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Air Force Institute of Technology

2004

Engineering Science and Materials

Articles 1 - 12 of 12

Full-Text Articles in Engineering

Role Of Plasticity On Fretting Fatigue Behavior Of Ti-6al-4v, Kisu Shin Sep 2004

Role Of Plasticity On Fretting Fatigue Behavior Of Ti-6al-4v, Kisu Shin

Theses and Dissertations

Fretting fatigue generally leads to the degradation of the fatigue strength of a material due to cyclic micro-slip between two contacting materials. Fretting fatigue is regarded as an important issue in designing aerospace structures. While many studies have evaluated fretting fatigue behavior under elastic deformation conditions, few studies have focused on fretting fatigue behavior under elastic-plastic deformation conditions. The primary goal of this study was to characterize the fretting fatigue crack initiation behavior in the presence of plasticity. Experimental tests were performed using pad configurations involving elastic-plastic deformations. In order to calculate stress distributions under elastic-plastic fretting fatigue conditions, FEA …

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The Physical Understanding Of The Use Of Coatings To Mitigate Hypervelocity Gouging Considering Real Test Sled Dimensions, Andrew G. Szmerekovsky Sep 2004

The Physical Understanding Of The Use Of Coatings To Mitigate Hypervelocity Gouging Considering Real Test Sled Dimensions, Andrew G. Szmerekovsky

Theses and Dissertations

A dimensional analysis with accompanying numerical investigation is conducted. A simplified model of the real test sled is created that allows test sled dimensions to be converted to a numerical model for analysis. The dimensional analysis is used as a means of directly applying the numerical results to real test sled conditions. Similarity principles are studied and tested by comparing the results from scaled numerical models. Strain rate and other time dependent parameters are not scaled, but the effect of these parameters may be quantified and studied further. The dimensional analysis also provides a comprehensive approach to the test sled …

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Fretting Fatigue Behavior Of Shot-Peened Titanium Alloy Tl-6al-4v Under Seawater Conditions, William Y. Allen Jun 2004

Fretting Fatigue Behavior Of Shot-Peened Titanium Alloy Tl-6al-4v Under Seawater Conditions, William Y. Allen

Theses and Dissertations

The fretting fatigue behavior of the shot-peened titanium alloy, Ti-6Al-4V, was investigated under a corrosive environment of synthetic seawater. Fretting fatigue tests were performed over a wide stress range to determine the effect of seawater at high and low cycle fatigue regimes. The results from this study showed: (1) seawater significantly reduces the fretting fatigue life of shot-peened Ti-6Al-4V at both high and low cycle fatigue relative to its counterpart in ambient laboratory conditions, (2) shot peening increases the fretting fatigue life of Ti-6Al-4V when tested under dry and seawater conditions relative to its counterpart of unpeened Ti-6Al-4V, (3) surface …

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Analytical Results For A Single-Unit System Subject To Markovian Wear And Shocks, Daniel E. Finkelstein Mar 2004

Analytical Results For A Single-Unit System Subject To Markovian Wear And Shocks, Daniel E. Finkelstein

Theses and Dissertations

This thesis develops and analyzers a mathematical model for the reliability measures of a single-unit system subject to continuous wear due to its operating environment and randomly occurring shocks that inflict a random amount of damage to the unit. Assuming a Markovian operating environment and shock arrival mechanism, Laplace-Stieltjes transform expressions are obtained for the failure time distribution and all of its moments. Moreover, an analytical expression is derived for the long-run availability of the single-unit system when it is subject to an inspect-and-replace maintenance policy. The analytical results are illustrated, and their results compared with those of Monte Carlo-simulated …

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Monotonic, Creep-Rupture, And Fatigue Behavior Of Carbon Fiber Reinforced Silicon Carbide (C/Sic) At An Elevated Temperature, John M. Engesser Mar 2004

Monotonic, Creep-Rupture, And Fatigue Behavior Of Carbon Fiber Reinforced Silicon Carbide (C/Sic) At An Elevated Temperature, John M. Engesser

Theses and Dissertations

The main objective of this research effort was to examine the impact that cyclic loading frequency has on the life of a C/SiC composite at an elevated temperature of 550°C. Cyclic loading of C/SiC was investigated at frequencies of 375 Hz, 10 Hz, 1 Hz, and 0.1 Hz. Creep-Rupture tests and tests that were combinations of creep-rupture and fatigue were also accomplished. A monotonic tensile test was performed at 550°C and compared to a room temperature monotonic test. This study showed that an elevated temperature of 550°C has very little effect on the Ultimate Tensile Strength (UTS) of C/SiC. The …

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Fretting Fatigue Behavior Of The Titanium Alloy Ti-6al-4v Under Seawater Conditions, Lewis C. Lietch Mar 2004

Fretting Fatigue Behavior Of The Titanium Alloy Ti-6al-4v Under Seawater Conditions, Lewis C. Lietch

