Engineering Commons^™

The Role Of Slip System Activation On Ni-Based Superalloy High Temperature Fatigue, Alexandru Lopazan

Doctoral Dissertations and Master's Theses

Nickel-based superalloys are used extensively in the aviation industry, particularly in aircraft engine components. These materials are desirable due to their high strength, resistance to creep, corrosive environment, and high temperature. It has been well documented that material fatigue is characterized by material microstructure, type of loading, and other parameters. Currently, research into the effects of fatigue on complex materials like nickel-based superalloys is being pursued. Previous research has found that preconditioning of Inconel 718 samples at 700 ℃ with 1.0% strain led to an improved fatigue life. It has been suggested that this could be caused by the activation …

Effect Of Cold Work Expansion On The Fatigue Life Of Pre-Cracked Al 2024-T3, Christopher Leirer

Doctoral Dissertations and Master's Theses

No abstract provided.

Pilot Acceptance Of Personal, Wearable Fatigue Monitoring Technology: An Application Of The Extended Technology Acceptance Model, Rachelle Lynne Strong

Doctoral Dissertations and Master's Theses

The research problem of pilot fatigue has been referenced as a causal factor for aircraft accidents in many United States National Transportation and Safety Board (NTSB) accident reports; however, the United States Code of Federal Regulations 14 CFR Part 117, Flight and Duty Limitations and Rest Requirements for Flight Crew Members, does not provide a tangible means of measuring fatigue for aircraft crew members. This problem is relevant to the airline industry and the travelling public because pilot fatigue is preventable as a causal factor in aviation accidents, and pilots need an accurate way to measure it. Adoption of a …

The Effect Of Task Load, Automation Reliability, And Environment Complexity On Uav Supervisory Control Performance, Sarah M. Sherwood

Doctoral Dissertations and Master's Theses

Over the last decade, military unmanned aerial vehicles (UAVs) have experienced exponential growth and now comprise over 40% of military aircraft. However, since most military UAVs require multiple operators (usually an air vehicle operator, payload operator, and mission commander), the proliferation of UAVs has created a manpower burden within the U.S. military. Fortunately, simultaneous advances in UAV automation have enabled a switch from direct control to supervisory control; future UAV operators will no longer directly control a single UAV subsystem but, rather, will control multiple advanced, highly autonomous UAVs. However, research is needed to better understand operator performance in a …

Proof Of Concept Test For Dual-Axis Resonant Phase-Locked Excitation (Phlex) Fatigue Testing Method For Wind Turbine Blades, Jenna Austin Beckwith

Doctoral Dissertations and Master's Theses

The installed capacity of wind turbines has grown steadily for the past decade with wind energy now providing 3.6-percent of the U.S.’s electricity supply [13]. This trend can be attributed to advancements in wind turbine technology and the ability to increase wind turbine sizes. As wind turbines grow in size, so do the loads experienced by the turbine. One of the most significant load increases is in the lead-lag direction of the wind turbine blades. The increase in lead-lag load is due to the increase in weight of the larger blades. Current wind turbine blades have lead-lag and flapwise loads …

Fatigue Damage Prognosis Of Internal Delamination In Composite Plates Under Cyclic Compression Loadings Using Affine Arithmetic As Uncertainty Propagation Tool, Audrey J-M Gbaguidi

Doctoral Dissertations and Master's Theses

Structural health monitoring (SHM) has become indispensable for reducing maintenance costs and increasing the in-service capacity of a structure. The increased use of lightweight composite materials in aircraft structures drastically increased the effects of fatigue induced damage on their critical structural components and thus the necessity to predict the remaining life of those components. Damage prognosis, one of the least investigated fields in SHM, uses the current damage state of the system to forecast its future performance by estimating the expected loading environments. A successful damage prediction model requires the integration of technologies in areas like measurements, materials science, mechanics …

Neural Network Fatigue Life Prediction In Steel I-Beams Using Mathematically Modeled Acoustic Emission Data, Prathikshen Nambiar Selvadorai

Doctoral Dissertations and Master's Theses

The purpose of this research is to predict fatigue cracking in metal beams using mathematically modeled acoustic emission (AE) data. The AE data was collected from nine samples of steel I-beam that were subjected to three-point bending caused by cyclic loading. The data gathered during these tests were filtered in order to remove long duration hits, multiple hit data, and obvious outliers. Based on the duration, energy, amplitude, and average frequency of the AE hits, the filtered data were classified into the various failure mechanisms of metals using NeuralWorks® Professional II/Plus software based self-organizing map (SOM) neural network. The parameters …

The Development Of An Adaptive Control System For A Phase-Locked Excitation (Phlex) Method For Advanced Wind Turbine Blade Fatigue Testing, William Michael Haupfear

Master's Theses - Daytona Beach

The National Renewable Energy Laboratory's (NREL) National Wind Technology Center (NWTC) provides the means necessary for advanced wind turbine blade testing. To improve on the current testing methods, a new testing method is being developed using the existing dual-axis fatigue testing capabilities in conjunction with another actuator to provide a phase-locked excitation method with adaptive algorithms and advanced control system strategies. This testing method will provide a more representative loading of the blade for fatigue testing as compared to loading seen in the field. The control system will integrate the MTS software and controller with a supervisory controller, programmed in …

The Development Of A Phase Locked Wind Turbine Blade Finite Element Model To Predict Loads And Deflections During Fatigue Testing, Kyle Andrew Freeman

Master's Theses - Daytona Beach

Full scale blade testing provides blade manufacturers with quantitative data in order to assess blade design, manufacturing and durability. Structural testing is a requirement in order to design reliable blades, and to develop a further understanding of the dynamics involved in a modern turbine blade. Blade tests can be conducted in either a single axis or dual axis configurations. Historically, fatigue testing has been performed by utilizing forced displacement systems. These systems do not allow for the load phase angle to be controlled, and the maximum load application in the edge and flap directions are allowed to vary. The PhLEX …

