The continuous miniaturization of electronic devices and the corresponding increase in computing powers have led to a significant growth in the density of heat dissipation within these devices. This increase in heat generation has challenged conventional air fan cooling and alternative solutions for heat removal are required to avoid overheating and part damage. Micro/Mini channel heat sinks (M/MCHS) that use liquids for heat removal appear as an attractive solution to this problem as they provide large heat transfer area per volume. Mini/microchannels traditionally have suffered from geometrical and material restrictions due to fabrication constraints. An emerging new additive manufacturing technique called binder jetting has the potential to overcome some of those restrictions. In this study, a straight minichannel heat sink is manufactured from stainless steel using binder jetting, and it is experimentally evaluated. The hydraulic performance of the heat sink is tested over a range of Reynolds numbers (150-1200). The comparison between the hydraulic results and standard correlations confirms that the targeted geometry was produced, although the high surface roughness created an early transition from laminar-to-turbulent flow. The heat transfer performance was also experimentally characterized at different heat flux conditions ($3000W/m^2$, $5000W/m^2$, $6500W/m^2$), and a range of Reynolds numbers (150-800). These results indicated that convection heat transfer coefficients on the order of $1000 W/m^2-K$ can be obtained with a simple heat sink design. Finally, the effects of the contact resistance on the results are studied, and contact resistance is shown to have critical importance on the thermal measurements. / Master of Science / The continuous miniaturization of electronic devices and the corresponding increase in computing powers have led to a significant growth in the density of heat dissipation within these devices. This increase in heat generation has challenged conventional air fan cooling and alternative solutions for heat removal are required to avoid overheating and part damage. Micro/Mini channel heat sinks (M/MCHS) that use water instead of air for heat removal appear as an attractive solution to this problem as they provide large heat transfer area per volume due to the small channels. Mini/microchannels are distinguished from conventional channels by the hydraulic diameter, where they range from $10mu m$ to $2mm$. M/MCHS are typically manufactured from a highly conductive metals with the channels fabricated on the surface. However, mini/microchannels traditionally have suffered from geometrical and material restrictions due to fabrication constraints. Complex features like curves or internall channels are difficult or even impossible to manufacture. An emerging new additive manufacturing technique called binder jetting has the potential to overcome some of those restrictions. Binder jetting possess unique advantageous as it uses precise control of a liquid binder applied to a bed of fine powder to create complex geometries Furthermore, it does not require extreme heating during the fabrication process. The advantages of binder jetting include that it is low cost, high speed, can be applied to a variety of materials, and the ability to scale easily in size. In this study, a straight minichannel heat sink is manufactured from stainless steel using binder jetting, and this heat sink is experimentally evaluated. The hydraulic performance of the heat sink is tested over different water flow rates (Reynolds numbers between 150-1200). The comparison between the hydraulic results and standard correlations confirms that the targeted geometry was produced, although the high surface roughness created an early transition from laminar-to-turbulent flow. The surface roughness effect should be considered in future designs of additively manufactured minichannels. The heat transfer performance was also experimentally characterized at different heat flux conditions ($3000W/m^2$, $5000W/m^2$, $6500W/m^2$), and different water flow conditions (Reynolds numbers 150-800). These results indicated that convection heat transfer coefficients on the order of $1000 W/m^2-K$ can be obtained with a simple heat sink design. However, a mismatch between the experimental data and the correlation requires further investigation. Finally, the effects of the contact resistance on the results are studied, and contact resistance is shown to have critical importance on the thermal measurements.

