Thermoelectric devices are useful for a variety of applications due to their ability to either convert heat directly into electricity, or to generate a temperature gradient from an electric current. These devices offer several attractive features including compact size, no moving parts, limited maintenance requirements, and high reliability. Thus thermoelectric devices are used for temperature-control, cooling, or power generation in various industrial systems such as automobiles, avionics, refrigerators, chillers, laser diodes, dehumidifiers, and a variety of sensors. In order to improve the efficiency of thermoelectric devices, many endeavors have been made to design and fabricate materials with a higher dimensionless thermoelectric figure of merit (ZT), as well as to optimize the device structure and packaging to manage heat more effectively. When evaluating candidate thermoelectric materials, one must accurately characterize the electrical conductivity, thermal conductivity, and the Seebeck coefficient over the temperature range of potential use. However, despite considerable research on thermoelectric materials for decades, there is still significant scatter and disagreement in the literature regarding accurate characterization of these properties due to inherent difficulties in the measurements such as requirements for precise control of temperature, simultaneous evaluation of voltage and temperature, etc. Thus, a well-designed and well-calibrated thermoelectric measurement system that can meet the requirements needed for multiple kinds of thermoelectric materials is an essential tool for the development of advanced thermoelectric devices. In this dissertation, I discuss the design, fabrication, and validation of a measurement system that can rapidly and accurately evaluate the Seebeck coefficient and electrical resistivity of thermoelectric materials of various shapes and sizes from room temperature up to 600 K. The methodology for the Seebeck coefficient and electrical resistivity measurements is examined along with the optimization and application of both in the measurement system. The calibration process is completed by a standard thermoelectric material and several other materials, which demonstrates the accuracy and reliability of the system. While a great deal of prior research has focused on low temperature thermoelectric materials for cooling, such as Bi2Te3, high temperature thermoelectric materials are receiving increasing attention for power generation. With the addition of commercial systems for the Seebeck coefficient, electrical resistivity, and thermal conductivity measurements to expand the temperature range for evaluation, a wide range of materials can be studied and characterized. Chapter Two of this dissertation describes the physical properties characterization of a variety of thermoelectric materials, including room temperature materials such as Bi0.5Sb1.5Te3, medium temperature level materials such as skutterudites, and materials for high temperature applications such as half-Heusler alloys. In addition, I discuss the characterization of unique oxide thermoelectric materials, which are Al doped ZnO and Ca-Co-O systems for high temperature applications. Chapter Four of this dissertation addresses the use of GaSn alloys as a thermal interface material (TIM), to improve thermal transport between thermoelectric devices and heat sinks for power generation applications at high temperature. I discuss the mechanical and thermal behavior of GaSn as an interface material between electrically insulating AlN and Inconel heat exchangers at temperatures up to 600 °C. Additionally, a theoretical model for the experimental thermal performances of the GaSn interface layer is also examined. / Ph. D. / Thermoelectric materials can directly convert heat into electricity for power generation, or they can be used for cooling or refrigeration applications when supplied with electric power. This dissertation primarily focuses on the evaluation of materials used in thermoelectric generators (TEGs). Specifically, Chapter Two of this work describes the design, development, and validation of a developed measurement system that can evaluate two important properties, the Seebeck coefficient and electrical resistivity, for a variety of thermoelectric materials. Next, Chapter Three discusses the work using other commercial measurement systems to evaluate several types of thermoelectric materials, including Bi2Te3 based materials, skutterudites, half-Heusler alloys, ZnO, and Ca-Co-O for a TEG module. Finally, I discuss the use of GaSn, a liquid metal alloy, as a thermal interface material to improve heat transport between dissimilar materials for TEGs. The GaSn was applied between a thermoelectric device and a heat exchanger for use in energy harvesting devices. The mechanical robustness and thermal reliability were tested, and the GaSn was shown to improve thermal performances both in experiments and through modeling.

