Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Mechanical Engineering

Damping is an essential element of any structure prone to vibration. The energy dissipation provided by dampers reduces structural vibration, enhancing serviceability of the structure and in some cases prevents damage caused by fatigue. When most of the vibration energy in a structure resides in a single mode, the go-to method of abating such vibration is tuned mass damping. Numerous applications, including pipework and structures, necessitate that the tuned mass damper be tuned to a specific natural frequency in a particular vertical or horizontal direction. When structure vibration occurs at multiples modes with their corresponding natural frequencies, then viscous dampers are the more suitable choice due to their broadband damping capacity. The motivation for conducting this study is to explore the use of eddy current damping as an alternative to liquid-based viscous and solid-based viscoelastic damping mechanisms in tuned mass dampers as well as stand-alone/broadband viscous dampers. Eddy current damping (also known as magnetic damping) is generated by the eddy current induced in a conductive material subjected to a time-varying magnetic field (normally created by several rare earth permanent magnets) and tuned mass damper that is used eddy current damper as damper element are explored. The eddy current in the conductor generates its own magnetic field resulting in an electromagnetic force opposing the force of the original time-varying magnetic field. The main contribution of this effort is the development of a numerical tool for synthesizing eddy current dampers and optimizing them for particular applications. The utility and efficacy of this numerical tool are demonstrated and verified by synthesizing two different designs of eddy current dampers and laboratory testing one of them. The first design consists of a stack of eight axially magnetized NdFeB (N42) permanent magnets that are separated by seven iron pole sections moving within a tubular (open full item for complete abstract)

Committee: Reza Kashani (Advisor); Timothy Reissman (Committee Member); David Myszka (Committee Member); Youssef Raffoul (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2024, Electrical and Computer Engineering

As manufacturing techniques such as topology optimization and additive manufacturing develop, components with increasing geometric complexity are becoming more common. Thus, it is necessary to develop automated non-destructive evaluation techniques that are adaptable to various surface geometries. This project seeks to leverage robotic simulation software to virtually plan and optimize eddy current inspections of various airplane components to detect flaws while eliminating false positives. The final deliverable will be a Robot Operating System (ROS) software package that generates an optimal tool path plan based on probe output for various scan resolutions.

Committee: Michael Groeber (Advisor); Balasubramaniam Shanker (Committee Member); Matthew Cherry (Advisor); LoriAnne Groo (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Automotive Materials; Computer Engineering; Computer Science; Electrical Engineering; Electromagnetics; Engineering; Experiments; Industrial Engineering; Materials Science; Mechanical Engineering; Robotics

Master of Science, The Ohio State University, 2023, Mechanical Engineering

This work leverages recent advances in the Robot Operating System (ROS) to design a platform capable of processing previously unknown geometries with minimal user interaction. Industry needs inspection platforms which are adaptable to multiple part families. An eddy current inspection tool was selected to prioritize design choices which accommodated micrometer-precision tool positioning when deployed on an 6-axis industrial robot. These robots offer the physical reach and flexibility required by in situ inspections at the refined control level necessary for accurate data collection. Surface scanning and reconstruction was achieved using a low-cost, commercially available stereoptic camera. Non-contact, material inspection techniques such as eddy current use electromagnetic field propagation to measure variation in electrical conductivity and magnetic permeability to detect defects. Geometry with sharp changes in topology causes magnetic variations which give improper eddy current readings. To circumvent this issue, an operator is used to interactively select inspection surfaces. This manuscript will focus on the design process and a representative deployment using a Yaskawa Motoman GP7 industrial robot. This study successfully implemented a high precision robotic inspection platform using highly configurable software controls while maintaining an easy-to-use user interface.

Committee: Michael Groeber (Advisor); Saeedeh Ziaeefard (Committee Member); Andrew Gillman (Committee Member) Subjects: Mechanical Engineering; Robotics

MS, University of Cincinnati, 2019, Engineering and Applied Science: Aerospace Engineering

