The purpose of this research was to investigate the potential application of additive friction stir deposition (AFSD) to repair corroded steel bridge members. AFSD is an emerging solid-state additive manufacturing (AM) technology with many advantageous qualities such as low porosity, low residual stresses, flexibility in material, and a high build rate allowing for large-scale deposits. Two parameters were studied to understand the quality of AFSD on corroded steel: surface roughness and surface cleanliness. Three rounds of depositions were done: AerMet100, a high-strength corrosion-resistant steel, deposited onto AISI 1018 plates, with varying degrees of section loss, sectioned from a bridge taken out-of-service; AISI 1018 steel deposited onto an A572 Gr. 50 plate with 12 holes of varying diameters and depths drilled into the plate to simulate surface roughness; and AISI 1018 steel deposited onto an A572 Gr. 50 plate with mill scale, corrosion, and an industrial three-coat bridge paint system. The repair quality of each deposition was studied using scanning electron microscopy, microhardness testing, and three-point bending. Results from these tests indicated the following: AFSD can sufficiently mix dissimilar steels and result in a fine-grained microstructure; depositing onto a rough surface appeared to aid bonding between the two materials with little to no adverse effects on the repair quality; and finally, depending on the chosen deposition parameters, AFSD can mix foreign surface material into the matrix or mechanically remove the bulk of the foreign surface material appearing to clean the surface during the deposition. / Master of Science / This research investigated the applicability of additive friction stir deposition (AFSD) to repair corroded steel bridge members. AFSD is an emerging technology that can deposit metals without melting and build a part layer by layer similar to 3D printing. Since this process uses relatively low temperatures, the deposited material is not melted thus reducing issues associated with rapid solidification of melted metal. Three studies were conducted to better understand the print quality of AFSD on corroded steel. First, steel was deposited onto a surface with varying sized holes drilled to different depths meant to simulate a corroded surface. Second, a high-strength corrosion-resistant steel was deposited onto a corroded steel plate cut from an old bridge. Last, steel was deposited onto a steel plate with varying prepared surfaces including paint and corrosion. The quality of the depositions was studied through microscopy and mechanical testing. Results from these tests indicated the following: AFSD can sufficiently bond two different types of steels; depositing onto a non-level surface appeared to aid bonding between the two steels; and finally, AFSD can deposit steel onto certain unclean surfaces.

<div>This work investigates several uses of additive manufacturing to meet modern security-related needs. All energetic materials when integrated in a practical system require an ignition device, e.g. a bridgewire or spark gap igniter, which is traditionally fabricated from metal components. A conductive polymer, polyaniline,</div><div>was chosen to create metal-free spark gap igniters in a process that lends itself well to large-scale manufacturing. The igniters proved consistent in terms of breakdown</div><div>voltage, as well as their effectiveness in igniting nanothermite, a representative energetic material. This work also establishes a simple and effective approach suitable for the precise material deposition of CL-20. This is relevant for the development of trace detection calibration standards. This work shows that CL-20 is compatible with inkjet</div><div>printing for this purpose. Furthermore, the need to secure sensitive information that is stored locally on electronic devices led to the study of the use of confined nanothermite to damage substrates used in electronics. The maximum thickness of PCB that permitted destruction with repeatable results was investigated o suggest a baseline for future system integration and production. In addition, the stress of the board was modeled using measured thrust data. In brief, this work has proven that the use of additive manufacturing with energetic materials is both a possible and effective means to secure devices, should a device containing sensitive material be unintentionally misplaced.</div>

Indiana University-Purdue University Indianapolis (IUPUI) / One of the primary challenges faced in Additive Manufacturing (AM) is reducing the overall cost and printing time. A critical factor in cost and time reduction is post-processing of 3D printed (3DP) parts, which includes removing support structures. Support is needed to prevent the collapse of the part or certain areas under its own weight during the 3D printing process. Currently, the design of self-supported 3DP parts follows experimental trials. A trial and error process is needed to produce high quality parts by Fused Depositing Modeling (FDM). An example for a chamfer angle, is the common use of 45 degree angle in the AM process. Surfaces that are more flat show defects than inclined surfaces, and therefore a numerical model is needed. The model can predict the problematic areas at a print, reducing the experimental prints and providing a higher number of usable parts. Physical-based models have not been established due to the generally unknown properties of the material during the AM process. With simulations it is possible to simulate the part at different temperatures with a variety of other parameters that have influence on the behavior of the model. In this research, analytic calculations and physical tests are carried out to determine the material properties of the thermoplastic polymer Acrylonitrile - Butadiene - Styrene (ABS) for FDM at the time of extrusion. This means that the ABS is going to be extruded at 200C to 245C and is a viscus material during part construction. Using the results from the physical and analytical models, i.e., Timoshenko’s modified beam theory for micro structures, a numerical material model is established to simulate the filament deformation once it is deposited onto the part. Experiments were also used to find the threshold for different geometric specifications, which could then be applied to the numerical model to improve the accuracy of the simulation. The result of the nonlinear finite element analysis is compared to experiments to show the correlation between the prediction of deflection in simulation and the actual deflection measured in physical experiments. A case study was conducted using an application that optimizes topology of complex geometries. After modeling and simulating the optimized part, areas of defect and errors were determined in the simulation, then verified and and measured with actual 3D prints.

