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Presley, MichaelThe Formation of Amorphous and Crystalline Damage in Metallic and Semiconducting Materials under Gallium Ion Irradiation
Doctor of Philosophy, The Ohio State University, 2016, Materials Science and Engineering
Gallium ion irradiation in dual-beam FIB microscopes is well known to cause some degree of damage during the milling process. Although it has been established that cleaning passes with low energy ions can mitigate the extent of this damage, the mechanisms, extent, and type of damage caused have not been well studied due to geometrical limitations inherent to thin foils. By adapting the needle geometry used for atom probe and tomographic work, we can directly measure the extent of damage layers created during milling. Needles were made of multiple semiconductor, intermetallic, and metal systems, confirming previous estimates of damage thickness in Si and GaAs. Materials tested fell into two distinct classes, amorphous dominated and crystalline defect dominated. Amorphous dominated materials consisted of semiconductors and narrow phase field intermetallics, fitting previous radiation work. Crystalline defect dominated materials had semi-crystalline damage layers under 5 nm at all accelerating voltages, and residual defects were shown to have significant effects on lattice clarity in HAADF-STEM. Contrast between amorphous layers in HAADF-STEM was found to be minimal even under ideal conditions, and HRTEM was necessary to accurately confirm and measure damage layer thickness. The causes and extent of damage layer minimization during low keV milling steps were shown to be consistent across all materials.

Committee:

Hamish Fraser (Advisor); Wolfgang Windl (Committee Member); Jinwoo Hwang (Committee Member)

Subjects:

Materials Science; Metallurgy; Radiation

Keywords:

Focused ion beam; radiation damage; FIB damage; collision cascade; sample preparation; TEM; STEM; FIB; crystalline defects; amorphous; amorphous damage; needle; damage measurement; semiconductor; metal; intermetallic;

Carroll, Turhan KendallRadiation Damage in GMR Spin Valves
Master of Science, The Ohio State University, 2010, Physics
The GMR effect has revolutionized the information technology industry. GMR read-out heads, MRAM and magnetic field sensors have become standard technologies of today’s society, while magnetic random access memory (MRAM) is one of several applications of this effect which are in earlier stages. The presumption is that these materials are radiation hard with respect to both photons and particles, potentially indicating utility for nuclear energy and space based applications. However, few detailed studies of magnetism in GMR devices have been performed in radioactive environments. This work explores the effects of gamma ray and neutron irradiation on GMR spin valves. The sample structure used in this experiment is Py/Cu/Py/FeMn/Ge. To study the effects of radiation three probes of magnetization, VSM, MR, and MOKE, are correlated pre and post radiation. We present characterization of the devices for multiple device geometries and doses up to 50Mrad for gamma rays and a minimum fast flux of (En>0.5MeV) of 6.3E12 nv for neutrons, both of which are well above the failure threshold for radiation-hard semiconducting devices. We found that these devices were hard to both gamma and neutron irradiation, but that there were environmental factors that caused accelerated aging of our samples during the gamma irradiation experiment. We show follow-up studies based on these results, and future experiments that are currently in their early stages.

Committee:

Ezekiel Johnston-Halperin, PhD (Advisor); Jay Gupta, PhD (Committee Member)

Subjects:

Materials Science; Physics

Keywords:

Radiation Damage; Giant Magnetoresistance; Radiation in Spin Valves; Neutron damage in magnetic metals; gamma damage in magnetic metals

Zhai, JinyuanModeling Ductile Damage of Metallic Materials
Doctor of Philosophy, University of Akron, 2016, Mechanical Engineering
In this dissertation, a comprehensive study of ductile damage of metallic materials is presented, covering constitutive modeling, numerical implementation and model calibration and verification. As the first part of this dissertation, a pressure-insensitive plasticity model, expressed as a function of the second and third invariants of the stress deviator (J2 and J3), is presented. Depending on whether the power of the J3 term is odd or even, the proposed model can capture either the tension-compression strength-differential (S-D) effect or the torsion-tension strength-differential effect of the material. The plasticity model with an odd power to the J3 item has been calibrated and validated using measured experimental data of a ß-treated Zircaloy-4 with a wide range of triaxiality and Lode parameter values. Results show that this model captures the strong strength-differential (S-D) effect in the material. The plasticity model with an even power to the J3 item is able to capture the isotropic plastic behavior of a stainless steel Nitronic 40, under various stress states with good accuracy and computational efficiency. Next, the effect of the material’s plasticity behavior on the ductile damage process is studied by conducting a series of unit cell analyses of a void-containing representative material volume (RMV), where the plastic response of the matrix material is governed by the J2-J3 dependent plasticity model. To simulate the ductile damage process in anisotropic materials, a new constitutive model, which combines the models proposed by Zhou et al. (2014) and Stewart and Cazacu (2011), is developed and employed to study the plasticity and ductile fracture behavior of a commercially pure titanium (CP Ti). In particular, a Gurson-type porous material model is modified by coupling two damage parameters, accounting for the void damage and the shear damage respectively, into the yield function and the flow potential. The plastic anisotropy and tension-compression asymmetry exhibited by CP Ti are accounted for by a plasticity model based on the linear transformation of the stress deviator. The theoretical model is implemented in the general purpose finite element software ABAQUS via a user defined subroutine and calibrated using experimental data. Good comparisons are observed between model predictions and experimental results for a series of specimens in different orientations and experiencing a wide range of stress states. The model is shown to capture the effect of stress state and the change of fracture mechanism. The results also reveal the important effect of the plastic anisotropy and tension-compression asymmetry on the ductile damage process. Literature review indicates that this is the first time to simulate failure under shear dominated conditions in an anisotropic and tension-compression asymmetric material.

Committee:

Xiaosheng Gao, Dr. (Advisor); Yalin Dong, Dr. (Committee Member); Chang Ye, Dr. (Committee Member); Ernian Pan, Dr. (Committee Member); Kevin Kreider, Dr. (Committee Member)

Subjects:

Mechanical Engineering; Mechanics

Keywords:

Ductile damage; Plasticity; Anisotropic material; Strength differential effect; Void damage; Shear damage; Unit cell analysis; Experiments and finite element analysis

