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- Composite materials--Creep (5)
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- Ceramic-matrix composites--Creep (3)
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- Metals--Creep (2)
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- Fiber-reinforced ceramics--Effect of temperature on (1)
- Finite element method--Data processing (1)
- Foam--Thermal properties (1)
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- Fretting corrosion--Mathematical models (1)
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- Functionally gradient materials (1)
- Gallium arsenide (1)
Articles 1 - 23 of 23
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An Exploration Of Several Structural Measurement Techniques For Usage With Functionally Graded Materials, Robert A. Reuter
An Exploration Of Several Structural Measurement Techniques For Usage With Functionally Graded Materials, Robert A. Reuter
Theses and Dissertations
Titanium / titanium boride functionally graded 6"x 1"x1" beams were subjected to a four-point beam test in order to critique the value of several measurement techniques. Also, finite element analysis results were compared with experimental values and general observations about the experiment were recorded. Uniform 85% TiB /15% Ti and uniform commercially pure titanium specimens were also subjected to the same loading conditions as a control. Techniques used include digital image correlation, fiber optic strain gauging, strain gauging, and differential infrared thermography techniques. The strain data results were compared with one another and to linear finite element models. It was …
Effects Of Polishing Shot-Peened Surfaces On Fretting Fatigue Behavior Of Ti-6al-4v, Kasey S. Scheel
Effects Of Polishing Shot-Peened Surfaces On Fretting Fatigue Behavior Of Ti-6al-4v, Kasey S. Scheel
Theses and Dissertations
The research of this thesis was done to investigate the effects of polishing a shot-peened specimen of Ti-6Al-4V on the fretting fatigue life of that specimen. The shot-peening process, though one of the most beneficial techniques in prolonging fretting fatigue life, creates a textured surface that may lead to problems on the micro level. This research was done in an attempt to further improve the peening process by examining the effects of another surface treatment to be used in conjunction, surface polishing. The rough peened surface may contain abrupt changes in surface geometry that act as stress risers, which are …
Modeling Fracture In Z-Pinned Composite Co-Cured Laminates Using Smeared Properties And Cohesive Elements In Dyna3d, Jason K. Freels
Modeling Fracture In Z-Pinned Composite Co-Cured Laminates Using Smeared Properties And Cohesive Elements In Dyna3d, Jason K. Freels
Theses and Dissertations
The purpose of the present research was three-fold: 1) gain a more sophisticated understanding of the response of co-cured composite joints with and without through-thickness reinforcement (TTR), 2) compare the behavior of specimens reinforced with various sizes and densities of reinforcement, and 3) use experimental data to verify the existing DYNA3D smeared property model. Double cantilever beam, end-notch flexure and T-section specimens reinforced with 0.011" diameter z-pins at 2% and 4% volume densities were tested to determine the mode I, mode II and mixed mode (I and II) behavior. Results were added to preliminary research in which tests were conducted …
Effects Of Environment On Creep Behavior Of Two Oxide-Oxide Ceramic Matrix Composites At 1200°C, Pavlos Koutsoukos
Effects Of Environment On Creep Behavior Of Two Oxide-Oxide Ceramic Matrix Composites At 1200°C, Pavlos Koutsoukos
Theses and Dissertations
Previous studies by the advisor and graduate students examined creep behavior of the Nextel720/Alumina CMC in air and in 100% steam environments at 1200 and 1330°C. Results showed that while this oxide/oxide system exhibits an exceptionally high fatigue limit at 1200°C it also experiences substantial strain accumulation under sustained loading conditions. Furthermore, these earlier investigations revealed a significant degrading effect of 100% steam environment on material performance under both static and cyclic loadings. The present effort will investigate creep rupture behavior of Nextel720/Alumina composite in the inert gas environment. In addition, creep rupture behavior of Nextel720/Aluminosilicate CMC will be investigated …
Characterization Of Passivated Indium Antimonide, Catherine Ann Taylor
Characterization Of Passivated Indium Antimonide, Catherine Ann Taylor
Theses and Dissertations
Infrared absorption and photoluminescence measurements have been used to optically characterize bulk-grown, 680-μm thick, indium antimonide (InSb), both as-grown and after passivation by either anodization or a 700-Å layer of silicon oxide (SiOx). Spectra were obtained using Fourier transform infrared (FT-IR) spectroscopy. Results include the effects of sample temperature in the range of 10 to 300 K and 4.636 μm laser pump power in the range of 28 mW to 1.43 W for the photoluminescence spectrum.
