Doctor of Philosophy, University of Akron, 2012, Civil Engineering

In the field of computational mechanics, there has been a very challenging problem, which is the characterization of heterogeneous media with randomly distributed material properties. In reality, no material is homogeneous and deterministic in nature and it has been well-known that randomness in microstructures and properties of materials could significantly influence scatter of structural response at larger scales. Therefore, stochastic characterization of heterogeneous materials has increasingly received attention in various engineering and science fields. In order to deal with this challenging problem, two major challenges need to be addressed: 1) developing an efficient modeling technique to discretize the material uncertainty in the stochastic domain and 2) developing a robust and general inverse identification computational framework that can estimate parameters related to material uncertainties. In this dissertation, two major challenges have been addressed by proposing a robust inverse analysis framework that can estimate parameters of material constitutive models based on a set of limited global boundary measurements and combining the framework with a general stochastic finite element analysis tool. Finally a new stochastic inverse analysis framework has been proposed, which has a novel capability of modeling effects of spatial variability of both linear and nonlinear material properties on macroscopic material and structural response. By inversely identifying statistical parameters (e.g. spatial mean, spatial variance, spatial correlation length, and random variables) related to spatial randomness of material properties, it allows for generating statistically equivalent realizations of random distributions of linear and nonlinear material properties and their applications to the development of probabilistic structural models. First, a robust inverse identification framework, called the Self-Optimizing Inverse Method (Self-OPTIM), has been developed. Unli (open full item for complete abstract)

Committee: Gun Jin Yun Dr. (Advisor); Wieslaw Binienda Dr. (Committee Member); Ernian Pan Dr. (Committee Member); Xiaosheng Gao Dr. (Committee Member); Kevin Kreider Dr. (Committee Member) Subjects: Civil Engineering; Engineering; Experiments; Materials Science; Mathematics

Doctor of Philosophy, University of Akron, 2025, Mechanical Engineering

While numerous linear elastic and hyperelastic tire cord models exist, the tire industry lacks an accurate tire cord model that can predict dynamic performance of tires at relevant Noise, Vibration and Harshness (NVH) frequencies (20 Hz-5,000 Hz). This critical gap in tire modeling limits the industry's NVH simulations using Finite Element Analysis. Addressing this need, this study characterizes the dynamic properties of Polyester 1500/2 tire cords at frequencies above 1kHz. The results from this study act as a building block for the development of an accurate tire dynamic model by providing cord material properties at high frequencies. This study focuses on experimentally evaluating the dynamic properties of the Polyester 1500/2 tire cords, which present unique experimental challenges because their fiber like geometry cannot withstand compressive loads. Although extensive research has been conducted on the thermomechanical and viscoelastic properties of tire cords under various conditions, no prior work has systematically evaluated their dynamic properties at high frequencies. This research addresses this gap by experimentally evaluating room temperature dynamic properties of a Polyester 1500/2 tire cord at strains just under 2% and frequencies exceeding 1kHz. Using a dynamic mechanical analyzer (DMA) machine, tensile, creep and DMA frequency sweep tests were conducted at both room and cold temperatures. Room temperature DMA results indicated that the storage modulus, loss modulus and tan  de-pended on both frequency and mean tensile strains. The room temperature data was then extended to higher frequencies using the time-temperature superposition (TTS) principle by conducting DMA frequency sweep tests at temperatures ranging between -35°C and 25°. The polyester tire cord expanded and became stiffer with decreasing temperature. This created a challenge to use TTS at a specified mean tensile strain. Separate creep experiments had to be performed to determine th (open full item for complete abstract)

Committee: Michelle S . Hoo Fatt Dr. (Advisor); Kwek Tze Tan Dr. (Committee Member); Weislaw K. Binienda Dr. (Committee Member); Christopher Barney Dr. (Committee Member); Hyeonu Heo Dr. (Committee Member) Subjects: Experiments; Industrial Engineering; Low Temperature Physics; Physics; Plastics; Science Education; Solid State Physics