Whitney, G. AdamCharacterization of the Frictional-Shear Damage Properties of Scaffold-Free Engineered Cartilage and Reduction of Damage Susceptibility by Upregulation of Collagen Content
Doctor of Philosophy, Case Western Reserve University, 2015, Biomedical Engineering
Cartilage tissue engineers have made great inroads on understanding the factors controlling chondrogenesis, however, the biomechanical properties of tissue engineered cartilage (TEC) are chronically inferior to that of native cartilage. The focus of this dissertation was to determine the ability of scaffold-free TEC to withstand frictional-shear stress, and if needed, to improve that ability to a physiologically relevant level. Frictional-shear testing performed at a sub-physiological normal stress of 0.55 MPa demonstrated that constructs exhibited lubrication patterns characteristic of native cartilage lubrication, but severe damage also occurred. Low absolute collagen content, and a low collagen-to-glycosaminoglycan (GAG) ratio were also found in the same constructs. Reduction in damage was attempted by increasing the collagen content of the ECM. Scaffold-free TEC treated with T4 at 25 ng/ml exhibited increased collagen concentration in a statistically significant manner, and the average collagen-to-GAG ratio was also increased although statistical significance was not achieved. Western blotting showed that type II collagen was increased, type X collagen was not detected. COL2A1, and biglycan gene expression were also found to have increased, no statistically significant difference was found for COLX gene expression. When compared to control constructs, T4 treated constructs exhibited a large and statistically significant decrease in the extent of damage incurred by frictional-shear testing. At the 2.8 MPa normal stress, total damage was reduced by 60% in the 2-month constructs. Correlation coefficients calculated between compositional properties and the amount of damage showed that at the 2.8 MPa normal stress collagen concentration and the collagen-to-GAG ratio exhibited the greatest correlation to damage (correlation coefficient of approximately -0.7 with a 95% confidence interval of approximately -0.87 to -0.38 for both). In conclusion, scaffold-free cartilage generated without special attention to increasing collagen content may be highly susceptible to damage from frictional-shear stress. Furthermore, the collagen-to-GAG ratio appears to be an important property in determining damage susceptibility. Collagen content can be improved by use of T4. Presumably as a result of the increased collagen content, scaffold-free TEC treated with T4 was able to withstand frictional-shear testing at physiologically relevant normal stresses.

Committee:

James Dennis, Ph.D. (Advisor); Joseph Mansour, Ph.D. (Advisor); Horst von Recum, Ph.D. (Committee Chair); Eben Alsberg, Ph.D. (Committee Member)

Subjects:

Biomechanics; Biomedical Engineering; Biomedical Research; Engineering; Materials Science

Keywords:

engineered cartilage; scaffold-free; frictional-shear damage; biphasic lubrication model; collagen upregulation; biglycan; tribology; support vector machine, friction based damage detection; signal processing; compositional-damage model; PC-QSM; arthritis

Kaliyaperumal, SaravananhMSH6 Protein Phosphorylation: DNA Mismatch Repair or DNA Damage Signaling?
Doctor of Philosophy in Biomedical Sciences (Ph.D.), University of Toledo, 2009, College of Medicine
The Mismatch repair (MMR) system maintains genomic stability byrepairing DNA mismatches and insertion-deletion loops (IDLs) resulting from replication and recombination errors. Defective MMR can lead to hereditary non-polyposis colorectal cancer (HNPCC) and sporadic forms of cancer. In human cells, mismatches are recognized and bound by a heterodimer, hMSH2-hMSH6 (hMutSα). A second heterodimer, hMLH1-hPMS2 (hMutLα) interacts with hMutSα and is thought to act as a mediator for downstream repair proteins. An additional role for MMR pathway is to trigger cell cycle arrest and apoptosis upon recognition and binding of MutSα to specific DNA lesions such as O6 methyldeoxyguanine (O6-meG). Limited information is available regarding the cellular regulation of these proteins. Within this report, we demonstrate that hMSH6, but not hMSH2, undergoes phosphorylation within cells. Phosphorylation of hMSH6 is enhanced by addition of TPA, a PKC activator. Alternatively, UCN-01, a PKC and Chk1/Chk2 kinase inhibitor, decreases hMSH6 phosphorylation and mismatchbinding activity of hMutSα to both G:T and O6 -meG:T-containing DNA. We show that phosphorylated hMSH6 is higher in concentration in the presence of a G:T mismatch, as compared to an O6 -meG:T lesion. However, the total quantity of hMutSα bound to O6 -meG:T–containing DNA is higher than that bound to G:T-containing DNA. We also demonstrate that MMR proficient cells treated with a low concentration of N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) undergo cell cycle arrest after one complete cell cycle. When these cells are co-treated with UCN-01 the G2/M arrest is abrogated and the cells rapidly die. This abrogation of arrest is not due to Chk1 kinase inhibition but rather through Cdc2 activation by increased Tyr15 dephosphorylation. Taken together, we hypothesize that both phosphorylation and total concentration of hMutSα are involved in the signaling of either DNA mismatch repair or damage recognition activities. We also hypothesize that decreased hMSH6 phosphorylation may be an integral part of UCN-01 mediated inhibition of G2/M cell cycle arrest in MNNG damage signaling response. A final vital outcome of these studies is a new gain of insight into the level of difficulty in expression of full-length hMSH6 cDNA in mammalian cells.

Committee:

Kandace Williams, Ph.D. (Committee Chair); Stephan Patrick, Ph.D. (Committee Member); William Maltese, Ph.D. (Committee Member); John David Dignam, Ph.D. (Committee Member); Venkatesha Basrur, Ph.D. (Committee Member)

Subjects:

Biology

Keywords:

DNA Repair; Protein Phosphorylation; mismatch repair; alkylation damage response; MSH6 Protein Phosphorylation; MNNG damage signaling

Swindeman, Michael JamesA Regularized Extended Finite Element Method for Modeling the Coupled Cracking and Delamination of Composite Materials
Doctor of Philosophy (Ph.D.), University of Dayton, 2011, Mechanical Engineering

As the use of composite materials in aerospace structures continues to increase, the need to properly characterize these materials, especially in terms of damage tolerance, takes on additional importance. The world wide failure exercises (WWFE) are an example of the international interest in this issue. But though there has been a great deal of progress in understanding the initiation of damage and modeling damage propagation along known interfaces, methods that can capture the effects of interactions among various failure modes accurately remain elusive.

A method of modeling coupled matrix cracks and delamination in laminated composite materials based on the finite element method has been developed and experimentally validated. Damage initiation is determined using the LARC03 failure criterion. Delamination along ply interfaces is modeled using cohesive zones. Matrix cracks are incorporated into the discretization of the problem domain through a robust Mesh-Independent Cracking (MIC) technique. The matrix cracking technique, termed the Regularized Extended Finite Element Method (Rx-FEM), uses regularized forms of the Heaviside and Dirac Delta generalized functions to transform the crack surface into a volumetric crack zone.

The Regularized Extended Finite Element method is compared to benchmark cases. The sensitivity of the solution to mesh size and parameters within the cohesive zone model is studied. Finally, the full method with delamination is employed to study a set of experimental tests performed on open-hole quasi-isotropic laminates. The trends of hole-size and ply thickness are well predicted for the laminates. Rx-FEM is also able to simulate the pattern of damage, as demonstrated by comparisons to x-ray images. From the results of this series of analyses it can be concluded that failures occur when delamination originating at the hole links up with delamination originating at the edge along the path of matrix cracks.