Effects Of Frequency And Environment On Fatigue Behavior Of An Oxide-Oxide Ceramic Matrix Composite At 1200°C, Griffin Hetrick
Effects Of Frequency And Environment On Fatigue Behavior Of An Oxide-Oxide Ceramic Matrix Composite At 1200°C, Griffin Hetrick
Theses and Dissertations
Advances in aeronautical engineering in the 21st century depend upon materials that can perform well in extreme environments such as high temperatures and oxidizing conditions. Nextel™720/Alumina (N720/A) is an oxide/oxide ceramic matrix composite with a porous alumina matrix that has been identified as a candidate material for such applications. This research investigated the effects of frequency on fatigue response of N720/A at 1200°C in both air and steam environment. Prior investigation of this material by Eber [8] in 2005 studied fatigue behavior at 1200°C in air and in steam environments at the frequency of 1.0 Hz. The current research focused …
Wear Analysis Of Cu-Al Coating On Ti-6al-4v Under Fretting, Karl N. Murray
Wear Analysis Of Cu-Al Coating On Ti-6al-4v Under Fretting, Karl N. Murray
Theses and Dissertations
The effects of changes in the coefficient of friction (CoF) between the contacting surfaces on the fretting wear characteristics of Cu-Al coating on Ti-6Al-4V were investigated. This Cu-Al coating is part of a system that is applied to titanium turbine blades to reduce fretting at the interface. In the application, there is a solid lubricant that is added on top of the coating as an assembly aid and to help reduce the friction while the lubricant remains within the contact. Previous studies have researched the characteristics of the coating without the additional lubricant. In this study, liquid motor oil was …
Effect Of Environment On Creep Behavior Of An Oxide/Oxide Cfcc With ±45° Fiber Orientation, Gregory T. Siegert
Effect Of Environment On Creep Behavior Of An Oxide/Oxide Cfcc With ±45° Fiber Orientation, Gregory T. Siegert
Theses and Dissertations
Aerospace applications require materials capable of maintaining superior mechanical properties while operating at high temperatures and oxidizing environments. Nextel™ 720/A (N720/A), an oxide/oxide ceramic matrix composite (CMC) with a porous alumina matrix was developed specifically to provide improved long-term properties and performance at 1200°C. This research evaluated the creep behavior of N720/A with a ±45° fiber orientation at 1200°C in: laboratory air, steam, and argon environments. Creep-rupture tests at the creep stress levels of: 45, 40, 35, and 15 MPa were conducted in each environment.
