A two-scale model consisting of ceramic grain scale and composite scale are developed to systematically evaluate the effects of microstructures (e.g., residual pores, grain size, texture) and geometry on the piezoelectric responses of the polarized triply periodic bi-continuous (TPC) piezocomposites. These TPC piezocomposites were fabricated by a recently developed additive manufacturing (AM) process named suspension-enclosing projection-stereolithography (SEPS) under different process conditions. In the model, the Fourier spectral iterative perturbation method (FSIPM) and the finite element method will be adopted for the calculation at the grain and composite scale, respectively. On the grain scale, a DL approach based on stacked generative adversarial network (StackGAN-v2) is proposed to reconstruct microstructures. The presented modeling approach can reconstruct high-fidelity microstructures of additively manufactured piezoceramics with different resolutions, which are statistically equivalent to original microstructures either experimentally observed or numerically predicted. Design maps for hydrostatic piezoelectric charging coefficients dh show they can achieve optimal performance at wide ranges of micro-porosity and geometry parameter u for the proposed TPC piezocomposites. In addition, geometry parameter u plays a dominant role in determining the intensity of hydrostatic voltage coefficient gh and hydrostatic figure of merit (HFOM) of all the presented TPC piezocomposites in the vicinity of the starting point of three-dimension (3D) interconnectivity. Within this range, these properties would increase first with the increasing of micro-porosity volume fraction (VF) and start to decrease once they reach peak values. The presented TPC piezocomposites exhibit a superb hydrostatic properties, with the same 20% VF of ceramics and 2% VF of micro-porosity with respect to composites and ceramics, respectively, TPC of face center cubic (FCC) demonstrates 327-fold enhancement of HFOM than that of the piezocomposite with three intersecting ceramic cuboids. The piezoelectric properties of FCC are superior to those of body center cubic (BCC) and simple cubic (SC). The calculated piezoelectric charging constants d33 and relative permittivity κ33 were then compared with the data measured from the products fabricated by the SEPS under different process conditions. The calculation results at both grain scale and composite scale were found to agree well with experimental results.

<p>Thesis Abstract: Laser powder bed fusion (LPBF), a specialization within additive manufacturing, is a high precision metal powder processing technique that has gained immense attentions in the past decade. The layer-by-layer densification technique provides a unique set of abilities that permits the large-scale production of geometrically complicated structures with highly tunable microstructures. Alloy 718 (718) is one of the most studied materials within the LPBF field due to its extraordinary printability. Although it has a significant industrial and academic focus, there are consequential questions that still need to be addressed because of the immense LPBF design space.</p><p>Our works demonstrate the multiple pathways that an alloy system like 718 can be optimized for specific applications by altering the processing parameters or by the addition of oxide particles to create a fine dispersion for high temperature capabilities. Room temperature tensile testing revealed that the processing parameters directly controlled the mechanical properties, allowing tailoring of the tensile strength and elongation to the needs of specific applications. Similar experiments were conducted to exhibit the flexibility of LPBF by incorporating a wider, economic, bimodal powder size distribution that maintained similar mechanical properties. Additions of oxide particles enabled the findings of the reactive nature within this welding process, which ultimately led to a refined oxide dispersion strengthened (ODS) 718 matrix with superior mechanical properties up to 900$^\circ$C. This novel metal matrix ceramic was lastly showcased by producing a complex microlattice structure. Detailed in-situ tensile tests in combination with electron backscatter diffraction (EBSD) and finite element modeling revealed that crystallographic reorientation around bending nodes enhanced the global ductility of the material.</p>