Committee:

Robert A. Brockman, PhD (Committee Chair); Steven L. Donaldson, PhD (Committee Member); Endel V. Iarve, PhD (Committee Member); James M. Whitney, PhD (Committee Member)

Subjects:

Mechanical Engineering; Mechanics

Keywords:

Regularized Extended Finite Element Method; Progressive Damage Modeling; Discrete Damage Modeling; Cohesive Zone Model; Laminated Composite Materials; Matrix Cracks; Delamination; Failure Criteria; Failure Analysis; Structural Analysis; Composites

Acharya, DabitCOMPARATIVE EXPERIMENTAL STUDIES FOR GLOBAL DAMAGE DETECTION IN PLATES USING THE SCANNING LASER VIBROMETER TECHNIQUES
Master of Science, University of Akron, 2006, Civil Engineering
The main objective of this study is to show the specific capabilities of the Scanning Laser Vibrometer (SLV) for global damage detection using a recent defect energy parameter technique proposed by Saleeb and coworkers. The experimental technique used for extraction of signature is the first and most important part in any damage detection technique. Signatures considered here are full-field SLV measurements for modal shapes and associated frequencies of plated structures. The damage feature extraction capability was studied extensively by analyzing various simulation and experimental results. The practical significance in structural health monitoring is that the detection at early stages of small-size defects is always desirable. The amount of changes in the structure’s response due to these small defects was determined to show the needed level of accuracy in the experimental methods. The signal – noise ratio of experiment shows the capability of the same experiment to be used for damage detection purpose. Various experiments were performed to verify a significant signal – noise ratio for a successful detection. Very high number of scanning points, for optical experimental measurement, for any civil structure can be impractical and uneconomical. So, a pragmatic direction for the development of new experimental measurement tools was studied where different number of scanning points and different types of statically loaded simulations were performed to verify the specific capabilities of the defect energy parameter technique. It was further observed that powerful graphic user interface should also be an integral part in any present in the damage detection scheme for successful and more accurate detection. Furthermore, some potential use of SLV techniques in detection are provided, both for dynamic and static applications.

Committee:

Atef Saleeb (Advisor)

Keywords:

damage detection; scanning laser vibrometer; vibrometer; vibrometry; detection; damage; NDT

Bhatnagar, HimanshuComputational Modeling of Failure in Thermal Barrier Coatings under Cyclic Thermal Loads
Doctor of Philosophy, The Ohio State University, 2009, Mechanical Engineering

In this dissertation, finite element models are used to investigate catastrophic failure of thermal barrier coatings (TBCs) due to delaminations along susceptible interfaces of thermally grown oxide (TGO) with the ceramic top coat and the inter-metallic bond coat. The materials and geometries in the studies are chosen to be representative of TBC materials in real applications.

The characteristics of the failure modes along the TGO and bond coat interface (e.g. buckling instability and strain energy driven delamination propagation) are investigated using thermo-elastic finite element models. The solution of a linear elastic eigen-value problem determines the onset of the buckling instability with a pre-existing delamination between bond coat and the TGO. The virtual crack extension method is employed to study strain energy release rate driven interfacial delamination at wavy interfaces. The materials and geometries in the study are chosen to be representative of TBC materials in real applications. Extensive sensitivity analyses are conducted to identify the critical design parameters affecting the onset of buckling and extension of interfacial delamination, as well as to develop parametric relations that enhance the understanding of these mechanisms. Finally, a numerical exercise demonstrates that the buckling instability is the leading failure mechanism at flat interfaces or at the locations of minimum cross-section in a wavy interface. However, in the vicinity of waviness, crack extension becomes a dominant mode of failure.

The top coat crack initiation and propagation is investigated using a thermo-elastic finite element model with bond coat creep. Cracks are assumed to initiate when the maximum principal stress exceeds rupture stress of the top coat. A sensitivity analysis estimates the contribution of geometric and material parameters and forms a basis to develop parametric relation to estimate maximum principal stress. Subsequently, crack propagation simulations using a hysteretic cohesive zone model are performed for parametric combinations which initiate cracks away from the interface. These analyses conclude that parametric combinations initiating top coat cracks also assist in propagation and eventual delamination of TGO and top coat interface.

A homogenization based continuum damage mechanics (HCDM) modeling framework is proposed for TBC failure effects of top coat microstructural defects. An extended Voronoi cell finite element (X-VCFEM)is employed to perform the micro-mechanical analysis of RVE and the results show that HCDM model has limited validity due to loss of material stability with significant damage. A sensitivity analysis reveals that the range of HCDM validity is dependent on top coat cohesive energy.

Committee:

Somnath Ghosh, PhD (Advisor); Mark Walter, PhD (Committee Member); James Williams, PhD (Committee Member); June Lee, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Thermal barrier coating; top coat; bond coat; TGO; interface debonding; buckling; instability; delamination; energy release rate; competing failure mechanisms; cracking; cyclic thermal loads; damage initiation; damage propagation; parametric studies

Renganathan, KutralanathanOxidative Damage and Age Related Macular Degeneration
Doctor of Philosophy, Case Western Reserve University, 2008, Chemistry
The purpose of this thesis research is to better understand the role of oxidative damage in age related macular degeneration (AMD), the most common cause of legal blindness in the elderly population. In angiogenesis studies, carboxyethylpyrrole (CEP) adducts, derived from free radical oxidation of docosahexaenoyl lipids, were found to stimulate neovascularization in chick chorioallantoic membrane and rat corneal micropocket assays. Monoclonal anti-CEP antibody was found to neutralize CEP stimulated neovascularization, however, anti- vascular endothelial growth factor antibody only partially neutralized vessel growth. Primary retinal pigment epithelial (RPE) cells and the human ARPE19 treated in vitro with CEP-dipeptide did not stimulate vascular endothelial growth factor secretion, suggesting CEP adducts follow a vascular endothelial growth factor independent pathway. Overall, these results suggest that CEP may play a role in choroidal neovascularization, and anti-CEP therapeutic modalities might be of value in limiting choroidal neovascularization in AMD. In retinal light damage studies, CEP, argpyrimidine, and nitrotyrosine immunoreactivities in rodent retina were found to be significantly greater after 4 h green light exposure compared with control animals maintained in the dark. These findings justify further consideration of protein modifications as mediators in the light-induced biochemical sequelae leading to photoreceptor cell death. Similar results were obtained with 6 h blue light exposure. CEP adducts and autoantibodies were lowered after pretreatment with drugs prior to blue light exposure. Because CEP adducts and autoantibodies are also elevated in human AMD plasma, experimental drugs that lowered retinal light damage may eventually become useful as therapeutics for dry AMD. In studies directed at characterizing RPE lipofuscin, lipofuscin granules were purified with proteinase K or with SDS. Purified and crude lipofuscin were found to be equally phototoxic to cultured RPE cells and to exhibit no difference in the content of A2E, isoA2E, all-trans-retinal dimer-phosphatidylethanolamine, CEP, iso[4]levuglandin E2-adducts, or nitrotyrosine. Notably the purified granules were found to contain very little protein that is degradable to amino acids (~2% w/w), implicating the bulk of the lipofuscin granule, which is not protein, as the bioactive component in phototoxicity. In studies of a superoxide dismutase2 knockdown mouse, CEP and nitrotyrosine immunoreactivities were found to be significantly greater in the RPE compared with wild type animals. The superoxide dismutase2 knockdown mouse develops an AMD-like phenotype, supporting a role for oxidative damage in AMD. Overall, this dissertation research provides mechanistic clues to the etiology and pathology of AMD.

