Master of Science in Engineering Mechanics, Cleveland State University, 2024, Washkewicz College of Engineering

This paper presents a computational finite element analysis (FEA) focused on the utilization of shape memory alloy (SMA) interfaces as thermal expansion compensators for ductile positive coefficient of thermal expansion (CTE) materials such as Aluminum 6061-T6. The investigation delves into the efficacy of superelastic, one-way, and two-way shape memory effects in mitigating thermal expansion-induced stresses within engineering structures utilizing beam components. The research examines critical structural factors in a fixed beam system such as thermally induced internal stresses and buckling resilience at varying thermal loads. Computational simulation software from ANSYS Mechanical was calibrated to fit previous data from the literature on commercially available NiTi-based SMA properties. Comparing noninterface and SMA-interfaced beam structures, this study demonstrates the potential of SMAs to mitigate thermally induced stresses, thereby enhancing the structural integrity and longevity of engineering structures in thermal gradient environments. Furthermore, this paper proposes potential industries where the implementation of SMA interfaces could prove advantageous over current thermal compensating practices, including aerospace, optical, and civil engineering. This paper also introduces employing two-way shape memory alloys (TWSMAs) in thermal compensation by using computational and numerical analysis to showcase that TWSMAs response can be trained to perform similarly to materials with a negative thermal coefficient. By leveraging the unique property of trained TSMAs of the bidirectional shape memory effect, the aim was to demonstrate a second stress-free thermal state at an elevated temperature to increase the structure's buckling resilience. This research underscores the practical feasibility and performance of SMA interfaces as thermal expansion compensators, setting the stage for further exploration of advanced SMA technologies.

Committee: Josiah Owusu-Danquah (Committee Chair); Michael Gallagher (Committee Member); Stephen Duffy (Committee Member) Subjects: Aerospace Engineering; Civil Engineering; Engineering; Materials Science; Mechanical Engineering; Mechanics

Master of Science, University of Toledo, 2024, Chemistry

Thermal expansion is a physical property that may contribute to materials' malfunctioning in applications ranging from various electronics to construction and other engineering fields. As heat is applied to or inherently generated by materials, they tend to expand, thereby causing stress, strain, cracks, and structural distortion at the interfaces between dissimilar materials. These structural misalignments, resulting from thermal expansion, adversely affect the properties of a material, which in turn leads to a change in a material's performance. This change in performance may disrupt the original purpose for which the material was made. These challenges make complementary materials that can reduce or eliminate the thermal expansion of other materials when incorporated into a composite attractive. Negative thermal expansion (NTE) materials are materials that contract upon heating. These materials can serve as fillers in composites to complement positive expansion materials and reduce overall thermal expansion in composite materials. Such composites can find applications in high precision optical mirrors, in the aerospace industry, in dental fillings, and ultimately, in various electronics. However, a thorough investigation of these promising materials is needed to understand some of the problems currently preventing full implementation. Among these challenges, avoiding temperature and pressure induced phase transitions that form positive expansion polymorphs has been an important factor. These phase transitions destroy the NTE property of the materials. Hence, stabilizing the NTE phase in a wider temperature and pressure range will enhance the materials' potential applications. This research focuses on the scandium tungstate (Sc2W3O12) family of NTE materials, represented as A2M3O12 (A = trivalent cation, M = tungsten, molybdenum). This family was chosen because of the wide range of cations that can be incorporated into the structure due to the chemical flexibil (open full item for complete abstract)

Committee: Cora Lind-Kovacs (Committee Chair); Michal Marszewski (Committee Member); Jon Kirchhoff (Committee Member) Subjects: Chemistry; Materials Science

Master of Science (M.S.), University of Dayton, 2021, Electro-Optics

The durability of thin film optical interference filters, integrated in systems ranging from imaging sensors to energy-efficient IR-blocking windows, is affected by its stress. The purpose of this work is to explore the thermal stress in thin films, the result of a contrast in the coefficient of thermal expansion (CTE) between the substrate and the film. While much research is focused on thin film intrinsic stress, thermal stress should also be considered for systems designed for high temperature variability and for systems where the film and substrate material properties vary greatly. This work characterizes the coefficient of thermal expansion and the Young's Modulus of SiO2 and Ta2O5 films, common low and high-index optical materials, along with composite SiO2-Ta2O5 thin films grown by reactive co-sputtering. A model for the variation of the CTE as a function of film composition is proposed, showing general agreement with the measured data. Characterization of the thermal stress in the film-substrate system is measured using a custom-built instrument, and the Young's Modulus is verified using nano-indentation. A method for evaluating the instrument noise, and its effect on the precision of the calculated CTE and Modulus values is characterized for this instrument. A model is proposed to enhance future designs-of-experiment using this instrument.

