Several active methods, which requires external control systems and moving parts, have been developed to control the fiber orientation during 3D printing. Active mechanisms like rotating nozzle, impeller, and magnetic field have been integrated to realize complex internal fiber structures. In this study, instead of using active methods, I investigate a passive method for controlling the fiber orientation without any moving parts or additional mechatronics added in the printing process. Composites of polydimethylsiloxane (PDMS) and glass fibers (GF) are 3D printed. Channels, such as helicoid, are designed and integrated to guide the ink flow and passively result in different pre-alignment of fibers before the ink flow into narrow nozzle space. While passing through the designed channels, the fibers orient due to the shear between channel walls and the ink. The effect of helicoids with different pitch sizes are investigated via mechanical experiments, microstructural analysis, and numerical simulations. The results show that both surface to volume ratio and helix angle of the channel affect pre-alignment of fiber orientation at the entry of nozzle. The internal fiber structures lead to enhanced and tunable mechanical properties of printed composites. Pitch size 7-9 mm (helix angle of 7.92- 10.15o) is found to be optimal for the 3D printed PDMS-GF composites. Stiffness and strength can be tuned up to 77.6% and 47.8%, respectively, compared with the case without helicoid channel. Channels of parallel holes, parallel holes with taper end and gradually changing pitch helicoids are experimentally tested, showing further enhancement in mechanical properties.

Silicon carbide is a useful monolithic and matrix ceramic due to its excellent mechanical properties and corrosion/oxidation resistance at high temperature. This makes it an attractive material for use in advanced applications, such as aircraft engines and high-speed flight. In this study, additively manufactured monolithic SiC and Cf/SiC CMCs, processed via direct ink writing (DIW) of a 53 vol% colloidal suspension, achieved >96% theoretical density through pressureless sintering. When present, fibers are aligned in the direction of the print path. Five different print paths were studied, including a 0o path, 90o path, 0/90o path, 0/15/30/45/60/75/90o path, and 0/30/60/90/60/30/0o path. Four-point bend testing was performed to determine flexural strength and Weibull analysis was performed. Strengths were highest for the 0o print path. The characteristic strength, σo, of this print path was 375 MPa with a Weibull modulus of 7.4 for monolithic SiC and a σo of 361 MPa with a Weibull modulus of 10.7 for Cf/SiC. Weibull modulus was greater for Cf/SiC samples compared to identically printed monolithic SiC samples. SEM and optical microscopy were used to analyze printed parts which showed a high degree of fiber alignment in the direction of the print. Fiber pullout was observed on the fracture surface, as well as intragranular fracture.

Anthropogenic emission of greenhouse gases has long been suspected to contribute to global warming and climate change. Most greenhouse gases are emitted in a mixture, so efficient methods and materials to separate and capture the gases are in demand in order to reduce emissions. A promising material group for this purpose is metal-organic frameworks (MOFs). This class of material have the ability to selectively adsorb green house gases due to its high porosity and high surface area. Zeolitic imidazolate frameworks (ZIFs) are a subclass of MOFs that are topologically similar to zeolites and are known for their good chemical and thermal stability.   The aim of this project was to investigate if the greenhouse gas (i.e. CO2 and SF6) capture performance of ZIFs could be improved and tuned using a mixed-linker approach with seven different imidazolate-based organic linkers of different sizes or with various functional groups. As well as to investigate the processability of MOFs using 3D printing. ZIFs composed of different ratios of 2-methylimidazolate as base linker and a second linker of imidazolate, benzimidazolate, 2-aminobenzimidazolate, 5,6-dimethylbenzimidazolate, and 4,5-dichloroimidazolate were succesfully made. The materials were all found to be crystalline, however, mixed-linker ZIFs containing 2-aminobenzimidazole, 5,6-dimethylbenzimidazole and dichloroimidazole were observed to contain more than a single phase. All samples showed to be somewhat porous towards CO2 and SF6, and there seem to be a trend where a low % of a bulkier linker (eg. bIm, ambIm) resulted in a higher uptake of SF6 whereas a high % resulted in a higher uptake of CO2. For dcIm it was the other way around, a low % showed a higher uptake for CO2  whereas a high % showed a higher uptake for SF6. For CO2, the ZIF containing 80% benzimidazolate showed the highest uptake of 9.81 wt%. For SF6, the 25% 4,5-dichloroimidazolate showed the highest uptake of 17.73 wt%. Furthermore, direct ink writing (DIW) 3D printing was also successfully utilized to process and structure a Mn-based MOF using carbopol as binder. The printed structure was found to have similar properties to the pristine MOF in regards to crystallinity and porosity.

