This dissertation presents innovative research at the intersection of thermoelectric solutions, additive manufacturing, and nuclear safety technology, addressing critical challenges in sensor powering for extreme environments, energy harvesting, and materials fabrication. The research is divided into three key areas, each contributing to advancements in its respective domain. First, a self-powered wireless through-wall data communication system was developed for monitoring nuclear facilities, specifically spent fuel storage dry casks. These facilities require continuous monitoring of internal conditions, including temperature, pressure, radiation, and humidity, under harsh environments characterized by high temperatures and intense radiation without any penetration through their walls. The constructed system integrated four modules: an energy harvester with power management circuits, an ultrasound wireless communication system using high-temperature piezoelectric transducers, electronic circuits for sensing and data transmission, and radiation shielding for electronics. Experimental validation demonstrated that the system harvests over 40 mW of power from thermal flow, withstands gamma radiation exceeding 100 Mrad, and survives temperatures up to 195°C. The system, designed to operate stably for fifty years, enables data transmission every ten minutes, ensuring reliable long-term monitoring for nuclear safety and security. Second, the efficiency of thermoelectric generators (TEGs), unique solid-state devices for thermal-to-electrical energy conversion, was explored through a novel manufacturing approach using selective laser melting (SLM) and direct energy deposition (DED). Conventional TEG fabrication methods have limitations in achieving optimal efficiency due to design and material constraints. SLM-based additive manufacturing offers a scalable solution for creating geometry-flexible and functionally graded thermoelectric materials. This research developed a physical model to simulate the SLM and DED process for fabricating Mg2Si thermoelectric materials with Si doping. The model incorporates conservation equations and accounts for fluid flow driven by buoyancy forces and surface tension, enabling detailed analysis of process parameters such as laser scanning speed and power input. The results provided insights into temperature distribution, powder bed shrinkage, and molten pool dynamics, advancing the understanding and optimization of thermoelectric device fabrication using additive manufacturing. One step further, SLM and DED experiments were carried out to validate the simulation results and testify to the feasibility of applying laser powder bed fusion on semiconductor materials. Third, the research investigates the application of laser additive manufacturing to improve performance and reduce the production costs of magnetic materials. Soft magnetic materials, critical for various industrial applications, are fabricated using DED. The research optimizes DED printing parameters and processes through quality control experiments inspired by the Taguchi method and analysis of variance models. The resulting silicon-iron samples exhibit minimal defects and cracks, demonstrating the feasibility of the approach. Detailed optical and scanning electron microscopy, coupled with magnetic characterization, reveal that the rapid cooling process inherent to laser-based AM enables unique microstructures that enhance magnetic properties. Collectively, this work addresses pressing technological challenges in energy harvesting, materials fabrication, and extreme environment monitoring. The developed systems and methodologies have broad implications for nuclear safety, additive manufacturing, and the efficient utilization of advanced materials. By integrating interdisciplinary approaches and leveraging cutting-edge manufacturing technologies, this dissertation contributes to the advancement of sustainable and resilient solutions for modern engineering challenges. / Doctor of Philosophy / This dissertation explores groundbreaking advancements in energy solutions, manufacturing techniques, and nuclear safety, presenting technologies that address challenges in powering sensors, creating efficient energy harvesters, and developing advanced materials. The research spans three main areas, each providing innovative contributions to these critical fields. The first part focuses on a wireless system that powers itself and communicates data from inside sealed nuclear storage containers. These containers, used to store spent nuclear fuel, must be closely monitored for temperature, pressure, radiation, and humidity to ensure safety. However, traditional monitoring methods cannot penetrate the container walls and withstand the extreme conditions inside. This project developed a system combining four key components: a thermal energy harvester, an ultrasound-based communication method, durable electronic circuits, and radiation shielding. The system successfully harvests energy from the container's heat and uses it to power sensors and transmit data wirelessly every ten minutes. It is designed to operate reliably for fifty years, even under intense radiation and high temperatures, providing long-term solutions for nuclear safety monitoring. The second area investigates thermoelectric generators (TEGs), devices that convert heat into electricity. While TEGs have significant potential, traditional manufacturing techniques limit their efficiency and adaptability. By using cutting-edge laser-based additive manufacturing methods—Selective Laser Melting (SLM) and Direct Energy Deposition (DED)—this research developed new ways to create flexible and efficient thermoelectric materials. Advanced simulations were performed to model the manufacturing process, analyzing how factors like laser speed and power affect the final material properties. These models provided valuable insights into optimizing the process, which were then validated through experimental testing. The findings open the door to scalable and efficient production of thermoelectric devices for various energy applications. The third area addresses the fabrication of magnetic materials, essential for many industrial technologies. Traditional methods of creating magnetic materials can be expensive and prone to defects. This research applied laser-based additive manufacturing to produce soft magnetic materials, such as silicon iron, with fewer flaws and improved performance. By optimizing the printing parameters through experiments and statistical analysis, the team created materials with enhanced magnetic properties. Microscopic analysis revealed that the rapid cooling during manufacturing produced unique structures that contribute to the materials' superior qualities. These advancements have the potential to reduce costs and improve the efficiency of magnetic products in various industries. In summary, this dissertation tackles some of the most pressing challenges in energy, manufacturing, and safety technology. By developing systems that can monitor nuclear storage for decades, improving methods to harvest energy from heat, and creating better magnetic materials, this work paves the way for safer and more efficient solutions to modern engineering problems. These innovations are not only critical for nuclear safety but also hold promise for broader applications in sustainable energy and advanced manufacturing, contributing to a safer and more efficient future for industries worldwide.