The ultimate tensile strength of N720/A with ±45° fiber orientation was 55 MPa, the elastic …
Optical Characterization Of Thick Growth Orientation-Patterned Gallium Arsenide, Joshua W. Meyer
Optical Characterization Of Thick Growth Orientation-Patterned Gallium Arsenide, Joshua W. Meyer
Theses and Dissertations
Tunable laser sources in the mid-infrared (MIR) spectral range are required for several Air Force applications. Existing lasers with output in the near-infrared can be converted to more desirable MIR by using nonlinear effects. Orientation patterned gallium arsenide (OPGaAs) is a promising nonlinear conversion material because it has broad transparency and can be engineered for specific pump laser and output wavelengths using quasi-phase matching techniques. This research examines the optical quality of seven OPGaAs crystal samples and explores the design of an optical parametric oscillator (OPO) device. The Air Force Research Laboratory Electro-Optical Countermeasures Technology Branch obtained the samples from …
Characterization Of Stress In Gan-On-Sapphire Microelectromechanical Systems (Mems) Structures Using Micro-Raman Spectroscopy, Francisco E. Parada
Characterization Of Stress In Gan-On-Sapphire Microelectromechanical Systems (Mems) Structures Using Micro-Raman Spectroscopy, Francisco E. Parada
Theses and Dissertations
Micro-Raman (µRaman) spectroscopy is an efficient, non-destructive technique widely used to determine the quality of semiconductor materials and microelectromechanical systems. This work characterizes the stress distribution in wurtzite gallium nitride grown on c-plane sapphire substrates by molecular beam epitaxy. This wide bandgap semiconductor material is being considered by the Air Force Research Laboratory for the fabrication of shock-hardened MEMS accelerometers. µRaman spectroscopy is particularly useful for stress characterization because of its ability to measure the spectral shifts in Raman peaks in a material, and correlate those shifts to stress and strain. The spectral peak shift as a function of stress, …
Passive Multiple Beam Combination In Optical Fibers Via Stimulated Brillouin Scattering, Kirk C. Brown
Passive Multiple Beam Combination In Optical Fibers Via Stimulated Brillouin Scattering, Kirk C. Brown
Theses and Dissertations
Many active methods of scaling laser brightness have been demonstrated in recent years. The goal of this research was to demonstrate the feasibility of passively combining multiple laser beams using Stimulated Brillouin Scattering (SBS) in a long multimode optical fiber. This method of combination employed a “Gatling gun” fiber array that allowed several collimated beams to be focused by a lens into an optical fiber. The retroreflected Stokes beam is passed through the center of the beam combiner for analysis. In addition to experimental methodology and equipment used, the theoretical and historical background of SBS in optical fibers is provided. …
Analysis Of Photoconductive Properties In Ge2Sb2Te5 (Gst) Chalcogenide Films For Applications In Novel Electronics, John R. V. Chezem
Analysis Of Photoconductive Properties In Ge2Sb2Te5 (Gst) Chalcogenide Films For Applications In Novel Electronics, John R. V. Chezem
Theses and Dissertations
This thesis investigated the thermal phase-change properties in Ge2Sb2Te5 (GST) chalcogenide-based films and determined the feasibility of coupling the GST with photosensitive DNA material for novel optical device applications. Modeling and testing of GST were researched with the approach that GST would react as a resistive mechanism through thermal manipulation. A test structure was fabricated with a 2-micronmeter MEMS fabrication process. GST material was deposited (by RF sputtering) on the surface of the test structures. The GST was analyzed primarily in the amorphous to crystalline transition states due to more distinct changes in the resistance …
Characterization Of Functionally Graded Materials, Benjamin D. Chapman
Characterization Of Functionally Graded Materials, Benjamin D. Chapman
Theses and Dissertations
The purpose of this study was to characterize the behavior of a functionally graded material through experimentation and analytical modeling. Functionally graded materials are a ceramic metal composite which transitions from metal on one face to ceramic on the opposite face. Creating reliable models required verifying the material properties. This was accomplished through the use of a static modulus of elasticity test as well as a dynamic ping test. The natural frequencies from the dynamic test were compared with finite element models to determine which material properties most accurately represented the functionally graded material. It was found that the material …