The Automated Design and Manufacturing Laboratory (ADML) is an automated assembly line located in the Engineering Product and Innovation Center (EPIC) that serves as the lab component for the course ME345: Automation and Manufacturing Methods. Over the semester the students learn how to program each automated component of the system, including Computer Numerically Controlled (CNC) mills, Universal Robot's 6 axis robotic arm, cameras, and Programmable Logic Controllers (PLC). Students then learn how to integrate each component together to develop a completely automated manufacturing process using an in-house manufacturing execution software. This integrated system is then used by the students to automatically manufacture new products of their own design that provide a societal benefit. Since 2019 multiple undergraduate students have worked on augmenting the ADML's capability with printing electronics by implementing Direct Ink Writing (DIW) based 3D printing and vacuum based pick and place into the ADML's assembly robot. Using these new capabilities, students in the ME345 will be able to design and manufacture electronic circuits. Moreover, a graduate level course will be developed based on this new addition to the ADML. The aim of this Thesis is to continue the work of previous students by finalizing the hardware and software necessary for the pick and place of electronic components and developing a conductive ink for electrical wiring and interconnects. A three component ink comprised of silver flake and a copolymer solution of acrylates/polytrimethylsiloxymethacrylate in a isododecane solvent was developed. This ink is biocompatible so it can be used by students without any hazard concern. It also exhibits a high degree of adhesion to the high-density polyethylene (HDPE) stock parts currently used in the ADML to ensure strong bonding to the electrical components. The mixing process, ink ingredient concentrations, and print parameters (i.e., extrusion pressure, print speed, and nozzle standoff distance) were optimized for compatibility with DIW based 3D printing, consistent and clog-free extrusion throughout the printing process, print fidelity, and a high electrical conductivity within approximately 1-2 orders of magnitude of bulk silver. / 2025-05-24T00:00:00Z

<p>  </p> <p>Silicon carbide (SiC) is a ceramic material of interest for many applications due to its mechanical properties, oxidation resistance, and high thermal conductivity. However, one limitation of SiC is its low fracture toughness. There is evidence that SiC with crystallographic texture and an anisotropic microstructure of aligned plate-shaped grains has improved fracture toughness without sacrificing strength. Previous techniques to create these materials have made use of either pressure during densification or a strong magnetic field, but these processes limit possible geometries that can be created. In this dissertation, the additive manufacturing technique direct ink writing (DIW) and pressureless templated grain growth (TGG) are proposed as a route to complex-shaped textured SiC. </p> <p><br></p> <p>DIW is a colloidal processing technique where ceramic suspensions are extruded through a nozzle along a path, building up a part layer-by-layer. High aspect ratio particles can be aligned via the forces in the print nozzle. In this work, single crystal SiC platelet seed particles were added to a SiC suspension and aligned with DIW. After densification, samples were annealed above the sintering temperature. During annealing, TGG occurs where the platelet seed particles grow at the expense of the finer matrix particles, and this results in crystallographic texture. </p> <p><br></p> <p>First, work on the development of the DIW process for the creation of textured SiC is shown. Aqueous SiC suspensions were developed with a high solids loading (> 50 vol%) and low polymer content (< 5 vol%) to maximize the density achieved during sintering, which is ideal for TGG. Four rheological parameters (viscosity of the suspension at 5 s­-1, zero shear viscosity, oscillatory yield stress, and equilibrium storage modulus) were related to the amount of viscosity modifying polymer (polyvinylpyrrolidone) and observed quality of prints. The best prints were made from suspensions that had a viscosity of 30-35 Pa s, ZSV of 5000-7000 Pa s, and yield stress 100-150 Pa. The best suspension for printing was identified to be 53 vol% solids with 0.2 vol% PVP due to its high particle loading and ability to create consistent prints. The addition of 5 vol% platelet particles to the suspension did not impact the rheology or printability significantly.</p> <p><br></p> <p>Next, textured SiC ceramics over 95% theoretical density were created via pressureless sintering and annealing. Samples were fabricated with and without 5 vol% platelet seeds, and with and without annealing at 2050 ºC and 2150 ºC. The effects of DIW, seed particles, and annealing temperature on the microstructure and crystallographic texture are presented. Annealing lead to the development of large, high aspect ratio plate-shaped grains among a matrix of many finer, low aspect ratio grains. Higher annealing temperatures and addition of platelet seeds both increased the size of the large grains. Samples were found to be textured regardless of having platelet seeds. Via x-ray diffraction and electron backscatter diffraction, unseeded SiC was found to have texture where the crystallographic direction [0001] had a preferred orientation perpendicular to the normal direction. This occurred for both DIW and cast SiC, so the texture development must have occurred during sintering, though the mechanism is unknown. For seeded SiC, platelet seeds aligned in DIW successfully seeded the grain growth to develop crystallographic texture. The texture was mainly influenced by the alignment of platelet seed particles via shear stresses in the print nozzle, causing a one-dimensional texture where [0001] is perpendicular to the printing direction. However, it was found that the texture was not the expected one-dimensional, concentric alignment of platelet particles in DIW, so the shear stresses in the nozzle are not solely responsible for the texture developed.</p> <p><br></p> <p>Finally, the mechanical behavior of these materials was explored via 4-point flexural strength testing and Weibull analysis. The effect of texture, print orientation, and printing defects on the mechanical and fracture behavior of these materials is discussed. Mechanical tests were conducted both parallel and perpendicular to the printing direction. DIW samples were found to have a variety of defects after densification, including visible print lines, air bubbles, and porosity. Unseeded SiC annealed at 2050 ºC tested parallel to the print direction was found to have the best combination of mechanical properties among all annealed SiC, with evidence of toughening on the fracture surface, flexural strength 405 ± 16 MPa, and Weibull modulus of 15.4. Seeded SiC annealed at 2050 ºC had a high degree of transgranular fracture among large plate-shaped grains, but still had a flexural strength 339 ± 41 MPa. However, improved alignment of grains in future work may increase the incidence of intergranular fracture. At both annealing temperatures, textured SiC created with aligned platelet seed particles was found to have comparable mechanical strength to those fabricated without seed particles despite having a coarser microstructure, suggesting texture may influence the mechanical properties. </p>