Master of Science (M.S.), University of Dayton, 2024, Electro-Optics

Material characterization begins with finding the refractive index of the respective materials. The goal of this thesis is to develop a method to find the refractive index utilizing a high-power tunable mid-wave infrared (MWIR) laser. The general techniques used to determine the refractive index using this laser follow the principles of the Fresnel equations of reflection and transmission coefficients. By collecting the Reflectance and Transmittance we can then determine the refractive index following the equations. Amid starting to use the laser there was a sudden and gradual drop in the laser power. From there the refractive index measurements turned into tests on the laser itself to find the root of the power drop. With a detour of working directly on the laser to provide the correct wavelength and adequate power began the direction of this thesis to find a reasonable method of finding the refractive index with this laser in its current state. While completing the multitude of refractive index tests, we explore the internal components of the laser and how it functions.

Committee: Paul McManamon (Advisor); Andrew Sarangan (Committee Member); Rita Peterson (Committee Member) Subjects: Optics

Master of Science in Engineering, University of Akron, 2024, Mechanical Engineering

Additively manufacturing (AM), which is also referred to as 3D printing, is a collection of innovations that generate 3D parts by printing materials in a layer-wise pattern. In comparison to subtractive manufacturing (SM), which includes the removal of material from a compact block or workpiece to produce a desired framework or structure, additive manufacturing (AM) uses adding a material to print out another material. Creating an effective and inexpensive 17-4 PH technology is crucial. A conventional 17-4 PH synthesis method is material extrusion additive manufacturing process. Data collection and aggregation are not done properly in large parts of the globe. The material extrusion additive manufacturing process operates on the premise of layer-by-layer framework and manufacturing of stainless steel. An extensive study into the development of stainless steel, its strength and weaknesses, and its behavior under various conditions has to be researched. The aim of this research was to implement the post processing techniques, using the Ultrasonic Nanocrystal Surface Modification (UNSM), and conventional grinding methods to improve the surface characteristics and mechanical properties of the additively manufactured 17-4 PH stainless steel. 17-4 PH stainless steel was produced using additive manufacturing, successfully. In addition, the microstructure of 17-4 PH stainless steel was characterized using optical microscopy. To satisfy the specific requirement of surface integrity, a finishing process was conducted for the manufacture of stainless steels. The article suggests that the use of Laser and UNSM (LA-UNSM) to improve on this technology should be considered for future works. Furthermore, targeted grinding cooling (TGC) fluid application should be considered for future studies on surface modification.

Committee: Manigandan Kannan (Advisor); Tanmay Tiwari (Committee Member) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

The central theme of this dissertation is to explore material interaction with electromagnetic waves in millimeter-wave (mmWave) and terahertz (THz) frequency bands spanning the range from 30 GHz to 3 THz. The implications of these interactions in the context of on-vehicle integration of mmWave automotive radars is discussed. Furthermore, specific mechanisms are exploited for broadband material characterization, and biomedical imaging. First, this research outlines the traditional broadband methods to characterize the electromagnetic properties of isotropic non-magnetic dielectric materials. In mmWave and THz regime, this data is not readily available in many cases. Utilizing established free-space techniques such as terahertz time-domain spectroscopy (THz-TDS) and quasi-optical transmission measurements, this research extracts this data for a diverse range of materials. In particular, we discuss the challenges related to the reliability of the permittivity extraction process in situations where the measurement may not have a high SNR across the bandwidth of interest. We circumvent this problem by cross-validating the data across multiple modalities to ensure consistency. Additionally, for thin dielectric films for which conventional methods fail, this research proposes a novel permittivity extraction technique from calibrated two-port S-parameter measurements of a coplanar waveguide. Interaction of mmWave radar signal with the near zone radome and bumper layers can impair the radar performance through reduction of signal-to-noise ratio and distortion of the pattern. Therefore, towards the goal of a `transparent' radome, the dissertation proposes a novel textured radome design aimed at optimizing transmission efficiency for mmWave automotive radar. Through a strategic optimization based on first-principles, this design exhibits an enhanced signal transmission throughout the entire automotive radar band of 76 – 81 GHz. The optimized design demonstrates an avera (open full item for complete abstract)

