in two silicon carbide (SiC) poly-types: single-crystal, hexagonally symmetric 6H-SiC, and polycrystalline, cubic 3C-SiC thin films deposited on Si substrates. Both are used in micro-electrical-mechanical systems (MEMS) devices. By employing an incorporated piezoelectric stage with submicron positioning capabilities along with the Raman spectral acquisition, spatial scans are performed to reveal areas in the 6H-SiC MEMS structures that contain residual stress. Shifts in the transverse optical (TO) Stokes peaks of up to 2 cm-1 are correlated to the material strain induced by the MEMS fabrication process through the development of phonon …

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Lethality Of Bacillus Anthracis Spores Due To Short Duration Heating Measured Using Infrared Spectroscopy, Kristina M. Goetz Mar 2005

Lethality Of Bacillus Anthracis Spores Due To Short Duration Heating Measured Using Infrared Spectroscopy, Kristina M. Goetz

Theses and Dissertations

There are a number of analytical and semi-empirical models that describe the behavior of particulate matter in the atmosphere. Many of these require modification for all types of weather, dry versus wet deposition, and overall effects can be quite non-linear. Rainfall (rate, drop size, etc.), snowfall (rate, flake size, etc.), humidity, pressure, temperature, and combination of these greatly affect particle settling and washout rates. To that end, a method for tracking released constituents using the Regional Atmospheric Modeling System (RAMS) microphysics package is developed by modifying one of the hydrometeor categories (hail) in the microphysics package. The RAMS microphysics package …

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A Comparison Of The Heft Subsurface And Delfic Particle Size Distributions And Effects In Hpac, Eric T. Skaar Mar 2005

A Comparison Of The Heft Subsurface And Delfic Particle Size Distributions And Effects In Hpac, Eric T. Skaar

Theses and Dissertations

The Heft subsurface three component lognormal fallout particle size distribution is compared and contrasted with the single lognormal fallout particle size distribution used by the Defense Land Fallout Interpretive Code (DELFIC). Comparison of the two distributions is accomplished with results from the AFIT smear code and the Hazard Prediction and Assessment Capability (HPAC). The effect of the distributions is explored in HPAC for varying yield weapons, varying surfaces, precipitation conditions, varying wind effects and varying dose rate times. The results from the two distributions are quantitatively compared using the concepts of grounded source normalization constant and the rate at which …

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Temperature Dependent Current-Voltage Measurements Of Neutron Irradiated Al0.27Ga0.73N/Gan Modulation Doped Field Effect Transistors, Troy A. Uhlman Mar 2005

Temperature Dependent Current-Voltage Measurements Of Neutron Irradiated Al0.27Ga0.73N/Gan Modulation Doped Field Effect Transistors, Troy A. Uhlman

Theses and Dissertations

In this research, the first ever neutron irradiation study of AlGaN/GaN MODFETs was conducted. Devices irradiated to a total 1 MeV Eq (Si) neutron fluence of 1.2x1016 n/sq cm demonstrated the temperature dependence of irradiation and annealing. Devices irradiated at 80 K exhibited significant persistent electrical degradation at only 5.4 rad (Si), whereas those irradiated at elevated temperatures exhibit transient increases in gate and drain current up to 400 krad (Si). I-V measurements indicate substantial radiation-induced increased gate and drain currents occur only at low-temperature irradiations. The introduction of a high-density of donor defects is hypothesized as the primary …

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Modeling Groundwater Flow And Contaminant Transporting Fractured Aquifers, Jason M. Bordas Mar 2005

Modeling Groundwater Flow And Contaminant Transporting Fractured Aquifers, Jason M. Bordas

Theses and Dissertations

The hybrid discrete fracture network/equivalent porous medium (DFN/EPM) model was selected for analysis and application to simulate a contaminated site in this study. The DFN/EPM was selected because it appeared to have the potential to aid decision making by remedial project managers at contaminated DoD fractured aquifer sites. This model can use data that are typically available at a site while incorporating the important processes relevant to describing contaminant transport in a fractured medium. The model was applied to simulate the operation of a pump-and-treat remedial action at a trichloroethene-contaminated fractured aquifer at Pease AFB. The model was able to …