Multi-material 3D Printing allows the ability to fabricate parts with tuned mechanical properties, multi-process 3D printing widens the choices of available fabrication materials. The objective of this study is to build a custom 3D printing test bed that is capable of printing multi-material parts with fused deposition modeling and direct ink writing techniques. A 3D printer, controlled by an industrial motion control system, with FDM and DIW capabilities was built by combining FDM extruders with a pneumatic dispensing system on a single platform. By utilizing the Direct Ink Writing function, we expand the number of printable materials to include some off the shelf silicones and epoxies, as well as custom, user made, materials. This study will further expand the manufacturing and research capabilities within the additive manufacturing discipline.

<div> <div> <div> <p>Transparent alumina is a candidate material for ballistic applications where visible or infrared wavelength transmission is required. However, the transparency of polycrystalline alumina can be limited due to the rhombohedral crystal structure being inherently birefringent. Birefringence causes light scattering at grain boundaries and is detrimental to the transparency. It has been shown experimentally that the application of a high magnetic field during processing can lead to crystallographic alignment and the reduction of birefringent light scattering. This alignment method is effective but is limited in terms of scalability. This research addresses these limitations through the use of simple and cost-effective shear and elongational forming processes such as uniaxial warm pressing and direct ink writing (DIW) for the improvement of final sintered transparency. To further support the improvement of these processes as alternatives and to evaluate the possibility of using powder ratios to improve the alignment, this research will also investigate the sintering behavior during hot-pressing of equiaxed and platelet powders. </p> <p>Platelet ceramic-filled thermoplastic blends were developed and formed into sheets through uniaxial warm pressing. The solids loading (30 – 40 vol.%) and platelet diameter (1.2 and 11μm) were varied to compare effects on viscosity, percent reduction, and final alignment. All ceramic- filled thermoplastic polymer blends exhibited pseudoplastic behavior. Crystallographic alignment of green body samples was quantified by the orientation parameter (r) and grain misalignment angle (full width at half maximum, FWHM) obtained from rocking curve analysis. Blends with 11μm diameter platelets displayed a higher temperature sensitivity constant, better flow properties, and higher alignment compared to blends with 1.2μm diameter platelets. Optimal samples produced with blends containing 30 vol.% of 11μm diameter platelets demonstrated an alignment of r = 0.251 +/- 0.017; FWHM = 11.16° +/- 1.16°. A sample with optimal alignment was hot-pressed to transparency and obtained an in-line transmission of 70.0% at 645nm. The final alignment of this pre-aligned hot-pressed sample (r = 0.254 +/- 0.008; FWHM = 11.38° +/- 0.54°) improved when compared to a non-pre-aligned sample (r = 0.283 +/- 0.005; FWHM = 13.40° +/- 0.38°).</p><p>Additionally, the use of direct ink writing, an additive manufacturing technique, as a viable alignment process for producing transparent alumina was investigated. Highly loaded (> 54 vol.%) equiaxed alumina suspensions were developed with platelet additions ranging from 0-20vol.% of the total solids loading. An increase in the amount of platelet powders from 5-20vol.% increased the dynamic yield stress from 104Pa to 169Pa and decreased in the equilibrium storage modulus from 17,036Pa to 13,816Pa. It was found that the DIW process significantly increased the alignment in one orientation when compared to samples cast from the same suspensions and this behavior may be connected to the rheological properties. Lastly, an optical analysis showed that sample developed with 5vol.% platelet suspensions had higher in-line transmission values across the visible spectrum when compared to samples developed with 20vol.% suspensions. A sample cast from a 5vol.% platelet suspensions had the lowest grain alignment but possessed an in-line transmission of 42.8% at 645nm, which was the highest of the samples produced in this study. An optical loss analysis showed, that this sample has the lowest backwards scattering losses due to residual porosity and this result was supported by the density data. It is suggested that the alignment of the DIW samples is more complex and a more advanced texture analysis will need to be conducted to properly characterize the grain alignment.