Additive friction stir deposition (AFSD) is a solid-state additive manufacturing (AM) technique that breaks down large constituent particles into more refined and uniformly disturbed microstructure. AFSD was used to print Al-Ce alloys. Current commercial Al-alloys upon elevated temperatures go through dissolution and coarsening of strengthening precipitates causing mechanical degradation of these alloys. Al-Ce alloys do not have this issue as cerium's low solubility restricts dissolution into the aluminum matrix at elevated temperatures, thus giving great thermal stability to the microstructure. Al-Ce alloys lack solid solubility that affects the solid solution strengthening and precipitation strengthening. Al-Ce alloys have limitation at room temperature as they can only reach a maximum of ~65 MPa yield strength. Elements like magnesium have been added to alloy to enable solid solution strengthening, and scandium to enable precipitation strengthening to improve strength before going through the AFSD process. By adding new elements to the Al-Ce alloys, an increase in the yield strength from ~60 MPa to ~200 MPa was achieved before AFSD. The casted alloys form coarse particles that reach 300 µm in size; resulting in stress concentration that causes material fracture before necking, giving >10% ductility. AFSD breaks down these coarse particles to increase strength and ductility increases. The particles were broken down to >20 µm which increased the ductility to 10%. The results of this research shows that Al-Ce alloys are able to reach commercial aluminum alloy mechanical standards of 400 MPa ultimate tensile strength and 10% ductility at room temperature for aerospace applications.

<p dir="ltr">Though vat photopolymerization-based Additive manufacturing (AM) technology shows potential in fabricating complex optical components rapidly, its poor surface quality and dimensional accuracy render it unqualified for industrial optics applications. The layer steps in the building direction and the pixelated steps on each layer’s contour result in inevitable microscale defects on the 3D-printed surface, far away from the nanoscale roughness required for optics.</p><p dir="ltr">To tackle the lateral stair-stepping issue caused by the pixelated projection pattern, we propose to defocus the curing image pattern by increasing the gap between the light source and the resin vat. This gap intentionally blurs the disconnected pixels to create a continuous and smooth projection pattern. Experiments verified that the smoothened image pattern led to an average 81.2% reduction in surface roughness, which was much more effective than grayscale pixels. The gap between the light source screen and the resin vat also enabled blowing air to dissipate the heat from the resin polymerization, reducing the part distortion and printing failure due to the thermal stress.</p><p dir="ltr">The precision spin coating process is reported to solve vertical stair-stepping defects. We establish a mathematical model to predict and control the spin coating process on 3D-printed surfaces precisely. In this work, a precision aspherical lens is demonstrated with less than 1 nm surface roughness and 1 µm profile accuracy. The 3D-printed convex lens achieves a maximum MTF resolution of 347.7 lp/mm.</p><p dir="ltr">Leveraging this low-cost yet highly robust and repeatable 3D printing process, we showcase the precision fabrication of multi-scale spherical, aspherical, and axicon lenses with sizes ranging from 3 mm to 70 mm using high clear photocuring resins. Additionally, molds were also printed to form multi-scale PDMS-based lenses. Following precision polishing, precision machining, and precision molding, we anticipate that precision spin coating will empower 3D printing as the fourth generation of lens making and unleash the power of 3D-printed lenses in rapid and massive customization of high-quality optical components and systems.</p>

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The study presents a normative framework for the Additive Manufacturing (AM) implementation process in the UK manufacturing sector. The motivations for the study include the lack of socio-technical studies on the AM implementation process and the need for existing and potential future project managers to have an implementation model to guide their efforts in implementing these relatively new and potentially disruptive technologies. The study has been conducted through case research with the primary data collected through the in-depth semi-structured interviews with AM project managers. Seven case studies were conducted representing AM implementation practice at different stages of the implementation cycle. The first stage involved a pilot study at a post-implementer to identify the main areas of interest for AM implementation research. The second involved a wider study of AM implementers at the post-implementation stage with cross case analysis of implementation practice. The final stage involved an investigation into pre-implementation of AM, applying the proposed framework in three companies yet to fully implement AM as a production method. Contribution towards the existing body of literature was in the form of a normative framework for AM implementation in a variety of industrial sectors. The framework describes the main activities in the implementation process and supports a taxonomy of implementers.