There is a growing need to determine the residual stress profiles in surface-treated components to accurately and reliably determine the remaining service life of the component and to reduce the risk of failure. To acquire depth-dependent residual stress profiles, the XRD technique requires multiple layers of material to be removed with electro-etching, which renders the tested component unsuitable for service use. The nondestructive evaluation community has been in search of a method that can determine the residual stress profiles in surface-treated aerospace engine alloy components nondestructively. A promising nondestructive technique using high-frequency eddy current spectroscopy has been investigated with much potential. However, the two principal effects of shot peening, namely residual stress and cold work, are opposite in sign in Ti-6Al-4V, resulting in almost complete cancellation between the two competing effects, causing the eddy spectroscopy technique to be incapable of determining the residual stress profile of shot-peened components. This study investigates an alternative electromagnetic residual stress profiling technique using a dual-mode inspection with Hall impedance and eddy current spectroscopy to separate the components of shot-peening. The effect of residual stress (elastic strain) and cold work (plastic strain) will be investigated on Ti-6Al-4V (36 HRC) using both Hall coefficient and eddy current techniques. Experimental results, relative Hall impedance and AECC change spectra, were 3 obtained on shot-peened Ti-6Al-4V (36 HRC) with Almen intensities of 4A, 8A, and 12A. Destructive XRD residual stress and cold work depth profiles were obtained from the literature on shot-peened Ti-6Al-4V (32 HRC) with Almen intensities of 4A, 8A, and 12A for comparison. Relative Hall coefficient and electric conductivity depth profiles were calculated from the XRD residual stress and cold work depth profiles on the shot-peened specimens, using electrom (open full item for complete abstract)

Committee: Peter Nagy Ph.D. (Committee Chair); Yao Fu Ph.D. (Committee Member); Francesco Simonetti Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science (MS), Wright State University, 2017, Physics

Covetics are hybrid materials fabricated by fusing carbon with metals in an induction furnace. There is an indication that covetics have better thermal and electrical proper-ties in comparison with pure metals. The main goal of this research is to study thermal transport in covetics measured by specific absorption rate using calorimetry. In addition, temperature distribution has been measured along the both metal and covetic wires carrying currents of 5 A and 10 A, respectively. The first set of copper covetic (Cu cov) samples with nominal content of 36 at% carbon were prepared by Third Millennium Materials Company (TMMC) in the induction furnace using ceramic mold. After cooling, these samples were subjected to cold rolling to make wires. To remove contamination, defused from ceramic molds into covetics, the samples were subjected to numerous remelting steps in the induction furnace. In addition to remove stresses, the samples were annealed at elevated temperature in argon. Overall four Cu cov samples: as-received, and 8 remelt, including annealing, were pre-pared by TMMC. The second set of six Cu cov including annealing samples with nominal contents of 0 at%, 5 at%, and 10 at% carbon were prepared in AFRL facilities using graphite mold. For comparison, four other silver covetic (Ag cov) samples with nominal con-tents of 0 at% and 36 at% carbon were prepared under three different cooling processes by the TMMC. The SAR measurements of all covetic samples were done in a calorimetric system at currents of 5 A, 10 A, and 15 A, and at 177 kHz of AC magnetic field. The experimental data show that covetic samples have mixed heating rates in comparison to the pure metals. For instance, all the silver and Cu cov samples show lower specific absorption rates than the corresponding host metals, except the annealed Cu cov and druzzy Ag cov (a molten Ag cov was slowly cooled and stirred with graphite) samples. Additionally, SAR was higher for all the sampl (open full item for complete abstract)

Committee: Gregory Kozlowski Ph.D. (Committee Chair); Zafer Turgut Ph.D. (Committee Member); Jason Deibel Ph.D. (Committee Member); John Boeckl Ph.D. (Committee Member) Subjects: Materials Science; Physics

Master of Science in Engineering (MSEgr), Wright State University, 2013, Renewable and Clean Energy

Electric wheelchairs have a considerable impact on improving the quality of life for the millions of disabled persons around the world. These modern pieces of technology offer freedom and mobility for disabled persons to interact with the world outside of their homes. The goal of this project is to assist in advancements of conventional electric wheelchairs. This includes replacing the heavy, bulky, and inefficient lead acid batteries and worm gear drive systems with lithium-ion batteries and wheel hub motors in order to decrease weight and size, and increase efficiency. This master thesis research is focused on designing, fabricating, and testing an eddy current brake dynamometer that can effectively determine the efficiency of the newly implemented wheel hub motor system at operational speeds. The importance of measuring the efficiency of the wheel hub motors used is to verify that they have a sufficient efficiency that would increase running time, extend traveling distances, and increase reliability. Because of the low speeds and high torque required, geared wheel hub motors were used instead of brushless permanent magnet hub motors. In this research, SolidWorks was used for modeling and to create an engineering drawing packet. The components of the dynamometer were machined and fabricated with a lathe and a milling machine. MATLAB was utilized for the calculations. With the help of the dynamometer platform, it was determined that the wheel hub motors have a higher efficiency but only at higher speeds. Although the geared hub motors used compromise some efficiency in order to produce greater torque at low speeds, they are light weight with compact size and have a much lower cost making them ease for maneuverability and economically feasible for next generation wheelchairs.