</p><p>Lastly, the densification behavior of equiaxed and platelet powder ratios with no intentional pre-alignment was investigated. An initial sintering investigation identified the optimum maximum pressure selected for the hot-pressing process as 20MPa. Under the selected hot- pressing parameters, the effects of 0, 25, 50, 75, and 100wt.% equiaxed powder additions on the sintering behavior, optical properties, and grain alignment was investigated. The data showed that an increase in the amount of equiaxed powders decreased the initial powder compact displacements rate. Additionally, an increase in the wt.% equiaxed powders from 0wt% to 75wt% decreases the in-line transmission from 70.9% to 40.2%, respectively at 645nm. Lastly, an increase in the wt.% equiaxed powders from 0wt% to 75wt decreased the alignment from (r = 0.321 +/- 0.005; FWHM = 16.26° +/- 0.40°) to (r = 0.509 +/- 0.022; FWHM = 34.63° +/- 2.61°), respectively.</p></div></div></div>

In this work, the use of a lunar regolith simulant as feedstock for the direct ink writing additive manufacturing process is explored, the purpose of which is to enable future lunar in-situ resource utilisation. The feasibility of this approach is demonstrated in a laboratory setting by manufacturing objects with different geometries using methyl cellulose or sodium alginate as binding agents and water as liquid phase together with the lunar regolith simulant EAC-1A to create a viscous, printable ‘ink’ that is used in combination with a custom three-axis gantry system to produce green bodies for subsequent sintering. The sintered objects are characterised using compressive strength measurements and scanning electron microscopy (SEM). It is proposed that the bioorganic compounds used in this work as additives could be produced at the site for a future lunar base through photosynthesis, utilising carbon dioxide exhaled by astronauts together with the available sunlight, meaning that all the components used for the dispersion – additive, water (in the form of ice) and regolith – are available in-situ. The compressive strength for sintered samples produced with this method was measured to be 2.4 MPa with a standard deviation of 0.2 MPa (n = 4). It is believed, based on the high sample porosity observed during SEM analysis, that the comparatively low mechanical strength of the manufactured samples is due to a non-optimal sintering procedure carried out at a too-low temperature, and that the mechanical strength could be increased by optimising the sintering process further.

In recent years, advancements in additive manufacturing (AM) technologies have paved the way for 3D-printed flexible hybrid electronics (FHE) and created opportunities for extending these gains to RF applications. However, printed metal interconnects and devices are typically characterized by high porosity and chemical impurities that significantly limit their electrical conductivity and RF performance compared to bulk equivalents. Using direct ink writing (DIW), two silver inks, a nanoflake suspension and a nanoparticle-reactive ink, were investigated to understand the relationship between free interfacial energy, sintering behavior, DC conductivity, and RF loss. The printed silver samples were characterized using scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy to monitor microstructural evolution, grain size and orientation, and chemical purity as a function of heat treatment temperature. Three heat treatments were applied to each ink: the manufacturer's recommendation, 225°C for 30 minutes, and 350°C for 30 minutes. Four-wire structures and coplanar waveguides were printed to compare the DC and RF performance up to 18 GHz, respectively. The results show that ink formulations that facilitate larger grains, high density, and good chemical purity have superior RF performance. A low resistivity of 1.4 times bulk Ag, average of 0.8% greater RF loss factor than evaporated Ag, and a maximum current density of 4.6 x 105 A/cm2 were achieved with printed structures. This work highlights the importance of engineering a high density and high purity microstructure in printed silver components necessary for high-performance printed electronics.

