A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item ELECTRICAL AND STRUCTURAL FORMATION OF TRANSIENT LIQUID PHASE SINTER (TLPS) MATERIALS DURING EARLY PROCESSING STAGE(2023) Nave, Gilad; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The growing demands of electrification are driving research into new electronic materials. These electronic materials must have high electrical conductivity, withstand harsh environments and high temperatures and demonstrate reliable solutions as part of complete electronic packaging solutions. This dissertation focuses on characterizing the initial stage of the manufacturing process of Transient Liquid Phase Sinter (TLPS) alloys in a paste form as candidates for Pb-free high-temperature and high-power electronic materials.The main objective of this dissertation work is to investigate the factors and decouple the multiple cross effects occurring during the first stage of TLPS processing in order to improve the understanding of material evolution. The work proposes, develops, and conducts in-situ electrical resistivity tests to directly measure material properties and analyze the dynamics at different stages of the material's evolution. The research explores various factors, including alloying elements, organic binders, and heating rates, to understand their effects on the development of electrical performance in electronic materials. More specifically, the work examines the performance of Ag-In, Ag-Sn and Cu-Sn TLPS paste systems. Additionally, packing density and changes in cross-section are investigated using imaging techniques and image processing to gain insights into the early formation of the material's structural backbone. An Arrhenius relationship together with Linear Mixed Models (LMM) techniques are used to extract the activation energies involved with each of the processing stages. The study then develops procedures to model different states of the TLPS microstructures at different heating stages based on experimentally observed data. Using these models, the study uses Finite Element Method (FEM) analysis to verify the experimental results and gain a better understanding and visualization into the involved mechanisms. This investigation not only sheds light on the material's behavior but also has implications for robust additive manufacturing (AM) applications.Item Additive Manufacturing for Recapitulating Biology in vitro and Establishing Cellular & Molecular Communication(2023) Chen, Chen-Yu; Bentley, William E.; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recapitulating biological systems within laboratory devices, particularly those with analytical instrumentation, has enhanced our ability to understand biology. Especially useful are systems that provide data at the length and time scales characteristic of the assembled biological systems. In this dissertation, we have employed two advanced technologies — additive manufacturing and electrobiofabrication to create systems that both recapitulate biology and provide ready access to molecular data. First, we utilized two-photon direct laser writing (DLW) and digital light processing (DLP) 3D printing to reconstruct morphologies of human gut villi. Our constructs enable small molecule diffusion through pores and enable epithelial cell growth and differentiation, as in the gastrointestinal (GI) tract. We also developed a cell/particle alignment methodology that applies a vacuum on the underside of a device to rapidly facilitate attachment to 3D printed scaffolds. These simple demonstrations of additive manufacturing show how one can better tailor geometric features of organ-on-a-chip and other in vitro models. We then added electrobiofabrication as a means create functionalized surfaces that rapidly assemble biological components, noted for their labile nature, onto devices with just an applied voltage. In one example, we show how a thiolated polyethylene glycol (PEG) can be electroassembled as a sensor interface that includes antibody binding proteins for both titer and glycan analysis. Rapid assessment of titer and glycan structure is important for biopharmaceuticals development and manufacture. While the interface and sensing methodology was performed using standard laboratory instrumentation, we show that the methodology can be streamlined and operated in parallel by incorporating into a microfluidic sensor platform. Additionally, we show how the combination of optical and electrochemical (redox) based measurements can be combined in a simplified insert that “fits” nearly any microplate reader or other fairly standardized laboratory spectrophotometric unit. We believe that by adapting transformative electrochemical analytical methods so they can augment more traditional optical techniques, we might ultimately generate devices that provide a far more comprehensive picture of the target, promoting better investigation. Specifically, we show how three important biological and chemical systems can be interrogated using both