<p>Fabricating complex submicron 3D structures can be achieved by multi-photon lithography, especially two-photon lithography is commonly used to obtain precision and flexibility in printing sophisticated sub-micron 3D structures. Several disadvantages stemmed from a two-photon lithography experiment setup, including cost, the necessity of a large laboratory space to use a femtosecond laser and a high-order process. A two-step absorption is chosen instead of two-photon lithography as a primary excitation process achieving the same degree of quadratic optical non- linearity as two-photon lithography at a lower cost with a relatively compact laboratory size. The working mechanism of Two-step absorption is the following. Quadratic nonlinearity comes from radicals from excited triplet states photoinitiators. Ground states of photoinitiators get excited by the incident laser. Those excited singlet photoinitiators go through the intersystem crossing, becoming the ground triplet state of photoinitiators. There are two branches after the ground triplet states, especially for photoinitiator benzil molecules with the incident laser on. Either it becomes a radical without photons received from the incident laser or gets excited again to an excited triplet state by the incident laser. Those excited triplet-state photoinitiator molecules become radicals that occur in polymerization. However, those from the ground triplet states add linearity to polymerization. When it comes to multiple exposures, the linearity becomes problematic, especially outside the region and tails of the voxel. For example, suppose the intensity at two tails of the voxel is 1% relative to the maximum intensity at the focal point. In that case, the absorbed dose will be added up to the maximum intensity at the focal point when it comes to 100 exposures. Quadratic nonlinearity and linearity are jumbled together in the current two-step absorption process. In this work, optimization of photoinitiator concentration was conducted to reduce the linearity. Confined and high throughput 3D structure fabrications are achieved by controlling initiator depletion. Simulations are also developed with multi-physics models to compare with the empirical results.</p>

No description available.

Additively manufactured parts produced using selective laser melting (SLM) are prone to defects created during the build process due to part shrinkage while cooling. Currently defects are found only after the part is removed from the printer. To determine whether cracks can be detected before a print is completed, this project developed print parameters to print a test coupon with inherent defects – warpage and cracking. Data recorded during the build was then characterized to determine when the defects occurred. The test coupon was printed using two sets of print parameters developed to control the severity of warpage and cracking. The builds were monitored using an accelerometer recording at 12500 samples per second, an iphone recording audio at 48000 samples a second, and a camera taking a photo every build layer. Data was analyzed using image comparison, signal amplitude, Fourier Transform, and Wavelet Decomposition. The developed print parameters reduced warpage in the part by better distributing heat throughout the build envelope. Reducing warpage enabled the lower portion of the part to be printed intact, preserving it to experience cracking later in the build. From physical evidence on the part as well as time stamps from the machine script, several high energy impulse events in the accelerometer data were determined to be when cracking occurred in the build. This project’s preliminary investigation of accelerometers to detect defects in selective laser melting will be used in future work to create machine learning algorithms that would control the machine in real time and address defects as they arise.

No description available.

Projektet syftar till att föreslå en rimlig riktning för hur additiva produktionsmetoder, alltså tillverkningsmetoder som använder lager-på-lager-teknik, kan tänkas påverka arkitekturen, att försöka sätta sig in i teknikerna och komma fram till vilken riktning som upplevs mest givande eller gångbar. Hur ska man nyttja potentialen med den nya tekniken på ett bra sätt? Jag har försökt ta fram en produkt som nyttjar potentialen hos de additiva produktionsmetoderna och som upplevs tänkbar för fullskalig realisering i byggsektorn i en närliggande framtid. Produkten består av en metod för framställning av en sandwichkonstruktion med hög trähalt och troligen lång livslängd. Metoden minskar byggsektorns klimatbelastning och kan ge stora rumsliga kvaliteter och formgivningsmöjligheter. Jag har genom fysiska experiment och utforskande av olika digitala fabrikationsmetoder försökt att visualisera och identifiera möjligheter med dessa nya tekniska hjälpmedel. Genom praktiska tester har jag prövat mina föreställningar av hur dessa metoder kan användas på effektiva sätt. Projektet vidga-des från att initialt omfatta additiva produktionsmetoder till att senare under tillämpningsfasen även omfatta digitala hjälpmedel såsom fotogrammetri och verktyg för parametrisk design. Projektet har resulterat i ett tillvägagångsätt för printning av cellulosabaserade sandwichkonstruktioner i printade formverk av återvinningsbar biokomposit. / The project aims to propose a direction for how additive manufacturing methods can influence architecture, to study the techniques and find out which direction could be perceived as most rewarding or viable. How to use the potential of the new technology in a good way? I have tried to develop a product that utilizes the potential of the additive manufacturing methods and which is conceivable for full-scale realization in the construction sector in the near future. The product consists of a method for producing long lasting sandwich constructions with high wood content. The method reduces the building industry's climate impact and can provide great spatial qualities and design possibilities. Through physical experiments and exploration of various digital fabrication methods, I have tried to visualize and identify possibilities with these new technological aids. Through practical tests, I have tested my ideas of how these methods can be used effectively. The project was expanded from initially studying additive production methods to, later during the application phase, also include digital aids such as photogrammetry and tools for parametric design. The project has resulted in a strategy for printing cellulose-based sandwich constructions in printed molds of recyclable biocomposite.