Este trabalho objetivou a manufatura de laminados híbridos metal-fibra (LMF) empregando-se chapas com 0,5 mm de espessura de liga-\'TI\'6\'AL\'4\'V\' com superfícies modificadas por laser de fibra de modo a otimizar a sua adesão com polímero termoplástico poli-sulfeto de fenileno (PPS). Observou-se que a microtextura superficial da liga metálica dependeu fortemente da potência do feixe laser, quando potências mais baixas levaram à verdadeira texturização da superfície metálica, enquanto que potências mais elevadas conduziram à ablação da mesma. A texturização superficial metálica sob laser de baixa potência aparentou ser a condição mais apropriada para a adesão metal-polímero por ancoragem mecânica de macromoléculas, o que foi contrabalanceado por elevados níveis de tensão residual das chapas metálicas, gerando grande distorção das mesmas e inviabilizando sua utilização. O emprego de uma potência intermediária (160 W) mostrou-se propício à otimização entre a adesão física entre metal-polímero e o nível de tensões residuais criado nas chapas metálicas. Concluiu-se que os espécimes extraídos do centro dos laminados metal-fibra exibem uma tensão limite média para falha por cisalhamento interlaminar consideravelmente superior à dos espécimes usinados a partir da borda dos LMF. O LMF manufaturado sob maiores pressão e temperatura exibiu uma maior compactação e melhor consolidação, culminando num máximo desempenho médio sob carga de cisalhamento interlaminar. Evidências de uma correlação entre o mecanismo de falha por cisalhamento interlaminar do corpo de prova e o seu nível de resistência a este tipo de carregamento mecânico foram documentadas e discutidas. / This work aimed at manufacturing hybrid fiber-metal laminates (FML) by employing 0,5 mm-thick \'TI\'6\'AL\'4\'V\'-alloy plaques with fiber laser modified surface in order to optimize metal adhesion with poli-phenylene sulfide (PPS) thermoplastic polymer. The surface microtexture of metallic alloy strongly depended upon the laser power, inasmuch as low-power laser led to true texturization of metal surface, whereas high-power laser light drove to its ablation. Surface metal texturization under low-power laser apparently was the most appropriate condition to metal-polymer adhesion via mechanical entanglement of macromolecules, which was offset by high levels of residual stresses on metallic plaques, bringing them quite warped and useless. The use of an intermediate laser power (160 W) has been shown benign to the optimization between metal-polymer physical adhesion and the residual stress level created in the metal plates. It has been concluded that testpieces machined from the FML central position exhibited average ultimate interlaminar shear strenght considerably higher than those extracted from the FML borders. The FML manufactured under higher pressure and temperature was more compacted and better consolidated, so that it displayed the greatest average performance under interlaminar shear loading. Evidences of a correlation between the failure mechanism by interlaminar shearing of test coupon and its allowance to this type of mechanical loading were documented and discussed.

