Mechanical Engineering Commons^™

An Investigation Of Friction Stir Welding Parameter Effects On Post Weld Mechanical Properties In 7075 Aa, Steven B. Dickson

Theses and Dissertations

The effects of weld temperature, travel speed, and backing plate thermal diffusivity on themechanical properties of a weld have been studied. A face centered cubic experiment of designwas completed in which the response variables were yield strength, minimum hardness in the HAZ, and charpy impact toughness. Three models were created from the data gathered usinga stepwise regression in order to see the effects of each parameter. For the yield strength andminimum hardness it was found that only travel speed and backing plate thermal diffusivities werestatistically significant to the properties. The charpy impact toughness saw that all three parameterswere statistically significant …

Temperature And Stress Effect Modeling In Fatigue Of H13 Tool Steel At Elevated Temperatures With Applications In Friction Stir Welding, Bradley Valiant Jones

Theses and Dissertations

Tooling reliability is critical to welding success in friction stir welding, but tooling fatigue is not well understood because it occurs in conditions that are often unique to friction stir welding. A fatigue study was conducted on a commonly used tooling material, H13 tool steel, using constant stress loading at temperatures between 300°C and 600°C, and the results are presented. A model is proposed accounting for temperature and stress effects on fatigue life, utilizing a two-region Arrhenius temperature model. A transition in temperature effect on fatigue life is identified. Implications of the temperature effect for friction stir welding suggest that …

Characterization Of Geometrically Necessary Dislocation Content With Ebsd-Based Continuum Dislocation Microscopy, Tim Ruggles

Theses and Dissertations

Modeling of plasticity is often hampered by the difficulty in accurately characterizing dislocationdensity on the microscale for real samples. It is particularly difficult to resolve measureddislocation content onto individual dislocation systems at the length scales most commonly of interestin plasticity studies. Traditionally, dislocation content is analyzed at the continuum levelusing the Nye tensor and the fundamental relation of continuum dislocation theory to interpret informationmeasured by diffraction techniques, typically EBSD or High Resolution EBSD. In thiswork the established Nye-Kroner method for resolving measured geometrically necessary dislocationcontent onto individual slip systems is assessed and extended. Two new methods are alsopresented to relieve …

Integrating The Curriculum Using A Small-Scale Hybrid Power Train, Mariaeugenia Salas Acosta

Theses and Dissertations

The project, a bench-scale hybrid electric powertrain system, is designed, analyzed and fabricated by students in six modules, starting in their sophomore year and culminating in their final semester as seniors. This complex project has been selected in order to integrate the core mechanical engineering courses: Mechanical Design, Thermodynamics, System Dynamics and Control, and Fluid Mechanics. A bench-scale hybrid-electric vehicle powertrain has sufficient complexity to involve all Mechanical Engineering disciplines and the simplicity to be built by students over the course of five semesters. The work is designed to test two hypotheses: 1) A long-term design project that integrates knowledge …

Quantification Of The Effect Of Tool Geometric Features On Aspects Of Friction Stir Welding, Md. Reza-E-Rabby

Theses and Dissertations

In the friction stir welding (FSW) process, tool stirring and synchronized movement of the weld materials along a pre-existing seam line causes thermal gradients and severe plastic deformation resulting in the bonding of the adjacent materials. For a given set of welding parameters, tool pin geometries (dimensions, shape) and vertical/helical features that dictate the material motion also have significant effects on process response variables during FSW. Among the primary process controlling parameters in FSW, tool pin geometry and feature vary multifariously in terms of shape, dimensions, feature insertion technique depending on the weld material and application of joint. The current …

Predictive Methods For End Of Life Prognosis In Composites, Vamsee Vadlamudi

Theses and Dissertations

The long-term properties of continuous fiber reinforced composite materials are increasingly important as applications in airplanes, cars, and other safety critical structures are growing rapidly. The mechanical, electrical, and thermal properties of composite materials are altered by the initiation and accumulation of discrete fracture events whose distribution and eventual interaction defines the limits of design, such as strength and life. There is a correlation that exists between the long term behavior of those materials under combined mechanical, thermal, and electrical fields, and the functional properties and characteristics of the composite materials that requires a fundamental understanding of the material state …