This research develops and validates computational tools for the design and analysis of structural components and systems constructed with Ultra-High Performance Concrete (UHPC). The modeling strategy utilizes the Lattice Discrete Particle Model (LDPM) to represent UHPC material and structural member response, and extends a structural-level triaxial continuum constitutive law to account for the addition of discrete fibers. The approach is robust, general, and could be utilized by other researchers to expand the computational capability and simulate the behavior of different composite materials. The work described herein identifies the model material parameters by conducting a complete material characterization for UHPC, with and without fiber reinforcement, describing its behavior in unconfined compression, uniaxial tension, and fracture toughness. It characterizes the effect of fiber orientations, fiber-matrix interaction, and resolves the issue of multi-axial stress states on fiber pullout. The capabilities of the computational models are demonstrated by comparing the material test data that were not used in the parameter identification phase to numerical simulations to validate the models' predictive capabilities. These models offer a mechanics-based shortcut to UHPC analysis that can strategically support ongoing development of material and structural design codes and standards. / Ph. D. / This research develops and validates new computer-based methods to analyze and design civil infrastructure constructed with ultra-high performance concrete (UHPC), achieved when steel fibers are combined with a finely graded cement matrix. With superior performance characteristics in comparison to regular concrete, UHPC is studied herein for its strong potential to advance the durability, efficiency, and resiliency of new and existing infrastructure. The simulation-based methods are extensively verified with novel experiments that evaluate the material limits and failure modes when compressed, bent, or stretched, considering fiber volume and orientation. The computer-based tools can be used to realistically assess the structural performance of innovative UHPC applications in buildings, bridges, and tunnels under natural hazards, leading to surpassed levels of structural efficiency and resiliency across civil infrastructure.

Utilizing carbon fiber reinforced polymers (CFRP) in design offers advantages including as mass reduction, increased stiffness, enhanced corrosion resistance, improved sound damping, and vibration absorption. The notable strength-to-weight ratio of CFRP has driven its adoption over traditional materials like aluminum and steel in various industries such as aerospace, automotive, and sports. The assembly of "Stack-ups," which are layered assemblies of CFRP and metal components, becomes crucial as CFRP increasingly replaces metallic parts in high mechanical loading structural situations. The high thrust force involved in machining fiber reinforced polymers (FRPs) causes a peel-up and push-out effect on the workpiece, leading to delamination of the plies. This study developed an FE tool to simulate the drilling of FRPs effectively, aiming to validate tool design and enhance the cutting process. Modeling the impact of fiber orientation in CFRP material on mechanical behavior is essential for optimizing component design and manufacturing. To reduce the exhaustive experimental work related to CFRP material characterization Abaqus Explicit is used to predict the tensile material response through fracture. FEA analyses included mesh size, mass/time scaling, failure models, and cohesive surfaces. Experimental results with the new fixturing-rig show consistent gauge region failure, regardless of fiber orientation. Puck's model accurately predicts fracture force and displacement for parallel fiber orientation. 45 and 90-degree orientations, maximum strain and LaRCO2 models offer better accuracy. Most apparent, was the criticality of cohesive surfaces to predict the nonlinear loading response observed experimentally. Simulations for various fiber layup orientations indicate similar force-displacement signatures, with a notable reduction in failure force at angles between parallel and 45 degrees. Simulating CFRP mechanical properties under three-point bending to understand cohesive interactions between plies in a laminate was investigated; this capability critical to effectively model the peel-up and push-out problem observed when drilling. A parametric FEA study investigated the affect of mesh size, mass/time scaling, failure models (Hashin, MCT, LaRC02, Maximum Strain, Puck), and cohesive surfaces versus loading response. Experimental results with a larger radius punch show failure on the intended bottom side, facilitating Aramis strain camera recording. Effective mass/time scaling reduces computation time while maintaining accuracy. For perpendicular fiber orientation, all failure models exhibit a similar force-displacement rate. Minimal difference exists among 0-degree models, except for a 4.18% underprediction by LaRC02. At 45 and 90 degrees, Maximum Strain and LaRCO2 models prove more accurate and converge well. The study underscores the need for cohesive surfaces to predict nonlinearity in loading responses for non-parallel bending setups. A 3D drilling model is developed discussing significance of modelling techniques and considerations. The removal of failed elements creates periodic voids between the workpiece and tool, underlining the importance of proper mesh development. Accurate, computationally efficient models with element lengths of 50-75 µm near the expected failure region were emphasized. Using a discrete rigid body yielded a 42.1% reduction in memory requirements and a 2.81x reduction in time step compared to deformable bodies with rigid constraints. Mass scaling led to over tenfold computation time reduction with a mere 5.3% mass change. Increasing viscosity parameters improved the loading response of CFRP laminate during high-speed drilling. Strain rate strengthening, aligned with literature, increased the load profile by 10.9%. Friction in the CFRP drilling model showed less sensitivity than estimated, with a 4.4% standard deviation. The FE model once confidently developed, was compared to experiments. The prediction aligned well with experiments, accurately predicting thrust force differences between CD854 and CD856 drills. The CD856 exhibited reduced inter-ply damage, highlighting the advantage of double-angle drill geometry. The CD854's "spur" cutting edge geometry improved hole quality. The "Stack-up" drilling model effectively predicted thrust force transitions between UD-CFRP and Aluminum layers, confirming the CD854's reduced thrust force when drilling Aluminum, as described by the tool manufacturer Sandvik. / Thesis / Doctor of Philosophy (PhD)

