Department of Mechanical Engineering

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3D Numerical Modelling of a Rarefied Gas Flow in the Nearby Atmosphere around a Rotating Cometary Nucleus
(2007) Volkov, Alexey N.; Lukyanov, German A.; University of Alabama Tuscaloosa
A combined 3D model of a nearby atmosphere around an arbitrary rotating spherical cometary nucleus is developed. The model includes a 3D unsteady model of solar radiation absorption and heating of the nucleus material (water ice), its evaporation and condensation and a 3D quasi-stationary kinetic model of flow inside the near nucleus coma. This model can be used to predict the coma flow in conditions typical for rendezvous projects such as ESA project Rossetta. Calculations are carried out with the help of this model to reveal the influence of nucleus rotation on its temperature field and the flow field in the nearby atmosphere. It was found that the nucleus rotation influences significantly the nucleus temperature field and the coma flow. Vapor flow around a rotating nucleus is essentially three dimensional and differs qualitatively from the coma flow around a non-rotating nucleus.
Acoustic methods for regionalizing an impact force acting on a helmet structure
(University of Alabama Libraries, 2018) Davis, Jacob; Shepard, W. Steve; University of Alabama Tuscaloosa
It is often desired to know the location and magnitude of a force acting on a structure. Unfortunately, it is not always possible or desirable to install a sensor at the force location, such as when the force location is unknown or when the application of a force sensor would change the force transmission characteristics. A structure subjected to an impact has many different vibrational modes that are excited to different levels based on the excitation location. These vibrations decay with time depending on their different rates of modal damping and the associated acoustic radiation characteristics. This response of the structure can be measured and used to inversely reconstruct the input force. It is theoretically possible to use acoustic measurements for force reconstruction, but the method involved would be extremely difficult. In this study, approaches that are much simpler and easier to implement were considered. Acoustic signatures for several structure impact locations were measured, normalized relative to the force magnitude, and processed to examine the ability to correlate the acoustic signal to the force impact location. Various processing techniques, such as the Short Time Fourier Transform, were considered. A primary interest focused on the ability of using single-number metrics that describe features of the acoustic signature to aid in identifying the force location. For the experiments, a football helmet structure was used and multiple impact locations on the helmet were tested. The ability of these acoustic signatures, including those processed into single-number metrics, to aid in identifying the impact location was assessed.
Age-related differences in gait adaptations during overground walking with and without visual perturbations using a virtual reality headset
(Nature Portfolio, 2020) Osaba, Muyinat Y.; Martelli, Dario; Prado, Antonio; Agrawal, Sunil K.; Lalwani, Anil K.; Columbia University; University of Alabama Tuscaloosa; NewYork-Presbyterian Hospital
Older adults have difficulty adapting to new visual information, posing a challenge to maintain balance during walking. Virtual reality can be used to study gait adaptability in response to discordant sensorimotor stimulations. This study aimed to investigate age-related modifications and propensity for visuomotor adaptations due to continuous visual perturbations during overground walking in a virtual reality headset. Twenty old and twelve young subjects walked on an instrumented walkway in real and virtual environments while reacting to antero-posterior and medio-lateral oscillations of the visual field. Mean and variability of spatiotemporal gait parameters were calculated during the first and fifth minutes of walking. A 3-way mixed-design ANOVA was performed to determine the main and interaction effects of group, condition and time. Both groups modified gait similarly, but older adults walked with shorter and slower strides and did not reduce stride velocity or increase stride width variability during medio-lateral perturbations. This may be related to a more conservative and anticipatory strategy as well as a reduced perception of the optic flow. Over time, participants adapted similarly to the perturbations but only younger participants reduced their stride velocity variability. Results provide novel evidence of age- and context-dependent visuomotor adaptations in response to visual perturbations during overground walking and may help to establish new methods for early identification and remediation of gait deficits.
