Master of Science, The Ohio State University, 2018, Civil Engineering

The design of residential structures has changed and evolved throughout years of research based on numerical modelling of real-world conditions. Wood design is controlled heavily by member use, baseline material load capacities, and wood species,all of which determine material properties. Extensive work has been done to determine the effects of altering material properties due to environmental stimuli, however, certain types of decay and wood rot have yet to be fully tested and understood. Certain microbial organisms, given the right conditions, can cause irreversible damage to wood structures. A particularly critical mode of failure is premature column collapse which is driven in part by degraded cross sectional and material properties. Using stiffness relationships smartly programmed into matrix form, it is possible to calculate reduced buckling capacities for these degraded members to draw some important conclusions. Two important items are to determine what degrees of wood decay are critical and what column heights are particularly susceptible to this type of premature failure. Finally, specifications and code should be developed further to assist engineers make choices about the criticality of wood decay without the use of personalized software. This can be done using pre-generated aids to help designers make smarter and more cost effective choices.

Committee: Natassia Brenkus PhD (Advisor); Anthony Massari PhD (Committee Member); Nan Hu PhD (Committee Member) Subjects: Civil Engineering

Master of Science in Engineering (MSEgr), Wright State University, 2009, Mechanical Engineering

Knowledge of critical structural items for an aircraft structural system is crucial for any risk integrated design and maintenance procedure. These critical items are those whose failure can cause catastrophic damage to the entire structure or result in loss of availability. For example, failure of the fuselage longeron of an F-15 aircraft resulted in the separation of the aircraft cockpit from the rest of the structure, resulting in a complete loss of the aircraft. This is clearly a critical structural item that was identified during the design process but did not have appropriate design, manufacturing, or maintenance controls that could have prevented the accident through early detection of manufacturing flaws. While this failure is catastrophic, there can be other damage scenarios that are not catastrophic but they could lower aircraft availability due to maintenance and repair requirements. Moreover, these critical structural items can be in areas of the aircraft that require extensive teardown in order to assess their condition. Therefore, along with the criticality of the structural failure, the location of the component also becomes important. In this research, Failure Modes Effects and Criticality Analysis (FMECA) will be used to integrate, event criticality, event frequency, and damage detection capability into one metric. This process enables integration of structural sizing and maintenance planning to minimize the operational cost while maximizing the aircraft availability. This process can also be used to quantify the impact of structural health monitoring system on the overall risk of failure of the structure. In this research, a Boeing 707 lower wing skin with stiffeners is used to demonstrate the process of developing an FMECA procedure for structural systems. In order to make this process applicable for large scale systems efficient structural re-analysis methods that minimize the analysis cost are also implemented. This FMECA process can be used to (open full item for complete abstract)

Committee: Ravi Penmetsa Ph.D. (Advisor); Eric Tuegel Ph.D. (Committee Member); Nathan Klingbeil Ph.D. (Committee Member) Subjects: Aerospace Materials; Design; Engineering; Industrial Engineering; Mechanical Engineering

PhD, University of Cincinnati, 2006, Engineering : Mechanical Engineering

Damping matrices have been formulated based on a simple model such as the proportional or structural damping when building a numerical model of a dynamic system. Such simple models, which were proposed largely for mathematical convenience, match only the overall effect of damping but ignore the actual mechanism or spatial distribution of damping. Motivated by the desire to obtain a more accurate damping matrix, various approaches have been proposed, which typically utilize some form of experiment. Among these methods, the dynamic stiffness matrix (DSM) based damping identification method is attractive because of its simplicity and generality. However, the damping matrices identified by the method were found to have unexpected forms, and also be heavily contaminated by experimental errors. Through numerical simulations and experimental work, the sources of experimental errors are identified and studied in this work. Based on the understanding obtained from the study, an improved experimental procedure is developed to minimize the errors involved in the DSM method. The test procedure is applied to two simple experimental cases to demonstrate the feasibility of the DSM based damping identification method. The development of the DSM based damping matrix identification method was motivated by the desire to apply it to building an experimental-analytical hybrid model by combining the damping matrix expanded from the experimentally identified damping matrix with analytically formulated stiffness and mass matrices. To enable this, two methods are developed to expand the experimental damping matrix to the size of the analytical model. A simple but effective method is developed to find the frequency range in which the matrix expansion is valid. As another important application of the DSM based damping identification method, the method is applied to the measurement of the property of viscoelastic materials. It is shown that how the method can be utilized to identify the struct (open full item for complete abstract)