Vascular networks are required to support the formation and function of three-dimensional tissues. Biodegradable scaffolds are being considered in order to promote vascularization where natural regeneration of lost or destroyed vascular networks fails. Particularly; composite materials are expected to fulfill the complex demands of a patient's body to support wound healing. Microbial biopolyesters are being regarded as such second and third generation biomaterials. Methylobacterium extorquens is one of several microorganisms that should be considered for the production of advanced polyhydroxyalkanoates (PHAs). M. extorquens displays a distinct advantage in that it is able to utilize methanol as an inexpensive substrate for growth and biopolyester production. The design of functionalized PHAs, which would be made of both saturated short-chain-length (scl, C [less than or equal to] 5) and unsaturated medium-chain-length (mcl, 6 [less than or equal to] C [less than or equal to] 14) monomeric units, aimed at combining desirable material properties of inert scl/mcl-PHAs with those of functionalized mcl-PHAs. By independently inserting the phaC1 or the phaC2 gene from Pseudomonas fluorescens GK13, recombinant M. extorquens strains were obtained which were capable of producing PHAs containing C-C double bonds. A fermentation process was developed to obtain gram quantities of biopolyesters employing the recombinant M. extorquens ATCC 55366 strain which harbored the phaC2 gene of P. fluorescens GK13, the better one of the two strains at incorporating unsaturated monomeric units. The PHAs produced were found in a blend of scl-PHAs and functionalized scl/mcl-PHAs (4 [less than or equal to] C [less than or equal to] 6), which were the products of the native and of the recombinant PHA synthase, respectively. Thermo-mechanical analysis confirmed that the functionalized scl/mcl-PHAs exhibited the desirable material properties expected. This project contributed to current research on polyhydroxyalkanoates at different levels. The terminal double bonds of the functionalized scl/mcl-PHAs are amenable to chemical modifications and could be transformed into reactive functional groups for covalently linking other biomacromolecules. It is anticipated that these biopolyesters will be utilized as tissue engineering materials in the future, due to their functionality and thermo-mechanical properties.

<p>Curiosity is a powerful tool, and combined with the ability to observe the natural world, grants humankind an unique opportunity, the opportunity to wonder why. Why do things exist?, why do they do the things they do?, why is this even possible?</p> <p>Research in our lab is focused on the basic understanding and potential application of biological materials, in particular, biological adhesives produced by marine organisms such as oysters. Oysters produce a cement-like material that is able to withstand the dynamic conditions found in coastal environments. The focus of this dissertation is to lay the basis of the characterization of new biological materials by observing and analyzing its physical properties, to measure the performance of the material in natural conditions and finally to identify the basic components that give the material the properties that we observe. The end goal of this project is to understand the properties of this material so we are able to develop a synthetic system that is able to imitate, as close as possible, what we find in nature. These results, and more importantly, the new questions that emerge from this research, provide a first look at the adhesive system of oysters leading the way to new discoveries in the future.</p>

Unintentional drop of munitions could be encountered during the storage, transportation, and loading processes. In such an impact, malfunctioning of crucial components of munitions is the worst scenario that may be encountered and level of loads should not reach to critical levels. From two possible methods, experimental one is not frequently applied owing to high cost of money and time. On the contrary, particularly in last couple of years, interest is shifted to numerical simulations such as finite element method. In this thesis, foam materials will be investigated as energy absorbers to reduce the effect of loads during the impact. However, modeling the behavior of foam materials by FE codes is a challenging task. In other words, more than a few material parameters which are not commonly specified in literature are sufficient to represent the behavior of foams in an appropriate way. For this reason, material characteristics of the selected two foam materials, expanded polypropylene and v polyethylene, have been obtained in this study. Characterization of EPP and PE is followed by the selection of the appropriate material models in LS-DYNA which is a nonlinear explicit finite element code. Drop tests of munitions on which initially specified foam materials are integrated were done to identify the load levels. Validation of drop tests which are explained in detail in this thesis has been accomplished by LS-DYNA. Final section of the thesis is related to optimization of the foam geometry which will provide reducing load levels to allowable limits. After optimization studies, three alternative geometries which succeed in to reduce loads to allowable load levels were reached. Finally, one of three alternatives is selected considering cost and manufacturing difficulties.