Este trabalho objetivou a manufatura de laminados híbridos metal-fibra (LMF) empregando-se chapas com 0,5 mm de espessura de liga-\'TI\'6\'AL\'4\'V\' com superfícies modificadas por laser de fibra de modo a otimizar a sua adesão com polímero termoplástico poli-sulfeto de fenileno (PPS). Observou-se que a microtextura superficial da liga metálica dependeu fortemente da potência do feixe laser, quando potências mais baixas levaram à verdadeira texturização da superfície metálica, enquanto que potências mais elevadas conduziram à ablação da mesma. A texturização superficial metálica sob laser de baixa potência aparentou ser a condição mais apropriada para a adesão metal-polímero por ancoragem mecânica de macromoléculas, o que foi contrabalanceado por elevados níveis de tensão residual das chapas metálicas, gerando grande distorção das mesmas e inviabilizando sua utilização. O emprego de uma potência intermediária (160 W) mostrou-se propício à otimização entre a adesão física entre metal-polímero e o nível de tensões residuais criado nas chapas metálicas. Concluiu-se que os espécimes extraídos do centro dos laminados metal-fibra exibem uma tensão limite média para falha por cisalhamento interlaminar consideravelmente superior à dos espécimes usinados a partir da borda dos LMF. O LMF manufaturado sob maiores pressão e temperatura exibiu uma maior compactação e melhor consolidação, culminando num máximo desempenho médio sob carga de cisalhamento interlaminar. Evidências de uma correlação entre o mecanismo de falha por cisalhamento interlaminar do corpo de prova e o seu nível de resistência a este tipo de carregamento mecânico foram documentadas e discutidas. / This work aimed at manufacturing hybrid fiber-metal laminates (FML) by employing 0,5 mm-thick \'TI\'6\'AL\'4\'V\'-alloy plaques with fiber laser modified surface in order to optimize metal adhesion with poli-phenylene sulfide (PPS) thermoplastic polymer. The surface microtexture of metallic alloy strongly depended upon the laser power, inasmuch as low-power laser led to true texturization of metal surface, whereas high-power laser light drove to its ablation. Surface metal texturization under low-power laser apparently was the most appropriate condition to metal-polymer adhesion via mechanical entanglement of macromolecules, which was offset by high levels of residual stresses on metallic plaques, bringing them quite warped and useless. The use of an intermediate laser power (160 W) has been shown benign to the optimization between metal-polymer physical adhesion and the residual stress level created in the metal plates. It has been concluded that testpieces machined from the FML central position exhibited average ultimate interlaminar shear strenght considerably higher than those extracted from the FML borders. The FML manufactured under higher pressure and temperature was more compacted and better consolidated, so that it displayed the greatest average performance under interlaminar shear loading. Evidences of a correlation between the failure mechanism by interlaminar shearing of test coupon and its allowance to this type of mechanical loading were documented and discussed.

<p>This study is focused on the prediction of residual stresses and microstructure development of steel and aluminum alloys during laser-based manufacturing processes by means of multi-physics numerical modeling.</p> <p>A finite element model is developed to predict solid-state phase transformation, material hardness, and residual stresses produced during laser-based manufacturing processes such as laser hardening and laser additive manufacturing processes based on the predicted temperature and geometry from a free-surface tracking laser deposition model. The solid-state phase transformational model considers heating, cooling, and multiple laser track heating and cooling as well as multiple layer tempering effects. The residual stress model is applied to the laser hardening of 4140 steel and to laser direct deposition of H13 tool steel and includes the effects of thermal strain and solid-state phase transformational strain based on the resultant phase distributions. Predicted results, including material hardness and residual stresses, are validated with measured values.</p> <p>Two dendrite growth predictive models are also developed to simulate microsegregation and dendrite growth during laser-based manufacturing processes that involve melting and solidification of multicomponent alloys such as laser welding and laser-based additive manufacturing processes. The first model uses the Phase Field method to predict dendrite growth and microsegregation in 2D and 3D. It is validated against simple 2D and 3D cases of single dendrite growth as well as 2D and 3D cases of multiple dendrite growth. It is then applied to laser welding of aluminum alloy Al 6061 and used to predict microstructure within a small domain. </p> The second model uses a novel technique by combining the Cellular Automata method and the Phase Field method to accurately predict solidification on a larger scale with the intent of modeling dendrite growth. The greater computational efficiency of the this model allows for the simulation of entire weld pools in 2D. The model is validated against an analytical model and results in the literature.

No description available.

No description available.

No description available.

No description available.

A matrix of variably processed Fe-30at%Ni was deposited with variations in laser travel speeds as well and laser powers. A complete shift in phase stability occurred as a function of varying laser travel speed. At slow travel speeds, the microstructure was dominated by a columnar fcc phase. Intermediate travel speeds yielded a mixed microstructure comprised of both the columnar fcc and a martensite-like bcc phase. At the fastest travel speed, the microstructure was dominated by the bcc phase. This shift in phase stability subsequently affected the magnetic properties, specifically saturation magnetization. Ni-Fe-Mo and Ni-Fe-V permalloys were deposited from an elemental blend of powders as well. Both systems exhibited featureless microstructures dominated by an fcc phase. Magnetic measurements yielded saturation magnetizations on par with conventionally processed permalloys, however coercivities were significantly larger; this difference is attributed to microstructural defects that occur during the additive manufacturing process.

No description available.