Committee: Dr. Jay Kim (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy, The Ohio State University, 2016, Biomedical Engineering

While the soluble biochemical environment has traditionally been viewed as the most important determinant of cell behavior, accumulating evidence indicates that insoluble cues from a cell's surroundings are crucial to a variety of cellular processes. Differences in matrix properties such as stiffness, adhesiveness, and microarchitecture can influence cell shape, cytoskeletal organization, and adhesion formation. These changes can modify enzymatic pathways, control the localization of transcription factors, and even directly modulate gene expression to change overall cell behavior in response to a cell's physical surroundings. While the effects of various insoluble cues have been successfully demonstrated in 2D culture, there has been a lack of fibrous, biomimetic substrates suitable for systematically studying the role of these insoluble cues within a more physiological 3D environment. To this end, we developed and characterized a two component self-assembling peptide (SAP) system that possessed tunable stiffness (controlled via KFE-8 concentration) and RGD binding site density (controlled via KFE-RGD concentration) as well as a fibrous microarchitecture similar to collagen. In contrast to other synthetic 3D matrices such as polyethylene glycol (PEG) or alginate gels which constrict cell spreading, cells encapsulated within these gels were able to adopt non-spherical morphologies similar to those of cells within hydrogels made of natural ECM components. Using this system, we observed that the presence of the RGD binding site was required for both human mesenchymal stem cells (hMSCs) and human umbilical vein endothelial cells (HUVECs) to initially spread within these SAP gels. Furthermore, the extent of this spreading and HUVEC microvascular network (MVN) formation was dictated by stiffness, but each cell type had a different optimal stiffness that was most conducive to these non-spherical morphologies. This culture system was then used to explore the differe (open full item for complete abstract)

Committee: Keith Gooch (Advisor) Subjects: Biomedical Engineering

MS, University of Cincinnati, 2002, Engineering : Mechanical Engineering

Modeling of distributed damping characteristics are increasingly important for validating analytical structural models and correlating experimental and analytical data. In addition, damping mechanisms are a measure of structural conditions since they are sensitive to small structural changes. Thus, identification of localized changes in damping has uses in the field of damage identification. A new method to experimentally identify spatial damping, which was developed by Lee and Kim, has been studied in this research. The method fits matrix coefficient polynomials to the real and imaginary parts of the dynamic stiffness matrix (DSM, the inverse of the frequency response matrix). The real DSM coefficients represent dynamically conservative features of the system, namely mass and stiffness. The imaginary DSM coefficients model the dynamic energy removal mechanisms of the structure, namely damping. The greatest strength of the method is its simplicity and computational efficiency. Once data is collected experimentally, only two steps are required: a FRF matrix inversion (frequency line by line), and a polynomial fit for the real and imaginary components of the DSM. Since both DSM components are fit independently, the damping properties of a system may be identified without any prior knowledge about the system's mass and stiffness. Likewise, the damping calculation is not subject to errors in any pre-determined structural values. The work is broken up into three segments. First, the DSM algorithm is derived and features of the algorithm are discussed. Next, the DSM algorithm is applied to several analytical systems and several qualitative and quantitative validation tools are presented. Finally, the DSM algorithm and validation tools are applied to three experimental case studies. Practical issues are discussed and benefits and limitations of the algorithm are observed.