Committee:

John Crabb (Advisor); Robert Salomon (Advisor)

Subjects:

Chemistry, Biochemistry

Keywords:

Oxidative Damage; Age related macular degeneration; carboxyethylpyrrole; Retinal light damage; lipofuscin; choroidal neovascularization

Zhou, JunNumerical Modeling of Ductile Fracture
Doctor of Philosophy, University of Akron, 2013, Mechanical Engineering

This thesis sought to investigate and develop valid numerical approaches to predict ductile fracture under different stress state and loading conditions.

As the first portion of this work, the plastic flow and fracture behaviors of three aluminum alloys (5083-H116, 6082-T6 and 5183 weld metal) under the effects of strain rate and temperature were studied through a series of experiments and finite element analyses. The fracture behavior under the influential factor of stress triaxiality was also studied. The applicability of the Johnson-Cook plasticity and fracture models were investigated with mixed results. For all three materials, the dependency of the failure strain on triaxiality is adequately described.

The stress state effect on plasticity and ductile fracture behaviors was further explored for aluminum alloy 5083-H116 through tests on plane strain specimens and torsion specimens, focusing on the third deviatoric stress invariant (lode angle). A stress state dependent plasticity model, J2-J3 model, together with the Xue-Wierzbicki fracture criterion which defined the damage parameter as a function of the stress triaxiality and the Lode angle, was implemented and calibrated with the test data. The calibrated model was utilized to study the residual stress effect on ductile fracture resistance, using compact tension specimens with residual stress fields generated from a local out-of-plane compression approach. Fracture tests with positive and negative residual stresses were conducted on the C(T) specimens. Both experimental and finite element results showed significant effect of residual stress on ductile fracture resistance.

In an attempt to predict ductile fracture under shear-dominated conditions, this study combined the damage mechanics concept with the Gurson-Tvergaard-Needleman porous plasticity model that accounts for void nucleation, growth and coalescence. The GTN model was extended by coupling two damage parameters, representing volumetric damage and shear damage respectively, into the yield function and flow potential. The new model was validated through a series of numerical tests in comparison with existing GTN type models, and applied to predict the ductile fracture behaviors of a beta-treated Zircaloy-4. With model parameters calibrated using experimental data, the model was able to predict failure initiation and propagation in various specimens experiencing a wide range of stress states.

Committee:

Xiaosheng Gao, Dr (Advisor); Shing-Chung Wong, Dr. (Committee Member); Gregory Morscher, Dr. (Committee Member); Ernian Pan, Dr. (Committee Member); Kevin Kreider, Dr. (Committee Member)

Subjects:

Mechanical Engineering; Mechanics

Keywords:

Ductile fracture; damage accumulation; Johnson-Cook models; stress triaxiality; Lode angle; plastic flow; residual stress; crack initiation and growth; void growth; shear damage; Gurson

Lee, Soon GieHybrid Damage Identification Based on Wavelet Transform and Finite Element Model Updating
Doctor of Philosophy, University of Akron, 2012, Civil Engineering

Structural health monitoring (SHM) has gained more attentions recently since nearly 140,000 of a total 600,000 highway bridges in the US are nearing 50 years of age and are approaching the end of their design life. Most in-service highway bridge structures are suspected to be undergoing deterioration processes induced by the physical and harsh environmental changes. Therefore, timely maintenance with a robust SHM system having capability of early detection of impending damage is required to prevent catastrophic events for the public safety with reduced expenses.

Vibrational modal properties may not be sufficient for detecting early damage in local regions of complex civil infrastructure. Moreover, most of current damage detection methods require reference data which are not always available. There have also been pressing needs for real-time monitoring to prevent sudden catastrophic disasters. This dissertation addresses current challenges and needs identified in existing vibration-based damage detection methods, focusing on wavelet-based reference-free real-time damage identification and subsequent finite element model updating for quantifying damage severity.

First, a damage detection method based on a wavelet entropy analysis has been embedded in wireless smart sensor nodes (Imote2) and tested with three-story shear building and a laboratory truss bridge structure. To realize the reference-free damage detection, a continuous relative wavelet entropy (CRWE)-based damage detectionmethod is also proposed and demonstrated with a laboratory truss bridge structure. Although the reference-free CRWE method can detect damage locations without reference data,computational times put limitations in its applications to a real-time SHM system. To make real-time monitoring feasible in SHM systems, a statistical referencefree real-time damage detection method has been developed based on the wavelet packet transformation and log likelihood ratios.

Second, finite element model updating has been conducted to quantify the level of damage at the identified damage locations. For an identification model, fracturemechanics based cracked beam element with local flexibility coefficients and rotational spring stiffness coefficients have been used. After experimental modal testing of the laboratory truss structure, modal properties are extracted by the output-only frequency domain decomposition method. Because of limited number of sensors, mode shapes of each panel of the structure are separately extracted and combined by the interface DOF-by-DOF decentralized modal identification method. Modal properties (i.e. mode shapes and natural frequencies) are used to quantify physical damage level in term of crack depth.

In summary, this dissertation proposed wavelet-based robust and viable real-time reference-free damage localization methods and conducted damage quantification by finite element model updating. The proposed method has been experimentally verified and evaluated using test-beds that include a three-story shear building structure and a laboratory truss bridge structure.

Committee:

GunJin Yun, Dr. (Advisor); Ernian Pan, Dr. (Committee Member); Joan Carletta, Dr. (Committee Member); Kevin Kreider, Dr. (Committee Member); David Roke, Dr. (Committee Member)

Subjects:

Civil Engineering

Keywords:

Structural Health Monitoring; Damage Identification; Wavelet Transform; Damage Quantification; Finite Element Model Updating

Blebo, Felix CParametric Study of Seismic-Resistant Friction-Damped Braced Frame System
Master of Science, University of Akron, 2013, Civil Engineering
Conventional braced frame systems have limited drift capacity before brace buckling and related damage leads to deterioration in strength and stiffness. A friction-damped braced frame (FDBF) system is being developed to provide significant drift capacity while limiting damage and residual drift. The FDBF system consists of beams, columns, and braces branching off a central column. Friction at lateral-load bearings that transfer inertia forces from the floor diaphragms to the FDBF is used to dissipate energy, to reduce the overall seismic response of the FDBF system, and to provide overturning moment resistance. Vertically oriented post-tensioning bars provide additional overturning moment resistance and help to reduce residual drift. The thesis introduces a preliminary design approach for FDBF systems. Several FDBF systems are designed, and pushover and dynamic nonlinear analysis results are presented. Dynamic analysis results confirm the expected drift capacity and behavior of the system.