Analysis and Elicitation of Electroencephalogram Data Pertaining to High Alert and Stressful Situations: Source Localization Through the Inverse Problem
(University of Alabama Libraries, 2021) Heim, Isaac C; Fonseca, Daniel J.; University of Alabama Tuscaloosa
This dissertation work deals with the design and development of a fuzzy controller to analyze electroencephalogram (EEG) data. The fuzzy controller made use of the multiple functions associated with the different regions of the brain to correlate multiple Brodmann areas to multiple outputs. This controller was designed to adapt to any data imported into it. The current framework implemented supports a math study and a police officer study. The rules for the interactions of the Brodmann areas have been set up for these applications, detailing how well the police subjects’ brains exhibited behavior indicative to activation relating to vision, memory, shape/distance, hearing/sound, and theory of mind. The math subjects’ outputs were attuned to their related study which involved transcranial direct current stimulation (tDCS), which is a form of neurostimulation. Anode affinity, cathode affinity, calculation, memory, and decision making were the outputs focused on for the math study. This task is best suited to a fuzzy controller since interactions between Brodmann areas can be analyzed and the contributions of each area accounted for.The goal of the controller was to determine long-term behavior of the subjects with repeated sampling. With each addition of data, the controller was able to develop new bounds related to the current condition of the data in the study. Processing this data was accomplished by the creation of an automated filtering script for EEGLAB in MATLAB. The script was designed to rapidly load and filter the files associated with any given dataset. These files were also automatically prepared for analysis with a program called Low Resolution Brain Electromagnetic Tomography i.e. (LORETA). LORETA was used to solve the inverse problem, which involves identifying where the signals from the surface electrodes originated within the brain through a process called source localization. Once the sources of the EEG signals were located, they were associated with the Brodmann areas. The fuzzy controller then processed this information to automatically generate heat maps which displayed information such as normalized data, z-score, and rankings. Each set of scores displays how the subject's brain was acting, which lined up with the expected results.
Analysis of a natural gas combined cycle powerplant modeled for carbon capture with variance of oxy-combustion characteristics
(University of Alabama Libraries, 2011) Breshears, Matthew Joseph; Midkiff, K. Clark; University of Alabama Tuscaloosa
The world's ever growing demand for energy has resulted in increased consumption of fossil fuels for electricity generation. The emissions from this combustion have contributed to increasing ambient levels of carbon dioxide in the atmosphere. Many efforts have been made to curb and reduce carbon dioxide emissions in the most efficient manner. The computer process modeling software CHEMCAD was used to model a natural gas combined cycle powerplant for carbon capture and sequestration. Equipment for two proven carbon capture techniques, oxy-combustion and post-combustion amine scrubbing, were modeled. The necessary components modeled included an air separation unit, powerplant, amine scrubbing unit, and a carbon dioxide compression and drying unit. The oxygen concentration in the oxidizer supplied to the powerplant was varied from ambient air, 21%, to nearly pure oxygen, 99.6%. Exhaust gas recirculation was incorporated to maintain a constant combustion temperature. At ambient conditions no air separation unit was necessary and all carbon capture was provided by the amine scrubbing unit. At concentrations ranging from 22 - 99% both oxy-combustion and amine scrubbing techniques are used at inversely varying degrees. At 99.6%, no amine scrubbing unit was necessary. As the oxygen concentration was varied operational parameters were investigated with the goal of identifying optimum operational conditions. Across the varying oxygen concentrations, the First Law efficiency losses ranged from 3.3 - 13.6%. The optimal operational point occurred when ambient air was supplied and exhaust gas recirculation was utilized for flame temperature control. A Second Law efficiency of 52.2% was maximized at an oxygen concentration of 22%. This corresponds to a 2.28% reduction in Second Law efficiency. An exergy analysis of each component identified the air separation unit as the component where the most improvements are possible. At 99% oxygen concentration, the Second Law efficiency of the air separation unit was 3%. Through modeling a natural gas combined cycle powerplant for carbon capture and varying the oxy-combustion characteristics, valuable information was gained in the understanding of operational losses associated with carbon capture.
Analytical modeling and design optimization of piezoelectric bimorph energy harvester
(University of Alabama Libraries, 2010) Zhang, Long; Williams, Keith A.; University of Alabama Tuscaloosa
As wireless sensor networks continue to grow in size and scope, the limited life span of batteries produces an increasingly challenging economic problem, in terms of not only the capital cost of replacing so many batteries, but also the labor costs incurred in performing battery replacement, particularly with sensor nodes in remote or limited-access locations. This growing problem has motivated the development of new technologies for harvesting energy from the ambient environment. Piezoelectric energy harvesters (PEH) are under consideration as a means for converting mechanical energy, specifically vibration energy, to electrical energy, with the goal of realizing completely self-powered sensor systems. There are three primary goals with regards to this study. The first goal is to develop an analytical model for the resonant frequency of a piezoelectric cantilever bimorph (PCB) energy harvester, aiming to study the geometric effects of both the piezoelectric bimorph and the proof mass on the resonant frequency of a PEH. The analytical model is developed using the Rayleigh-Ritz method and Lagrange's equation of motion and is validated by finite element analysis (FEA) and laboratory experiments. It is shown that this analytical model is better at predicting resonant frequencies than a model currently available in the literature. The second goal is the development of an enhanced analytical model for the voltage and power output of the PCB. The modified analytical model is realized using the conservation of energy method and Euler-Bernoulli beam theory. It is compared with a general equivalent spring-mass-damper model and an equivalent electrical circuit model, and validated by the laboratory prototype experiments. The results show that the modified model provides improved prediction of PCB voltage and power output. Simultaneously, finite element analysis on piezoelectric structures using the commercially available software package ANSYS® Multiphysics is also carried out to study the dynamic response of the PCB in terms of both tip displacements and the electrical potentials of the top and bottom electrodes. It is shown that the simulations are quite close to the experimental results, in terms of both peak frequencies and peak amplitudes. The third goal is the design optimization of the PCB energy harvester in order to maximize the power harvesting from the ambient vibration. Three design optimization approaches are carried out, including multi-parameter optimization of the single PCB generator using a genetic algorithm (GA), a band-pass generator design with a group of the PCB generators based on the system transfer function, and the new design features of the PCB generator for consideration of the improvements of the strain energy and the lifetime. The results of the optimized designs are validated through FEA, and the discrepancies between the theoretical derivation and FEA are also analyzed. Other optimal design considerations are also discussed.