Development Of A Thickness Accommodation Technique For Origami-Inspired Design, Bryce Edmondson

Theses and Dissertations

Designers are constantly searching for new sourcing of inspiration for innovative design. Recently, origami has gained interest as one of these potential sources. Origami literally translated from Japanese means “paper folding” where “oru” means “to fold” and “kami” means “paper”. Since paper is insufficient to solve many engineering design problems, designers must turn to other materials. These materials will inevitably be thicker than paper and will often require different folding techniques and considerations. This thesis provides background information describing previous methods to accommodate thickness in origami-inspired design, presents a newly developed technique to address limitations of other methods, and explores …

Ultrafine Particle Generation And Measurement, Qiaoling Liu

Theses and Dissertations

Ultrafine particles (UFPs) with diameters smaller than 100 nm are omnipresent in ambient air. They are important sources for fine particles produced through the agglomeration and/or vapor condensation. With their unique properties, UFPs have also been manufactured for industrial applications. But, from the toxicological and health perspective, ultrafine particles with high surface-to-volume ratios often have high bio-availability and toxicity. Many recent epidemiologic studies have evidence UFPs are highly relevant to human health and disease. In order to better investigate UFPs, better instrumentation and measurement techniques for UFPs are thus in need. The overall objective of this dissertation is to advance …

Design Of Experiments Analysis Of Non-Standard Inputs For The Optimization Of Friction Stir Welding, Ryan Widejko

Theses and Dissertations

The purpose of this study was to use non-standard Design of Experiments (DoE) inputs in Friction Stir Welding (FSW) to deduce relationships between various weld input and response variables. Typically, inputs for FSW DoE are tool rotational speed, welding speed and forge force. In this study, three different input factors were investigated: travel speed, thermal boundary conditions (TBC), and advance per revolution (APR). The experimental design included a full factorial with each factor at two levels plus two centerpoint runs. Response variables included weld temperature, microstructure, hardness, power, weld energy, and in plane forces.

An investigation of the effect of …

Fabrication And Characterization Of Anode-Supported Micro-Tubular Solide Oxide Fuel Cell By Phase Inversion Method, Cong Ren

Theses and Dissertations

Nowadays, the micro-tubular solid oxide fuel cells (MT-SOFCs), especially the anode supported MT-SOFCs have been extensively developed to be applied for SOFC stacks designation, which can be potentially used for portable power sources and vehicle power supply. To prepare MT-SOFCs with high electrochemical performance, one of the main strategies is to optimize the microstructure of the anode support. Recently, a novel phase inversion method has been applied to prepare the anode support with a unique asymmetrical microstructure, which can improve the electrochemical performance of the MT-SOFCs. Since several process parameters of the phase inversion method can influence the pore formation …

Methods For Determining Grease Service Levels In An Ah-64d Intermediate Gearbox Using On-Board Sensors, Travis Steven Edwards

Theses and Dissertations

The intermediate gearbox (IGB) on the AH-64D was chosen as the subject for this study based on the persistent grease leaks that require grounding aircraft. The aircraft is not currently equipped with a method of detecting grease loss during flight, so techniques for analyzing the usefulness of old metrics and possible new techniques can be tested. The main objective of this study is to use the aircraft’s on-board sensors to develop a method of determining the lubrication level of the IGB. Currently, the most reliable method for detecting a fault on the aircraft is through the use of vibration-based condition …

Generation And Delivery Of Charged Aerosols To Infant Airways, Landon T. Holbrook

Theses and Dissertations

The administration of pharmaceutical aerosols to infants on mechanical ventilation needs to be improved by increasing the efficiency of delivery devices and creating better ways of evaluating potential therapies. Aerosolized medicines such as surfactants have been administered to ventilated infants with mixed results, but studies have shown improvement in respiratory function with a much lower dose than with liquid instillation through an endotracheal tube (ETT). An aerosolized medicine must be transported through the ventilation tubing and deposit in the lungs to have the desired therapeutic response.