Effect Of Hold Times On Fatigue Behavior Of Nextel 720™/Alumina Ceramic Matrix Composite At 1200°C In Air And In Steam Environment, John M. Mehrman
Effect Of Hold Times On Fatigue Behavior Of Nextel 720™/Alumina Ceramic Matrix Composite At 1200°C In Air And In Steam Environment, John M. Mehrman
Theses and Dissertations
The aerospace field requires structural materials that can maintain superior mechanical properties while subjected to high temperatures and oxidizing environments. This research investigated the effect of hold times at maximum load on fatigue performance of a Nextel 720/Alumina ceramic matrix composite at 1200 C, explored the influence of environment on material response to cyclic loading with hold times at maximum load, and assessed the effects of loading history on material behavior and environmental durability. The N720/A composite relies on an oxide/oxide composition for inherent oxidation resistance and a porous matrix with no interphase between the fiber and matrix for damage …
Some Aspects Of The Mechanical Response Of Bmi 5250-4 Neat Resin At 191°C: Experiment And Modeling, John G. Balaconis
Some Aspects Of The Mechanical Response Of Bmi 5250-4 Neat Resin At 191°C: Experiment And Modeling, John G. Balaconis
Theses and Dissertations
The mechanical response of BMI 5250-4 neat resin at 191 degrees C was studied using both creep and recovery tests where several variables were allowed to change. In these tests, the effect of stress rate, prior history, and panel variability were all taken into account. During the creep test, the material showed both primary and secondary creep over 20 h. The recovery tests showed full recovery after it was subjected to 80% UTS. The higher stress rate caused a much greater response in both creep and recovery tests. The prior history was studied by allowing the specimens to go through …
Carrier Lifetime Dynamics Of Epitaxial Layer Hvpe Gallium Arsenide Using Time-Resolved Experiments, Wayne E. Eikenberry
Carrier Lifetime Dynamics Of Epitaxial Layer Hvpe Gallium Arsenide Using Time-Resolved Experiments, Wayne E. Eikenberry
Theses and Dissertations
GaAs is a potential semiconductor material for producing both mid-infrared and terahertz radiation using the new technique of quasi-phase matching in an orientationally patterned GaAs (OP-GaAs) crystal. OP-GaAs is grown using a fast growth process called hydride vapor phase epitaxy (HVPE). Unfortunately, HVPE produces a high number of defects. These defects cause Shockley-Read-Hall recombination rates to dominate over Auger and radiative recombination rates. The carrier lifetime from four OP-GaAs samples are reported here using two different experimental techniques. The first experiment used a streak camera to measure the carrier lifetime via time-resolved photoluminescence. The temporal resolution of the streak camera …
Graphitized Carbon Foam With Phase Change Material, Angelinda D. Fedden
Graphitized Carbon Foam With Phase Change Material, Angelinda D. Fedden
Theses and Dissertations
This thesis examines the transient heating and cooling responses of graphitized carbon foam infiltrated with phase change material (PCM). The carbon foam provides rapid heat transfer throughout the PCM volume, while the PCM stores the heat for later removal. The foam/PCM system was heated with a copper heating block, and then cooled with a liquid-cooled heat removal block. Infiltrating the foam with PCM significantly increased the length of time before the system reached maximum temperature. The temperature response of the foam/PCM system was consistent over multiple cycles of heating and cooling. A high density foam had a faster heating and …
Fretting Fatigue Behavior Of Shot-Peened In 100, Jonathan L. Ng
Fretting Fatigue Behavior Of Shot-Peened In 100, Jonathan L. Ng
Theses and Dissertations
The fretting fatigue behavior of shot-peened of IN 100 was investigated in this study. S-N curves were obtained for two different shot-peened intensities (7A and 12A) and were compared to those of unpeened specimens. Stress relaxation behavior under fretting fatigue was also investigated after their measurements were obtained using the X-ray diffraction method. The crack initiation location and the crack angle orientation along the surface were determined using optical and scanning electron microscopy (SEM). Cracks initiated near the trailing edge and on the contact surface for both 7A and 12A shot-peened specimens. Finite element analysis was performed using commercially available …
