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

Additive Manufacturing (AM), particularly laser powder bed fusion, is being studied for use in critical component applications. Tensile and fatigue testing shows differences when built using different laser powers. However, when fabricated in an as-printed geometry, the gauge sections of the two specimens are different and experience different thermal behavior. This work explores microhardness, microstructure size, Niobium segregation, and porosity from samples made with varying laser power and different build geometry sizes representative of the gauge sections in the tensile and fatigue bars. Results show that microhardness varies spatially across the sample. Smaller diameter metallographic coupons (fatigue diameter) have a coarser microstructure and lower microhardness than the larger diameter (tensile diameter) when built using the same parameters. Therefore, the fatigue and tensile properties are not comparing the same material structure. Understanding the effect of build geometry on microstructure provides insight towards consistency in AM mechanical properties testing strategies.

Committee: Henry D. Young Ph.D. (Committee Co-Chair); Joy Gockel Ph.D. (Committee Co-Chair); Onome Scott-Emuakpor Ph.D. (Committee Member) Subjects: Engineering; Materials Science

Master of Science in Engineering, Youngstown State University, 2018, Department of Mechanical, Industrial and Manufacturing Engineering

The objective of this research is to determine if surface finish influences the mechanical properties of cast heat treated aluminum (A356-T6). Binder jetting of sand allows for complex molds to be designed and printed to decrease the amount of time, cost and material. This project is separated into three phases. First phase of the project is the development of a benchmark casting and evaluation of surface roughness. In this phase, the surface finish of several angles of print orientation were compared. Certain angles produced a very noticeable stair step feature. Second phase of the project characterizes the static tensile and fatigue properties of A356-T6 cast flat bars from molds of four print orientation angles (0°, 5°, 15°, 30°). Lastly, the third phase of the project is fluid penetrant inspection (FPI) testing. The intent of this phase is to determine if stair step features would affect the outcome of this common nondestructive evaluation process.

Committee: Brett Conner PhD (Advisor); Jason Walker PhD (Committee Member); Virgil Solomon PhD (Committee Member) Subjects: Mathematics; Mechanical Engineering

Master of Science, University of Akron, 2020, Chemical Engineering

Nanocellulose has been investigated for use in food packaging, biomedical applications, and electronics. This work attempted to isolate and evaluate crystalline nanocellulose from soybean hulls in the form of cellulose nanofibrils (CNFs) as reinforcing fillers in natural rubber composites. CNFs and nanocrystalline cellulose (CNCs) have previously been derived from different types of lignocellulosic biomass. Previous work in this area used alkali pretreatments and acid hydrolysis to break down the complex network of cellulose, hemicellulose, and lignin present in plant cell walls. CNCs and CNFs have previously been isolated using high shear microfluidization, cryocrushing, freeze drying, and ultrafiltration. In this work, enzyme cocktails of carbohydrases produced from Aspergillus niger were used to hydrolyze the polysaccharides in soybean hull and soybean flour. Solids were separated from soluble sugars and other components after enzyme hydrolysis for 24 hours, and these washed solids were treated with sonication, blending, and homogenization to reduce the size of these solids. Particle size analysis showed that enzyme hydrolysis did indeed generate nanoparticles, the majority of which were between 150-200 nm. The quantity of these insoluble nanoparticles was found to be small, however, relative to that of solids and seed coat fragments approximately 100-200 µm in length. Further analysis with microscopy and SEM imaging revealed that the enzyme hydrolysis was able to cleave sclereid structures from the seed coat and breakdown soybean hull into fragments. Smaller particle size loading at the beginning of enzyme hydrolysis was found to release more sugar, so intermediate sizes were sieved in order to maximize solids recovery and minimize sugar release. These washed and mechanically treated solids were next mixed at alkaline pH (9.8–10) with natural rubber latex and oven dried overnight to create rubber composites. The resulting composites were masticated, vulcanized, (open full item for complete abstract)

Committee: Lu-Kwang Ju (Advisor); Jie Zheng (Committee Member); Qixin Zhou (Committee Member) Subjects: Chemical Engineering

Master of Science (MS), Ohio University, 2020, Mechanical Engineering (Engineering and Technology)

Fatigue failures are sudden and catastrophic, and for critical parts must be prevented through proper design. Fatigue testing of materials yields data critical for proper design but takes large spans of testing time to complete with conventional methods. Therefore, high speed fatigue testing that produces quality data is advantageous for reducing costs and time. However, it has been shown that testing speeds may affect material performance, both in static tensile testing and dynamic fatigue testing. The effect of strain rate on material performance in static tensile testing and how it relates to fatigue testing performance at commensurate strain rates was the primary objective for this thesis work for sheet Ti-6Al-4V and Inconel 718. Implementing a vibration-driven, fully reversed bending fatigue test protocol leveraging high speed testing capability, a comparable forced displacement bending fatigue test protocol, and a high speed tensile test protocol implementing Digital Image Correlation (DIC), stress versus strain data and S-N curve data was acquired to examine two strain-rates of fatigue and tensile testing. Higher ultimate tensile strengths were observed in high strain rate tests as compared to low strain rate tests, 4.23% higher for Ti-6Al-4V and 1.91% for Inconel 718. Ti-6Al-4V exhibited higher fatigue strength in high speed tests than low speed, but Inconel 718 exhibited lower fatigue strength at high speeds as compared to low speeds.