The growing popularity of additive manufacturing in commercial applications has al- lowed for new ideas and new ways of thinking when designing components. Further optimization at the component level is possible, though powder metallurgy is in its infancy. This study explores the possibility of using additive manufacturing to develop better labyrinth seals in turbomachinery. Labyrinth seals have a torturous fluid path with high losses, thus limiting the amount of fluid leakage. These types of seals can be non-rotating, allowing them to better take advantage of the additive manufacturing process due to the absence of rotating stresses. Labyrinth seal performance is defined by its ability to limit leakage through a seal. Investigations on the ability to reduce this leakage using the inherent roughness from the additive manufacturing process and the addition of complex geometry only capable of being produced by additive manufacturing are explored. Incompressible and compressible fluid models are utilized in the study. Perfectly smooth seals with tooth counts of four, six, and eight are first simulated using ANSYS FLUENT and compared to theoretical models to determine accuracy. Roughness is then applied to the seals and leakage decreases of 0.5% to 1.5% are experienced for the incompressible model. Decreases of 1.0% to 3.5% are experienced for the compressible model. Flow visualization and line analysis are conducted for all seals tested to understand how fluid flow is behaving within the clearance region of the seal and seal chambers. Several additive manufacturing geometries are simulated against a control seal to determine geometries with the largest effect on leakage rates. These geometries are then adapted to a six tooth seal and simulated with roughness. This additively manufactured seal is then compared to the smooth and rough six tooth seal for both incompressible and compressible fluids. Leakage was decreased by 5% to 8% for the incompressible model and 5% to 7% reductions for the compressible model when compared to the smooth seal. Flow visualization and line analysis were also conducted for the additively manufactured six tooth seal. A basic outline for an experiment and test stand were developed for future work.

Processing of ceramics has always been difficult due to how hard and brittle the material is. Fused Deposition of Ceramics (FDC) is a method of additive manufacturing which allows ceramic parts to be built layer by layer, abetting more complex geometries and avoiding the potential to fracture seen with processes such as grinding and milling. In the process of FDC, a polymeric binder system is mixed with ceramic powder for the printing of the part and then burned out to leave a fully ceramic part. This experiment investigates a new combination of materials, zirconia and acrylic binder, optimizing the process of making the material into a filament conducive to the printer system and then performing trials with the filament in the printer to assess its feasibility. Statistical analysis was used to determine optimal parameter levels using response surface methodology to pinpoint the material composition and temperature yielding the highest quality filament. It was discovered that although the mixture had adequate melting characteristics to be liquefied and printed into a part, the binder system did not provide the stiffness required to act as a piston to be fed through the printer head. Further studies should be completed continuing the investigation of zirconia and acrylic binder, but with added components to increase strength and rigidity of the filament.

