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Theses and Dissertations

2006

Articles 1 - 18 of 18

Full-Text Articles in Engineering Science and Materials

Some Aspects Of The Mechanical Response Of Pmr-15 Neat Resin At 288°C: Experiment And Modeling, Christina M. Falcone Sep 2006

Some Aspects Of The Mechanical Response Of Pmr-15 Neat Resin At 288°C: Experiment And Modeling, Christina M. Falcone

Theses and Dissertations

The mechanical response of PMR-15 neat resin was investigated at 288?C. Monotonic loading/unloading tests performed at several constant stress rates revealed considerable rate dependence, especially on the unloading path. Effect of prior stress rate on creep behavior was evaluated in creep tests preceded by uninterrupted loading to a target stress. Creep response was dependent on the prior stress rate. Effect of loading history was studied in stepwise creep tests, where specimens were subjected to a constant stress rate loading followed by unloading to zero stress with intermittent creep periods during both loading and unloading. Comparison of creep strains accumulated during …

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Effects Of Polishing Shot-Peened Surfaces On Fretting Fatigue Behavior Of Ti-6al-4v, Kasey S. Scheel Sep 2006

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 …

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Rate Dependence Of Tensile Properties And Stress-Strain Behavior Of An Oxide/Oxide Ceramic Matrix Composite At Elevated Temperature And The Effects Of Low-Magnitude Sustained Loading On Composite Microstructure, Andrew T. Radzicki Sep 2006

Rate Dependence Of Tensile Properties And Stress-Strain Behavior Of An Oxide/Oxide Ceramic Matrix Composite At Elevated Temperature And The Effects Of Low-Magnitude Sustained Loading On Composite Microstructure, Andrew T. Radzicki

Theses and Dissertations

Advanced aerospace structures and components require materials that exhibit high strength at high operating temperatures. Nextel ™ 720/Alumina (N720/A) is an oxide/oxide, porous-matrix ceramic-matrix composite developed for load bearing applications at elevated temperatures. The current research investigates the rate dependence of tensile properties of the N720/A CMC at 1200°C as well as the creep behavior of this composite under applied stresses in the 1-25 MPa range. In addition, influence of prior loading rate on the creep response of N720/A under applied stresses above 50 MPa was evaluated at 1200°C. Tensile tests conducted at loading rate of 0.0025 and 25 MPa/s …

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Effects Of Environment On Creep Behavior Of Two Oxide-Oxide Ceramic Matrix Composites At 1200°C, Pavlos Koutsoukos Sep 2006

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 …

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Effects Of Phase Difference Between Axial And Contact Loads On Fretting Fatigue Behavior Of Titanium Alloy, Mohammad Almajali Sep 2006

Effects Of Phase Difference Between Axial And Contact Loads On Fretting Fatigue Behavior Of Titanium Alloy, Mohammad Almajali

Theses and Dissertations

Fretting fatigue is the surface damage that occurs at the interface between two components that are undergoing a small amplitude oscillatory movements. It results in a reduction of the material life as compared to the plain fatigue. Most of the previous works were accomplished under a constant applied normal load and a little effort was done under a variable contact load, while none of these studies has considered the phase difference between the axial load and the contact load. The primary goal of this study is to investigate the effect of phase difference between axial and contact loads on fretting …

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Effect Of Environment On Creep Behavior Of An Oxide/Oxide Cfcc With ±45° Fiber Orientation, Gregory T. Siegert Jun 2006

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 …

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Effects Of Frequency And Environment On Fatigue Behavior Of An Oxide-Oxide Ceramic Matrix Composite At 1200°C, Griffin Hetrick Jun 2006

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 …

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Wear Analysis Of Cu-Al Coating On Ti-6al-4v Under Fretting, Karl N. Murray Jun 2006

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 …

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Analysis And Simulation Of Hypervelocity Gouging Impacts, John D. Cinnamon Mar 2006

Analysis And Simulation Of Hypervelocity Gouging Impacts, John D. Cinnamon

Theses and Dissertations

In this work, a summary of past and present research efforts, as well as the theoretical foundation, of hypervelocity gouging is presented. As the Holloman AFB High Speed Test Track (HHSTT) sled's speed has increased to Mach 8.5, material interactions develops which causes "gouging" - this can result in catastrophic failure. A characterization of gouging, including a thermodynamic history, is developed from an examination of a gouged rail. An extensive study is performed that determines the specific material flow models for VascoMax 300 and 1080 steel. The models are validated utilizing several experimental tests which are successfully simulated using CTH …