Analyzing industrial energy use through ordinary least squares regression models
(University of Alabama Libraries, 2014) Golden, Allyson Katherine; Woodbury, Keith A.; University of Alabama Tuscaloosa
Extensive research has been performed using regression analysis and calibrated simulations to create baseline energy consumption models for residential buildings and commercial institutions. However, few attempts have been made to discuss the applicability of these methodologies to establish baseline energy consumption models for industrial manufacturing facilities. In the few studies of industrial facilities, the presented linear change-point and degree-day regression analyses illustrate ideal cases. It follows that there is a need in the established literature to discuss the methodologies and to determine their applicability for establishing baseline energy consumption models of industrial manufacturing facilities. The thesis determines the effectiveness of simple inverse linear statistical regression models when establishing baseline energy consumption models for industrial manufacturing facilities. Ordinary least squares change-point and degree-day regression methods are used to create baseline energy consumption models for nine different case studies of industrial manufacturing facilities located in the southeastern United States. The influence of ambient dry-bulb temperature and production on total facility energy consumption is observed. The energy consumption behavior of industrial manufacturing facilities is only sometimes sufficiently explained by temperature, production, or a combination of the two variables. This thesis also provides methods for generating baseline energy models that are straightforward and accessible to anyone in the industrial manufacturing community. The methods outlined in this thesis may be easily replicated by anyone that possesses basic spreadsheet software and general knowledge of the relationship between energy consumption and weather, production, or other influential variables. With the help of simple inverse linear regression models, industrial manufacturing facilities may better understand their energy consumption and production behavior, and identify opportunities for energy and cost savings. This thesis study also utilizes change-point and degree-day baseline energy models to disaggregate facility annual energy consumption into separate industrial end-user categories. The baseline energy model provides a suitable and economical alternative to sub-metering individual manufacturing equipment. One case study describes the conjoined use of baseline energy models and facility information gathered during a one-day onsite visit to perform an end-point energy analysis of an injection molding facility conducted by the Alabama Industrial Assessment Center. Applying baseline regression model results to the end-point energy analysis allowed the AIAC to better approximate the annual energy consumption of the facility's HVAC system.
AnkleImage - An ultrafast ultrasound image dataset to understand the ankle joint muscle contractility
(2024) Zhang, Qiang; Akinniyi, Oluwasegun
The role of the human ankle joint in activities of daily living, including walking, maintaining balance, and participating in sports, is of paramount importance. Ankle joint dorsiflexion and plantarflexion functionalities mainly account for ground clearance and propulsion power generation during locomotion tasks, where those functionalities are driven by the contraction of ankle joint skeleton muscles. Studies of corresponding muscle contractility during ankle dynamic functions will facilitate us to better understand the joint torque/power generation mechanism, better diagnose potential muscular disorders on the ankle joint, or better develop wearable assistive/rehabilitative robotic devices that assist in community ambulation. This data descriptor reports a new dataset that includes the ankle joint kinematics/kinetics, associated muscle surface electromyography, and ultrafast ultrasound images with various annotations, such as pennation angle, fascicle length, tissue displacements, echogenicity, and muscle thickness, of ten healthy participants when performing volitional isometric, isokinetic, and dynamic ankle joint functions (walking at multiple treadmill speeds, including 0.50 m/s, 0.75 m/s, 1.00 m/s, 1.25 m/s, and 1.50 m/s). Data were recorded by a research-use ultrasound machine, a self-designed ankle testbed, an inertia measurement unit system, a Vicon motion capture system, a surface electromyography system, and an instrumented treadmill. The descriptor in this work presents the results of a data curation or collection exercise from previous works, rather than describing a novel primary/experimental data collection.