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Using Value-Focused Thinking To Evaluate The Practicality Of Ground-Source Heat Pumps At Military Installations, Jimmy J. Jeoun Mar 2005

Using Value-Focused Thinking To Evaluate The Practicality Of Ground-Source Heat Pumps At Military Installations, Jimmy J. Jeoun

Theses and Dissertations

Because of potential cost and energy savings, military decision-makers may want to consider the use of energy-efficient heating, ventilating, and air-conditioning (HVAC) systems at their installations. Ground source heat pumps (GSHPs), in particular, show great promise because of their low energy requirements and low life-cycle costs. However, there currently exists no design guidance or established criteria for HVAC selection. Consequently, military decision-makers have no basis for comparing conventional HVAC systems and GSHPs. The Value-Focused Thinking (VFT) methodology was used to create a multi-objective decision analysis model that measures the value of different HVAC systems. Consisting of five bottom-tier values and …

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Comparing Management Approaches For Automatic Test Systems: A Strategic Missile Case Study, William C. Ford Mar 2005

Comparing Management Approaches For Automatic Test Systems: A Strategic Missile Case Study, William C. Ford

Theses and Dissertations

From 1980 to 1992, the DoD spent over $50 billion acquiring Automatic Test Systems (ATS) used to test weapon systems. At that time, procuring unique ATS to support single weapon systems was the norm. In 1994, the DoD made a dramatic change to their ATS acquisition policy; common ATS that supported multiple weapon systems was preferred over ATS tailored to support a single weapon system. Expected benefits of this new policy included: more reliable equipment, increased supportability, decreased cost, smaller logistics footprint, and decreased manning. To date, the common ATS initiative has garnered little support AF-wide due to lack of …

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Output Analysis And Comparison Of Deployment Models With Varying Fidelity, Matthew M. Gill Mar 2005

Output Analysis And Comparison Of Deployment Models With Varying Fidelity, Matthew M. Gill

Theses and Dissertations

This thesis explores the changes in insights that result from using different types of models to assess the capability of deploying the Stryker Brigade within specific timeline goals. The thesis uses as its primary base a study conducted in 2002 by USTRANSCOM to evaluate the ability of Stryker to meet stated deployment timeline goals. Specifically, the author compares the outputs from four different models as they change over three different deployment scenarios and 10 different routes. The study investigates the relationships among the outputs of spreadsheet models, spreadsheet models with elements of variability added, and low- and high-level discrete-event simulations. …

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Evaluating Management Strategies For Automated Test Systems/Equipment (Ats/E): An F-15 Case Study, Jeremy A. Howe Mar 2005

Evaluating Management Strategies For Automated Test Systems/Equipment (Ats/E): An F-15 Case Study, Jeremy A. Howe

Theses and Dissertations

The management of United States Air Force ATS/E presents a variety of issues that affect the long-term capability and mission readiness of weapon systems. Traditional procurement processes suggest that individual aircraft platform System Program Offices (SPOs) developed, improved and replaced ATE on an "as-required" basis. Increased obsolescence, however, and a concern for maintaining longer-term viability provided the necessary inertia for a movement towards the procurement and development of consolidated, common test equipment that would support multiple weapon systems. In 1998, the Air Force Chief of Staff directed HQ AFMC to establish a Common Support Equipment office to facilitate the combination …

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Estimating Resource Requirements To Support Multi-Echelon F-15e Deployments, David R. Maxwell Mar 2005

Estimating Resource Requirements To Support Multi-Echelon F-15e Deployments, David R. Maxwell