Committee: Timothy Cyders Dr. (Advisor); Brian Wisner Dr. (Committee Member); Young David Dr. (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Experiments; Mechanical Engineering; Systems Design

Doctor of Philosophy, University of Akron, 0, Biomedical Engineering

The tricuspid valve, which is located on the right side of the heart, prevents blood backflow from the right ventricle to the right atrium. Regurgitation in this valve occurs when its leaflets do not close normally. Tricuspid valve regurgitation is one of the most common tricuspid valve dysfunctions, often requiring valve repair or replacement. The long-term success rate of the repair surgeries has not been promising; in many cases, reoperations are required within a few years after the first surgery. A limiting factor in understanding the etiology of tricuspid valve repair failure is our lack of knowledge regarding tricuspid valve biomechanics. In particular, tricuspid valve mechanical behavior has not been accurately studied. In addition, there is no precise analytical and/or computerized model to predict the mechanical responses of the valve under normal and pathological conditions. In the current study, we have used biaxial tensile testing, small angle light scattering, ex-vivo passive heart beating simulation, and sonomicrometry techniques to quantify the mechanical characteristics, microstructure, dynamic deformations, and geometric parameters of the tricuspid valve. We aimed to develop a more accurate computerized model of the tricuspid valve for simulation purposes. Our studies are important both for understanding the normal valvular function as well as for development/improvement of surgical procedures and medical devices.

Committee: Rouzbeh Amini Dr. (Advisor); Brian Davis Dr. (Committee Member); Ge Zhang Dr. (Committee Member); Francis Loth Dr. (Committee Member); Rolando Ramirez Dr. (Committee Member) Subjects: Anatomy and Physiology; Biomechanics; Biomedical Engineering; Biomedical Research; Engineering; Surgery; Technology

Doctor of Philosophy, Case Western Reserve University, 2015, Materials Science and Engineering

Al-Mg 5xxx alloys are desirable in a wide array of structural applications that require a weldable alloy with good corrosion resistance. However, significant changes in the mechanical properties have been shown to occur after both short-term high temperature (e.g. 175°C, < 100 hours) and long-term low temperature (e.g. 60°C, 1000's hrs) laboratory thermal exposures. Commercially available 5083-H116, 5456-H116 and 5083-H131 alloy plates were thermally exposed to various low and intermediate temperatures for times in excess of 20,000 hrs. Significant changes to the strength and fatigue crack growth behavior have been observed after such exposures. In particular, the longitudinal splitting in the short-transverse (ST) direction has been exhibited during fatigue crack growth of L-T samples tested in laboratory air after sufficient time and temperature exposure combinations. In order to directly examine environmental effects on cracking in the ST plane, slow strain rate tensile tests have been conducted in the S-T orientation in various environments (e.g. Lab Air, Dry, and Corrosive). These tests showed significant reductions in ductility and time to failure depending upon the degree of sensitization and type of environment. In order to quantify these effects in more details, environmentally enhanced cracking experiments using J-based fracture mechanics tests were conducted in similar environments on fatigue-precracked samples in the S-T orientation. The evolution of properties (i.e. fracture/fatigue) and the effects of microstructural features (e.g. grain boundary segregation, grain boundary precipitation, grain orientation and misorientation, etc.) and environmentally enhanced cracking are provided along with the effects of various remediation treatments.

Committee: John Lewandowski (Advisor); Henry Holroyd (Committee Member); Rimnac Clare (Committee Member); Schwam David (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Master of Science, The Ohio State University, 2014, Mechanical Engineering