Application of macroscopic elasticity models to predict microstructurally small crack growth
(University of Alabama Libraries, 2018) Cauthen, Tanner; Daniewicz, Steven R.; University of Alabama Tuscaloosa
The need for a more lightweight and structurally stable alloy is evident in industry. Before a specific alloy is put into industrial use, the alloy must be properly tested such that structural integrity is insured. In this study, the microstructurally small crack growth behavior in aluminum and magnesium alloys and its relationship with material microstructure is investigated under fatigue loading. Surfaces of the alloys tested were replicated using a two-part silicon epoxy where the microstructurally small surface cracks were analyzed and measured. The microstructure of the alloys tested was also investigated to see if a correlation between crack growth and microstructure could be found. Fractography and Electron Back Scatter Diffraction (EBSD) were conducted on all three alloys. In addition to the experimental aspects of this study, two linear elastic fracture mechanics models were implemented to see if the trends in crack growth rate could be predicted. The first model, a modified strip-yield model that allowed for plasticity ahead of the crack tip, adequately predicted microstructurally small crack growth for a rolled AZ31 magnesium alloy. The second model, a dislocation distribution theory model (DDM) that allowed for stress intensity factor prediction of a multiply kinked crack in a field of cracks, less than adequately predicted the small crack growth of a rolled AA2XXX and AA7XXX alloy.
As-deposited microstructure and tensile behavior of solid-state additive manufactured Ti–6Al–4V
(University of Alabama Libraries, 2019) Miller, Mary Olivia; Allison, Paul G.; University of Alabama Tuscaloosa
Ti–6Al–4V (Ti64) is the most widely used titanium alloy on the market today due to its high strength-to-weight ratio and excellent corrosion resistance. Because of expensive Ti64 material costs, fusion based additive manufacturing (AM) methods are heavily utilized in the fabrication of Ti64 parts. This research presents the as-deposited properties and microstructure of Ti64 after additive friction stir-deposition (AFS-D): a layer-by-layer solid state AM process that provides the capability to produce fully dense, near-net shape parts from a variety of alloys, including Ti64. Microstructural characteristics of AFS-D Ti64 were determined using Electron Backscatter Diffraction (EBSD) and Energy Dispersive Spectroscopy (EDS). A Vickers hardness test measured the hardness of the AFS-D Ti64 deposition cross section. Quasi-static tensile experiments performed on as-built AFS-D Ti64 samples quantified the strength and ductility, and the results were compared to the data available in the open literature of Ti64 produced by other popular AM methods. In conclusion, the as-deposited AFS-D Ti64 performed as well as or better mechanically than cast and wrought Ti64, with a Vickers hardness of 348 HV and average ultimate tensile strength (UTS) of 1.2 GPa. Compared to other fusion based AM methods, AFS-D performed similarly, while possessing faster deposition rates with a more refined and equiaxed microstructure.
Assessing the validity, reliability, and practicality of ASHRAE's performance measurement protocols (ASHRAE Research Project 1702)
(Taylor & Francis, 2019) Wang, Liping; Mcmorrow, Gabrielle; Zhou, Xiaohui; O'Neill, Zheng D.; University of Wyoming; University of Alabama Tuscaloosa
The objective of this study was to provide a basis for future updates to the 2010 ASHRAE Performance Measurement Protocols for Commercial Buildings (PMP) through case studies. The PMP defines a standardized method of measuring and analyzing building performance in six categories: energy, water, thermal comfort, indoor air quality, lighting, and acoustics. We conducted case studies for five buildings following the PMP. Based on experiences following the protocol in this wide range of buildings, we assessed the validity, reliability, and practicality of the PMP and provided comments and recommendations for future revisions. Most of the measurement protocols at the basic level are reliable, practical, and valid. Many tasks at the intermediate and advanced levels, however, can be difficult to perform for some building types. Some of the tasks or measurement procedures were results from past research projects, and the software or tools recommended may not be readily available or fully supported. The measurement protocols at the intermediate level are only somewhat reliable and some of them are impractical. Most measurement protocols at the advanced level are complex and need to be performed by qualified or specially trained personnel and, thus, are impractical as a performance measure, except for specialized applications.