This work has taken a systematic approach to (i) develop new devices for the …

A Study To Evaluate Non-Uniform Phase Maps In Shape Memory Alloys Using Finite Element Method, Naren Motte

Theses and Dissertations

The unique thermo-mechanical behavior of Shape Memory Alloys (SMAs), such as their ability to recover the original shape upon heating or being able to tolerate large deformations without undergoing plastic transformations, makes them a good choice for actuators.

This work studies their application in the aerospace and defense industries where SMA components can serve as release mechanisms for gates of enclosures that have to be deployed remotely. This work provides a novel approach in evaluating the stress and heat induced change of phase in a SMA, in terms of the transformation strain tensor. In particular, the FEA tool

ANSYS has …

Micro- And Macro-Scale Modeling Of Filter Aging: Effects Of Particle Poly-Dispersity And Fiber Cross-Sectional Shape, Ahmed M. Saleh

Theses and Dissertations

The goal of this study is to further advance the state of the art in developing self-sufficient methods to predict the performance of an aerosol filter. The simulation methods developed in this study are based on first principles and consequently, they do not rely on empirical correction factors. These simulation methods can be used to predict the instantaneous collection efficiency and pressure drop of a filter under dust-loading conditions. In the current study, 3-D micro- and macroscale CFD models are developed to simulate the service life of flat-sheet and pleated filters. These CFD micro- and macroscale models are also used …

Computational Modeling To Assess Surgical Procedures For The Treatment Of Adult Acquired Flatfoot Deformity, Brian A. Smith

Theses and Dissertations

Several surgically corrective procedures are considered to treat Adult Acquired Flatfoot Deformity (AAFD) patients, relieve pain, and restore function. Procedure selection is based on best practices and surgeon preference. Recent research created patient specific models of Adult Acquired Flatfoot Deformity (AAFD) to explore their predictive capabilities and examine effectiveness of the surgical procedure used to treat the deformity. The models’ behavior was governed solely by patient bodyweight, soft tissue constraints, and joint contact without the assumption of idealized joints. The current work expanded those models to determine if an alternate procedure would be more effective for the individual. These procedures …

On The Development Of High Strain Rate Experiments For The Characterization Of Engineering Materials, Silas P. Mallon

Theses and Dissertations

In order to predict the damage accumulation and failure processes associated with highly dynamic events such as blast loading, shock wave loading, and ballistic impact loading, a commensurate understanding of the fundamental constitutive and fracture behavior of materials subjected to such high rate loading conditions is necessary. In this effort, high strain rate experimental facilities consisting of a shock tube apparatus and a torsional split Hopkinson bar apparatus have been designed, constructed, and subsequently used to investigate the mechanical properties of an array of engineering materials subjected to a variety of dynamic loading conditions. Designs for the experimental equipment utilized …

Fabrication And Characterization Of Novel Electrodes For Solid Oxide Fuel Cell For Efficient Energy Conversion, Yu Chen

Theses and Dissertations

Solid oxide fuel cells (SOFCs) have been considered as one of the most promising technologies for future energy conversion since they can in principle be operated with fuels ranging from H2 to any hydrocarbon fuel. However, the system cost and coking (when using hydrocarbon as fuel) issues for the state-of-art electrode materials/designs often limit their further application. The objective of this Ph.D dissertation is aiming at overcoming these problems and accelerating SOFC commercialization. One approach to cost reduction is lowering the SOFC operating temperature to below 800 or even 600 oC, so that inexpensive materials can be used and quick …

Cost Avoidance Analysis Of Military Aircraft Components Utilizing Condition-Based Maintenance Practices, Erin Ballentine

Theses and Dissertations

This research involves two major case studies. Both look at the current maintenance practices done by the United States Army and propose a solution for improvement utilizing condition-based maintenance (CBM) practices. Each study details a cost avoidance that can be earned by implementing the solutions and the resulting benefits that can be experienced. Case Study I is a return on investment (ROI) that analyzes the benefits of the implementation of elastomeric wedges as vibration control on the Apache (AH-64D) aircraft. Analysis of the material and operational costs shows that the use of self-adhering elastomeric trailing edge wedges on the Apache …