Blade vibrations are a concern when designing turbo machinery. Traditionally, different types of dampers are used to dissipate the mechanical energy and reduce the risk of resonances that lead to high cycle fatigue (HCF). In the case of a blisk for which the blades are integral with the disk, the blades and disk are machined from a single forging, or the blades are frictional welded to the disk. This design is being utilized more in Aviation turbo machinery applications such as the Fans, Boosters, and Compressors. Blisks are prone to larger resonance responses in the absence of damping from the dovetail slot interfaces. To combat this potential issue, new coating materials are being developed to increase the damping of the airfoil. To cost effectively assess the damping qualities of these new coatings, a laboratory apparatus and specimen, intended to emulate the typical modes seen during engine operation, were designed and procured. The specimen's shoulders are sandwiched between two plates and bolted in an effort to eliminate the introduction of twisting or bending. Applying a load to one end of the specimen causes friction between the plates to transmit a uniform tensile load through the specimen. The open face rig design allows access to the specimen so that it can be excited by an external source. This design will allow for damping measurements to be taken of the excited specimen while it is subjected to a static load. The primary purpose of this thesis is to perform experiments with this new rig in order to validate that the device as constructed meets uniaxial loading requirements of the design intent which is to minimize constraint damping while achieving sufficient strain in the specimen. Initial measurements will be needed to verify that the specimen is in pure tension. Then additional data will validate that the specimen experiences sufficient strain. This thesis will document and discuss the evaluation of the facility design. First, a stress an (open full item for complete abstract)

Committee: Michael Dunn Dr. (Advisor); Randall Mathison (Committee Member) Subjects: Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2014, Materials Science and Engineering

Multi-pass welding of low alloy steels has been shown to cause regions of low toughness in the reheated heat affected zone (HAZ) due to the formation of islands of untempered martensite and austenite called `M-A constituents’. Traditional research in this area has focused on studying the formation of these constituents and its effect on properties of one particular region of the HAZ zone called the `intercritically reheated coarse grained heat affected zone’. Although, modern engineering steels are an eclectic mixture of microstructures, the effect of initial microstructure on the formation of these M-A constituents and on the properties of weld HAZ has mostly been ignored and has gone uninvestigated. In this document, some of the previous work related to multi-pass weld HAZ properties is revisited and fundamental issues in need of further research related to initial microstructure and microstructural factors governing HAZ properties are highlighted. A study has been conducted to analyze the role of initial microstructure on HAZ properties of multi-pass welds on four pipeline grade microalloyed steels. These steels had minor differences in compositions with respect to certain alloying elements. For each of the four steels, two different microstructures were developed that acted as initial microstructures for HAZ simulation. One set of initial microstructure was developed using thermo-mechanical controlled processing (TMCP) and the second kind of microstructure was obtained using heat treatments. The steels with differing initial microstructures but same compositions were subjected to intercritically reheated HAZ thermal cycles using Gleeble thermo-mechanical simulator. The microstructures thus obtained were studied using advanced characterization techniques and their properties were evaluated and compared using mechanical testing. Dilatometric analysis of phase transformations occurring during the HAZ simulation indicated difference in the transf (open full item for complete abstract)

Committee: John Lippold PhD (Advisor); Sudersanam Suresh Babu PhD (Committee Member); David Phillips PhD (Committee Member); Glenn Daehn PhD (Committee Member) Subjects: Materials Science; Metallurgy

MS, University of Cincinnati, 2008, Engineering : Materials Science

In this thesis we report the change in the orientation of the polymer lamellae and clay platelets from a PE-Nanocomposite film to that in the pressed composite sample, when a number of such films are hot pressed to form a pressed sample (strip), about 5 mm in thickness. Small-angle x-ray scattering (SAXS) was used to compare the quantitative and qualitative information regarding the structure and orientation of these structures in the film and the pressed strip. It was observed that the polymer lamellar normals in the composite film which were oriented in the MD get oriented in the ND in the pressed film sample. Diffraction studies carried out on both the samples show that the clay platelet normals for the film samples show a stronger orientation in the ND than for the pressed film sample. The tensile properties of the PE-Nanocomposite pressed sample (strip) and that of the Polyethylene (HDPE) film pressed sample (strip) was measured using an instron tensile machine and the values compared. The composite showed an increase in the modulus as compared to that observed in the virgin HDPE sample.

Committee: Gregory Beaucage PhD (Advisor); Jude Iroh PhD (Committee Member); Rodney Roseman PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy, Case Western Reserve University, 1992, Physics

Finite element analysis was used to study stress-strain relations in free-standing thin films, specifically during tensile testing. The technique and the program were verified through comparison to experimental results as well as analytical calculations. Limits on sample aspect ratio and mounting misallignment were established. Internal stress and displacement contours for films undergoing tensile testing were examined. Simulations of films mounted using adhesives were undertaken to determine if low adhesive modulus as well as shearing or cracking in the adhesive could account for erroneous experimental results. Multilayer films were modeled to predict Young's modulus results for tensile testing. Low interfacial moduli and cracking in the film layers were investigated as possible causes for experimental results deviating from those of the simulations.

Committee: R. Hoffman (Advisor) Subjects: Physics, Condensed Matter