Atomistic simulations, mesoscopic modeling, and theoretical analysis of thermal conductivity of bundles composed of carbon nanotubes
(American Institute of Physics, 2013-09-10) Volkov, Alexey N.; Salaway, Richard N.; Zhigilei, Leonid V.; University of Virginia; University of Alabama Tuscaloosa
The propensity of carbon nanotubes (CNTs) to self-organize into continuous networks of bundles has direct implications for thermal transport properties of CNT network materials and defines the importance of clear understanding of the mechanisms and scaling laws governing the heat transfer within the primary building blocks of the network structures-close-packed bundles of CNTs. A comprehensive study of the thermal conductivity of CNT bundles is performed with a combination of non-equilibrium molecular dynamics (MD) simulations of heat transfer between adjacent CNTs and the intrinsic conductivity of CNTs in a bundle with a theoretical analysis that reveals the connections between the structure and thermal transport properties of CNT bundles. The results of MD simulations of heat transfer in CNT bundles consisting of up to 7 CNTs suggest that, contrary to the widespread notion of strongly reduced conductivity of CNTs in bundles, van der Waals interactions between defect-free well-aligned CNTs in a bundle have negligible effect on the intrinsic conductivity of the CNTs. The simulations of inter-tube heat conduction performed for partially overlapping parallel CNTs indicate that the conductance through the overlap region is proportional to the length of the overlap for CNTs and CNT-CNT overlaps longer than several tens of nm. Based on the predictions of the MD simulations, a mesoscopic-level model is developed and applied for theoretical analysis and numerical modeling of heat transfer in bundles consisting of CNTs with infinitely large and finite intrinsic thermal conductivities. The general scaling laws predicting the quadratic dependence of the bundle conductivity on the length of individual CNTs in the case when the thermal transport is controlled by the inter-tube conductance and the independence of the CNT length in another limiting case when the intrinsic conductivity of CNTs plays the dominant role are derived. An application of the scaling laws to bundles of single-walled (10,10) CNTs reveals that the transition from inter-tube-conductance-dominated to intrinsic-conductivity-dominated thermal transport in CNT bundles occurs in a practically important range of CNT length from similar to 20 nm to similar to 4 mu m. (C) 2013 AIP Publishing LLC.
Atomization and combustion of liquid biofuels
(University of Alabama Libraries, 2011) Simmons, Benjamin; Agrawal, Ajay K.; University of Alabama Tuscaloosa
Biofuel research will continue to be important as the world seeks to address limited fossil fuel supplies, concerns over greenhouse gases, and demand for energy independence. Biofuels can meet these needs by being a potentially carbon neutral energy source that can be utilized wherever any of a vastly varied feedstock is available. Since much of the energy infrastructure is set up for liquid fuels, liquid biofuels should fill many needs. One common biofuel is biodiesel, produced from bio-oil to match physical properties (like viscosity) of conventional fuels such as diesel. Biodiesel is produced through the transesterification of a source bio-oil and results in the byproduct, glycerol. This study seeks to investigate the combustion performance of a soy biodiesel, the source vegetable oil (VO), and the byproduct glycerol, while using number 2 diesel as the baseline for comparison. This study implements a novel fuel atomization technique known as flow-blurring (FB) atomization to atomize and cleanly combust not only biodiesel but also VO and glycerol. FB atomization uses a simple geometry to create a two-phase air/fuel mixture upstream of an orifice to produce which results in very fine sprays which burn cleanly and produce lower CO and NOX as compared to standard air-blast (AB) fuel injectors. First, the combustion performance of biodiesel and VO are compared to a diesel baseline. Results indicate that the FB mechanism provides a simple technique that can be used to successfully atomize and combust VO with resulting emissions comparable to diesel fuel. It was also observed that the FB atomizer incurred no adverse pressure drop penalties when operating with VO or biodiesel. Next, a study into the combustion performance of glycerol was conducted. First glycerol was co-fired with methane in an un-insulated quartz combustor. Results show high combustion efficiency, although CO emissions at the combustor wall were high (~5000 ppm) because of heat loss. Insulating the combustor made it possible to burn pure glycerol flames. An optimum air to liquid mass ratio (ALR) was found and used to investigate combustion performance at three different heat release rates. Residence time in the combustor was found to be an important parameter to achieve low CO emissions. Finally, glycerol/ methane flames were investigated in the insulated chamber to demonstrate dual fuel capabilities of the combustor. The emissions were minimized by splitting methane flow between primary and atomizing air lines. Next, spray characteristics of the FB atomizer were compared to the AB atomizer using a phase Doppler particle analyzer (PDPA) system. Results for water as the liquid show that the FB atomizer produces sprays with smaller droplets and also a narrower range of droplet sizes. The FB injector also incurred a smaller pressure drop in the atomizing air line. The FB atomizer incurred higher pressure drop in the liquid supply line resulting from the intense two-phase mixing at the tip of the liquid tube. Next, non-reacting VO and diesel sprays were compared using the PDPA technique. Diesel sprays resulted in smaller droplets compared to VO sprays. Upon further investigation it was revealed that the majority of the fuel mass flow within both sprays passes through a region with similar droplet diameter. Therefore, the mass-weighted Sauter mean diameter (SMD) was similar for VO and diesel sprays in spite of the large difference in their kinematic viscosity. Finally, a reacting glycerol spray flame was investigated with the PDPA technique to establish velocity and droplet size trends. Glycerol sprays contain droplets comparable to those from VO cold sprays. In summary, this study establishes the potential of the FB atomizer: the ability to successfully atomize and combust highly viscous fuels with performance much superior to AB atomizers.