Committee: Niru Nahar (Advisor); Kubilay Sertel (Committee Member); Asimina Kiourti (Committee Member); Alebel Arage (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

Contactless, nondestructive measurements of minority carrier lifetime by transient microwave reflectance (TMR) and photoluminescence are used to study the carrier dynamics of several ternary materials: InGaAs, GaAsSb, and InAsSb. As contactless measurements, TMR and photoluminescence can determine quality of as-grown wafers. The minority carrier lifetime is inversely proportional to the diffusion component of the dark current and can be used as an indicator of device performance, without the need for full device fabrication. The ability to yield useful information about wafer quality without the time and cost used for fabrication allows for quick feedback to growers. GaAsSb and InGaAs lattice-matched to InP are candidates for short-wave infrared (SWIR) detection at 1.5 μm, a wavelength used for eye safety and optical communication. The high speed or low signal applications at this wavelength benefit from the use of separate absorber, charge, and multiplier (SACM) avalanche photodiodes (APDs). In these devices, the absorber is optimized for detection at the wavelength of interest, and the multiplier is optimized for gain through impact ionization. InGaAs-based SACM APDs are a mature technology and are available commercially. The multipliers paired with InGaAs, however, typically have high noise. Research into low-noise multipliers has resulted in the demonstration of AlGaAsSb as a low noise material. When AlGaAsSb is paired with InGaAs, the grading material AlInGaAs creates a conduction band offset with AlGaAsSb, limiting bandwidth. GaAsSb lattice-matched to InP has similar properties to InGaAs and could be implemented without a conduction band offset due to the grading material being AlGaAsSb. When a GaAsSb/AlGaAsSb SACM APD was demonstrated, it was found to have higher dark current than commercial InGaAs-based devices. Because these materials are so similar, this was unexpected. As mentioned, the diffusion component of the dark current is inversely proportio (open full item for complete abstract)

Committee: Sanjay Krishna (Advisor); Steve Ringel (Committee Member); Preston Webster (Committee Member); Anant Agarwal (Committee Member); Shamsul Arafin (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2023, Welding Engineering

Metal matrix nanocomposites (MMNCs) have attracted great interest in various industries due to their excellent potential for light-weight applications. However, the enhanced hardness of MMNCs also increases the difficulties for machining. Besides, the agglomeration of nanoparticles in MMNCs deteriorates the final properties and limits the extended application of MMNCs. To address both issues, a novel approach of ultrasonically assisted wire arc additive manufacturing (UA-WAAM) was newly developed for fabrication of TiB2 nanoparticle-reinforced AA7075 MMNC with near-net-shape. The novel UA-WAAM process in current work adapted a conventional gas tungsten arc welding (GTAW) incorporating a UA probe directly immersed into the molten pool for better UA efficiency and homogeneity. Compared to previous UA-WAAM approaches that apply UA vibration to the substrate, the current approach provided a constant UA amplitude at the probe tip and direct UA-melt interactions. The process-microstructure-property relationship of the UA-WAAM process was comprehensively studied via in-situ monitoring and post-mortem characterizations. First, the relevant background information of this research was introduced. The mechanisms regarding strengthening effect and solidification cracking elimination of MMNCs were summarized. The propagation, transmission, and attenuation of ultrasound in melt and probe were discussed, showing that the direct probe immersion approach in current studies provides less attenuation along the propagation path compared to the conventional substrate-probing method. The mechanisms of UA-induced grain refinement, degassing, and de-agglomeration were thoroughly summarized and discussed. Second, preliminary results with a prototype UA-WAAM setup showed the feasibility and efficacy of the UA, including reduced porosities, refined grain structures, less nanoparticle agglomerations at the grain boundary, and improved mechanical properties. The coarsening of grains induced (open full item for complete abstract)

Committee: Xun Liu (Advisor); Yi Zhao (Committee Member); Carolin Fink (Committee Member); Dennis Harwig (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, The Ohio State University, 2023, Mechanical Engineering