This dissertation presents a thesis on the use of additive manufacturing in the development and evaluation of a computer-assisted system for wrist-fracture repair. The work developed tools for performing navigated wrist surgery, developed methods for evaluating surgical performance, and provided novel experience with model-based surgical evaluation. Patient-derived bone models, fabricated using additive manufacturing, were proposed as an alternative to cadaver specimens for testing and validating the new surgical system. The accuracy of fabricating these models from computed-tomography imaging was investigated using laser scanning and was found to be reproducible to within half a millimeter. Three generations of a surgical system for navigated wrist-fracture repair were developed and evaluated using a wrist model that was produced by additive manufacturing. Compared to cadaver specimens, the model was less expensive and performed equally well under simulated surgical conditions. The model-based evaluation permitted larger study sizes that increased the statistical power of the experimental results. Criteria for surgical performance included surgical and technical measurement of screw placement. The navigation system was superior in optimizing screw placement compared to conventional surgical methods. Navigation also reduced the risk of radiation exposure and clinical complications of wrist-fracture repair. Surgical tools, including a drill guide and wrist-stabilization device were developed with the use of additive manufacturing. Prototype devices could be quickly and economically fabricated for testing under realistic conditions. A system for performing navigated wrist fracture repair was successfully developed through the use of additive-manufacturing prototyping and evaluation. Additive manufacturing was integral to the successful evaluation of the system's improvement in performance. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2012-12-19 11:40:46.269

Additive Manufacturing (AM) is a class of echnologies whereby components are made in an additive, layer-by-layer fashion enabling production of complex parts in which complexity has little or no effect on cost. However typical components roduced using these techniques are basic structural items with no major strength requirement and low geometric tolerances made from a single material. his thesis develops a low-cost Fused Filament abrication (FFF) based AM technique to produce functional parts. This is achieved by through esearching and implementing new materials in ombination and using precise control of infill tool paths for existing materials. Robocasting has previously been shown to be extremely versatile, however is known to offer poorer build quality relative to its ess-versatile counterparts. Research was ndertaken to enable Robocasting to be combined with FFF to enable the print quality and practical benefits of FFF with the material flexibility of Robocasting. This resulted in the manufacture of several multiple-material omponents using the technique to demonstrate its potential. In order to minimise the number of materials required to obtain desired properties, the effect of process parameters such as layer height, infill angle, and infill porosity were investigated. In total over an order of agnitude variation in Young’s modulus and tensile strength were achieved, enabling these properties to be actively controlled within the manufactured components. Finally a novel non-eutectic low melting point alloy was developed to be compatible with the FFF process. Its greater viscosity compared to traditional eutectics resulted in improved print quality and the reliable deposition of electrically conductive track 0.57x0.25mm in cross-section. In addition the material is approximately three orders of magnitude more conductive that typical printable organic inks. A micro-controller was produced using the technique in conjunction with traditional electronics components. This represents the first time a functional electrical circuitry, with sufficient conductivity for the majority of applications and interfacing directly with standard electrical components, has been produced using a very low-cost AM technique such as FFF. The research undertaken builds components with substantially improved functionality relative to traditional AM products, enabling electromechanical components with varying mechanical and electrical properties. It is anticipated that this could substantially reduce the part-count for many engineering assemblies and open up Additive Manufacturing to many new applications.

Ductal Carcinoma in Situ (DCIS) does not have a clinically useful indicator of malignancy, and it is often benign, except in 20% of cases. Even more important, it has a cure – removal of the affected breast. DCIS patients overwhelmingly elect for invasive therapies to escape that 20% malignant chance. Overtreatment such as this costs the patients, and it highlights the need for a DCIS model capable of distinguishing the 20% in need of treatment. Some labs have taken steps toward three-dimensional, complex, and biomimetic models of mammary tissues using a variety of endogenous and synthetic gels and 3D printing. We developed FRESH (Freeform Reversible Embedding of Suspended Hydrogels) as the first method capable of 3D printing highly biomimetic shapes from endogenous gels. Utilizing FRESH, we aim to rapid prototype models of mammary duct epithelia that are biomimetic, parametric, and capable of iterative evolution. First, we investigate the principles of 3D printers modified for extruding fluids and construct a comprehensive hardware and software platform for printing gelling fluids. Second, we apply the FRESH method to 3D print collagen and alginate hydrogels, demonstrating patency of printed vascular models, topological fidelity, and the synergistic combination of hydrogel properties in multi-material prints. Finally, we rapid prototype an epithelial monolayer by seeding a 3D printed collagen manifold, and we demonstrate maintenance of the tissue’s geometry across a week of culture. We provide evidence of fidelity in prints such as an epithelial tree printed at 200% scale using unmodified collagen type I, and we investigate the combination of hydrogel properties in multi-material prints by utilizing a second hydrogel (alginate) to reinforce and preserve the fidelity of this collagen tree during handling. Our approach utilizes faster (>40 mm/s), cheaper (