Low Reynolds Number Turbulence: Mechanisms And Applications, Wei Zhao

Theses and Dissertations

Turbulence, as one of "the most important unsolved classical problem in physics" (R. Feynman, 1932), has been investigated for more than 130 years. Conventionally, turbulence is believed to be a phenomenon of high Reynolds numbers (Re). However, we find that turbulence can also be achieved at low Re by proper external forcing, either in macroflows or in microflows. In macroflows, the characteristics of high Re turbulence can be achieved in confined flows, when the bulk flow Re is around 400, by external forcing at its optimal frequency (Wang 2003; Wang 2006). Interestingly, the optimal narrow band of frequency is fixed …

Applications Of Advanced Imaging Methods: Macro-Scale Studies Of Woven Composites And Micro-Scale Measurements On Heated Ic Packages, Siming Guo

Theses and Dissertations

As a representative advanced imaging technique, the digital image correlation (DIC) method has been well established and widely used for deformation measurements in experimental mechanics. This methodology, both 2D and 3D, provides qualitative and quantitative information regarding the specimen’s non-uniform deformation response. Its full-field capabilities and non-contacting approach are especially advantageous when applied to heterogeneous material systems such as fiber-reinforced composites and integrated chip (IC) packages. To increase understanding of damage evolution in advanced composite material systems, a series of large deflection bending-compression experiments and model predictions have been performed for a woven glass-epoxy composite material system. Stereo digital image …

Behavior Of Piezoelectric Wafer Active Sensor In Various Media, Tuncay Kamas

Theses and Dissertations

The dissertation addresses structural health monitoring (SHM) techniques using ultrasonic waves generated by piezoelectric wafer active sensors (PWAS) with an emphasis on the development of theoretical models of standing harmonic waves and guided waves. The focal objective of the research is to extend the theoretical study of electro-mechanical coupled PWAS as a resonator/transducer that interacts with standing and traveling waves in various media through electro-mechanical impedance spectroscopy (EMIS) method and guided wave propagation. The analytical models are developed and the coupled field finite element analysis (CF-FEA) models are simulated and verified with experiments. The dissertation is divided into two parts …

Characterization Of Smoothness In Wrist Rotations, Layne Hancock Salmond

Theses and Dissertations

Smoothness is a hallmark of healthy movement and has the potential to be used as a marker of recovery in rehabilitation settings. While much past research has focused on shoulder and elbow movements (reaching), little is known about movements of the wrist despite its importance in everyday life and its impairment in many neurological and biomechanical disorders. Our current lack of knowledge regarding wrist movement prevents us from improving current models, diagnosis, and treatment of wrist disorders. In particular, while movement smoothness is a well-known characteristic of reaching movements and may potentially be used to diagnose and monitor recovery from …

Modeling And Testing Of Bistable Waterbomb Base Configurations, Brandon Holbrook Hanna

Theses and Dissertations

Origami is making an impact in engineering as solutions to problems are being found by applying origami principles (eg. flat-foldability) and using specific crease patterns as inspiration. This thesis presents an in-depth analysis of a particular origami fold -- the waterbomb base -- to facilitate its use in future engineering problems. The watebomb base is of interest due to its familiarity to the origami community, simple topology (can be made by folding a single sheet of paper four times), scalability, generalizability, and interesting kinetic behavior. It can behave as a nonlinear spring as well as a one- or two-way bistable …

A Hybrid Method For Sensitivity Optimization With Application To Radio-Frequency Product Design, Abraham Lee

Theses and Dissertations

A method for performing robust optimal design that combines the efficiency of experimental designs and the accuracy of nonlinear programming (NLP) has been developed, called Search-and-Zoom. Two case studies from the RF and communications industry, a high-frequency micro-strip band-pass filter (BPF) and a rectangular, directional patch antenna, were used to show that sensitivity optimization could be effectively performed in this industry and to compare the computational efficiency of traditional NLP methods (using fmincon solver in MATLAB R2013a) and they hybrid method Search-and-Zoom. The sensitivity of the BPF's S11 response was reduced from 0.06666 at the (non-robust) nominal optimum to 0.01862 …