Theses and Dissertations

Since the end of the Cold War, the United States has become focused on developing the capability to rapidly respond to emerging crises. Strategic and operation planning play key roles in order to effectively implement this concept. During the planning process, separate courses of action (COAs) are developed. These COAs are evaluated based upon their operational effect, resource availability, nuclear and transportation feasibility. Currently, transportation feasibility assessments are based on the resources contained within a full Unit Type Code (UTC). Some COAs are eliminated based on these factors. However, most deployments occur at reduced levels. Situational factors, such as the …

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Determining Pacaf Transportation Alternatives To The General Purpose Vehicle, Andrew H. Pate Mar 2005

Determining Pacaf Transportation Alternatives To The General Purpose Vehicle, Andrew H. Pate

Theses and Dissertations

Vehicle fleets under gird the mission of Air Force bases. Under funding for vehicle replacement requirements raised concerns and has led to purchasing alternative vehicles classified as equipment items to supplement budget shortfalls. In order to effectively use funds and meet mission requirements, Pacific Air Force (PACAF) commanders need an adjustable multifactor decision tool that will allow them to make an informed purchasing decision from among appropriately classified equipment item vehicles. This research will discuss existing regulatory restrictions to alternative transportation purchases, consider available alternative vehicles, and determine the attributes important to vehicle purchases. A review of current Air Force …

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Optimization Model For Base-Level Delivery Routes And Crew Scheduling, Young-Ho Cha Mar 2005

Optimization Model For Base-Level Delivery Routes And Crew Scheduling, Young-Ho Cha

Theses and Dissertations

In the U.S. Air Force, a Logistic Readiness Squadron (LRS) provides material management, distribution, and oversight of contingency operations. Dispatchers in the LRS must quickly prepare schedules that meet the needs of their customers while dealing with real-world constraints, such as time windows, delivery priorities, and intermittent recurring missions. Currently, LRS vehicle operation elements are faced with a shortage of manpower and lack an efficient scheduling algorithm and tool. The purpose of this research is to enhance the dispatchers' capability to handle flexible situations and produce "good" schedules within current manpower restrictions. In this research, a new scheduling model and …

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Stochastic Capability Models For Degrading Satellite Constellations, Cole W. Gulyas Mar 2005

Stochastic Capability Models For Degrading Satellite Constellations, Cole W. Gulyas

Theses and Dissertations

This thesis proposes and analyzes a new measure of functional capability for satellite constellations that incorporates the instantaneous availability and mission effectiveness of individual satellites. The capability measure yields a continuous score between zero and one accounting for the degree to which the constellation meets operational requirements. The measure is computed from an average of satellite capabilities, composed of the product of the satellite's instantaneous availability and value score. Instantaneous availability is acquired by modeling the satellite degradation status as either a time-homogenous, continuous-time Markov chain (CTMC) if it possesses functions with exponential lifetime distributions, or as a time-homogenous, semi-Markov …

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An Investigation Of The Effects Of Correlation And Autocorrelation In Classifier Fusion With Non-Declarations, Frank M. Mindrup Mar 2005

An Investigation Of The Effects Of Correlation And Autocorrelation In Classifier Fusion With Non-Declarations, Frank M. Mindrup

Theses and Dissertations

Air Force doctrine requires reliable and accurate information when striking targets. Further, this doctrine states that fusion should be utilized whenever possible to ensure the best possible information is conveyed; there is no specific guidance as to how to fuse this information. This thesis extends the research found in Leap, Bauer, and Oxley (2004) to include a non-declared class. The Identification system operating characteristic (ISOC) was adapted to allow for non-declarations both at the individual sensor level as well as the fused output level. A probabilistic neural network (PNN) was also used as a fusion technique. A cost function was …

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Selection And Application Of Distorted Risk Measures, Edwin J. Offutt Mar 2005