As emission standards of passenger vehicles become more and more strict, automotive manufacturers are seeking lightweight solutions to increase vehicle's fuel economy. Fibrous reinforced polymers (FRPs) are known to have high strength to weight ratios, and thus, made them good candidates for the application in the automotive industry. FRP is a composite material made of a polymer matrix reinforced with fibers. The inhomogeneity, anisotropy, visco-elasticity/plasticity, mechanical degradation due to temperature/damage, brittleness characteristics of the unidirectional FRP composites bring challenges to determine mechanical responses both experimentally and numerically. In this dissertation, mechanical behavior of unidirectional carbon fiber reinforced polymer (CFRP) made of Toray T700S carbon fiber and G83-CM prepreg system is studied. Specimens are fabricated from 8-ply and 16-ply CFRP plates. An experimental series is performed including tension, compression, and shear coupon tests at various strain rates ranging from 0.001 to 1000 s-1. Anisotropy is studied by conducting tension, compression, and shear coupon tests in different fiber orientations. Thermal dependence of the material is investigated by performing coupon tests under temperatures ranging from 25 °C to 120 °C. CFRP has been found that loading in one direction can potentially lead to damage in other directions. Thus, coupled, and uncoupled damage testing is performed to characterize such behavior. Digital image correlation (DIC) is applied for deformation and strain measurement on the surface of the specimens. The coupon test data and damage test data are used to calibrate the deformation and damage sub-models of the constitutive material model, *MAT_COMPOSITE_TABULATED_PLASTICITY_DAMAGE, also called *MAT_213, in LS-DYNA. The deformation sub-model predicts elasto-plastic behavior, and it uses a strain-hardening-based orthotropic yield function with a non-associated flow rule extended from Tsai-Wu fail (open full item for complete abstract)

Committee: Amos Gilat (Advisor); Prasad Mokashi (Committee Member); Kelly Carney (Committee Member); Jeremy Seidt (Committee Member) Subjects: Mechanical Engineering

Master of Science (MS), Ohio University, 2023, Mechanical Engineering (Engineering and Technology)

Bituminous coal was utilized as a particulate filler in polymer-based composites to fabricate standard 1.75 mm coal-plastic composite filaments for use in commercially available fused deposition modeling 3D printers. The composites were formulated by incorporating Pittsburgh No. 8 coal into polylactic acid, polyethylene terephthalate glycol, high-density polyethylene, and polyamide-12 resins with loadings ranging from 20 wt.% to 70 wt.%. CPC filaments were extruded and printed using the same processing parameters as the respective neat plastics. All coal-plastic composite filaments exhibited uniform particle dispersion throughout the microstructure. The mechanical properties of the 3D printed composites were characterized and compared to composites fabricated using traditional compression molding. Tensile and flexural moduli as well as hardness had direct proportionality with increasing coal content while flexural strength, tensile strength, and impact resistance decreased for most composite formulations. Interestingly, polyamide-based composites demonstrated greater maximum tensile and flexural strengths than unfilled plastic. Microscopy of as-fractured samples revealed that particle pull-out and particle fracture were the predominant modes of composite failure. The introduction of coal reduced the coefficient of thermal expansion of the composites, ameliorating the warping problem of 3D printed high-density polyethylene and allowing for additive manufacturing of an inexpensive and widely available thermoplastic. The high-density polyethylene composites demonstrated increased heat deflection temperatures, but all composites maintained comparable glass and metal transition temperatures, allowing them to be processed with commercial 3D printer extruders. The composites exhibited decreased specific heat capacities suggesting lower energy requirements for processing the material. Coal reduced the composite thermal conductivities compared to the neat plastics but improv (open full item for complete abstract)

Committee: Jason Trembly (Advisor); Yahya Al-Majali (Committee Member); Brian Wisner (Committee Member); David Drabold (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering; Sustainability

Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2022, Materials Science and Engineering

This work investigates processing parameters for laser powder bed fusion (LPBF) additive manufacturing (AM) to produce bismuth telluride coupons. AM provides the ability to fabricate complex geometries, reduce material waste, and increase design flexibility. The processing parameters for LPBF were varied in single bead experiments guided by analytical modeling to identify conditions that result in uniform beads. Coupons were built using these processing parameters and the cross-sections characterized using optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). Porosity analysis using OM concluded most coupons had porosity levels less than 10% by area. SEM and EDS analysis revealed there were slight composition and microstructure variations throughout the cross-sections depending on the processing conditions. These results show that LPBF is a viable process for producing bismuth telluride coupons with low porosity. Investigations of the microstructure and composition of the coupons indicate further research opportunities.