Committee: Junghsen Lieh Ph.D. (Advisor); Hong Huang Ph.D. (Advisor); Ha-Rok Bae Ph.D (Committee Member) Subjects: Electrical Engineering; Energy; Mechanical Engineering

Master of Science in Engineering (MSEgr), Wright State University, 2010, Electrical Engineering

Pulse Width Modulated (PWM) Forward DC-DC converter is a buck-derived isolated power converter which is used extensively in low power to medium power applications. Satisfactory operation of the transformer utilized in forward converter plays a crucial role in the overall operation of the forward converter. Hence detailed analysis pertaining to design of forward transformer is important. The forward transformer is unique as the magnetizing inductance is not required to store magnetic energy. Additionally, the forward transformer has a tertiary winding, which is required to reset the core and to prevent core saturation. This adds to the complexity of design and analysis as compared to a flyback transformer. The effect of winding losses due to High-Frequency (HF) eddy currents caused by harmonics is also considered in this work. Dowell's equation was extended to determine the winding resistances for forward transformer in Continuous Conduction Mode (CCM). The Fourier series of the transformer winding current waveforms are derived. The winding resistances derived based on the Dowell's expression and the current expressions derived based on spectral analysis are employed in evaluating the winding losses. The procedure to design a HF forward transformer in CCM is presented. The effect of harmonics was computed using MATLAB, and verified by circuit simulation with Saber Sketch. The results were found to be in good agreement.

Committee: Marian K. Kazimierczuk PhD (Advisor); Ronald G. Riechers PhD (Committee Member); Saiyu Ren PhD (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Engineering

Master of Science (MS), Wright State University, 2010, Physics

The research work is focused on conducting a feasibility study on a new “non-contact” single probe dual coil inductive sensor for sensing the proximity and thickness of Aluminum (Al) 3003 alloy metal sheets, which is a non-magnetic metal. A bulk of the research and development work has already been done in the area of non-destructive testing (NDT) using eddy current technology targeted to various applications like corrosion detection, material thickness, material conductivity, etc. The research work presented in this thesis uses the prior research and development work completed in NDT as a platform for conducting this study to estimate proximity and thickness of Aluminum 3003 alloy metal sheets, which is not considered a flaw detection application. Some of the current technologies in the area of eddy current NDT for proximity and thickness estimation, each with its own limitations, include single probe ‘contact' sensors for magnetic metals, single probe ‘non-contact' sensors with separation distance of less than 1 mm and dual probe sensors that requires probes on both sides of the metal sheet. A swept multi-frequency scanning technique is used together with an automated data collection system to measure and collect output voltage and phase difference data over a wide range of frequencies. The skin effect in conductors and its associated property of skin depth is used to extract proximity and thickness information from the data collected, and then correlated with reference values to validate the results. Experimental results show the output voltage and phase difference of the sensor is dependent on the metal parameters (resistivity ‘ρ', permeability ‘μ', thickness ‘T') and coil parameters (diameter ‘D', frequency ‘F', lift-off ‘L'). Further, proximity is estimated from output voltage difference, and metal thickness (single/double) is estimated from phase difference independent of lift-off, which is a novel approach for thickness detection. The test sensor provides an (open full item for complete abstract)

Committee: Douglas T. Petkie PhD (Committee Chair); Jerry D. Clark PhD (Committee Member); Jason A. Deibel PhD (Committee Member) Subjects: Aerospace Materials; Electrical Engineering; Electromagnetism; Engineering; Physics

PhD, University of Cincinnati, 2007, Engineering : Aerospace Engineering

Recent research results indicated that eddy current conductivity measurements can be exploited for nondestructive evaluation of near-surface residual stresses in surface-treated nickel-base superalloy components. Most of the previous experimental studies were conducted on highly peened (Almen 10-16A) specimens that exhibit harmful cold work in excess of 30% plastic strain. Such high level of cold work causes thermo-mechanical relaxation at relatively modest operational temperatures; therefore the obtained results were not directly relevant to engine manufacturers and end users. The main reason for choosing peening intensities in excess of recommended normal levels was that in low-conductivity engine alloys the eddy current penetration depth could not be forced below 0.2 mm without expanding the measurements above 10 MHz which is beyond the operational range of most commercial eddy current instruments. As for shot-peened components, it was initially felt that the residual stress effect was more difficult to separate from cold work, texture, and inhomogeneity effects in titanium alloys than in nickel-base superalloys. In addition, titanium alloys have almost 50% lower electric conductivity than nickel-base superalloys; therefore require proportionally higher inspection frequencies, which was not feasible until our recent breakthrough in instrument development. Our work has been focused on six main aspects of this continuing research, namely, (i) the development of an iterative inversion technique to better retrieve the depth-dependent conductivity profile from the measured frequency-dependent apparent eddy current conductivity (AECC), (ii) the extension of the frequency range up to 80 MHz to better capture the peak compressive residual stress in nickel-base superalloys using a new eddy current conductivity measuring system, which offers better reproducibility, accuracy and measurement speed than the previously used conventional systems, (iii) the lift-off effect on hi (open full item for complete abstract)