Selection And Application Of Distorted Risk Measures, Edwin J. Offutt

Theses and Dissertations

This thesis develops and illustrates a methodology for the selection of probability distributions and distortion functions associated with risk scenarios resulting from military capability shortfalls. Distorted (or transformed) risk measures are analyzed and applied to account for loss scenarios that may occur with low frequency but result in catastrophic outcomes. After reviewing the rudimentary concepts of distortion, four well-known continuous distributions, suitable for modeling risk scenarios, are chosen using defined criteria. Based on subject matter expert inputs, a simple method for assigning exactly one of the four distributions to any risk scenario is proposed. Four parametric distortion functions from the …

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Optimal Sampling Of A Chemical Hazard Area, Jennifer R. Plourde Mar 2005

Optimal Sampling Of A Chemical Hazard Area, Jennifer R. Plourde

Theses and Dissertations

This thesis proposes a methodology for optimally sampling a chemical hazard area subsequent to a chemical weapons attack. The objective is to identify the maximum number of areas that no longer require protective gear for safe operations. We model the area as an undirected graph and employ network analysis techniques to provide a methodological framework for identifying an optimal sampling sequence within a fixed time limit. We propose four models that characterize the secondary vapor concentrations: i) static and deterministic, ii) static and stochastic, iii) dynamic and deterministic, and iv) dynamic and stochastic. Comparisons of the static cases and their …

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Strategic Airlift En Route Analysis And Considerations To Support The Global War On Terrorism, Michael C. Sere Mar 2005

Strategic Airlift En Route Analysis And Considerations To Support The Global War On Terrorism, Michael C. Sere

Theses and Dissertations

The Global War on Terrorism has mandated the need for additional global en route airfields. En route airfields consist of bases that are strategically located at intermediate locations between the Continental United States and the intended theater of operations. These airfields serve as refueling, crew staging, or maintenance stops for strategic airlift aircraft flying transoceanic routes. The focus of this study is to examine concepts to meet this need and to address important aspects that should be considered in devising new en route strategies. Based on various important factors associated with potential en route airfields, a goal programming methodology was …

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An Evaluation Of Wind Turbine Technology At Peterson Afb, Randy C. Combs Mar 2005

An Evaluation Of Wind Turbine Technology At Peterson Afb, Randy C. Combs

Theses and Dissertations

Wind energy technology is a viable source for attaining the emission reduction and renewable energy use goals set forth by the executive office. In accordance with Executive Orders, the Air Force must reduce greenhouse emissions and energy consumption, and expand the use of renewable energy sources within its facilities nation-wide by year 2010. This mandate requires that the Air Force look at alternative electrical production and rely more on such renewable energy resources as wind power. The specific problem addressed by this research is whether on-site wind energy generation can be more economically feasible than the conventional energy consumption at …

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A Qualitative Study Of Industry And Air Force Commodity Council Processes, Robert J. Irvine Mar 2005

A Qualitative Study Of Industry And Air Force Commodity Council Processes, Robert J. Irvine

Theses and Dissertations

The purpose of this research was to compare industry and Air Force commodity council processes. More specifically, this research used a survey to gather strategic sourcing philosophies and procedures (with respect to small business participation in procurement strategies) from successful industry firms. Industry source selection documentation, applicable government contracting guidelines, and a literature review of strategic sourcing materials were also reviewed. The current Air Force commodity council process and associated historical documents were then studied using a business process modeling tool. It was determined that the Air Force process differs from industry in how small business participation is addressed, the …

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An Analysis Into The Effectiveness Of Aircraft Maintenance Under The Combat Wing Structure, Derrick R. Barthol Mar 2005

An Analysis Into The Effectiveness Of Aircraft Maintenance Under The Combat Wing Structure, Derrick R. Barthol

Theses and Dissertations

Organizational structure builds the foundation from which organizations operate. To gain full potential of structural efficiencies in the current operating environment, public and private firms are continually modifying their organizational structure. The U.S. Air Force is no different and underwent its most recent reorganization in the fall of 2002 replacing the post-Gulf War format of the previous decade. Air Force leadership needs to understand how well the current structure is performing at achieving its intended objectives. This research investigates the effectiveness of the recent change to Air Force organizational structure on aircraft maintenance performance through an analysis of aircraft maintenance …