Neural Network Fatigue Life Prediction In Notched Aluminum Specimens From Acoustic Emission Data, Muhammed Arif Okur

Master's Theses - Daytona Beach

This purpose of this research was to identify fatigue crack growth and predict failure for 7075-T6 aluminum notched bars under uniaxial tensile loading using acoustic emission (AE) data. The experiments performed in this study extend the results obtained by previous researchers who used maximum cyclic loads of 4,000, 3,000, and 2,000 pounds at a stress ratio of R = 0.0 and a frequency of 1 Hz to perform the fatigue tests. For this research the cyclic load remained at 2,000 pounds, but an additional ten specimens were tested in order to increase the amount of AE data available to the …

Acoustic Emission Fatigue Crack Monitoring Of A Simulated Aircraft Fuselage Structure, Jeremy James Lucas

Doctoral Dissertations and Master's Theses

The purpose of this research was to replicate the fatigue cracking that occurs in aircraft placed under loads from cyclical compression and decompression. As a fatigue crack grows, it releases energy in the form of acoustic emissions. These emissions are transmitted through the structure in waves, which can be recorded using acoustic emission (AE) transducers. This research employed a pressure vessel constructed out of aluminum and placed under cyclical loads at 1 Hz in order to simulate the loads placed on an aircraft fuselage in flight. The AE signals were recorded by four resonant AE transducers. These were placed on …

Prediction Of Fatigue Life In 7075-T6 Aluminum From Neural Network Analysis Of Acoustic Emission Data, Nicholas S. Spivey

Master's Theses - Daytona Beach

Through the use of an acoustic emission (AE) data acquisition system, a Kohonen self-organizing map, and a back-propagation neural network, AE data from 7075-T6 aluminum specimens were used to classify failure mechanisms and predict the number of fatigue cycles to failure. AE waveforms were captured from 40 notched tensile specimens during the low-cycle fatiguing process. A Kohonen self-organizing map and initial data filters were used to classify the data into two distinct failure mechanisms, plane strain and plane stress fracture, plus a third less prevalent mechanism. These results were employed to construct a back-propagation neural network to predict the number …

Neural Network Fatigue Life Prediction In 7075-T6 Aluminum From Acoustic Emission Data, Emeka Chigozie Ibekwe

Master's Theses - Daytona Beach

The objective of this research was to classify acoustic emission (AE) -data associated with fatigue cracks in aluminum fatigue specimens and to use early cycle life AE data to predict failure in such members. An AE data acquisition system coupled with a Kohonen self organizing map and a back propagation neural network were used to perform the analysis. AE waveforms were recorded during fatigue cycling of twenty-four notched 7075-T6 aluminum specimens using broad-band piezoelectric transducers. A Kohonen self organizing map was used to classify the AE flaw growth signals. The signals were classified into three categories based on their AE …

Classification Of In-Flight Fatigue Cracks In Aircraft Structures Using Acoustic Emission And Neural Networks, Christopher Lee Rovik

Master's Theses - Daytona Beach

The research encompassed within this paper deals with the analysis and classification of fatigue cracks in aircraft structures. The particular structure that was examined was the vertical tail section of a Cessna T-303 Crusader aircraft. The analysis was performed using the nondestructive evaluation technique known as acoustic emission (AE), as well as the artificial intelligence of neural networks. Data were taken in a controlled laboratory environment as well as in a flying testbed aboard the aircraft.

The first part of the research involved the analysis of a typical aircraft structure in a controlled laboratory environment. This support structure was fabricated …

In-Flight Fatigue Crack Monitoring Of An Aircraft Engine Cowling, Samuel Gordon Vaughn Iii

Master's Theses - Daytona Beach

This research investigates the feasibility of implementing an in-flight fatigue crack monitoring system in an airplane to identify fatigue crack growth. An acoustic emission data acquisition system coupled with a Kohonen self organizing map neural network were used to perform the analysis.

Fatigue cracking was responsible for ripping the top of a fuselage off an Aloha Airlines Boeing 737-200 as it carried passengers over the Pacific Ocean, killing some aboard. This tragedy is perhaps a precursor of problems to come, as our nation’s aircraft age. These planes experience fatigue as they perform their daily routine of ferrying passengers from location …

Fatigue: Investigation Of A Human Factor For Regional Airline Pilots, Doug Mikkelsen

Master's Theses - Daytona Beach

This study analyzed the causes of regional airline pilot fatigue and the impact on pilot performance. An instrument was developed and refined through a field study validation by a panel of experts. The final instrument was distributed to three groups of regional airline pilots. The data supported the literature review, which revealed many causes of pilot fatigue, including flight crew schedules that are not compatible with human limitations; Federal Aviation Regulations (FARs) that have not evolved with the advancement of aircraft performance and the public demand for 24 hour availability of flights; and poor personal habits. An analysis of the …

Detection Of Fatigue Crack Growth In A Simulated Aircraft Fuselage, Michael Lee Marsden

Master's Theses - Daytona Beach

Acoustic emission (AE) nondestructive testing can detect fatigue cracks as they occur in complex structures. One use for AE has been in-flight detection of fatigue cracks in aircraft. The KC-135 aircraft were successfully monitored as early as 1979. The main problem with this and subsequent applications was an unfavorable signal to noise ratio, the key being to separate the small amplitude crack signals from the large amplitude ambient noise. This was accomplished here through the use of a Kohonen self-organizing map (SOM) neural network.

In order to simulate a fuselage undergoing fatigue, a pressure vessel was constructed from a 0.040 …