Background UV in the 300 to 400 nm region affecting the extended range detection of radioactive material
(University of Alabama Libraries, 2010) West, William Carey; Fonseca, Daniel J.; University of Alabama Tuscaloosa
The desire to find alternative methods for the detection of radioactive material at extended ranges has resulted in an increased interest in the detection of the air fluorescence resulting from the alpha or beta radioactive particle's interaction with molecules of air. Air fluorescence photons travel further than the radioactive particles, allowing for detections at longer distances. However, any detection of the ultraviolet (UV) air fluorescence is dependent on overcoming natural and man-made background UV to achieve favorable signal to noise ratios. This research describes laboratory and field experiments conducted to determine the background UV in the 300 to 400 nm region of the electromagnetic spectrum for certain detection scenarios, and number of UV air fluorescence photons required to achieve detections with a certain confidence limit. The reflective, scintillation, and transmissive UV characteristics of some common materials are discussed and their contribution to a successful detection explored. Additionally, the contributions to the UV background from natural and man-made light sources are investigated. The successful outside optical detection of alpha and beta radioactive isotopes in the 300 to 400 nm region is possible in the lower part of the spectral region (i.e., near 316 nm), when there is no UV light from man-made sources in that band and only natural light exists. Alpha sources (i.e., ^241 Am) equal to or larger than 1.017 curies, theoretically can be detected with 95% confidence during nighttime scenarios with moonless overcast skies at a distances of 20 meters at 316 nm with the optical system assumed for these calculations. Additionally, where scintillators are available that can be employed near ^90 Sr radioactive sources, the detectable activities can be reduced by factors as high as 250. This allows for detections of sources in the millicuries. Tests results are presented for several common materials (e.g., polypropylene, high density polyethylene, low density polyethylene, etc.) that scintillate in the presence of ^90 Sr and can be used to achieve gains in the 100s in the air fluorescence bands centered on 316 nm and 337 nm.
CAD modeling and interface stress analysis of diamond-coated tooling
(University of Alabama Libraries, 2010) Miao, Chao; Chou, Y. Kevin; University of Alabama Tuscaloosa
Diamond-coated cutting tools have been widely employed in machining applications due to their superior properties. However, during the deposition process, significant residual stresses will be generated to affect the coating-substrate adhesion quality. In addition, interface delamination is another major factor causing catastrophic tool failure. The objectives of this research consist of: (1) to evaluate deposition-induced residual stresses of diamond-coated drills, (2) to analyze the interface failure of diamond-coated tools by numerical simulations of indentations, and (3) to evaluate deposition-induced residual stresses developed on diamond-coated macro/micro end mills with the inclusion of a cohesive zone model. The research scopes of this research are to investigate diamond-coated tool residual stresses as well as interface behaviors under the contact loading. The research methodologies include: (1) 3D CAD modeling of diamond coated drills and macro/micro end mills, (2) finite element analysis (FEA) of diamond-coated cutting tools after the deposition, and (3) indentation based simulations incorporating a cohesive zone model for the analysis of interface behaviors. The major findings were summarized as follows: (1) for diamond-coated drills, FEA results indicated that the edge radius had the most dominant effect on interface stresses, which were 1.41 GPa, 3.11 GPa for 3 µm re and 0.73 GPa, 2.94 GPa for 15 µm re in terms of σ_rmax and σ_θmax, (2) for the indentation with a spherical indenter, increasing the coating Young's Modulus reduced delamination sizes, and a thicker coating tended to have greater resistance to the interface delamination. Residual stresses facilitated the interface delamination. For the indentation with a wedge indenter, substrate surface curvature slightly affected the loading vs. displacement curve. Residual stresses increased delamination sizes. The coating with a larger Young's Modulus had less delamination sizes, and (3) as for diamond-coated end mills, the edge radius still dominantly affected residual stresses. When the size of macro end mills was scaled down to micro level, interface stresses were increased. The existence of a CZM reduced residual stresses. The major achievements included (1) diamond-coated tool geometry and cohesive zone effects on residual stresses and interface stresses, and (2) coating attribute, residual stresses, and substrate surface curvature effects on the interface behavior.