Committee:

David Roke, Dr. (Advisor); Kallol Sett, Dr. (Committee Member); Qindan Huang, Dr. (Committee Member)

Subjects:

Civil Engineering; Design

Keywords:

Self-centering, damage free seismic resistant structures, higher mode effects, friction damped, post-tensioned steel braced frame,

Stenta, AaronOne Dimensional Approach to Modeling Damage Evolution in Galvanic Corrosion
Master of Science, University of Akron, 2013, Applied Mathematics
A one-dimensional mathematical model is developed to describe damage evolution in galvanic corrosion for a variety of geometries. An asymptotic procedure taking advantage of disparity in length scales is used to derive the model. The focus of this thesis is to detail the formulation and solution of the 1D model for basic cartesian and cylindrical configurations. The cartesian model defines a rectangular domain, while the cylindrical model defines a system of concentric disks. For each model a thin film approximation for the thickness of the electrolyte and a well-mixed assumption describing uniform concentration of species in the electrolyte is used. Further, the Wagner relationship restricts the size of the electrolyte thickness as compared to the solution conductivity and polarization slope. Numerical solutions, using Matlab, are obtained for the potential, current density, and corrosion damage through time. The initial time solutions are compared to solutions obtained through the software package, GalvanicMaster, and excellent agreement is found. The damage evolution results are verified using experimental data and corrosion simulations that are cited in the literature. A comparative analysis is performed considering the effect of changing area ratio, electrolyte thickness, IR drop, and Wagner relationship for each system. Fully derived 1D governing equations for additional geometries are also proposed.

Committee:

Gerald Young, Dr. (Advisor); Curtis Clemons, Dr. (Committee Member); Kevin Kreider, Dr. (Committee Member)

Subjects:

Chemical Engineering; Engineering; Mathematics

Keywords:

Galvanic; Corrosion; Damage; Evolution; Mathematical; Modeling; Magnesium; Mild Steel; Aluminum; Copper; Thin Film; Wagner; 1D; Matlab; GalvanicMaster; 2D

Doudican, Bradley MModeling Repair of Fiber Reinforced Polymer Composites Employing a Stress-Based Constitutive Theory and Strain Energy-Based Progressive Damage and Failure Theory
Doctor of Philosophy, The Ohio State University, 2013, Civil Engineering
Material system selection for primary structures requires a decision matrix that evaluates not only the initial design but also the full lifecycle economy. The ability to economically repair structural components over time may control initial design decisions, especially for structures tat are routinely repaired such as aircraft components. Composite materials in their virgin condition often provide substantial mechanical and environmental advantages over metals. However, the repair of composite materials has historically been more costly, time-consuming, and mechanically conservative than metallic repair, and thus is a barrier in the continued advancement of their use. The state of the art of composite repair analysis and substantiation in practice is often limited to simplified and conservative methodologies. While these methods of analysis may be acceptable for secondary or tertiary composite structures, the advancement in analysis of repair for primary composite structures must advance in order for composite materials to become a material system of choice. The state of the art of composite repair analysis and substantiation in published theory has advanced to include displacement-based, nonlinear, and fully three-dimensional finite element models; however, these current models also include geometric, loading, and material model simplifications and limitations that inhibit their general application. Given these limitations, the effective and optimal use of composite materials for primary structures over their complete lifecycle, fully developing the capabilities of their advantages over other material systems, is limited. The research herein documents the development of a composite repair model to advance the state of the art by addressing some of the limitations found in the current literature. A constitutive formulation based on a stress-based laminated plate theory was implemented through a finite element numerical solution algorithm to model the stress and displacement behavior of the composite laminate and coupled with a strain energy based progressive damage and failure theory. Further, the progressive damage and failure theory is deployed through a user subroutine for the Abaqus commercial finite element package for the analysis of progressive damage and failure of unidirectional fiber or woven fabric lamina. The model more accurately predict composite laminate constitutive response for both elastic and progressive damage modes, including the free edge effects and more complicated stress fields through a repair zone. A demonstration of the model’s predictive capabilities is provided by comparison to closed- and open-form analytical solutions, other numerical studies, and experimental data for lap joints and scarf repaired specimens. The findings from this research can be employed to both substantiate composite repair analyses and to predict the ultimate response of repaired components. Tangential benefits will include the development of improved constitutive modeling and progressive damage and failure modeling capabilities that will permit their deployment through powerful proprietary software platforms such as Abaqus, and the demonstration of the strengths and weaknesses of the composite modeling methods incorporated in current proprietary software codes.

Committee:

William Wolfe (Advisor); Tarunjit Butalia (Advisor); Ethan Kubatko (Committee Member); Gregory Schoeppner (Committee Member); Dean Foster (Committee Member)

Subjects:

Aerospace Engineering; Civil Engineering; Mechanical Engineering; Mechanics

Keywords:

Composite repair, stress based plate theory, progressive damage and failure, scarf repair, finite element analysis of composite materials

Wang, HongMACHINE HEALTH MONITORING OF ROTOR-BEARING-GEAR TRANSMISSION SYSTEM
Master of Science, University of Akron, 2005, Mechanical Engineering
Presently there are some on-line vibration monitoring methods which do not require a shut down of the rotating of gear-rotor-bearing transmission machinery and can be used as an in-flight diagnostic and trend monitoring device. However, very little work has been accomplished on the detection and quantification of combined gear damages and bearing faults in a bearing-rotor-gear transmission system. Vibrations caused by the combined damages in gears and bearing usually can not be identified readily without special procedure applied to the vibration signature. In this thesis, under a variety operating cases, vibration signature due to the combined damage between the outer race of bearing and the teeth of gear were examined in both time and frequency domains for identification purposes. Joint time-frequency analysis such as the Wigner-Ville Distribution (WVD) was used in detecting and identifying various types of gear and bearing damage. The modified Poincare Maps based on chaotic vibration were also successfully applied in analyzing the vibration from gear and bearing damages. The objective of this work is to develop an on-line Health Monitoring system to detect faults in gear and bearing. Considerable success has been achieved in this work to identify faults in both bearing and gear components. Based on the experimental results, a comprehensive database for vibration signature identification with various component faults is recommended for future study.