optical measurements and electrochemistry: the oxidation state of proteins including monoclonal antibodies, redox status of hydrogel materials, and electrobiofabrication and electrogenetic induction. Lastly, we demonstrate how electrobiofabrication can be used to create designer communities of bacteria — artificial biofilms — the study of which is important for understanding phenomena from infectious disease to food contamination. That is, we discovered that by varying the applied voltage, surface area, and composition of the to-be-assembled hydrogel solution, we can precisely control the intercellular environment among bacterial populations. In sum, this dissertation integrates advances in assembly, through additive manufacturing, electrobiofabrication, with advances in electrochemical analysis to bring to the fore an electronic understanding of complex biological phenomena. We believe that the capability of translating biological information into a processible digital language opens tremendous opportunities for advancing our understanding of nature’s amazing systems, potentially enabling electronic means to control her subsystems.Item MANUFACTURABILITY AND RELIABILITY OF ADDITIVELY MANUFACTURED PLANAR TRANSFORMER WINDINGS USING SILVER-BASED PASTE(2023) Yun, He; McCluskey, F. Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation is primarily concerned with the integration of additive manufacturing (AM) techniques into planar magnetics to achieve more efficient designs for power modules, which are in high demand. The two main focuses of this dissertation are: (1) the use of a paste-based AM technique called syringe-printing to create planar transformer windings without the need for pressure, using silver-based paste. The dissertation will address manufacturing considerations such as trace width, gaps, and heights that are printable, as well as the impact of electrical resistivity on the sintering process for the syringe-printed silver-based windings; and (2) the evaluation of the reliability of the syringe-printed silver-based windings, which will involve assessing adhesion performance between the metal/ceramic interface, conducting accelerated life tests (including thermal aging and thermal cycling tests), and identifying failure modes, failure sites, failure mechanisms, and developing degradation/failure models.In order to achieve the desired printing geometry in terms of width and gaps between segments, printing settings were studied parametrically by fitting targeted values with actual values. A low-temperature sintering profile was optimized, with a dwell time of 8 hours at 350°C resulting in a resistivity as low as 4.39E-8 Ω∙m, which was approximately 2.5 times higher than bulk silver. To improve bonding prior to syringe-printing the silver-based windings, it was suggested that an adhesive layer consisting of titanium (Ti) and silver (Ag) be deposited onto the alumina substrate. A degradation model was developed for thermal aging tests. Two batches of single-layer 7-turn syringe-printed windings were subjected to thermal cycling tests, and the corresponding failure modes and mechanisms were investigated. The failure data was used to combine with the strain-energy density extracted from the finite element simulation to develop the fatigue model, with the Coffin-Mason model being fitted for future comparison. A more conservative model could be recommended for real-world applications. Finally, the silver-based paste was syringe-printed onto a cooler with a limited footprint area, which served as the primary and secondary planar transformer board and was used in a 10 kW DC-DC full-bridge power converter with 97% efficiency. Corresponding thermal and electrical performance were discussed.Item Design and Characterization of Additively Manufactured Lightweight Metal Structures with Equivalent Compliance and Fatigue Resistance(2021) Santos, Luis S; Bruck, Hugh A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Additive Manufacturing (AM) has been a disruptive manufacturing technology allowing for control of geometric features and material distributions, potentially starting at the atomistic level, to realize structures with lighter weights. However, it is still begin used primarily as a rapid prototyping tool due to challenges arising from various issues that need to be addressed before commercial parts can be deployed. Three of those issues are: (1) characterization of mechanical properties that may vary spatially, (2) identification of novel defects in the parts, and (3) new design approaches that account for the unique capabilities of AM processes and their impact on fatigue resistance.This dissertation addresses these three issues by developing a cyclical indentation technique to characterize the fatigue properties of geometric features only capable with AM. The method produces the degradation of the material stiffness as the number of cyclic loads increases and is capable of generating an entire S-N curve with a single