Les dispositifs optoélectroniques sont devenus un élément essentiel de la technologie moderne visant à exploiter des applications de niche pour l'électronique flexible à base de composés organiques. Jusqu'à présent, les films minces préparés à partir de composés polymères conjugués ont été les principaux concurrents pour les dispositifs optoélectroniques organiques. Avec l'apparition de nouvelles méthodes de mise en œuvre et de nouveaux besoins électroniques, les méthodes de fabrication additive des matériaux optoélectroniques suscitent de plus en plus d'intérêt. Malgré l'intérêt croissant et la variété des méthodes de mise en œuvre tridimensionnelles, on comprend encore mal l'impact de la technique de mise en œuvre sur l'organisation moléculaire des échantillons. Ici, une étude est présentée impliquant l’impression 3D assistée par évaporation de solvant et le poly(3-hexylthiophène) (P3HT) qui est bien décrit dans la littérature, et, dans ce cas-ci, mélangé à diverses matrices thermoplastiques. Dans un premier temps, les matrices thermoplastiques employées, i.e. le polystyrène (PS), le polypropylène carbonate (PPC), le polyméthacrylate de méthyle (PMMA) et le polyoxyéthylène (PEO) sont évaluées en fonction de leurs propriétés rhéologiques et de leur imprimabilité en 3D, qui ne sont que très peu affectées par l'introduction du P3HT. Par la suite, le P3HT à régiorégularité élevée et faible est mélangé dans chacune des matrices thermoplastiques. L'organisation moléculaire des deux composantes dans les architectures imprimées a été évaluée par des techniques de spectroscopie UV-visible et de fluorescence. Les phases en présence ont été analysées à l'aide d’analyse calorimétrique différentielle à balayage, de microscopie optique polarisée et de diffraction des rayons X, ce qui a également permis d'analyser l'état d'agrégation du P3HT par rapport à celui retrouvé dans les films minces. Il est intéressant de noter que les propriétés optiques montrent peu ou pas de différence entre les architectures 3D et les films minces, ce qui indique vraisemblablement que l'efficacité d'un dispositif optoélectronique imprimé en 3D ne serait pas affectée par l’impression 3D assistée par évaporation de solvant. Cette étude pourrait permettre de mieux comprendre comment il serait possible de mettre au point des dispositifs optoélectroniques, y compris des photoconducteurs, des photovoltaïques organiques, des transistors à effet de champ organiques, etc. à l’aide de techniques de fabrication additive, ce qui ouvrira la voie à une nouvelle ère en électronique organique imprimée en trois dimensions. / Optoelectronic devices have become a staple in modern day technology which aims to transition to flexible electronics that are developed from organic compounds. To date, 2-dimensional films of conjugated polymer compounds have been the main contender for organic optoelectronic devices. As new processing methods and electronic needs become present in the modern day, a focus on 3-dimensional processing methods of optoelectronic materials have become increasingly of interest. With the increasing interest and variety of 3-dimensional processing methods, there is little understanding of how the processing technique molecularly affects the final product. Herein is presented a study on the extrusion-based, direct-ink writing of the well understood poly(3-hexylthiophene-2,5-diyl) (P3HT) blended into a variety of thermoplastic matrices. Initially the pristine thermoplastics of polystyrene (PS), poly(propylene carbonate) (PPC), poly(methyl methacrylate) (PMMA), and poly(ethylene oxide) (PEO) were evaluated based on their rheological and printable properties which are negligibly affected by the introduction of P3HT. Subsequently, after the blending of both high and low regioregular P3HT into each of the thermoplastic matrices, the printed architectures were further analyzed by X-Ray diffraction, UV-vis, and fluorescence techniques to assess the aggregation state of P3HT in comparison to 2-dimensional processed films. Interestingly, the electronic properties show little to no difference between 3-dimensional architectures and 2-dimensional films, which presumably indicates that the efficiency would not be affected by the direct-ink writing technique. This study could contribute to the beginning of producing optoelectronic devices, including photoconductors, organic photovoltaic and organic field effect transistors, in 3-dimensions resulting in a new age of electronics.