Committee: Joy Gockel Ph.D. (Advisor); Henry D. Young Ph.D. (Committee Member); Raghavan Srinivasan Ph.D., P.E. (Committee Member) Subjects: Engineering; Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2021, Mechanical Engineering

To numerically simulate and predict the plastic deformation of aerospace metal alloys during extreme impact events (e.g., turbine engine blade-out and rotor-burst events, and foreign object damage), accurate experimental knowledge of the metal's hardening behavior at large strains is requisite. Tensile tests on round cylindrical specimens are frequently used for this purpose, with the metal's large-strain plasticity ultimately captured by an equivalent true stress vs. equivalent true plastic strain curve. It is now well known that if axial strain is measured using an extensometer, the equivalent true stress-strain curve calculated from this measurement is valid only up to the onset of diffuse necking. That is, once the strain field heterogeneously localizes in the specimen gage (onset of necking), extensometers, which average the strain field over the gage section, are unable to capture the local strain at the site of fracture initiation. Thus, a number of approaches have been proposed and employed to correct the post-necking hardening response. One commonly-used technique is an iterative approach commonly referred to as finite-element model updating (FEMU). This approach involves inputting a suite of candidate post-necking equivalent true stress-strain curves into finite-element software. The true stress-strain curve that produces the best agreement between simulation and experiment is ultimately adopted. In this document, a novel variation of this iterative approach is presented, aimed at decreasing computational expense and iterative effort with a better first guess that bounds this fan of prospective true stress-strain curves. In particular, we use local surface true (Hencky) strain data at the fracture location in an approximate analytical formula to generate a first guess curve and upper bound on the candidate true stress-strain fan of curves. To assess its performance and robustness, the proposed approach is verified using experimental data for a menu of ae (open full item for complete abstract)

Committee: Robert Lowe Ph.D. (Advisor); Luke Sheridan Ph.D. (Committee Member); Dennis Buchanan Ph.D. (Committee Member); Jeremy Seidt Ph.D. (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 2019, Electrical and Computer Engineering

Utility of wireless connectivity has been steadily increasing as broadband internet becomes widely available and having low-cost technology leads to more devices built with Wi-Fi capabilities and sensors. As the traditional radio-frequency (RF) bands (sub 3 GHz) become congested, the mmW band offering vast amount of spectrum, is poised to be the backbone of 5G wireless networks. Particularly, thanks to much smaller wavelengths, antenna-integrated transceivers are viable solutions for the future 5G wireless networks. However, key challenges still remain for on-chip implementation of efficient radiators at such high frequencies. Namely, poor antenna bandwidths, severely low radiation efficiencies, as well as laborious and expensive antenna-transceiver integration (wire bonds, flip-chip, ball grid arrays, etc.) limit the utility of truly-integrated on-chip antennas. To overcome these prevailing obstacles we present an ultra-wideband (UWB), low-profile, high efficiency, tightly-coupled array topology which is adopted from RF-frequency realizations and modified as a multilayered structure suitable for standard micro-fabrication process. Through this work, we show that on-chip radiation efficiency is well above 60% over the entire impedance bandwidth. The proposed array exhibits wideband performance, covering 35-75 GHz, achieving an unprecedented coverage that spans most of the bands allocated for mobile communications. Utilization of low-loss materials in such designs can address the substrate coupling issues and improve the radiation efficiency. Moreover, the structural support and packaging materials that exhibit low loss are indispensable for cost-effective realization of integrated high frequency systems. To effectively address these requirements, polymers are a natural, low-cost choice for structural support and packaging of microchips due to their favorable chemical, thermal, and mechanical properties. However, many polymers have not been studied for mmW and TH (open full item for complete abstract)