Committee: Andrew Sarangan (Advisor); Christopher Muratore (Committee Member); Jonathan Vernon (Committee Member); Lirong Sun (Committee Member) Subjects: Materials Science; Optics

Doctor of Philosophy (PhD), Ohio University, 2017, Civil Engineering (Engineering and Technology)

Low-temperature cracking is a major pavement distress for asphalt pavements in most northern parts of the United States and other colder regions of the world. Pavements exposed to cold conditions are subjected to thermal stresses which can result in cracking when the induced stresses exceed the tensile strength. Local governments and road agencies spend large sums of money annually to repair defects in pavements caused by low-temperature cracking. Researchers need straightforward and routine test devices to characterize asphalt mixture's low-temperature performance in the laboratory. These tools are also required to design pavements that can perform satisfactorily in cold temperatures, and for the prediction of frequency and magnitude of cracks developed in asphalt pavements. The low-temperature performance characteristics of asphalt mixtures can be grouped into two broad components. There is the stiffness and thermal contraction component which accounts for the magnitude of strains or stresses induced in the mixture during cooling. The strength or fracture toughness component accounts for the ability of the mixture to resist the induced stresses and to prevent cracking. The main objective of this dissertation was to develop straightforward and routine tests devices for low-temperature characterization that would account for these two components of mixture's low-temperature performance. The Ohio Coefficient of Thermal Contraction (CTC) device developed as part of this dissertation was shown to produce repeatable test data. Asphalt mixture thermal strains recorded from the CTC device fitted the Bahia-Anderson CTC mathematical model for mixtures with a coefficient of determination (R2) greater than 0.999. Mixture properties such as binder grade, binder content, aging and the inclusion of recycled materials [Recycled Asphalt Pavement (RAP) and Recycled Asphalt Shingles (RAS)] resulted in a significant change in the CTC. Asphalt mixtures prepared with two aggrega (open full item for complete abstract)

Committee: Kim Sang-Soo Dr. (Advisor); Nazzal Munir Dr. (Committee Member); M. Sargand Shad Professor (Committee Member); Masada Teruhisa Professor (Committee Member); Mark McMills Dr. (Committee Member); Yu Xiong Dr. (Committee Member) Subjects: Civil Engineering; Engineering; Geotechnology

Master of Science in Engineering, Youngstown State University, 2018, Department of Civil/Environmental and Chemical Engineering

The incorporation of additive manufacturing (AM) enables the ability to fabricate composite tooling molds rapidly and in a cost effective manner. This work has demonstrated the practice of an additive technology for manufacturing composite processing tools. In particular, this work has addressed tooling that is functional in the range of autoclave temperatures around 180°C. This has led to the use of Invar and ceramic materials for use in composite molding tools because of their relatively low coefficient of thermal expansion (CTE) performance, which is in range to that commonly displayed by carbon fiber reinforced composites during their solidifying curing process. In this project, three main approaches have been considered. The first innovative approach was based on printing a mold based on silica sand and infiltrating it with a polymer to yield a robust ceramic composite tooling. The second approach investigated the use of binder jetting to 3D print sand molds to cast molten Invar to produce the composite tooling. Indeed, 3D sand printing offers the ability to cast complex geometries without the geometric limitations associated with conventional pattern making. An additional technology using a Hybrid Direct Energy Deposition (DED) System for cladding Invar upon a steel molding structure has also been considered for producing potential composite tooling. Indeed, this unique approach could represent a promising technology for producing low cost composite tooling since only a small layer of Invar would be cladded to a non-expensive substrate. The results have shown that the aforementioned processes have successfully resulted in low CTE composite tooling molds. This work presents innovative AM processes by initially investigating additive manufacturing processes for composite tooling.

Committee: Pedro Cortes PhD (Advisor); Brett Conner PhD (Committee Member); Jason Walker PhD (Committee Member) Subjects: Materials Science