Committee:

Fred Choy (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

VIBRATION ANALYSIS TO COMBINED DAMAGE IN BOTH BEARINGS AND GEARS

Fife, Jane PattersonInvestigation of the effect of agricultural spray application equipment on damage to entomopathogenic nematodes - a biological pest control agent
Doctor of Philosophy, The Ohio State University, 2003, Food, Agricultural, and Biological Engineering
Biological pesticides (i.e., biopesticides) are living systems, which introduce additional challenges with respect to formulation and delivery not previously encountered with conventional chemical pesticides. Understanding the effects of the different physical phenomena within a spray system is important to begin identifying the equipment characteristics and operating conditions that are least detrimental to the biological agents. Specifically, this work considered the effects of pressure differentials and hydrodynamic stress on damage to a benchmark biological pest control agent, entomopathogenic nematodes (EPNs). Four EPN species were evaluated in this work: Heterorhabditis bacteriophora, H. megidis, Steinernema carpocapsae, and S. glaseri. Additionally, temperature influences due to pump recirculation were investigated. Results from this work indicate that S. carpocapsae nematodes were able to withstand greater pressure differentials and more intensive hydrodynamic conditions than the other EPN species. Consequently, EPN species is an important factor to consider when defining spray operating conditions. Operating pressures within a spray system should not exceed 2000 kPa (290 psi) for H. bacteriophora and S. carpocasae, and 1380 kPa (200 psi) for H. megidis. Other EPN species may require lower pressure. Experimental results of EPN damage after passage through an abrupt contraction and two common types of hydraulic nozzles (flat fan and cone) were compared to flow parameters from numerical simulations of the experimental flow fields using FLUENT, a commercial computational fluid dynamics (CFD) program. Based on the flow field characteristics, the rotational flow regime within a cone type nozzle produces hydrodynamic conditions that are less damaging to EPNs compared to the extensional flow developed within the narrow, elliptic exit orifice of the flat fan nozzle. It was found that the tensile stress loading that occurs during flow into a constricted region, which characterizes an extensional flow, is damaging to the biological material. An empirical model comparing average energy dissipation rates computed in FLUENT to observed EPN damage was developed. Overall, the model was able to predict the EPN damage after treatment with the hydraulic nozzles well, in many cases within 5%. These results show that CFD is a feasible method to evaluate the flow conditions within an equipment component to assess its compatibility with a biological agent. Finally, extensive recirculation of the tank mix can cause considerable increases in the liquid temperature. It was found that either a diaphragm or roller pump is better suited for use with biopesticides, compared to a high-capacity centrifugal pump, which contributes significant heat to the spray system.

Committee:

H. Ozkan (Advisor)

Keywords:

entomopathogenic nematodes; spray application equipment; hydraulic nozzles; pressure differential; hydrodynamic stress; damage; computational fluid dynamics; energy dissipation rate; pump recirculation; temperature

Zoofan, BahmanQuantitative microradiography and its applications to microdamage assessment
Doctor of Philosophy, The Ohio State University, 2004, Welding Engineering
A state-of-the art microradiographic system including an imaging chain and a micro-focus X-ray source has been used for development of a quantitative nondestructive evaluation (NDE) tool in characterizing material microdamages. In contrast to conventional radiographic systems, where the performance is well understood, there is limited scientific data available for the evaluation of microradiographic system performance in terms of the effect of projection magnification and the geometric unsharpness on system detectability. Evaluating the detectability of a microradiographic system is a further challenge in this research. Quantitative methods are developed to characterize the detectability of a microradiographic system. The concept of optimum magnification and the effect of unsharpness on detectability of the system are studied. The enlarged and high resolution images are used to develop a microradiographic method for microdamage depth measurement. The method was applied to quantify micro-damage due to pitting corrosion in Al 2024-T3 alloy. The accuracy of the developed technique was then validated using other methods such as comparison with optical microscopy data, comparison with the 3-D images taken by profilometry, direct reading of the thickness lost by cutting the actual corroded samples, radiography of samples with two perpendicular shots, and also quantitative pixel-by-pixel comparison was done between data from profilometry and those from the microradiographic method. Hidden microdamage in materials is a challenging area for NDE; in order to characterize this sort of damage, the effect of contrast change on detectability was studied and compared with the theoretical predictions. Also a microradiographic technique has been developed to study initiation, growth and locations of fine primary and secondary cracks in dwell fatigue testing on titanium samples. Microradiographic data then has been compared with in-situ ultrasonic signals for further evaluation. This research also involves the study of the phase-contrast imaging applicability for microradiographic characterization of damage in structural materials. It has been shown that by optimization of the exposure parameters, the X-ray beam from a micro-focus system can be used as a phase contrast imaging technique in engineering settings. For the first time the phase-contrast imaging is done with a micro-focus system on an aluminum sample with a pit. Optimization of the radiographic parameters to receive the enhanced phase-contrast images of microdamages has been done quantitatively on an epoxy sample with pores and an aluminum specimen with an artificial pit. The experimental data from the obtained images has been compared with the theoretical results based on the refraction model. This research shows some successful efforts in how quantitative microradiography has been applied as an in-situ NDE technique for different applications like: studying the localized microdamage growth in aluminum in corrosive solutions, the study of real-time microradiography of keyhole formation in laser beam welding combined with a high-speed camera and porosity formation in welding of titanium.

Committee:

Stanislav Rokhlin (Advisor)

Keywords:

Microradiography; micro-focus; X-ray imaging; corrosion damage; Phase-contrast imaging

Connelly, Sandra J.Effects of Ultraviolet Radiation (UVR) Induced DNA Damage and Other Ecological Determinants on cryptosporidium Parvum, Giardia Lamblia, and Daphnia spp. in Freshwater Ecosystems
Doctor of Philosophy, Miami University, 2007, Zoology

Freshwater ecosystems are especially susceptible to climatic change, including anthropogenic-induced changes, as they are directly influenced by the atmosphere and terrestrial ecosystems. A major environmental factor that potentially affects every element of an ecosystem, directly or indirectly, is ultraviolet radiation (UVR). UVR has been shown to negatively affect the DNA of aquatic organisms by the same mechanism, formation of photoproducts (cyclobutane pyrimidine dimers; CPDs), as in humans. First, the induction of CPDs by solar UVR was quantified in four aquatic and terrestrial temperate ecosystems. Data show significant variation in CPD formation not only between aquatic and terrestrial ecosystems but also within a single ecosystem and between seasons. Second, there is little quantitative data on UV-induced DNA damage and the effectiveness of DNA repair mechanisms on the damage induced in freshwater invertebrates in the literature. The rate of photoproduct induction (CPDs) and DNA repair (photoenzymatic and nucleotide excision repair) in Daphniafollowing UVR exposures in artificial as well as two natural temperate lake systems was tested. The effect of temperature on the DNA repair rates, and ultimately the organisms’ survival, was tested under controlled laboratory conditions following artificial UVB exposure. The results of these studies suggest a significant interaction of UVR and temperature on individual survival and ultimately population dynamics in freshwater systems.