Committee: Kubilay Sertel (Advisor); Niru Nahar (Committee Member); Fernando Teixeira (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Electromagnetism

Master of Science, The Ohio State University, 2019, Mechanical Engineering

Elastodynamic characterization of adhesive layers at bimaterial interfaces is important in the field of adhesive bonding. The present thesis is an investigation of the mechanical behavior of adhesive interfaces using spring models and cohesive zone models. Linear and nonlinear spring models were considered, where the nonlinear behavior was approximated using piece-wise linear segments. Horizontally polarized shear (SH) waves were used as the body force input in this study. A boundary element methodology (BEM) was developed, which adopts either linear spring or nonlinear spring or cohesive boundary conditions, for potential use by an NDE practitioner in the non-destructive evaluation of adhesive bonds. The BEM results, along with ultrasonic measurements, provide insight into damage characterization of adhesively bonded structures.

Committee: Prasad Mokashi (Advisor); Amos Gilat (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2017, Mechanical Engineering

Understanding wave phenomena at material interfaces is an important problem in non-destructive evaluation / material characterization. Modeling the behavior of the interface presents interesting opportunities in this field. The present work attempts to understand the effect of an interface on transient and steady-state wave propagation through a bi-material system. Horizontally polarized shear waves (SH) are chosen as candidates in the analysis. The interface itself is considered to be spring-like with non-linear load-displacement characteristics. The non-linear behavior of the spring can easily be treated as approximate linearized segments. Transient analytical solution forms for reflected and transmitted waves are obtained by considering linear spring interface model using Cagniard-de Hoop technique. Numerical results for time-harmonic SH wave interaction are obtained considering a non-linear spring model using perturbation technique. The methodology presented should enable a practicing engineer to draw insights into interface strength / damage.

Committee: Prasad Mokashi (Advisor); Daniel Mendelsohn (Advisor) Subjects: Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2016, Mechanical Engineering

Due to their low density, high toughness and elevated temperature performance, Ceramic Matrix Composites (CMCs) are attractive candidates for replacing metals in many high temperature applications, such as gas turbine engines and exhaust nozzles. While there are numerous benefits to CMCs, there are several limitations hindering the full-scale application within the aerospace industry. One significant limitation is the ability to accurately model and predict CMC damage behavior. A mechanistic approach to modeling the damage behavior in CMCs was previously developed by Structural Analytics. The damage model, CLIP (Ceramic Matrix Composite Life Prediction), is embedded in a software package that consists of an ABAQUS user-subroutine, as well as a standalone application. The current study verifies the model by calibrating it to a slurry melt-infiltrated SiC/SiC composite. A series of experimental tests were conducted at the Air Force Research Laboratory (AFRL) including montonic tensile tests at 23°C, 800°C and 1200°C, a creep test at 1200°C and a sequentially loaded tensile test at 23°C. The results from the experimental tests were used to calibrate the damage model. The calibration was concluded as successful when the model could produce matching stress-strain curves to the experimental data at the respective temperatures. Finally, the model was used to make predictions for intermediate temperature ranges of monotonic tension, sequentially loaded tension, and off-axis tension.

Committee: Pinnell Margaret Ph.D. (Advisor); Jefferson George Ph.D. (Committee Member); Whitney Thomas Ph.D. (Committee Member) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2015, Civil Engineering