Catalytic converter thermal model for hybrid electric vehicle engine on/off control strategy development
(University of Alabama Libraries, 2017) Young, Karissa; Puzinauskas, P.; University of Alabama Tuscaloosa
A 3-dimensional (3-D), thermochemical catalytic converter model was developed to investigate the effects of engine-off periods typical in hybrid electric vehicle (HEV) operation on overall emissions conversion effectiveness. The model includes a 3-reaction mechanism to account for the majority of heat generation due to exhaust species chemical conversion during engine operation. The modeled cross-sectional area of the catalytic converter was decreased to reduce computational complexity. This simplification resulted in an over prediction of shell heat loss to the surroundings due to the incorrect shell surface area to volume ratio. Therefore, an adiabatic assumption was used to analyze the substrate’s thermal behavior without the influence of external heat transfer. The analytical model was experimentally validated with an engine that provided feedgas to a catalytic converter. The catalytic converter was instrumented with thermocouples for internal and surface temperature measurement. The reduced-size, catalytic converter model with the adiabatic assumption produced mid-catalytic converter temperature predictions within 3%. However, thermal behavior during engine-off period could not be predicted since radial heat transfer was eliminated with the adiabatic assumption but is the dominating effect in real cool-down. Accurate temperature predictions during cool-down requires modeling a realistic surface area to volume ratio which is outside of the computational limitations of the modeling platform used in this work.
Characteristics of hydrogen combustion in a direct injected constant volume combustion chamber using rainbow schlieren deflectometry
(University of Alabama Libraries, 2011) Booker, Tanisha Latrina; Agrawal, Ajay K.; University of Alabama Tuscaloosa
The nation's need for alternative fuels for Internal Combustion Engines (ICEs) has been a major concern for automotive researchers. The need for a sustainable energy system has lead researchers to consider alternative fuels such as hydrogen and thus, several studies have been conducted on this fuel since the 1930s. In particular, understanding the combustion performance of hydrogen at varying equivalence ratios, ignition timings, and volumetric percentages with other fuels is necessary to optimize engine operations. This study investigates the combustion performance of hydrogen injected into a constant volume combustion chamber (CVCC). The properties studied include flame structure, combustion duration, flame front speed, chamber pressure, and net heat transfer rate. The fuel was injected directly into the chamber containing quiescent air at atmospheric pressure. An ignition system consisting of a coil and a spark plug was used to ignite fuel/air mixtures. This study implemented an optical technique, Rainbow Schlieren Deflectometry, to visualize fuel jet penetration, turbulent fuel-air mixing, flame structure, and flame propagation. Schlieren images were analyzed by a cross-correlation technique to compute flame front speed. A dynamic pressure sensor was used to acquire instantaneous chamber pressures which were used to estimate transient chamber net heat transfer rates. First, experiments were conducted by varying the fuel supply pressure to the chamber and the overall equivalence ratio. An investigation of the fuel jet penetration showed that it takes the fuel jet 2.25 ms to reach the igniter. This result was helpful in establishing ignition times for later experiments. Results showed that fuel supply pressure does not affect fuel jet penetration. The fuel jet, however, creates turbulence in the chamber that affects combustion processes. The equivalence ratios tested were ö = 1.0, 0.804, and 0.318. Results showed that equivalence ratio has a significant impact on flame front speed which decreased as the equivalence ratio decreased. Next, experiments were conducted to study the effects of ignition time on combustion processes. A programmable logic controller was added to the experimental setup to control ignition time and aid in sequencing events. The ignition times tested were t = 3, 5, and 10 ms in the early ignition group, t = 20, 30, and 40 ms in the mid-ignition group, and t = 60, 80, 240, and 540 ms in the late ignition group, where t = 0 refers to the start of fuel injection. Ignition time affects the flame structure and flame propagation. Results showed that at ignition times prior to the close of the fuel injector, the initial flame front speed is high because of fuel-jet generated turbulence. After the fuel injector closes, increasing the ignition time increases the combustion duration because of dissipating fuel-jet generated turbulence. Ignition time also has significant effects on chamber pressure variations and net heat transfer rates. Next, the effect of ignition time for varying equivalence ratios was studied. Experiments were conducted at three equivalence ratios, ö = 0.6, 0.8, and 1.0 and four ignition times, t = 3 ms, 10 ms, tend, and tend + 50 ms. An ultra-high speed camera was incorporated into the experimental setup to acquire schlieren images at a frame rate of 50,000 Hz and exposure time of 19.8µs. Results show that equivalence ratio has minor effects on chamber pressure variations and net heat transfer rate at early ignition times and on flame structure and flame propagation at any ignition times. Ignition time has a significant effect on all combustion processes. Finally, experiments were conducted to determine the effect of hydrogen percentages by volume on methane combustion at varying ignition times. A second high pressure injector was incorporated into the experimental setup to inject the methane into the combustion chamber. Experiments were conducted at the following methane/hydrogen percentages: 23% CH4 - 77% H2, 33% CH4 - 67% H2, 43% CH4 - 57% H2, 53% CH4 - 47% H2, and 63% CH4 - 37% H2. The two ignition times were t = tend and t = tend + 50 ms. Results show that combustion duration decreases as hydrogen percentage increases for identical ignition times, and as ignition time decreases at identical hydrogen percentages. Flame front speed increases as hydrogen percentage increases. Peak chamber pressure and peak net heat transfer rate decreases for the late ignition time at fixed hydrogen percentages.