Creep-Rupture Behavior Of A Woven Ceramic Matrix Composite At Elevated Temperatures In A Humid Environment, Jennifer L. Ryba
Creep-Rupture Behavior Of A Woven Ceramic Matrix Composite At Elevated Temperatures In A Humid Environment, Jennifer L. Ryba
Theses and Dissertations
This study focused on moisture and temperature effects on the embrittlement and stress-rupture life of the SiC/SiC CMC Syl-iBN/BN/SiC. The Syl-iBN/BN/SiC is composed of Sylramic fibers with an in-situ layer of boron nitride (Syl-iBN), boron nitride interphase (BN), and SiC matrix. Stress rupture tests and monotonic tests were performed on the specimens. Tests were conducted under 100% humidity and laboratory air environments at three temperatures, 450°C, 750°C, and 950°C. These temperatures were chosen because they fall below the intermediate range, within the range, and above the range, respectively. This study found that while this CMC does experience embrittlement at intermediate …
Characterization Of Compressive Creep Behavior Of Oxide/Oxide Composite With Monazite Coating At Elevated Temperature, Patrick R. Jackson
Characterization Of Compressive Creep Behavior Of Oxide/Oxide Composite With Monazite Coating At Elevated Temperature, Patrick R. Jackson
Theses and Dissertations
The compressive creep behavior of a N610/monazite/alumina composite was investigated in this work. The composite consists of a porous alumina matrix reinforced with NextelTM610 fibers coated with monazite in a symmetric cross-ply (0°/90°/0°/90°)s orientation. Compressive stress-strain behavior was investigated as well. The addition of monazite coating resulted in ~ 35% loss in compressive strength at 900°C and in ~45% loss in compressive strength at 1100°C. Compressive creep behavior was examined at 900 and 1100°C for creep stresses ranging from 50 to 95 MPa. Primary and secondary creep regimes were observed at both temperatures. Minimum creep rate was reached in all …
Validation Of A Scaled Plane Strain Hypervelocity Gouging Model, Ronald J. Pendleton
Validation Of A Scaled Plane Strain Hypervelocity Gouging Model, Ronald J. Pendleton
Theses and Dissertations
The phenomenon of high speed impact is of great interest to the Air Force of Scientific Research and the Air Force Research Laboratory's Holloman High Speed test track. Rocket sled tests at the facility frequently are limited to velocities lower than actually attainable due to damage to the rail in the form of gouges. Direct observation of the gouging phenomenon is not currently possible. This leaves computational modeling as the only means to study the phenomenon. A computer model has previously been used to model the development of gouging at the Holloman High Speed Test Track. However, this model has …
Creep-Rupture And Fatigue Behaviors Of Notched Oxide/Oxide Ceramic Matrix Composite At Elevated Temperature, Mark A. Sullivan
Creep-Rupture And Fatigue Behaviors Of Notched Oxide/Oxide Ceramic Matrix Composite At Elevated Temperature, Mark A. Sullivan
Theses and Dissertations
Oxide/oxide composites are being considered for use in high temperature aerospace applications where their inherent resistance to oxidation provides for better long life properties at high temperature than most other ceramic matrix composites (CMCs). One promising oxide/oxide CMC is Nextel 720/A (N720/A) which uses an 8-harness satin weave (8HSW) of Nextel 720 fibers embedded in a porous alumina matrix. Possible aerospace applications for N720/A will likely require inserting holes into the material for mounting and cooling purposes. The notch characteristics must be understood to ensure designs using the material are sufficient for the desired application. This research effort examined the …
Characteristics Of Two-Dimensional Triangular And Three-Dimensional Face-Centered-Cubic Photonic Crystals, Jeffery D. Clark
Characteristics Of Two-Dimensional Triangular And Three-Dimensional Face-Centered-Cubic Photonic Crystals, Jeffery D. Clark
Theses and Dissertations
The fabrication of photonic crystals (PhC) with photonic band gaps (PBG) in the visible range is a difficult task due to the small structural feature sizes of the PhC. The particular type of PhC examined is a two-dimensional (2-D) triangular structure with a PBG designed for visible wavelengths with applications in visible integrated photonic systems. This work examines the processes involved and viability of fabricating 2-D triangular PhC's by a variety of techniques: focused ion beam, electron lithography and holographic photo-polymerization/lithography. The design of the PhC was based on a program created to display gap maps for triangular structures. The …