Committee: Dr. Peter Nagy (Advisor) Subjects:

PhD, University of Cincinnati, 2005, Engineering : Aerospace Engineering

Surface enhancement methods, which produce beneficial compressive residual stresses and increased hardness in a shallow near-surface region, are widely used in a number of industrial applications, including gas-turbine engines. Nondestructive evaluation of residual stress gradients in surface-enhanced materials has great significance for turbine engine component life extension and their reliability in service. It has been recently found that, in sharp contrast with most other materials, shot-peened nickel-base superalloys exhibit an apparent increase in electrical conductivity at increasing inspection frequencies, which can be exploited for nondestructive residual stress assessment.The primary goal of this research is to develop a quantitative eddy current method for nondestructive residual stress profiles in surface-treated nickel-base superalloys. Our work have been focused on five different aspects of this issue, namely, (i) validating the noncontacting eddy current technique for electroelastic coefficients calibration, (ii) developing inversion procedures for determining the subsurface residual stress profiles from the measured apparent eddy current conductivity (AECC), (iii) predicting the adverse effect of surface roughness on the eddy current characterization of shot-peened metals, (iv) separating excess AECC caused by the primary residual stress effect from intrinsic conductivity variations caused by material inhomogeneity, and (v) investigating different mechanisms through which cold work could influence the AECC in surface-treated nickel-base superalloys. The results of this dissertation have led to a better understanding of the underlying physical phenomenon of the measured excess AECC on nickel-base engine alloys, and solved a few critical applied issues in eddy current nondestructive residual stress assessment in surface-treated engine components and, ultimately, contributed to the better utilization and safer operation of the Air Force's aging aircraft (open full item for complete abstract)

Committee: Dr. Peter Nagy (Advisor) Subjects: Engineering, Aerospace

Master of Science, The Ohio State University, 2011, Mechanical Engineering

This research entails the design, fabrication, and characterization of an electromagnetic (EM) probe capable of detecting variations in EM properties in conducting media by generating eddy currents in the sample. A targeted application of this method is to distinguish cancer from normal tissue, in hopes eventually to serve as a real-time, intraoperative detection tool for surgeons in the operating room (OR). The probe, similar to a transformer, consists of a primary coil and secondary (detector) coil, inductively coupled by virtue of a time varying current applied to the primary coil. This results in a periodic detector coil voltage trace comprising several peaks. When a conductive sample such as tissue is placed in close proximity to the probe, changes in magnitude and temporal occurrence of these peaks are observed. The shifts observed in the detector coil voltage peaks are affected by the path the eddy current travels in the conducting specimen and by the magnitude of the eddy current itself. This work differs from previous work in two principal aspects. First, the prototype probe known in this work as B1 is hardwired to a printed circuit board, as opposed to being non-permanently connected on a breadboard. Experimental measurements show that differences between the permanent and non-permanent configurations are negligible. A second aspect is the design methodology used to make B1 smaller than any of its predecessors, roughly on the order of millimeters in diameter. In making a smaller probe, each coil's self inductance is inherently smaller; however, by placing additional capacitors in parallel with each coil to increase the net capacitance, a temporal response mimicking that of its larger predecessor can be obtained provided the characteristic LC response is maintained. The experimental measurements and numerical simulations discussed in this thesis demonstrate the significance of the circuit element properties of the probe and how these can be used to model (open full item for complete abstract)

Committee: Vish Subramaniam (Advisor); William Rich (Committee Member) Subjects: Biomedical Engineering; Mechanical Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2012, Materials Engineering