The goal of this work is to develop and characterize a manufacturing process that is able to create metal matrix composites with complex cellular geometries. The novel manufacturing method uses two distinct additive manufacturing processes: i) fabrication of patternless molds for cellular metal castings and ii) printing an advanced cellular ceramic for embedding in a metal matrix. However, while the use of AM greatly improves the freedom in the design of MMCs, it is important to identify the constraints imposed by the process and its process relationships. First, the author investigates potential differences in material properties (microstructure, porosity, mechanical strength) of A356 — T6 castings resulting from two different commercially available Binder Jetting media and traditional 'no-bake' silica sand. It was determined that they yielded statistically equivalent results in four of the seven tests performed: dendrite arm spacing, porosity, surface roughness, and tensile strength. They differed in sand tensile strength, hardness, and density. Additionally, two critical sources of process constraints on part geometry are examined: (i) depowdering unbound material from intricate casting channels and (ii) metal flow and solidification distances through complex mold geometries. A Taguchi Design of Experiments is used to determine the relationships of important independent variables of each constraint. For depowdering, a minimum cleaning diameter of 3 mm was determined along with an equation relating cleaning distance as a function of channel diameter. Furthermore, for metal flow, choke diameter was found to be significantly significant variable. Finally, the author presents methods to process complex ceramic structure from precursor powders via Binder Jetting AM technology to incorporate into a bonded sand mold and the subsequently casted metal matrix. Through sintering experiments, a sintering temperature of 1375 °C was established for the ceramic insert (78% cordierite). Upon printing and sintering the ceramic, three point bend tests showed the MMCs had less strength than the matrix material likely due to the relatively high porosity developed in the body. Additionally, it was found that the ceramic metal interface had minimal mechanical interlocking and chemical bonding limiting the strength of the final MMCs. / Ph. D.

The overall goal of this work is to improve the structural performance of cellular structures in bending applications by incorporating tensegrity behavior using long continuous fibers. The designs are inspired by the hierarchical cellular structure composition present in pomelo fruit and the structural behavior of tensegrity structures. A design method for analyzing and predicting the behavior of the structures is presented. A novel manufacturing method is developed to produce the cellular structures with tensegrity behavior through the combination additive manufacturing and metal casting techniques. Tensegrity structures provide high stiffness to mass ratio with all the comprising elements experiencing either tension or compression. This research investigates the possibility of integrating tensegrity behavior with cellular structure mechanics and provides a design procedure in this process. The placement of fibers in an octet cellular structure was determined such that tensegrity behavior was achieved. Furthermore, using finite element analysis the bending performance was evaluated and the influence of fibers was measured using the models. The overall decrease in bending stress was 66.6 %. Extending this analysis, a design strategy was established to help designers in selecting fiber diameter based on the dimensions and material properties such that the deflection of the overall structure can be controlled. This research looks to Additive Manufacturing (AM) as a means to introduce tensegrity behavior in cellular structures. By combining Binder Jetting and metal casting a controlled reliable process is shown to produce aluminum octet-cellular structures with embedded fibers. 3D-printed sand molds embedded with long continuous fibers were used for metal casting. The fabricated structures were then subjected to 4 point bending tests to evaluate the effects of tensegrity behavior on the cellular mechanics. Through this fabrication and testing process, this work addresses the gap of evaluating the performance of tensegrity behavior. The overall strength increase by 30%. The simulation and experimental results were then compared to show the predictability of this process with errors of 2% for octet structures without fibers and 6% for octet structures with fibers. / Master of Science / Cellular materials are a class of lightweight structures composed by a network of cells comprising inter-connected struts, which help in reducing the material present in the structure. These structures provide high stiffness for low mass, better shock-absorption, thermal and acoustic insulation. Best known examples in nature include honeycomb, bamboo and cedar. There is a constant desire to improve strength of the cellular structures while wanting low mass. This research aims to provide a new approach towards the enhancing structural performance of cellular structures for bending applications through designs featuring long continuous fibers to impose tensegrity behavior. The designs in this research are inspired by the structural composition of pomelo fruit and tensegrity arrangements, where continuous long fibers are observed to enhance structural performance. Tensegrity structures are another class of lightweight structures composed of compressive bars and pre-stressed strings/fibers such that the structural elements undergo either tension or compression. The absence of bending stress makes these structures more efficient. A design method for analyzing and predicting the behavior of the structures is presented. To address the imposing manufacturing challenges, a novel manufacturing method is developed, producing cellular structures with tensegrity behavior through the combination of Binder Jetting and metal casting techniques. Binder Jetting is an additive manufacturing process, which selectively binds sand, layer by layer to create molds of desired designs and metal can be cast into the printed molds to realize parts. The bending performance was evaluated and the influence of fibers was measured using the models. The overall decrease in bending stress was 66.6 %. The fabricated structures were then subjected to 4 point bending tests. The overall strength increased by 30%. The simulation and experimental results were then compared to show the predictability of this process with errors of 2% for octet structures without fibers and 6% for octet structures with fibers. This research takes another step towards creating efficient lightweight structures and adds to the efforts taken to build multifunctional hierarchical cellular materials, which can provide better performance while saving material. Potential applications of these structures include earthquake resistant wall panels, aircraft fuselage/interior supports, automotive chassis structure, beams for supporting roof loads, armor panels in battle tanks, ship building and packaging (electromechanical systems).