test at sub-millimeter scales. Geometric features are then analyzed by running a thermal and mechanical simulation of a Direct Metal Laser Sintering (DMLS) printing process. The new simulation can account for buckling of features with high aspect ratios, such as low percentage infills or high levels of unit cell porosity, and predicts distortions with less than 5% error. This computational approach is useful for analyzing parts before printing and informs designers about regions in the part that may need modification to prevent buckling. Finally, the experimental and computational techniques are combined to design structures with macroscale topological features and microscale unit cell features that are fatigue resistant.Item ADVANCED PACKAGING AND THERMAL MANAGEMENT OF DC-DC CONVERTERS AND NOVEL CORRELATIONS FOR MANIFOLD MICROCHANNEL HEATSINKS(2021) Yuruker, Sevket Umut; Ohadi, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An advanced packaging configuration of a dual-active-bridge 10 kW DC-DC converter module is introduced in this dissertation. Through utilization of novel heatsinks for the power switches and the transformer assembly, ~20 kW/Lit converter volumetric power density based on numerical and experimental analysis is obtained. Through a unique placement of the high power/high frequency SiC switches on the printed circuit board, many beneficial features such as double-sided cooling, complete elimination of wirebonding, and circumvention of the need for TIM layers between the switches and the heatsinks, and multi functioning heatsinks as electrical busbars is achieved. A Vertically Enhanced Manifold Microchannel System (VEMMS) cooler is developed to address the thermal challenges of a pair of power switches, simultaneously. Both air and liquid cooled versions of VEMMS cooler is presented, thermal resistances of 1.1 K/W and 0.3 K/W for the air and liquid cooled versions, respectively, at reasonable flow rates and pressure drops was obtained. Besides the power switches, thermal management of the transformer assembly is accomplished via Combined Core and Coil (C3) Coolers, where both the magnetic core and coils are liquid cooled simultaneously with electrically insulating but thermally conductive 3D printed Alumina heatsinks, where thermal resistances as low as 0.3 K/W for the magnetic core and 0.09 K/W for the transformer windings is experimentally demonstrated. Furthermore, a system level model was built to investigate the effect of various components in the cooling loop on each other, and what are the limiting factors to prevent a possible thermal runaway failure. Lastly, using a metamodeling approach, closed form pressure drop and heat transfer correlations are developed for thermo-fluidic performance prediction of manifold microchannel heatsinks. Due to complexity and vastness of design variables present in manifold microchannel systems, adequate CFD analysis and optimization require significant computational power. Through utilization of the developed correlations, orders of magnitude reduction in computational time (from days to milliseconds) in prediction of pressure drop and heat transfer coefficient is demonstrated. Extensive mesh independence and residual convergence algorithms are developed to increase accuracy of the created database. Between the correlation and mesh independent CFD results, a mean error of 3.9% and max error of 24% for Nusselt number, and a mean error of 4.6% and max error of 37% for Poiseuille Number predictions are achieved.Item Additive Manufacturing of Microfluidic Technologies via In Situ Direct Laser Writing(2021) Alsharhan, Abdullah; Sochol, Ryan; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Innovations in microfluidic technologies hold great promise for a wide range of chemical, biomedical, and soft robotic applications. Unfortunately, key drawbacks associated with soft lithography-based microfabrication processes hinder such progress. To address these challenges, we advance a novel submicron-scale additive manufacturing (AM) strategy, termed “in situ direct laser writing (isDLW)”. IsDLW is an approach that benefits from the architectural versatility and length scales inherent to two-photon polymerization (2PP), while simultaneously supporting the micro-to-macro interfaces required for its effective utilization in microfluidic applications. In this dissertation, we explore isDLW strategies that enable passive and active 3D microfluidic technologies capable of enhancing “on-chip” autonomy and sophistication. Initially, we use poly(dimethylsiloxane) (PDMS)-based isDLW to fabricate microfluidic diodes that enable unidirectional rectification of fluid flow. We introduce a novel cyclic olefin polymer (COP)-based isDLW strategy to address several limitations related to structural adhesion and compatibility of PDMS microchannels. We use this COP-based approach to print microfluidic transistors comprising flexible and free-floating components that enable both “normally open” (NO) and “normally closed” (NC) functionalities—i.e., source-to-drain fluid flow (QSD) through the transistor is either permitted (NC) or obstructed (NO) when a gate input (PG) is applied. As an exemplar, we employ COP-based isDLW to print an integrated microfluidic circuit (IMC) comprised of soft microgrippers downstream of NC microfluidic transistors with distinct PG thresholds. All of these microfluidic circuit elements are printed within microchannels ≤ 40 μm in height, representing the smallest such components (to our knowledge). Theoretical and experimental results illustrate on the operational efficacy of these components as well as characterize their performance at different input conditions, while IMC experimental results demonstrate sequential actuation of the microrobotic components to realize target gripper operations with a single PG input. Furthermore, to investigate the utility of this strategy for static microfluidic technologies, we fabricate: (i) interwoven bioinspired microvessels (inner diameters < 10 μm) capable of effective isolation of distinct microfluidic flow streams, and (ii) deterministic lateral displacement (DLD) microstructures that enable continuous sorting of submicron particles (860 nm). In combination, these results suggest that the developed AM strategies offer a promising pathway for advancing state-of-the-art microfluidic technologies for various biological and soft robotic applications.Item Experimental Study of Segmented Constrained Layer Damping in Rectangular and Sinusoidal Beams(2020) Ude, Chinonso Oscar; Wereley, Norman M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the aerospace engineering field, structures are constantly subjected to vibrations that are detrimental to the effectiveness and lifespan of the technology in use. In this work the performance of segmented constrained layer damping (SCLD) treatments for reducing vibration amplitudes is experimentally evaluated. In addition, two methods of manufacture and application are presented that employ 3D printed approaches. SCLD performance is evaluated by observing the bending response of cantilevered beams and the axial response of straight and sinuous springs. Measurements show that precise sample construction using a multi-jet modeling 3D printing approach and segment spacing based on a genetic optimization algorithm, leads to SCLD treatments that are effective for reducing vibration in cantilevered beams. Results also show that curved structures can also exploit SCLD treatments to enhance damping in axial springs, but that different algorithms for optimum segment size and spacing would be needed to create treatments that are tailored to the more complex spring structures.Item IN-SITU ADDITIVE MANUFACTURING OF METALS FOR EMBEDDING PARTS COMPATIBLE WITH LIQUID METALS TO ENHANCE THERMAL PERFORMANCE OF AVIONICS FOR SPACECRAFT(2020) Armen, Jerald; Bruck, Hugh; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With advances in micromachinery, the aggregation of sensors, and more powerful microcontroller platforms on satellites, the size of avionics for space missions are getting dramatically smaller with faster processing speeds. This has resulted in greater localized heat generation, requiring more reliable thermal management systems to enhance the thermal performance of the avionics. The emergence of advanced additive manufacturing (AM), such as selective laser melting (SLM) and engineering materials, such as low-melting eutectic liquid metal (LM) alloys and synthetics ceramics offer new opportunities for thermal cooling systems. Therefore, there has been an opportunity for adapting in-situ AM to overcome limitations of traditional manufacturing in thermal application, where improvements can be achieved through reducing thermal contract resistance of multi-layer interfaces. This dissertation investigates adapting in-situ AM technologies to embed LM compatible prefabricated components, such as ceramic tubes, inside of metals without the need for a parting surface, resulting in more intimate contact between the metal and ceramic and a reduction in the interfacial thermal resistance. A focus was placed on using more ubiquitous powder bed AM technologies, where it was determined that the morphology of the prefabricated LM compatible ceramic tubes had to be optimized to prevent collision with the apparatus of powder bed based AM. Furthermore, to enhance the wettability of the ceramic tubes during laser fusion, the surfaces were electroplated, resulting in a 1.72X improvement in heat transfer compared to cold plates packaged by conventional assembly. Additionally, multiple AM technologies synergistically complement with cross platform tools such as magnetohydrodynamic (MHD) to solve the corrosion problem in the use of low melting eutectic alloy in geometrically complex patterns as an active cooling system with no moving parts. The MHD pumping system was designed using FEA and CFD simulations to approximate Maxwell and Navier-Stokes equations, were