Investigating The Relationship Between High Temperature Flow Stress And Friction Stir Weldability In Hsla Steels, David Jordan Walser

Theses and Dissertations

The feed rate at which a defect free friction stir weld can be run (friction stir weldability) on an HSLA steel plate can vary widely between heats that meet the same specified physical properties. Consequently, every time a new heat of HSLA steel is obtained, exploratory welds must be run to determine the proper feed rate for that plate. Previous research suggests that the varying levels of alloying elements related to high temperature physical properties between the different heats causes the observed change in friction stir weldability. Because of this, it was hypothesized that the high temperature physical properties of …

Light Field Imaging Applied To Reacting And Microscopic Flows, Jonathon Remy Pendlebury

Theses and Dissertations

Light field imaging, specifically synthetic aperture (SA) refocusing is a method used to combine images from an array of cameras to generate a single image with a narrow depth of field that can be positioned arbitrarily throughout the volume under investigation. Creating a stack of narrow depth of field images at varying locations generates a focal stack that can be used to find the location of objects in three dimensions. SA refocusing is particularly useful when reconstructing particle fields that are then used to determine the movement of the fluid they are entrained in, and it can also be used …

A Variable-Stiffness Compliant Mechanism For Stiffness-Controlled Haptic Interfaces, Jeffrey C. Hawks

Theses and Dissertations

In this research a variable-stiffness compliant mechanism was developed to generate variable force-displacement profiles at the mechanisms coupler point. The mechanism is based on a compliant Roberts straight-line mechanism, and the stiffness is varied by changing the effective length of the compliant links with an actuated slider. The variable-stiffness mechanism was used in a one-degree-of-freedom haptic interface to demonstrate the effectiveness of varying the stiffness of a compliant mechanism. Unlike traditional haptic interfaces, in which the force is controlled using motors and rigid links, the haptic interface developed in this work displays haptic stiffness via the variable-stiffness compliant mechanism. The …

Design Considerations In The Development And Actuation Of Origami-Based Mechanisms, Eric W. Wilcox

Theses and Dissertations

Origami-based mechanisms have unique characteristics that make them attractive for engineering applications. However, origami-based design is still a developing area of design. Continued work to increase general understanding of key design parameters specific to origami-based mechanisms will increase the ability of designers to capture the potential benefits of origami-based mechanisms. This thesis presents a fundamental study of origami to assist designers in gaining a stronger understanding of the key parameters and capabilities of origami-based mechanisms. As a starting point a study of fundamental motions in action origami models (those that exhibit motions in their folded state) is presented to explore …

Compliant Mechanisms For Deployable Space Systems, Shannon Alisa Zirbel

Theses and Dissertations

The purpose of this research is to develop fundamentals of compliant mechanisms in deployable space systems. The scope was limited to creating methods for thick origami, developing compliant deployable solar arrays, and developing methods for stowing and deploying the arrays. The research on actuation methods was focused on a one-time deployment of the array. Concepts for both passive and active actuation were considered. The primary objective of this work was to develop approaches to accommodate thickness in origami-based deployable arrays with a high ratio of deployed-to-stowed diameter. The HanaFlex design was derived from the origami flasher model and is developed …

Fault Detection For Unmanned Aerial Vehicles With Non-Redundant Sensors, Brandon Jeffrey Cannon

Theses and Dissertations

To operate, autonomous systems of necessity employ a variety of sensors to perceive their environment. Many small unmanned aerial vehicles (UAV) are unable to carry redundant sensors due to size, weight, and power (SWaP) constraints. Faults in these sensors can cause undesired behavior, including system instability. Thus, detection of faults in these non-redundant sensors is of paramount importance.The problem of detecting sensor faults in non-redundant sensors on board autonomous aircraft is non-trivial. Factors that make development of a solution difficult include both an inability to perfectly characterize systems and sensors as well as the SWaP constraints inherent with small UAV. …