The objective of this research is to determine the ability of several Non-Destructive Inspection (NDI) methods to detect various levels of High Cycle Fatigue fretting fatigue damage induced in simulated Ti-6Al-4V dovetail engine components. To generate various levels of fretting fatigue damage; a specially designed dovetail specimen is utilized which more accuracy simulates the cyclic loading interaction between a compressor blade and disk of an aircraft turbine engine. All fretting fatigue tests were conducted with un-coated Ti-6Al-4V alloy at ambient temperature, at a load ratio of 0.1, and two 30 Hz cyclic load levels (10% and 30% of expected life). In addition, two microstructures (α+β, β-annealed) are utilized to determine their effect on fretting fatigue as well as the NDI signal response. To quantify the extent of fretting fatigue damage; mini-C specimens are extracted from the fretted dovetail specimens and “step-tested” to quantify the debit in fatigue strength. Specimens are heat-tinted after fretting fatigue to help qualify the extent of fretting fatigue damage and aid in crack initiation site identification using both optical microscope and the Scanning Electron Microscope (SEM). Three NDI techniques are used to qualify the extent of fretting fatigue damage in Ti-6Al-4V and relate this damage to the NDI signal response and the debit in fatigue strength. The NDI techniques utilized in this research include: White Light Interference Microscopy (WLIM), Wyle Lab Eddy Current Inspection System (ECIS) and the JENTEK Meandering Winding Magnetometer (MWM) Array. Note: these NDI techniques are used “as is” and were not modified for fretting fatigue detection. However, in the case of the WLIM, a fretting fatigue damage parameter methodology is utilized to specifically quantify the extent of fretting damage. In addition, the Scanning Electron Microscope (SEM), Auger Electron Spectroscopy (AES), and Knoop micro-hardness tester were utilized to investigate the c (open full item for complete abstract)

Committee: Dr. Daniel Eylon D. Sc. / Materials Engineering (Committee Chair); Dr. James A. Snide Ph.D. / Materials Engineering (Committee Member); Dr. Terrence P. Murray Ph.D. / Materials Engineering (Committee Member); Professor Gerald Shaughnessy M.S. / Mathematics (Committee Member) Subjects: Aerospace Materials; Materials Science

Doctor of Philosophy (Ph.D.), University of Dayton, 2009, Mechanical Engineering

This dissertation describes the design and development of a new high-resolution electrical conductivity imaging technique combining the basic principles of eddy currents and atomic force microscopy (AFM). An electromagnetic coil is used to generate eddy currents in an electrically conducting material. The eddy currents induced in the sample are detected and measured with a magnetic tip attached to the AFM cantilever. The interaction of eddy currents with the magnetic tip-cantilever is theoretically modeled. The model is then used to estimate the eddy current forces generated in a typical metallic material placed in induced current field. The magnitude of the eddy current force is directly proportional to the electrical conductivity of the sample. The theoretical eddy current forces are used to design a magnetic tip-cantilever system with appropriate magnetic field and spring constant to facilitate the development of a high-resolution, high sensitivity electrical conductivity imaging technique. The technique is used to experimentally measure eddy current forces in metals of different conductivities and compared with theoretical and finite element models. The experimental results show that the technique is capable of measuring pN range eddy current forces. The experimental eddy current forces are used to determine the electrical resistivity of a thin copper wire and the experimental value agrees with the bulk resistivity of copper reported in literature. The imaging capabilities of the new technique are demonstrated by imaging the electrical conductivity variations in a composite sample and a dual-phase titanium alloy in lift mode AFM. The results indicate that this technique can be used to detect very small variations in electrical conductivity. The spatial resolution of the technique is determined to be about 25 nm by imaging carbon nanofibers reinforced in polymer matrix. Since AFM is extensively used to characterize nanomaterials, the newly developed technique is (open full item for complete abstract)

Committee: Sathish Shamachary PhD (Committee Chair); P. Terrence Murray PhD (Committee Member); Donald Klosterman PhD (Committee Member); Chakrapani Varanasi PhD (Committee Member); Mark Blodgett PhD (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, University of Akron, 2008, Electrical Engineering

A novel eddy current (EC) system was developed for the measurement of torque in a rotating shaft, resulting in the following new contributions beyond the current "state of the art" in the field.1. Outline of a general methodology for shaft torque measurements and the development of an adaptable EC test system that can be applied to a variety of torque measuring applications with diverse constraints. 2. EC characterization of torque-stressed 18% Ni maraging steel at various excitation directions and test frequencies using a specially designed U-core EC sensor and fundamental and harmonic data analysis. 3. Design, development, and evaluation of a novel probe-type EC sensor with dual excitation windings, dual focused U-core elements at 90° to each other, and dual differentially connected sensing windings for static and dynamic shaft torque measurements. 4. System analysis for optimum shaft torque measurement accuracy taking into consideration the EC response behavior of torque-stressed 18% Ni maraging steel, the EC sensor characteristics, the effects of excitation field strength and test frequency, and the applied shaft torque and sensor air gap variations. 5. Design, development, and evaluation of a constant air-gap EC sensor assembly for shaft torque measurements. 6. The developed EC system can be applied in a wide variety of torque measurement or control systems to improve system performance and reliability.

Committee: Nathan Ida PhD (Advisor) Subjects: Electrical Engineering