The focus of this literary study was additive manufacturing (AM) and the purpose was to find general trends for selected materials that have been additively manufactured and compare them to results from other reviews. The raw materials studied were stainless steels 316L, 17-4 PH, 15-5 PH and 420, as well as tool steel H13 and nickel alloys 625, 718 and Hastelloy X.The AM techniques studied were selective laser melting (SLM), electron beam melting (EBM) and binder jetting (BJG).  A total of 69 articles have been studied to fulfill the purpose above. The articles were used to write a summary of the techniques, compare them to each other and to conventional methods. They were also used to create a database to compile information on mechanical properties, microstructure and process parameters. Based on the database mechanical properties for SLM tend to be higher compared to EBM. This however varied somewhat depending on the processed material. Furthermore the yield and tensile strength obtained from the database for SLM seemed to be higher compared to the values in review articles for almost all materials. Unfortunately not enough values were found for BJG to compare it to SLM and EBM.AM seems to produce weaker, equal and superior products compared to conventional methods. However due to the limited nature of the project and the research found no conclusions can be drawn about any trends, how to achieve the different results or how parameters affect the finished product. To be able to say anything with more certainty more research has to be done. Not only in general concerning the AM techniques, but more studying of existing articles is needed. Finally a standardization on how to reference properties and process parameters is necessary. Currently it is very difficult to compare results or draw conclusions due to different designations, units and a lot of missing essential information.

The focus of this literary study was additive manufacturing (AM) and the purpose was to find general trends for selected materials that have been additively manufactured and compare them to results from other reviews. The raw materials studied were stainless steels 316L, 17-4 PH, 15-5 PH and 420, as well as tool steel H13 and nickel alloys 625, 718 and Hastelloy X. The AM techniques studied were selective laser melting (SLM), electron beam melting (EBM) and binder jetting (BJG).  A total of 69 articles have been studied to fulfill the purpose above. The articles were used to write a summary of the techniques, compare them to each other and to conventional methods. They were also used to create a database to compile information on mechanical properties, microstructure and process parameters. Based on the database mechanical properties for SLM tend to be higher compared to EBM. This however varied somewhat depending on the processed material. Furthermore the yield and tensile strength obtained from the database for SLM seemed to be higher compared to the values in review articles for almost all materials. Unfortunately not enough values were found for BJG to compare it to SLM and EBM.AM seems to produce weaker, equal and superior products compared to conventional methods. However due to the limited nature of the project and the research found no conclusions can be drawn about any trends, how to achieve the different results or how parameters affect the finished product. To be able to say anything with more certainty more research has to be done. Not only in general concerning the AM techniques, but more studying of existing articles is needed. Finally a standardization on how to reference properties and process parameters is necessary. Currently it is very difficult to compare results or draw conclusions due to different designations, units and a lot of missing essential information.