Theses and Dissertations

The fretting fatigue behavior of Ti-6A1-4V was investigated in laboratory air and under a controlled environment consisting of synthetic seawater. Fretting fatigue tests were performed for both low and high cycle fatigue regimes. Finite element analysis was utilized to model and analyze the experimental data. The applied stress range and the Modified Shear Stress Range were evaluated as potential fatigue parameters. The results found from this study can be summarized as: (1) seawater had a deleterious effect on fretting fatigue life in the low cycle fatigue regime but improved life in the high cycle fatigue regime, (2) although the Q/P …

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Structural Design And Analysis Of A Rigidizable Space Shuttle Experiment, Raymond G. Holstein Iii Mar 2004

Structural Design And Analysis Of A Rigidizable Space Shuttle Experiment, Raymond G. Holstein Iii

Theses and Dissertations

AFIT is in the process of designing a Space Shuttle experiment designated as the Rigidized Inflatable Get-Away-Special Experiment (RIGEX) to study the effects of microgravity on the deployment of rigidizable composite structures. Once in space, the experiment will inflate and rigidize three composite structures and perform a vibration analysis on each by exciting the tubes using piezoelectric patches and collecting data via an accelerometer. This paper presents the structural and vibration analysis of the RIGEX assembly and inflatable composite tubes using ABAQUS Finite Element Analysis (FEA) software. Comparison of the analysis has been carried out with Eigenvalue/Eigenvector experimentation by means …

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The Evaluation Of The Damping Characteristics Of A Hard Coating On Titanium, Christopher M. Blackwell Mar 2004

The Evaluation Of The Damping Characteristics Of A Hard Coating On Titanium, Christopher M. Blackwell

Theses and Dissertations

Engine failures due to fatigue have cost the Air Force an estimated $400 million dollars per year over the past two decades (Garrison, 2001). Damping treatments capable of reducing the internal stresses of fan and turbine blades to levels where fatigue is less likely to occur have the potential for reducing cost while enhancing reliability. This research evaluates the damping characteristics of magnesium aluminate spinel, MgO+Al2O3, (mag spinel) on titanium plates. The material and aspect ratio were chosen to approximate the low aspect ratio blades found in military gas turbine fans. The plates were tested with …

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Vibrometric Detection Of Beam Damage Due To Inclusions, Aaron J. Reifsnyder Mar 2004

Vibrometric Detection Of Beam Damage Due To Inclusions, Aaron J. Reifsnyder

Theses and Dissertations

The Air Force Institute of Technology, in conjunction with the Structural Health Monitoring branch of the Air Force Research Laboratory, is researching methods of determining effects of notch location and size on beam structures using modal frequency analysis. This thesis explores the ability to detect included notches of varying magnitudes and locations within the frequency domain of an isotropic cantilever beam. A series of experiments employing centerline-notched 2024 T3 and 2024 0 aluminum beams was used to determine whether natural frequency measurement in beam structures is a valid mechanism for damage detection. Each specimen was excited by a strain actuator …

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Optimization Process For Configuration Of Flexible Joined-Wing, Cody C. Rasmussen Mar 2004

Optimization Process For Configuration Of Flexible Joined-Wing, Cody C. Rasmussen

Theses and Dissertations

This study established a weight optimized configuration design of a joined-wing sensor-craft. The joined-wing aircraft concept fulfills a proposed long-endurance surveillance mission that contains an antenna structure embedded in the wing skin. The analysis was completed utilizing structural optimization, aerodynamic analyses, and response surface methodology. A sample of 62 joined-wing configurations were weight optimized. Each optimized structure was determined through a change of skin, spar, and rib thickness in the wing box by determining trimmed maneuver and gust conditions for critical flight mission points. Since the joined-wing concept has non-linear deformation characteristics, the structural optimization used both strain and buckling …

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Effect Of A Variable Contact Load On Fretting Fatigue Behavior Of Ti-6al-4v, Andrew J. Jutte Mar 2004

Effect Of A Variable Contact Load On Fretting Fatigue Behavior Of Ti-6al-4v, Andrew J. Jutte

Theses and Dissertations

Effects of a variable contact load on the high cycle fretting fatigue behavior of Ti-6AL-4V were investigated. Experimental tests were performed using a new test setup capable of applying a contact load varying in amplitude, frequency, and phase and independently measuring shear forces on opposite sides of a specimen. Finite element analysis (FEA) of experimental and idealized loading conditions was performed and local mechanistic parameters and the Modified Shear Stress Range (MSSR) fatigue parameter were determined. Correlations between contact width, slip amplitude, fatigue life and a variable contact load were established with variable contact loading shown to have a damaging …

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An Electromagnetic Tool For Damping And Fatigue Analysis, Todd M. Hoover Mar 2004

An Electromagnetic Tool For Damping And Fatigue Analysis, Todd M. Hoover

Theses and Dissertations

An automated test system was developed by the USAF Turbine Engine Fatigue Facility (TEFF). This system was initially designed to reduce the time and manpower required to characterize damping treatments. It is based on a digitally controlled environmental chamber with automated data acquisition and processing. Several outputs are available including identification of natural frequencies, modal damping ratios from the acquired frequency responses, and changes in damping with response amplitude; however, the TEFF additionally desires the capability to study fatigue under a free boundary condition. The system consists of a test specimen suspended by a pendulum to closely simulate free boundary …

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