Lastly, freshwater human pathogens have negative effects ranging from gastrointestinal distress in otherwise healthy individuals to death in the immunocompromised and elderly. The control of infectious pathogens in water treatment is imperative. The abiotic and biotic environmental stressors of human pathogens are not well understood. Herein, solar radiation and artificial UVB are shown to significantly decrease the infectivity of Cryptosporidium parvum in vitro. The generalist filter feeder, Daphnia pulicaria, was shown to have significant effects on the viability, excystation, and infectivity of both Cryptosporidium parvumand Giardia lambliaunder laboratory-controlled conditions. Both of these studies have significant implications for the natural control and potable water pretreatment approaches to human pathogen control.

Committee:

Craig Williamson (Advisor)

Keywords:

UV; DNA damage; DNA repair; Human pathogens; Disinfection; Daphnia; Cryptosporidium; Giardia

Aminjikarai Vedagiri, Srinivasa BabuAn Automated Dynamic Fracture Procedure and a Continuum Damage Mechanics Based Model for Finite Element Simulations of Delamination Failure in Laminated Composites
PhD, University of Cincinnati, 2009, Engineering : Aerospace Engineering

An active field of research that has developed due to the increasing use of computational techniques like finite element simulations for analysis of highly complex structural mechanics problems and the increasing use of composite laminates in varied industries such as aerospace, automotive, bio-medical, etc. is the development of numerical models to capture the behavior of composite materials. One of the big challenges not yet overcome convincingly in this field is the modeling of delamination failure which is one of the primary modes of damage in composite laminates. Hence, the primary aim of this work is to develop two numerical models for finite element simulations of delamination failure in composite laminates and implement them in the explicit finite element software DYNA3D/LS-DYNA.

Dynamic fracture mechanics is an example of a complex structural analysis problem for which finite element simulations seem to be the only possible way to extract detailed information on sophisticated physical quantities of the crack-tip at any instant of time along a highly transient history of fracture. However, general purpose, commercial finite element software which have capabilities to do fracture analyses are still limited in their use to stationary cracks and crack propagation along trajectories known a priori. Therefore, an automated dynamic fracture procedure capable of simulating dynamic propagation of through-thickness cracks in arbitrary directions in linear, isotropic materials without user-intervention is first developed and implemented in DYNA3D for its default 8-node solid (brick) element. Dynamic energy release rate and stress intensity factors are computed in the model using integral expressions particularly well-suited for the finite element method. Energy approach is used to check for crack propagation and the maximum circumferential stress criterion is used to determine the direction of crack growth. Since the re-meshing strategy used to model crack growth explicitly in the model induces spurious high-frequency oscillations in the finite element results after crack initiation, a “gradual nodal release” procedure is implemented as part of the model to overcome this problem. Also, an in-built contact algorithm of DYNA3D is modified to adapt it to the re-meshing strategy to maintain proper contact conditions at newly added elements. Finally, the model is suitably modified for simulating delamination failure in laminated composites and used to predict delamination resistance characteristics which are important considerations for effective use of composite structures.

Continuum damage mechanics is a popular approach for modeling the in-plane failure modes in composites. However, its applicability to modeling delamination has not been sufficiently analyzed yet. Hence, as the second part of this dissertation work, a new material model is developed for unidirectional polymer matrix composites in which this approach is used to predict delamination failure and used to perform a qualitative study of the damage mechanics approach to modeling delamination. The new material model is developed using micro-mechanics and accounts for the strain-rate dependent behavior of polymer matrix composites. It is implemented for three different element formulations with different transverse shear strain assumptions and the effect of these assumptions on the delamination prediction using this approach is analyzed.

Committee:

Dr. Ala Tabiei (Committee Chair); Dr. Jandro Abot (Committee Member); Dr. Shaaban Abdallah (Committee Member); Dr. James Wade (Committee Member)

Subjects:

Aerospace Materials; Automotive Materials; Mechanical Engineering; Mechanics

Keywords:

automated fracture procedure; dynamic fracture mechanics; energy release rate; stress intensity factors; gradual nodal release technique; delamination; delamination resistance characteristics; continuum damage mechanics model; micro-mechanical model

Adkins, Keith AA Model for Prediction of Fracture Initiation in Finite Element Analyses of Welded Steel Connections
MS, University of Cincinnati, 2014, Engineering and Applied Science: Civil Engineering
This paper investigates the implementation of damage mechanics into finite element models of fillet-welded structural steel assemblies in order to predict connection fracture at realistic displacements. Utilizing a previously developed IDS (instability, ductile, and shear) material failure envelop for aluminum extrusions, the failure loci of the aluminum material were scaled to meet the point of fracture in welded steel lap splice assemblies, loaded in-plane at various angles, with a fillet weld leg size of 5 mm. The weld electrode under investigation was CSA E480xx, which is equivalent to AWS E70xx electrodes. A linear relationship for damage data scaling factors, as they relate to the loading angle of the fillet weld, was established. Three similar assemblies with fillet leg sizes of 9 mm were modeled employing this damage scaling relationship and deformations at fracture were found to coincide with experimental results and established relationships. This modeling methodology was also investigated for use in a T-stub connection tension scenario.

Committee:

James Swanson, Ph.D. (Committee Chair); Kenneth Wurzelbacher, M.S. (Committee Member); Gian Rassati, Ph.D. (Committee Member)

Subjects:

Civil Engineering

Keywords:

Finite Element Analysis;Damage Mechanics;Fillet Weld;IDS Criteria;Lap Splice;T-Stub

Mitchell, Robert AndrewUnderstanding Femtosecond-Pulse Laser Damage through Fundamental Physics Simulations
Doctor of Philosophy, The Ohio State University, 2015, Physics
It did not take long after the invention of the laser for the field of laser damage to appear. For several decades researchers have been studying how lasers damage materials, both for the basic scientific understanding of highly nonequilibrium processes as well as for industrial applications. Femtosecond pulse lasers create little collateral damage and a readily reproducible damage pattern. They are easily tailored to desired specifications and are particularly powerful and versatile tools, contributing even more industrial interest in the field. As with most long-standing fields of research, many theoretical tools have been developed to model the laser damage process, covering a wide range of complexities and regimes of applicability. However, most of the modeling methods developed are either too limited in spatial extent to model the full morphology of the damage crater, or incorporate only a small subset of the important physics and require numerous fitting parameters and assumptions in order to match values interpolated from experimental data. Demonstrated in this work is the first simulation method capable of fundamentally modeling the full laser damage process, from the laser interaction all the way through to the resolidification of the target, on a large enough scale that can capture the full morphology of the laser damage crater so as to be compared directly to experimental measurements instead of extrapolated values, and all without any fitting parameters. The design, implementation, and testing of this simulation technique, based on a modified version of the particle-in-cell (PIC) method, is presented. For a 60 fs, 1 µm wavelength laser pulse with fluences of 0.5 J/cm2, 1.0 J/cm2, and 2.0 J/cm2 the resulting laser damage craters in copper are shown and, using the same technique applied to experimental crater morphologies, a laser damage fluence threshold is calculated of 0.15 J/cm2, consistent with current experiments performed under conditions similar to those in the simulation. Lastly, this method is applied to the phenomenon known as LIPSS, or Laser-Induced Periodic Surface Structures; a problem of fundamental importance that is also of great interest for industrial applications. While LIPSS have been observed for decades in laser damage experiments, the exact physical mechanisms leading to the periodic corrugation on the surface of a target have been highly debated, with no general consensus. Applying this technique to a situation known to create LIPSS in a single shot, the generation of this periodicity is observed, the wavelength of the damage is consistent with experimental measures and, due to the fundamental nature of the simulation method, the physical mechanisms behind LIPSS are examined. The mechanism behind LIPSS formation in the studied regime is shown to be the formation of and interference with an evanescent surface electromagnetic wave known as a surface plasmon-polariton. This shows that not only can this simulation technique model a basic laser damage situation, but it is also flexible and powerful enough to be applied to complex areas of research, allowing for new physical insight in regimes that are difficult to probe experimentally.