In der vorliegenden Arbeit werden verschiedene Simulationsansätze angewandt um die Hydrodynamik in einem neu entwickelten Wirbelschichtvergaser zu untersuchen. Die Ansätze umfassen a) entdimensionalisierter Ähnlichkeitskennzahlen und empirischer Gleichungen, b) 1D Simulationen mittels ASPEN Plus®, c) 3D CFD Simulationen mittels Ansys Fluent® zur detaillierten Abbildung der zu erwartenden Hydrodynamik. Vor- und Nachteile der jeweiligen Ansätze sowie Klassen von ermittelbaren Simulationsdaten werden diskutiert. Ein Schwerpunkt der Arbeit liegt in der Identifizierung geeigneter Experimente aus der Literatur, auf Basis von Ähnlichkeitskennzahlen, um die Simulationen zu validieren. Die Vergasersimulationen zeigen, dass sich erwartungsgemäß ein aus hydrodynamischer Sicht gestufter Prozess ausbildet. Die entstehenden Zonen lassen sich als Festbett, blasenbildende Wirbelschicht, Jet-Wirbelschicht mit Rezirkulationszelle und strähnenbildende, zirkulierende Wirbelschicht identifizieren und entsprechen demnach dem Verfahrensanspruch.

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The effectiveness of removing anomalous material from cast-in-drilled-hole (CIDH) piles by water jetting was examined. The primary objectives of this research were to examine how reinforcing steel influences water jetting and to evaluate how jetting pressures and standoff distance from the material surface affect water jetting of concrete type materials and PVC tubing. The experimental work consisted of water blasting submerged test specimens using rotary jets, nozzles, pumping equipment, and testing procedures currently used in construction practice. The concrete test specimens were comprised of ring- and cylinder-shaped samples, containing materials with compressive strengths of approximately 160 and 3,600 psi. Typical PVC tubing used as inspection access holes for non-destructive testing in CIDH piles was utilized for tubing specimens. During testing, erosion depths were measured as a function of standoff distance and jetting pressure. Water jetted specimens containing reinforcing steel were cut apart after testing to permit inspection of the erosion cavity and eroded material surfaces behind the steel reinforcement. Reinforcing steel bars in CIDH piles do interfere with the jet path and will locally influence material erosion and water-jetting effectiveness. For a relatively weak material, water-jetting pressures between 10,000 and 11,000 psi produced erosion up to a radial distance of approximately 12 inches from the water jet. This erosion distance is less than half the typical maximum design spacing of PVC inspection access tubing installed in CIDH piles.

Binder jetting (BJT) is a powder bed based additive manufacturing (AM) process where the interaction of inkjetted droplets of a binder and particles in the powder bed create 3D geometries in a layerwise fashion. The fabricated green parts are usually thermally post-processed for densification and strengthening. BJT holds distinct advantages over other AM processes as it can fabricate parts with virtually any materials (metals, ceramics, and polymers) in a fast and cost-effective way, while achieving isotropic material properties in the parts. However, broad adoption of this process for production is still lagging, partially due to the lack of repeatable part quality, which largely stems from the limited understanding of the process physics, namely binder-powder (B/P) interaction. To bridge this knowledge gap, it is necessary to understand the implications of B/P interaction on process-structure-property relationships and discover ways to achieve new functionalities for enhanced properties. Thus, this research is broadly focused in establishing understanding in (i) binder-powder interaction and (ii) the impact of binder on part densification. Prior studies have focused on the effects of powder interaction with micro/meso-scale binder droplets, despite commercial BJT systems featuring picoliter-scale droplets. These studies have explored the effects of B/P interaction on printed primitive formation, but it's implication on final part properties have not been studied. In this work, the effects of particle size distribution and droplet size variation on final part properties are explored. Additionally, the effects of B/P interaction on accuracy and the resolution of the printed parts are investigated. Densification of parts is a primary focus of many BJT studies as it dictates the final part properties and is influenced by factors from both the printing process and post-processing treatments. Binder plays an integral role in the shaping of parts and maintaining part integrity until densification through sintering. Prior studies on the effects of binder content on densification are inclusive. In this work, a new approach termed as "shell printing" is introduced to vary the binder content in the parts. The process-structure-properties influenced by this approach are investigated. It was found that binder hinders