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

Smart materials are a class of materials that couple different regimes, such as thermal, mechanical, electrical, and magnetic. Shape memory alloys (SMAs) are classified as such due to their ability to couple the thermal and mechanical regimes. One particular type of SMA is nickel-titanium (NiTi), which can recover up to 8\% elastic strain. In this study, the large strain recovery of NiTi is used in the development of a metal matrix composite that exhibits low to near-zero coefficient of thermal expansion. This is done by utilizing the strain recovery of NiTi fibers to offset the expansion of the aluminum matrix in which they are embedded. The fabrication of this metal matrix composite is made possible through the use of ultrasonic additive manufacturing (UAM). Ultrasonic additive manufacturing combines ultrasonic welding with subtractive machining operations to create complex parts from dissimilar metals. The resulting parts can be made of similar or dissimilar materials. In UAM, 20kHz vibrations created by piezoelectric transducers are transferred to a textured steel horn, which presses a thin strip of metal to a substrate with a normal force in excess of 5000 Newtons. Under these conditions, the surface oxides and asperities are broken down, producing atomically clean faces on both pieces, allowing for pure metal-to-metal contact and instantaneous bonding to take place. Unique to UAM is its low-temperature, solid-state operation, which means no melting of the constituent materials takes place. This feature provides the unprecedented opportunity to embed materials that are thermally sensitive, such as SMAs. This study focuses on the fabrication and characterization of NiTi-Al UAM composites with an emphasis on developing a method of producing composite structures. Process parameters that were studied include securing the NiTi ribbons during fabrication, ensuring proper placement of the ribbons in the composite, and applying the necessary pre-stress to produce (open full item for complete abstract)

Committee: Marcelo Dapino PhD (Advisor); Mark Walter PhD (Committee Member) Subjects: Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2012, Mechanical Engineering

Solid oxide fuel cells (SOFCs) are electrochemical energy conversion devices capable of producing electrical power with high efficiency and low emissions. SOFCs are characterized by ceramic electrolyte membranes which transport oxide ions in the range of temperatures between 600°C and 1000°C. In order to facilitate efficient, low-range temperature operation the electrolyte is typically made very thin, on the order of 40 µm. SOFCs also employ porous electrodes on either side of the electrolyte which are then placed in contact with current collectors and seals. In the fuel cell environment, with high temperatures, substantial thermal gradients, mechanical loading between layers, as well as the desire to be able to thermally cycle the cell, one of the layers or components must provide mechanical support. It is typical for either the anode or electrolyte to provide the necessary mechanical support. This thesis focuses on an electrolyte that is used for electrolyte-supported SOFC configuration. To address the need for mechanically robust electrolytes, NexTech Materials has developed the FlexCellTM electrolyte. This electrolyte design incorporates 40 µm thick conducting regions in a honeycomb pattern, and surrounding 200 µm thick stability regions. Various experiments on and determinations about this material and design must be made to ensure sufficient mechanical stability during fuel cell operation. Thermal stresses from high temperatures, temporal and spatial temperature gradients, and differential thermal expansion of contacting materials, are critical issues within SOFCs. The critical property related to these issues, coefficient of thermal expansion (CTE), was measured in this work. An apparatus to measure the CTE of the FlexCellTM electrolyte material was designed and implemented. The average CTE of 3 mol% Y2O3-ZrO2 (yttria stabilized zirconia or 3YSZ) was found to increase from 9 µm•m-1•°C-1 between room temperature (RT) and 180°C to nearly 11.5 µm•m-1•°C-1 from R (open full item for complete abstract)

Committee: Dr. Mark E. Walter (Advisor); Dr. Brian D. Harper (Committee Member) Subjects: Materials Science; Mechanical Engineering

Master of Science, University of Akron, 2009, Chemical Engineering

Solder is used in nearly all electronic packages to provide mechanical, electrical and thermal contact between various components. The mismatch between the components‟ coefficient of thermal expansion results in thermal stresses which can damage components or connections and render the circuit board useless. In order to reduce this mismatch, a novel fabrication method was developed to produce composites of solder and ceramic reinforcement are presented. Composites were prepared by uniaxial compression of 63Sn/37Pb solder powder and various morphologies of titania reinforcement. A solution of poly(vinyl pyrrolidone), ethanol and tetraisopropyl titanate was used to produce beaded nanofibers; acetic acid was added to the solution in order to lower the dielectric constant of the solution and produce smooth nanofibers. Ultrasonication was used to cut the calcined, electrospun nanofibers to consistent lengths of about 6μm. Optical microscopy, electron microscopy and x-ray diffraction were used to characterize the size, shape and crystalline phase of the filler. Analysis of the different fillers revealed three distinct categories of shape and size, including spherical titania powder (6.5μm diameter), smooth cylindrical titania nanofibers (150nm diameter) and a mixture of 80wt% spherical beaded titania (3.5μm diameter) with 20wt% cylindrical nanofibers (400nm diameter). A 25% reduction in the coefficient of thermal expansion of the composite was achieved regardless of the shape, size or quantity of reinforcement. The melting and freezing points of the composite samples were not statistically different from that of pure solder but the specific gravity was lowered by about 1.5%. During reflow it was observed that the majority of the filler was expelled from the molten solder core. The differences in density between the filler and solder provide a buoyant force that tends to expel the less dense titania from the more dense molten solder. A force balance on a rigid cylinder flo (open full item for complete abstract)

Committee: Edward Evans PhD (Advisor) Subjects: Chemical Engineering; Mechanical Engineering