Committee:

Douglass Schumacher (Advisor)

Subjects:

Physics

Keywords:

Laser Damage; LIDT; Simulation; Particle-in-cell; Modeling; Short-pulse; femtosecond

Nowacki, Brenna M.Verification and Calibration of State-of-the-Art CMC Mechanistic Damage Model
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

Keywords:

ceramic matrix composite; ABAQUS; CLIP; damage model; calibration; SiC-SiC; material characterization

Duning, Solomon George3D Textile PMC Damage Evolution: Effects of Fiber Volume Fraction and Morphology Variation
Master of Science (M.S.), University of Dayton, 2016, Mechanical Engineering
3D textile polymer matrix composites (PMC) exhibit geometric and material state variances due to differences in manufacturing processes and a variety of other factors. Developing a more thorough understanding of these strength and damage variations is a vital aspect of generating an accurate predictive model for the material response of a 3D textile PMC. This work entails both experimental and modeling efforts in order to gain a more thorough understanding of how tow level geometric variations relate to damage evolution in a 3D textile PMC. A 3D orthogonal weave textile is imaged utilizing an X-Ray micro-CT to examine the fiber volume fraction and fiber path distributions within the composite. Additionally, damage evolution is observed at different load steps and CT images are utilized for Digital Volume Correlation analysis. Modeling efforts are primarily focused on tow morphology simulations within the software package- Virtual Textile Morphology Suite (VTMS). Damage evolution analysis on the VTMS models are performed using an advanced Regularized eXtended Finite Element Method (RX-FEM) within the Air Force Research Laboratory developed B-Spline Analysis Method (BSAM) program. Local fiber volume fraction variation in the specimens is examined through serially sectioned images obtained using Robo-Met 3D. Fiber volume fraction distributions are compared to VTMS predictions and VTMS predictions are modified to reflect experimental values. The effect of these local fiber volume fraction distributions on damage evolution in the composite are examined through experimentation and modeling efforts.

Committee:

Margaret Pinnell, Ph.D. (Advisor); David Mollenhauer, Ph.D. (Committee Member); Tom Whitney, Ph.D. (Committee Member)

Subjects:

Engineering; Materials Science; Mechanical Engineering; Mechanics

Keywords:

3D Textile Polymer Matrix Composite; Fiber Volume Fraction Variation; Discrete Damage Modeling; Textile Morphology Variation; Inter-tow Property Variation; Tow Fiber Path Distribution

Alakrawi, MariamTranscriptional Regulation of the Human Angiotensinogen Gene
Master of Science in Biomedical Sciences (MSBS), University of Toledo, 2016, Biomedical Sciences (Cardiovascular and Metabolic Diseases)
The human angiotensinogen (hAGT) locus is linked to essential hypertension. The hAGT gene has -6A/G polymorphism and -6A (rs5051) allele is associated with increased blood pressure (5). We have identified that hAGT gene has polymorphisms in its 2.5Kb promoter that forms two haplotype: -6A haplotype, or Hap I, (containing -6A, -1561T, -1562C, -1670A) and -6G haplotype, or HapII, (containing -6G, -217G, - 1561G, -1562G, -1670G). Hap -6A/- 217A (Hap -6Aor Hap I ) is associated with human hypertension whereas, Hap - 6G/-217G (Hap -6G or Hap II) reduces cardiovascular risk (6). To study the regulation of the hAGT gene in an in vivo situation, we have also generated transgenic mice (TG) containing either Hap -6A or Hap -6G of the hAGT gene. Aging and high fat diet (HFD) is shown to increase hAGT expression though the renin angiotensinogen aldosterone system (RAAS) activation, which results on increase in ANG II and blood pressure in haplotype dependent manner. To better demonstrate this relationship, we propose a predictive model for blood pressure measurement based on the haplotype group, age, and body weight of each mouse. Through computational statistics, we have figured a linear model equation to estimate blood pressure readings. We have found strong contribution of HFD and hAGT gene haplotype on increasing blood pressure. However, age has shown not to be that significant. Our study has also demonstrated that HFD increases kidney biomarkers involved in inflammatory pathway activation. These results suggested that HFD, Haplotype I, and high blood pressure are risk factors for the pathogenesis of kidney disease in essential hypertension.

Committee:

Kumar Ashok, PhD (Committee Chair); Nitin Puri, M.D., PhD (Committee Member); Meenakshi Kaw, M.D., PhD (Committee Member)

Subjects:

Biomedical Research; Health; Medicine

Keywords:

Angiotensinogen, haplotype, hypertension, high fat diet, kidney damage

Oaks , Rosemary JaneExamining the Relationship Between Coxsackievirus Infection and Coxsackievirus and Adenovirus Receptor Expression in NOD Mouse Kidneys
Bachelor of Science (BS), Ohio University, 2018, Biological Sciences
Coxsackievirus (CV) infection has been associated with acute kidney damage, a problem that can be life-threatening. An observed lack of kidney damage following CV infection of the non-obese diabetic (NOD) mouse strain suggested a relationship between virus infection and expression of its receptor, Coxsackievirus and Adenovirus receptor (CAR), which could influence the effect of the virus on the kidney. Very little is known about the mechanism of virus-induced kidney injury in humans or in mice, but it appeared that NOD mice may be utilizing a protection mechanism. This project analyzed the influence of CV infection on CAR expression in the kidneys of NOD mice as a first step toward defining the mechanism of protection from viral damage. This study showed that virus can gain access to kidney cells and that receptor expression is affected by viral presence, indicating that decreased access to receptor is limiting viral spread. Because viral infection itself can cause kidney damage in humans and other animal models, defining the mechanism of how NOD mice protect themselves could someday help humans who have been infected with a virus and are at risk for kidney damage.

Committee:

Karen Coschigano, PhD. (Advisor); Debra Walter , MS. (Other)

Subjects:

Biology; Biomedical Research

Keywords:

Coxsackievirus; Coxsackievirus and Adenovirus Receptor; Non-obese Diabetic; Virus; Kidney; Kidney damage

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