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An Approach For Optimizing The On-Orbit Servicing Architecture For The Space-Based Radar Constellation, Michael L. Mcconnell Mar 2005

An Approach For Optimizing The On-Orbit Servicing Architecture For The Space-Based Radar Constellation, Michael L. Mcconnell

Theses and Dissertations

Satellite systems, once operational, are essentially a consumable item with no capacity to maintain, repair, or upgrade them while on-orbit. In order to avoid having to replace costly space assets, the Defense Advanced Research Projects Agency (DARPA) and Air Force Space Command (AFSPC) are looking to developing programs to provide an on-orbit servicing capability for future satellite systems under development, such as the Space-Based Radar (SBR) system. DARPA and AFSPC are studying on-orbit servicing using the Orbital Express platform as part of an Analysis of Alternatives for the SBR program. Like their satellite clients, on-orbit servicing assets are expected to …

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Barriers To Electronic Records Management (Erm): An Exploratory Case Study Investigating Erm In The Deployed Environment During Operations Enduring Freedom And Iraqi Freedom, Brian G. Hobbs Mar 2005

Barriers To Electronic Records Management (Erm): An Exploratory Case Study Investigating Erm In The Deployed Environment During Operations Enduring Freedom And Iraqi Freedom, Brian G. Hobbs

Theses and Dissertations

Corporate and government organizations can use electronic records as an important strategic resource, if the records are managed properly. In addition to meeting legal requirements, electronic records can play a vital role in the management and operation of an organization's activities. Corporate America is facing challenges in managing electronic records, and so too is the U.S. Air Force (USAF). The deployed environment is particularly problematic for electronic records management (ERM). This research, thus, investigates ERM in the deployed environment to identify and characterize the barriers faced by USAF personnel who deployed to locations supporting Operations Enduring Freedom and Iraqi Freedom. …

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Tensile Stress Rupture Behavior Of A Woven Ceramic Matrix Composite In Humid Environments At Intermediate Temperature, Kevin J. Larochelle Mar 2005

Tensile Stress Rupture Behavior Of A Woven Ceramic Matrix Composite In Humid Environments At Intermediate Temperature, Kevin J. Larochelle

Theses and Dissertations

Stress rupture tests on the SylramicTM fiber with an in-situ layer of boron nitride, boron nitride interphase, and SiC matrix ceramic matrix composite were performed at 550°C and 750°C with 0.0, 0.2, or 0.6 atm partial pressure of water vapor, pH2O. The 550°C, 100-hr strengths were 75%, 65% and 51% of the monotonic room temperature tensile strength, respectively. At 750°C, the strengths were 67%, 51%, and 49%, respectively. Field Emission Scanning Electron Microscopy analysis estimated the total embrittlement times for 550°C with 0.0, 0.2, and 0.6 atm pH2O were >63 hrs, >38 hrs, and between …

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Pulse Detonation Engine Thrust Tube Heat Exchanger For Flash Vaporization And Supercritical Heating Of Jp-8, Christen L. Miser Mar 2005

Pulse Detonation Engine Thrust Tube Heat Exchanger For Flash Vaporization And Supercritical Heating Of Jp-8, Christen L. Miser

Theses and Dissertations

Research has shown that performance of liquid hydrocarbon fueled pulse detonation engines is limited by the time required to evaporate liquid fuel droplets within the mixture. Vaporization of liquid fuels prior to injection has been shown to decrease ignition times and also increases fuel efficiency; however, the size and efficiency of the vaporization system used are not feasible for use in future pulse detonation aircraft concepts. The purpose of this research is to harness the waste heat of pulse detonation engine thrust tubes to generate a steady-state, self-sustained flash vaporization and supercritical heating system using JP-8 as the working fluid …

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