Pavement design methodologies have over the past decades seen philosophical evolutions and eventually practical implementation of new postulates. As more contributions are made by pavement researchers to the State-of-the-Art in pavement design, there exist a chasm between pavement engineers and state-of-the-art pavement research in terms of incorporation into pavement design guidelines. In developing countries such as Guyana in South America, as well as several departments of transportation, municipalities and townships in the United States, pavement engineers still use the American Association of State Highway and Transportation Officials (AASHTO) Pavement Design Guide (1993). This empirical pavement design guide and its previous iterations were based primarily on data that was collected and processed from the then American Association of State Highway Officials (AASHO) Road Test conducted between 1958 and 1960. The limitations with continued use of this method are obvious since the data was gathered under specific environmental conditions, a specific subgrade type, and with specific materials as well as specific pavement cross-sections. The continued use of this guide does not account for advances in material technology, different types and volumes of vehicular traffic, changing climatic conditions and also can be costly in expanding road networks. To solve this dilemma pavement researchers started working toward a more mechanistic approach for design and through the work of National Cooperative Highway Research Program (NCHRP), culminated in the publishing of the Mechanistic-Empirical Pavement Design Guide (MEPDG) in 2004. The finite element model used in the MEPDG is premised upon a displacement based theory. These theories are capable of making good predictions regarding global responses such as displacements and sometimes in-plane stresses but not the transverse stress distribution. To predict transverse stress distribution, stress based theories are more su (open full item for complete abstract)

Committee: William Wolfe PhD (Advisor); Tarunjit Butalia PhD (Committee Co-Chair); Frank Croft PhD (Committee Member); Fabian Tan PhD (Committee Member) Subjects: Civil Engineering; Transportation

Doctor of Philosophy, The Ohio State University, 2015, Welding Engineering

When an ultrasonic wave propagates in polycrystalline materials, the wave is scattered on grain boundaries and the scattered waves carry important information on material microstructure, e.g. grain size and texture. Using grain scattering information for nondestructive testing purposes can be useful as quality control in many manufacturing processes. In particular, measurement and interpretation of ultrasonic scattering can be very useful in the development of practical methods for nondestructive ultrasonic characterization of microtextured regions in titanium alloys that are widely used for aeroengine components. Ultrasonic scattering and scattering-induced ultrasonic attenuation are two measurable ultrasonic characteristics that can be employed for material microstructures characterization. Most past studies address ultrasonic attenuation and scattering in polycrystals with macroscopic isotropy or simple artificial textures and equiaxed grains of high crystallographic symmetry (cubic or hexagonal). However, most manmade materials, as a result of thermomechanical processing, exhibit nonequiaxed grains and complex forms of macroscopic texture. One objective of this dissertation is to provide a better understanding of ultrasonic propagation and scattering in textured polycrystyals. In this dissertation, general attenuation and scattering models are developed for polycrystals with arbitrary macrotexture and ellipsoidal grain shape with triclinic symmetry. The attenuation coefficients were derived in the Born approximation by generalizing previous theoretical models that were suitable for equiaxed grains and uniaxial hexagonal textures. The general scattering coefficients were obtained from the integrand of the attenuation coefficients. The second major objective is to ultrasonically characterize the microtextured regions (MTRs) in Ti alloys which is a result of orientation clustering of crystallites and leads to a reduction of dwell fatigue properties of the m (open full item for complete abstract)

Committee: Stanislav Rokhlin (Advisor); Dave Farson (Committee Member); Daniel Mendelsohn (Committee Member); Adam Pilchak (Committee Member) Subjects: Acoustics; Materials Science

Doctor of Philosophy, University of Akron, 2013, Civil Engineering

Among the various combinations of metals used to form alloys, certain combinations, such as Ni and Ti, are known to exhibit unique properties, like the ability to remember a shape after deformation. Because of these novel and unique properties, they are known as `Shape Memory Alloys (SMAs)’ and are desirable for use in various fields of engineering application; eg., in sensors, actuators, biomedical stents and devices, energy absorption, vibration damping, etc, as they can absorb and dissipate mechanical/thermal energies by undergoing a reversible hysteretic shape change under the applied mechanical/thermal cyclic loadings. This reflects the effects of microstructural changes occurring during phase transformation between Austenite (A) and Martensite(M) phases, as well as the martensite-variants orientations at high stress levels ( Mi to Mj, where i and j are different variants). As typically utilized in applications, a particular shape memory alloy (SMA) device or component also need to operate under a large number of thermo-mechanical cycles, hence, the importance of accounting for the cyclic behavior characteristics in modeling and characterization of these systems. This dissertation work focus on: (1) a detailed study of a recently-formulated, multi-mechanism-based, comprehensive, thus complex modeling framework formulated by Saleeb et al, in particular the physical significance of the multiple, inelastic mechanisms that are used to regulate the partitioning of energy dissipation and storage governing the evolutionary thermo-mechanical response of shape memory behavior; (2) a comprehensive characterization of the cyclic response of the specific complex real shape memory alloy like Ni49.9Ti50.1, also commonly known as 55NiTi, for isobaric tests under the entire relevant bias stress range from 10 to 300MPa, and for sufficient number of thermal cycles (100 cycles here); (3) implementation of the calibrated SMA model in the study of its effectiveness in the (open full item for complete abstract)