Characterization and comparison of white layer by hard turning versus grinding
(University of Alabama Libraries, 2004) Sahani, Jasdeep Singh; University of Alabama Tuscaloosa
Compared with grinding, hard turning has the potential to make a variety of precision components of superior surface integrity, such as bearings, gears, cams, shafts, tools, dies, etc., while reducing investment, increasing production rate, and eliminating environmental pollution. Despite its spectrum of advantages over cost intensive grinding process, industrial realization of hard turning still remains in incipient stage. The low industrial acceptance of hard turning may be attributed to uncertainty related to surface quality especially for the white layer which is a key factor of surface integrity and thus product performance.
Characterization Of Multi-layered Fish Scales (Atractosteus spatula) Using Nanoindentation, X-ray CT, FTIR, and SEM
(MyJove Corporation, 2014) Allison, Paul G.; Rodriguez, Rogie I.; Moser, Robert D.; Williams, Brett A.; Poda, Aimee R.; Seiter, Jennifer M.; Lafferty, Brandon J.; Kennedy, Alan J.; Chandler, Mei Q.; United States Department of Defense; United States Army; U.S. Army Corps of Engineers; U.S. Army Engineer Research & Development Center (ERDC); University of Alabama Tuscaloosa
The hierarchical architecture of protective biological materials such as mineralized fish scales, gastropod shells, ram's horn, antlers, and turtle shells provides unique design principles with potentials for guiding the design of protective materials and systems in the future. Understanding the structure-property relationships for these material systems at the microscale and nanoscale where failure initiates is essential. Currently, experimental techniques such as nanoindentation, X-ray CT, and SEM provide researchers with a way to correlate the mechanical behavior with hierarchical microstructures of these material systems. However, a well-defined standard procedure for specimen preparation of mineralized biomaterials is not currently available. In this study, the methods for probing spatially correlated chemical, structural, and mechanical properties of the multilayered scale of A. spatula using nanoindentation, FTIR, SEM, with energy-dispersive X-ray (EDX) microanalysis, and X-ray CT are presented.
Characterization of the evolution of 2219-T87 aluminum as a function of the self-reacting friction stir welding process
(University of Alabama Libraries, 2019) Anderson, Kathryn; Daniewicz, Steve; University of Alabama Tuscaloosa
The self-reacting friction stir welding (SR-FSW) process is a primary method used by NASA to construct the Space Launch System (SLS) vehicle. This method uses large scale shear to plastically deform and mechanically mix base materials. This solid-state process causes the fabricated material to reach a temperature below the melting point, and as such, there are lower residual stresses and less warping than that observed in traditional fusion welding processes. The process parameters responsible for heat generation in the SR-FSW process include: the tool rotational speed, the tool translational speed, the crown plunge force, and the root/pin reaction force. Optimization of these process parameters is required to produce sound welded joints with the appropriate microstructural constituents. This work characterizes the effect of SR-FSW on AA2219-T87. Specifically, the material’s microhardness, strength, and θ-phase evolution are studied as a function of time and temperature. These data sets are compared to the microhardness in the friction stir weld stir zone, thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ), and base material. Additionally, residual stresses produced as a function of the friction stir welding process are quantified. Furthermore, fatigue crack growth rate data and plane-strain fracture toughness data of the welded material are compared to that of the base material. Finally, all data collected is used to calibrate a tool that determines the relative contribution from various strengthening mechanisms to the overall strength of the weld.

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