then validated using experiments with model heat exchanger to determine the tradeoff in performance with conventional pumping systems. The MHD cooling prototype was shown to reach volumetric flow rates of up to 650 mm3/sec and generated flow pressure due to Lorentz forces of up to 230 Pa, resulting in heat transfer improvement relative to passive prototype of 1.054.Item DESIGN AND EXPERIMENTAL CHARACTERIZATION OF METAL ADDITIVE MANUFACTURED HEAT EXCHANGERS FOR AEROSPACE APPLICATION(2020) Battaglia, Fabio; Ohadi, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High temperature heat exchangers are key to the success of emerging high-temperature, high-efficiency solutions in energy conversion, power generation and waste heat recovery applications. When applied to the aerospace applications, the main objective is to develop heat exchangers that can realize significant performance improvement in terms of gravimetric heat exchange density (kW/kg). In the present study, two air-to-air crossflow heat exchangers were designed, built and tested to determine their potential for high performance, pre-cooling heat exchanger for aircraft applications. A novel design based on manifold-microchannel technology was chosen as it provided localized and optimum distribution of the flow among the heat transfer surface micro channels, offering superior heat transfer performance and low pressure drops, when compared to conventional, state of the art heat exchangers for the chosen application. However, fabrication of the manifold microchannel design for high temperature with super alloys as the heat exchanger material presents serious manufacturing challenges fabrication techniques. To overcome this limit, direct metal laser sintering (DMLS) additive manufacturing technique was selected for the fabrication of the Ni-based superalloy manifold-microchannel heat exchangers in the present study. Extensive work was performed to characterize the printing capability of different metal 3D-printers in terms of printing orientation, printing accuracy and structure density. Based on the knowledge acquired, two units were printed, with overall size of 4”x4”x4” and 4.5”x4”x3.5” and fin thickness of 0.220 mm and 0.170 mm, respectively. The printed units were the largest additively printed, superalloy-based manifold-microchannel heat exchangers found in the literature. The experimental characterization was carried at high temperature (600°C) and the model prediction of the performance was updated to characterize the behavior of the heat exchangers in this operational conditions. Based on the experimental results, a gravimetric heat duty of 9.4 kW/kg for an effectiveness (ε) of 78% was achieved, which corresponds to an improvement of more than 50% compared to the conventional designs. The characterization of the performance at high temperature was then completed by analyzing the thermo-mechanical stress generated by the simultaneous presence of temperature gradient and pressures. The current study is the first to characterize the behavior of manifold-microchannel heat exchanger under high temperature in terms of performance prediction and thermo-mechanical analysis.Item Dynamic Control of Fiber Orientation for Additive Manufacturing via a Soft-Actuating Nozzle(2019) Armstrong, Connor; Bigio, David I; Sochol, Ryan D; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently, additive manufacturing of fiber-reinforced composite hydrogels has been used to create self-assembling and self-folding structures through hydration-triggered shape change. Additive manufacturing of shape-changing structures has applications in spatially-limited environments such as in-vivo biological implants and components for space travel. Fiber orientation in composite hydrogels dictates the degree of anisotropic swelling deformation of hydrated structures. This thesis explores the impact of extrusion channel geometry on fiber orientation as well as the relationship between fiber orientation and swelling deformation of composite hydrogels. To study the impact of fiber orientation on swelling deformation, fiber orientation in composite hydrogels was varied using diverging extrusion dies of increasing divergence angles. It was found that increasing channel divergence angle reduced the number of fibers oriented in the direction of flow, which led to increasingly isotropic swelling deformations. To create a gradient of fiber orientations in extruded structures, an extrusion nozzle utilizing soft actuators to alter its divergence angle in real-time was developed. Hydrogels extruded through the soft-actuated dynamic nozzle exhibited similar fiber orientation and swelling behavior to those extruded through the fixed divergence angles. Spatially-varied swelling deformation characteristics promise to improve additive manufacturing of self-assembling and self-folding structures by increasing the complexity of controllable shape change geometries achievable in extruded composite polymer structures.