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Development Of In-Plane Surface Deformation Sensing For Thin Film Pvdf Actuated Membrane Mirrors, John J. Cornelius Mar 2006

Development Of In-Plane Surface Deformation Sensing For Thin Film Pvdf Actuated Membrane Mirrors, John J. Cornelius

Theses and Dissertations

This study investigated the feasibility of surface deformation sensing of a membrane mirror using only embedded PVDF sensors. Results were compared to measured deformations using a scanning laser vibrometer. The frequency response function (FRF) was measured based on recorded voltages of a single-layer 7-sensor mirror actuated externally from the embedded PVDF actuators. Additionally, a two-layer, 7-sensor, 7-actuator membrane mirror was constructed for use, with one layer acting as the sensing layer and the other acting as the actuation layer. The measured FRF for this mirror was compared to previous results. Finally a single-layer 61-sensor PVDF mirror was constructed to experimentally …

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Characterization Of Compressive Creep Behavior Of Oxide/Oxide Composite With Monazite Coating At Elevated Temperature, Patrick R. Jackson Mar 2006

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 …

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Creep-Rupture And Fatigue Behaviors Of Notched Oxide/Oxide Ceramic Matrix Composite At Elevated Temperature, Mark A. Sullivan Mar 2006

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 …

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Application Of Spline Variational Analysis Method In The Modeling Of Composite Repairs, Brian M. Fredrickson Mar 2006

Application Of Spline Variational Analysis Method In The Modeling Of Composite Repairs, Brian M. Fredrickson

Theses and Dissertations

The purpose of this thesis is to apply a non-commercialized spline-based (BSpline Analysis Method or BSAM) computer program to model and predict strain fields in two composite repairs, a scarf joint and a stepped-lap joint, subjected to static tensile loading. Test specimens with scarf and stepped-lap joints are fabricated using quasiisotropic sixteen ply panels made from IM6/3501-6 prepreg with a [+452/02/-452/902]s lay-up. The panels were bonded together with FM-300M (0.05psf), a 176°C cure film adhesive, under positive pressure. A total of five coupons of each joint type are made. Two of …

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Fretting Fatigue Behavior Of Nickel Alloy In-100, Elhoucine Madhi Mar 2006

Fretting Fatigue Behavior Of Nickel Alloy In-100, Elhoucine Madhi

Theses and Dissertations

In this study, a systematic investigation of the fretting fatigue behavior of nickel alloy, IN-100 was carried out. The study includes both experimental work and the corresponding analysis of the contact conditions, and the latter is accomplished using the finite element method. Fretting fatigue tests were performed over a wide range of axial stresses to examine both low and high cycle fretting fatigue under constant contact load and the influence of different pad geometries was also explored. It was observed that fretting reduced the fatigue strength of IN- 100, and that increasing cylindrical pad radii does not have the same …

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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 Mar 2006

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 …

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Validation Of A Scaled Plane Strain Hypervelocity Gouging Model, Ronald J. Pendleton Mar 2006

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 …

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Structural Health Monitoring Considering Internal Beam Damage, Jessica B. Chronister Mar 2006

Structural Health Monitoring Considering Internal Beam Damage, Jessica B. Chronister

Theses and Dissertations

The present study establishes a nondestructive method of damage detection and assessment in cantilever beams. The specimens used are twelve-inch aluminum 2024-T3 beams with machined notches of varying lengths and locations. Laser Doppler vibrometry is used to obtain the frequency response of vibrating beams. Experimental methods are developed to detect the presence, location and extent of damage by direct observation of the eigenvector in the third through eighth modes. Models in MATLAB and ABAQUS are used to predict and validate the observed data. With this experimental method developed, the validity of the method is tested for specimens that have been …

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Evaluation Of Factors Contributing To Damping Of Coated And Uncoated Titanium Plates, Dustin W. Lee Mar 2006

Evaluation Of Factors Contributing To Damping Of Coated And Uncoated Titanium Plates, Dustin W. Lee

Theses and Dissertations

High Cycle Fatigue (HCF) is the leading cause of component failure in gas turbine engines today, which poses great risk to aircraft, engines, and their crews. Mitigation of HCF effects has become a priority topic, and the damping benefits of hard coatings are being reevaluated for this purpose. Research was conducted to further understanding of damping measurements on these coatings. This study continues work to characterize the damping effects of a magnesium aluminate spinel (mag spinel) coating applied to a titanium plate via vibration testing. Two different plate sizes were evaluated in a clamped-free-free-free condition and a free-free-free-free condition, respectively. …

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