Committee: Dr. David Brown (Advisor) Subjects: Engineering, Mechanical

Master of Science, The Ohio State University, 2012, Materials Science and Engineering

Myocardial infarction, one of the deadly disease in the world, is caused by the blockage of coronary artery. The resulting ischemia and nutrient starving conditions induce extensive death of cardiomyocytes, which is non-regenerative. The ensuing remodeling process causes the thinning of left ventrical wall and increase in wall stress. This entire process resulted in permentent damage in heart function. Stem/progenitor cell therapy that employing stem/progenitor cells, extracellular matrix, and regulatory factors has been demonstrated to be effective in restoring heart function. However, two key issues need to be addressed: 1) reestablishing vasculatures in engineered cardiac tissue constructs; 2) stimulating the survival and differentiation of transplanted stem/progenitor cells. The overall objective of this thesis is to design a series of 3-D tissue constructs to address these two major issues. To better mimic the morphology and mechanical anisotropy of the natural ECM, electrospining was employed to fabricate anisotropic fibrous tissue constructs, thus providing a native-like structural environment and stress transfer pattern for embedded cells. To accelerate vasculaturization in fibrous constructs, a growth factor gradient was introduced into electrospun PCL scaffolds to emulate the in vivo chemotaxis microenvironment for native blood vessel formation. Both in vitro and in vivo studies demonstrated that the bFGF gradients were able to attract cell migration into the scaffolds. After subcutaneous implantation, a high density of mature (CD31+ and α-SMA+) blood vessels was formed in scaffold loaded with bFGF gradient, which demonstrated that mimicking the in vivo chemotaxis microenvironment could accelerate angiogenesis in the constructs. To ameliorate the deleterious effect of hypoxic condition, insulin like growth factor (IGF-1), basic fibroblast growth factor (bFGF), and oxygen releasing complex PVP/H2O2, were encapsulated into PLGA microspheres and delivered in (open full item for complete abstract)

Committee: Jianjun Guan (Advisor); John Lannutti (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2012, Mechanical Engineering

A new analytical stiffness model for the double row angular contact ball bearings is proposed since the current methods do not provide stiffness matrix formulations for double row bearings except for self-aligning (spherical) bearings in which angular deflections and tilting moments are negligible. The moment stiffness terms and the cross-coupling stiffness elements in double row angular contact ball bearings are significant; and the stiffness coefficients are highly dependent on the configuration of the rolling elements. Also, unlike roller-type bearings, the contact angle of ball-type bearings depends on the static load(s). The five-dimensional bearing stiffness matrix is first developed for three configurations (face-to-face, back-to-back, and tandem) from basic principles. The diagonal and off-diagonal (cross-coupling) elements of the matrix are calculated from the explicit expressions given the mean bearing load or displacement vector. Modeling approaches between a double row bearing vs. two single row bearings are also analyzed from statics and stiffness perspective. The proposed stiffness matrix is valid for duplex (or paired) bearings assuming all structural elements (such as the shaft and bearing rings) are sufficiently rigid. Next, a new modal experiment consisting of a vehicle wheel bearing assembly with a double row angular contact ball bearing in a back-to-back arrangement is designed. The bearing is subjected to axial or radial preloads in a controlled manner. Modal experiments with two preloading mechanisms (under non-roatating conditions) show that the nature and extent of bearing preloads considerably affect the natural frequencies and resonant amplitudes, thus influencing the vibration behavior of the shaft-bearing assembly. A five-degree-of freedom vibration model of the shaft-bearing assembly (including the proposed bearing stiffness matrix) is developed to describe the modal experiment. Two alternate (preload-dependent and preload-independent) v (open full item for complete abstract)

Committee: Rajendra Singh PhD (Advisor); Marcelo Dapino PhD (Committee Member); Ahmet Kahraman PhD (Committee Member); Ahmet Selamet PhD (Committee Member) Subjects: Mechanical Engineering