The cohesive fracture of thin films is a concern for the reliability of many devices in microelectronics, MEMS, photovoltaics, and other applications. In microelectronic packaging the cohesive fracture toughness has become a concern with new low-k dielectric materials currently being used. To obtain the low-k values needed to meet electrical performance goals, the mechanical strength of the material has decreased. This has resulted in cohesive cracks occurring in the Back End of Line (BEoL) dielectric layers of the microelectronic packages. These cracks lead to electronic failures and occur after thermal loading (due to CTE mismatch of materials) and mechanical loading. To prevent these cohesive cracks, it is necessary to measure the cohesive fracture resistance of these thin films to implement during the design and analysis process. Many of the current tests to measure the cohesive fracture resistance of thin films are based on methods developed for larger scale specimens. These methods can be difficult to apply to thin films due to their size and require mechanical fixturing, physical contact near the crack tip, and complicated stress fields. Therefore, a fixtureless cohesive fracture resistance measurement technique has been developed that utilizes photolithography fabrication processes. This technique uses a superlayer thin film with a high intrinsic stress deposited on top of the desired test material to drive cohesive fracture through the thickness of test material. In addition to developing a technique to measure the fracture resistance of dielectric thin films, the use of carbon nanotube (CNT) forests as off-chip interconnects is investigated as a potential method to mitigate the fracture of these materials. The compressive and tensile modulus of CNT forests is characterized, and it is seen that the modulus is several orders of magnitude less than that of a single straight CNT. The low-modulus CNT forest will help mechanically decouple the chip from the board and reduce stress occurring in the dielectric layers as compared to the current technology of solder ball interconnects and therefore improve reliability. The mechanical performance of these CNT interconnects is investigated by creating a finite-element model of a flip chip electronic package utilizing CNT interconnects and comparing the chip stresses to a traditional solder ball interconnect scenario. Additionally, flip chips are fabricated with CNT forest interconnects, assembled to an FR4 substrate, and subjected to accelerated thermomechanical testing to experimentally investigate their performance.

<p>Extrusion Deposition Additive Manufacturing (EDAM) is a process in which fiber-filled thermoplastic polymers are mixed and melted in an extruder and deposited onto a build plate in a layer-by-layer basis. Anisotropy caused by flow-induced orientation of discontinuous fibers along with the non-isothermal cooling process gives rise to internal stresses in printed parts which results in part deformation. The deformation and residual stresses can be abated by modifying the fiber orientation in the extrudate to best suit the print geometry. To that end, the focus of this research is on understanding the effect of fiber orientation state and fiber properties on effective properties of the printed bead and the final deformation of a part. The properties of three different orientation tensors of glass fiber-filled polyamide and carbon fiber-filled polyamide were experimentally and virtually characterized via micromechanics. A thermo-mechanical simulation framework developed in ABAQUS© was used to understand the effects of the varying fiber orientation tensor and fiber properties on the final deformation of printed parts. In particular, a medium-size geometry that is prone to high deformation was simulated and compared among the three orientation tensors and two material systems. This serves to be a good preliminary study to understand microscopic properties induced deformations in EDAM.</p>

This doctoral thesis investigates the application of laser-induced breakdown spectroscopy (LIBS) for detection of labeled biomolecules on nitrocellulose paper. Nitrocellulose paper is a material often used for assays involving the concentration and labeling of a target analyte, followed by label detection. Among paper-based diagnostics are lateral-flow immuno-assays (LFIAs). Research efforts have made LFIAs into accessible, portable,and low-cost tools for detecting targets such as allergens, toxins,and microbes in food and water.Gold (Au) nanoparticles are standard biomolecular labels among LFIAs, typically detected via colorimetric means.Other labels, such as quantum dots, are also often metallic, and research is ongoing to expand the number of portable instrumentations applied to their detection. A wide diversity of lanthanide-complexed polymers (LCPs) are used as immunoassay labels but have been inapt for portable paper-based assays owing to lab-bound detection instrumentation, until now. LIBS is a multi-element characterization technique which has recently developed from a bench-top to a portable/hand-held analytical tool. This is among the first studies to show that LCPs can be considered as options for biomolecule labels in paper-based assays using bench-based and hand-held LIBS as label detection modalities.<div>Chapter one reviews the importance of rapid, multiplexed detection of chemical and biological contaminants, the application of current biosensors, and the role of LIBS as an emerging biosensor. Paper-based bioassays were identified as a promising approach for contaminant detection whose capabilities could be enhanced by LIBS. The next chapter dives into LIBS system designs to address which LIBS parameters were appropriate for label detection on paper assay material. A balance of LIBS parameters was found to be important for successful analyte detection. Chaptert hree optimizes a LIBS design for sensitive detection of 17 metals and establishes limit of detection values for 7 metals. Optimal detection parameters depended on the metal being detected and were applied to the objective of the final chapter: LIBS detection of labeled antigen immobilized on a paper-based assay. Both antibody and bacteria detection assays were successfully performed and analyzed using bench top and portable LIBS,suggesting an exciting future for the use of LIBS as a biosensor.The prospect of using LIBS for multiplexed, rapid and sensitive detection of biomolecules in assays is explored, laying grounds for future work in the ever-relevant field of biological and chemical hazard detection.<br></div>

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