Committee: Atef F Saleeb Dr. (Advisor); Wieslaw K. Binienda Dr. (Committee Member); Ernian Pan Dr. (Committee Member); Xiaosheng Gao Dr. (Committee Member); Kevin L. Kreider Dr. (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Civil Engineering; Materials Science

MS, University of Cincinnati, 2012, Engineering and Applied Science: Mechanical Engineering

The mechanical response of human skin and underlying tissue (hereafter, referred to as only skin) is a subject that has been studied by professionals and scientists for many years. However, the current methods require large specialized equipment in a laboratory to measure the response of skin. Handheld devices that perform compression and extension measurements of skin have the potential to replace bulky lab equipment and have the advantage of making in vivo measurements. In this research we explore the use of handheld devices to measure the mechanical response of skin in compression and extension. Further, this research aims to use simulation and optimization techniques to develop a method of determining material parameters based on the measurements recorded by the handheld devices. This work has two major components. First, we study the use of two proprietary handheld devices on a viscoelastic foam material, and second we research the use of the handheld devices on human skin. Using the handheld devices on a viscoelastic foam holds a three-fold purpose. First, the device's accuracy and precision are determined. Second, simple compression and extension tests are used to determine a constitutive material model for the foam. Third, a combination of the physical handheld device results and constitutive material model are used to study a simulation model that replicates the handheld device's boundary conditions. Once these three steps are completed, an optimization method is used to determine the material parameters needed to replicate the physical test. In this process, we find that the handheld devices can provide test data that then can be used with the simulation and optimization methods to determine the material parameters to replicate the viscoelastic foam response. In the second major part of this work, the handheld devices are used to study the response of human skin in vivo. The optimization methods are then applied to two different simulation models. First, (open full item for complete abstract)

Committee: Kumar Vemaganti PhD (Committee Chair); Richard W. Hamm MS (Committee Member); Yijun Liu PhD (Committee Member); Dong Qian PhD (Committee Member) Subjects: Engineering

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

The mechanical behavior of soft cellular tissue such as the liver has been rarely characterized to the extent of load-bearing tissue. Most of the available material parameters of soft tissue found in the literature are phenomenological, i.e., they do not provide a link between the mechanical response of the tissue to its overall mechanical response. However, there is a need to characterize the nonlinear mechanical behavior of liver tissue due to the potential impact such information has on technologies in disease diagnosis, injury prevention, automated surgery, etc. Robust mechanical characterization based on underlying tissue structure has the potential to provide significant enhancements to each of these technologies. This dissertation focuses on two major aspects of the nonlinear material characterization of the liver tissue: experimentation and correlation of the overall mechanical behavior to the underlying tissue structure. Uniaxial compression experiments with no-slip edge conditions are conducted to extract bulk nonlinear properties. A computational “correction factor approach” is developed to extract “real” material parameters by eliminating the frictional effects resulting from the no-slip edge conditions. No-slip experimental results at various strain rates are then corrected to extract time-dependent nonlinear parameters. Using the cellular mechanical properties associated with the liver, a multiscale homogenization approach is employed in bridging the overall tissue behavior to the microstructural architecture. The multiscale approach is validated through a comparison of computationally derived bulk response to the equilibrium response of the liver tissue obtained using no-slip experiments at various strain rates.

Committee: Dr. Kumar Vemaganti (Advisor) Subjects: