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Articles 1 - 15 of 15
Full-Text Articles in Engineering
Multiple Channel Laser Beam Combination And Phasing Using Stimulated Brillouin Scattering In Optical Fibers, Brent W. Grime
Multiple Channel Laser Beam Combination And Phasing Using Stimulated Brillouin Scattering In Optical Fibers, Brent W. Grime
Theses and Dissertations
Brightness scaling lasers using stimulated Brillouin scattering (SBS) in optical fibers is explored. A multiple-channel amplifier approach is used to increase the total power of a laser system while avoiding a significant burden on a single channel. The work explores two approaches utilizing both SBS beam cleanup and SBS piston error conjugation. A unique beam combiner that takes advantage of the SBS beam cleanup properties of a long, gradient-index multimode fiber was designed and tested. The beam combiner was developed to combine multiple-channel laser beams simultaneously with high input and output coupling efficiency. The design for the SBS beam combiner …
Rate Dependence And Short Term Creep Behavior Of Pmr-15 Neat Resin At 23 And 288°C, Candice M. Westberry
Rate Dependence And Short Term Creep Behavior Of Pmr-15 Neat Resin At 23 And 288°C, Candice M. Westberry
Theses and Dissertations
This research focuses on experimental investigation of rate-dependent behavior and short-term creep of PMR-15 neat resin at 23 and 288°C. Effect of loading rate on monotonic stress-strain behavior was explored in monotonic tests at constant stress rates of 0.75, 0.075, and 0.0075 MPa/s at 23 and 288°C. In addition, effect of prior stress rate on creep behavior was explored in creep tests preceded by uninterrupted loading to a target stress. At each temperature three creep tests were conducted for a given stress level, where loading rate was changed from test to test. Creep stress levels were 30 and 25 MPa …
Determination Of The Constitutive Equations For 1080 Steel And Vascomax 300, Zachary A. Kennan
Determination Of The Constitutive Equations For 1080 Steel And Vascomax 300, Zachary A. Kennan
Theses and Dissertations
The objective of this research is to establish a better representation of the components utilized in a gouging event being considered in research leading to a better understanding of the Holloman High Speed Test Track. Gouging occurs when two metals are traveling at a slight incline to each other at velocities nearing 1.5 kilometers per second, and results in a structural failure of both the metals. The gouging process occurs at very high strain rates, which results in non-linear stress-strain relations. The coefficients that lead to the Johnson-Cook equations have been determined by the Split Hopkinson Bar test for 1080 …
High Temperature Chemical Degradation Of Pmr-15 Polymer Resins, Grant W. Robinson
High Temperature Chemical Degradation Of Pmr-15 Polymer Resins, Grant W. Robinson
Theses and Dissertations
PMR-15 is a polymer resin for glass and carbon reinforced composites used for high temperature, civilian and military aerospace applications. The harsh environments of PMR-15 applications lead to long term structural degradation and, in turn, impact the readiness capabilities of the system. This study investigated the thermal and oxidative degradation of PMR-15 neat resin powder through the use of thermal gravimetric analysis (TGA) in oxygen, argon and air at isothermal hold temperatures of 260, 288, 316, and 343 °C for 250 hours. The TGA measured the degradation by recording the change in neat resin powder mass versus time. The qualitative …
An Investigation Of A Simplified Gouging Model, Gregory S. Rickerd
An Investigation Of A Simplified Gouging Model, Gregory S. Rickerd
Theses and Dissertations
Gouging is a type of structural failure that becomes important when two metals slide against each other at velocities in the range of 1.5 kilometers per second. A computer model has previously been used to model the development of gouging at the Holloman High Speed Test Track. This model has not been experimentally verified to be correct, due to the complexity of the model. This research develops a simplified model that can be experimentally verified. The computer program utilized in this research was studied to determine the most appropriate options to use in simulations. This was accomplished by modeling a …
Dynamic Characterization Of Thin Deformable Pvdf Mirror, Eric M. Trad
Dynamic Characterization Of Thin Deformable Pvdf Mirror, Eric M. Trad
Theses and Dissertations
Methodology for the design and fabrication of 5 inch diameter membrane-like mirror structures is explored, resulting in test articles with areal densities as low as 1.57 kg/m2 and a thickness of 1.5 mm. Each optical structure has 7 control patches etched into the PVDF layer, which can be used as actuators. These test articles are utilized to demonstrate the capabilities of an acquisition system to make measurements of static and dynamic actuation of the mirror surface. Static deformations are analyzed statistically and determined to yield maximum deformations in the actuated regions of -2.1 micro with a standard deviation of 0.33 …
Biaxial Fatigue Behavior Of Niti Shape Memory Alloy, Daniel M. Jensen
Biaxial Fatigue Behavior Of Niti Shape Memory Alloy, Daniel M. Jensen
Theses and Dissertations
Nitinol is a shape memory alloy (SMA) capable of martensite-to-austenite phase transformations enabling shape-memory behavior. Shape-memory properties make Nitinol a strong candidate material for use in aircraft applications such as actuators. Structural integrity and reliability of torque tube actuators must be assured before this material can be used in flight-critical components. Thorough understanding of the fatigue response of the material is essential for a structurally-sound SMA actuator design. The present effort investigates pure torsion and combined tension-torsion fatigue behavior of Nitinol at room temperature. Monotonic tests in tension and torsion were conducted to typify uni-directional stress-strain behavior. Fully-reversed torsion fatigue …
Tensile Stress Rupture Behavior Of A Woven Ceramic Matrix Composite In Humid Environments At Intermediate Temperature, Kevin J. Larochelle
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 …
Effects Of Temperature And Shot-Peening Intensity On Fretting Fatigue Behavior Of Titanium Alloy Ti-6al-4a, Salman Albinali
Effects Of Temperature And Shot-Peening Intensity On Fretting Fatigue Behavior Of Titanium Alloy Ti-6al-4a, Salman Albinali
Theses and Dissertations
Effects of temperature and shot-peening intensity on fretting fatigue behavior of Ti-6Al-4A were investigated in this study. S-N curves were obtained for both room and elevated temperatures (260 C) for two different shot-peened intensities (4A and 10A). Stress relaxation behavior under both fretting fatigue at elevated temperature and temperature exposure only were also investigated after their measurements were calculated using 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 of the tested specimens. Cracks initiated on the contact surface …
Application Of Functionally Graded Materials In Aircraft Structures, William G. Cooley
Application Of Functionally Graded Materials In Aircraft Structures, William G. Cooley
Theses and Dissertations
A Functionally Graded Material (FGM) is a material which has a continuous variation of material properties through-the-thickness. This thesis will explore analysis of FGM flat plates and shell panels, and use FGM's unique characteristics to retrofit a cracked exhaust wash structure. FGMs are first characterized as flat plates under pressure and thermal loading. Next, FGM shell panels are characterized under thermal loading. Conclusions drawn from FGM characterization are used to develop a patch to retrofit a cracked aircraft exhaust wash structure. The exhaust wash structure is first analyzed to provide a baseline and then several FGM patches are evaluated on …
Creep Behavior Of An Oxide/Oxide Composite With Monazite Coating At Elevated Temperatures, Sean S. Musil
Creep Behavior Of An Oxide/Oxide Composite With Monazite Coating At Elevated Temperatures, Sean S. Musil
Theses and Dissertations
This study focuses on experimental investigation of stress-rupture behavior (creep response) of an oxide/oxide composite in a cross-ply (0/90) lay-up at elevated temperature. The test material, Nextel 610/monazite/alumina composite, employs monazite, an oxidation-resistant interfacial coating designed to improve performance at elevated temperatures. The experimental program included monotonic tensile tests to failure and creep-rupture tests at elevated temperatures. Tensile tests served to establish an ultimate tensile strength (UTS) for the material. The ensuing creep-rupture tests involved stress levels at varying percentages of the UTS. Stress-rupture curves at 900 and 1100 degrees C were established. A family of creep curves for various …
Experimentation And Analysis Of Composite Scarf Joint, Benjamin M. Cook
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 …
Effect Of Temperature And Steam Environment On Fatigue Behavior Of An Oxide-Oxide Continuous Fiber Ceramic Composite, Chalene A. Eber
Effect Of Temperature And Steam Environment On Fatigue Behavior Of An Oxide-Oxide Continuous Fiber Ceramic Composite, Chalene A. Eber
Theses and Dissertations
There is an ever-increasing need for materials that maintain high strength and fracture toughness at elevated temperatures and in complex environments. Advanced aerospace applications are motivating the development of composite materials that can meet demanding requirements. This research effort investigates mechanical behavior of an oxide-oxide continuous fiber ceramic composite (CFCC) consisting of a porous alumina matrix reinforced with mullite/alumina Nextel 720 fibers developed specifically for advanced aerospace applications. Tension-tension fatigue behavior of this CFCC was studied at 1200 and 1330 °C in laboratory air and 100% steam environments. Fatigue resistance and retained strength properties were determined. Effects of environmental degradation …
Thermal Characteristics Of Pitch Based Carbon Foam And Phase Change Materials, Kevin W. Wierschke
Thermal Characteristics Of Pitch Based Carbon Foam And Phase Change Materials, Kevin W. Wierschke
Theses and Dissertations
Phase-change thermal energy storage devices offer thermal control systems an option that allows a smaller heat sink to be used by absorbing the thermal energy quickly and storing it in the phase change to prevent failure of electronic components and then slowly releasing the heat to the heat sink. This paper experimentally determined the transient response of carbon foam with a phase-change material by measuring the response to a step temperature input to test samples. The transient response was recorded until steady state was reached. An analytic response was created and compared against the measured response. A simplified analytic prediction …
Detection Of Residual Stress In Sic Mems Using Μ-Raman Spectroscopy, John C. Zingarelli
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 …