densification, and through the selective variation of binder content throughout the part volume, this new approach is introduced as a means for enhancing part properties. Finally, the insights from the impact of binder on densification are leveraged to create an anti-counterfeiting tagging strategy by controlling the pores and grain microstructures inside a part. In this novel approach, binder concentration is controlled in a manner that the stochastically formed pores are clustered to create a designed domain that represents a secret 'tag' within the part volume. The created tagging domains, and the feature resolvability of this approach are investigated through metallographic characterization and non-destructively evaluated through micro-computed tomography. / Doctor of Philosophy / Binder jetting (BJT) is an additive manufacturing (AM) process to create 3D geometries from powder particles. Liquid droplets of binder from an inkjet printhead are jetted on a bed of packed powders, binding the particles. The as-printed parts, known as green parts, are generally fragile and require thermal post-processing (through sintering) for densification and strengthening. BJT holds distinct advantages over other AM processes as it can fabricate parts with virtually any powdered materials (metals, ceramics, and polymers) in a fast and cost-effective way. However, broad adoption of this process for production is still lagging, partially due to the lack of repeatable part quality, which largely stems from the limited understanding of the process physics, namely binder-powder (B/P) interaction. In this study the implications of B/P interaction on part quality (e.g., density, strength) and dimensional accuracy are studied. Additionally, the impact of binder on sintering densification is studied. Specifically, the effects of varying amount of binder on sintered part density, strength and internal pore and grain microstructures are empirically investigated. Finally, a novel anti-counterfeiting method for BJT printed parts is introduced based on the insights gained from the study of the impact of binder on densification. Through control over binder placement throughout the part, porous regions can be generated selectively throughout the part volume, which can be detected through x-ray computed tomography. Overall, an improved understanding of BJT processing conditions is achieved through this research, which can guide future designers to fabricate BJT parts with enhanced part properties and functionality.

Au passage d’un choc sur la surface rugueuse d’un métal, un nuage de débris micrométriques est éjecté. Sa signature spectrale temps-vitesse est mesurée au moyen d’un système optique interférométrique : la Vélocimétrie Hétérodyne (VH).Dans un régime de diffusion simple de la lumière, une étude paramétrique a mis en évidence l’influence des paramètres clés du nuage sur sa réponse Doppler. Nous avons estimé, par Maximum de Vraisemblance, la courbe masse-vitesse d’un nuage d’étain et l’incertitude associée. L’allure de la mesure a également été étudiée en incorporant aux calculs le rendement optique de la sonde.Nous présentons une méthode de calcul Monte Carlo, rendant compte des effets de diffusion multiple. Appliquée à trois expériences d’éjection d’or et d’étain, la présence de vitesses non physiques sur la mesure VH, liée aux diffusions multiples nuage-surface-nuage, a été soulignée, et les décroissances progressives de la visibilité en vitesse et de la puissance rétrodiffusée justifiées. Quelle que soit la masse éjectée, la diffusion multiple doit être intégrée aux calculs, un régime de diffusion simple n’étant valable qu’asymptotiquement, dans les limites d’un temps infini et/ou d’un faisceau sonde de dimension réduite par rapport aux libres parcours moyen de diffusion. / As a shockwave reaches a roughened metal’s surface, high-speed micron-sized particles are ejected. The spectral signature of the cloud can be measured using a fiber-based interferometric setup, so-called Photon Doppler velocimetry (PDV).In the single scattering regime, we study how the parametric dependencies of the cloud influence its Doppler response. Using a Maximum Likelihood technique, we estimate the mass-velocity function of ejected material, and its uncertainty. The time-dependent statistical properties of the spectrum, coming from the complex optical collection efficiency of the probe, are also explained.We present a Monte Carlo method to incorporate multiple scattering. Three different ejecta experiments are studied and the presence of non-physical velocities attributed to multiple scattering between surface and ejecta. Cloud’s visibility and backscattered power decrease with time due to the existence of different scattering regimes. Whatever the ejected mass, multiple scattering effects have to be integrated in PDV calculations. A single scattering will only be asymptotically valid, when time reaches infinity and/or the beam diameter is negligible with respect to the scattering mean free paths.