Additive manufacturing (AM) fabricates complex geometries inaccessible through other manufacturing techniques. However, each AM platform imposes unique process-induced constraints which are not addressed by traditional polymeric materials. Vat photopolymerization (VP) represents a leading AM platform which yields high geometric resolution, surface finish, and isotropic mechanical properties. However, this process requires low viscosity (<20 Pa·s) photocurable liquids, which generally restricts the molecular weight of suitable VP precursors. This obstacle, in concert with the inability to polymerize high molecular weight polymers in the printer vat, effectively limits the molecular weight of linear network strands between crosslink points (Mc) and diminishes the mechanical and elastic performance of VP printed objects. Polymer colloids (latex) effectively decouple the relationship between viscosity and molecular weight by sequestering large polymer chains within discrete, non-continuous particles dispersed in water, thereby mitigating long-range entanglements throughout the colloid. Incorporation of photocrosslinking chemistry into the continuous, aqueous phase of latex combined photocurability with the rheological advantages of latex and yielded a high molecular weight precursor suitable for VP. Continuous-phase photocrosslinking generated a hydrogel scaffold network which surrounded the particles and yielded a solid "green body" structure. Photorheology elucidated rapid photocuring behavior and tunable green body storage moduli based on scaffold composition. Subsequent water removal and annealing promoted particle coalescence by penetration through the scaffold, demonstrating a novel approach to semiinterpenetrating network (sIPN) formation. The sIPN's retained the geometric shape of the photocured green body yet exhibited mechanical properties dominated by the high molecular weight latex polymer. Dynamic mechanical analysis (DMA) revealed shifting of the latex polymer and photocrosslinked scaffold T_g's to a common value, a well-established phenomenon due phasemixing in (s)IPN's. Tensile analysis confirmed elastic behavior and ultimate strains above 500% for printed styrene-butadiene rubber (SBR) latexes which confirmed the efficacy of this approach to print high performance elastomers. Further investigations probed the versatility of this approach to other polymer compositions and a broader range of latex thermal properties. Semibatch emulsion polymerization generated a systematic series of random copolymer latexes with varied compositional ratios of hexyl methacrylate (HMA) and methyl methacrylate (MMA), and thus established a platform for investigating the effect of latex particle thermal properties on this newly discovered latex photoprocessing approach. Incorporation of scaffold monomer, N-vinyl pyrrolidone (NVP), and crosslinker, N,N'-methylene bisacrylamide (MBAm), into the continuous, aqueous phase of each latex afforded tunable photocurability. Photorheology revealed higher storage moduli for green bodies embedded with glassy latex particles, suggesting a reinforcing effect. Post-cure processing elucidated the necessity to anneal the green bodies above the T_g of the polymer particles to promote flow and particle coalescence, which was evidenced by an optical transition from opaque to transparent upon loss of the light-scattering particle domains. Differential scanning calorimetry (DSC) provided a comparison of the thermal properties of each neat latex polymer with the corresponding sIPN. Another direction investigated the modularity of this approach to 3D print mixtures of dissimilar particles (hybrid colloids). Polymer-inorganic hybrid colloids containing SBR and silica nanoparticles provided a highly tunable route to printing elastomeric nanocomposite sIPN's. The bimodal particle size distribution introduced by the mixture of SBR (150 nm) and silica (12 nm) nanoparticles enabled tuning of colloid behavior to introduce yield-stress behavior at high particle concentrations. High-silica hybrid colloids therefore exhibited both a shear-induced reversible liquid-solid transition (indicated by a modulus crossover) and irreversible photocrosslinking, which established a unique processing window for UV-assisted direct ink write (UV-DIW) AM. Concentric cylinder rheology probed the yield-stress behavior of hybrid colloids at high particle concentrations which facilitated both the extrusion of these materials through the UV-DIW nozzle and the retention of their as-deposited shaped during printing. Photorheology confirmed rapid photocuring of all hybrid colloids to yield increased moduli capable of supporting subsequent layers. Scanning electron microscopy (SEM) confirmed well-dispersed silica aggregates in the nanocomposite sIPN's. DMA and tensile confirmed significant reinforcement of (thermo)mechanical properties as a result of silica incorporation. sIPN's with relative weight ratio of 30:70 silica:SBR achieved maximum strains above 300% and maximum strengths over 10 MPa. In a different approach to enhancing VP part mechanical properties, thiol-ene chemistry provided simultaneous linear chain extension and crosslinking in oligomeric diacrylate systems, providing tunable increases to Mc of the photocured networks. Hydrogenated polybutadiene diacrylate (HPBDA) oligomers provided the first example of hydrocarbon elastomer photopolymers for VP. 1,6-hexanedithiol provided a miscible dithiol chain extender which introduced linear thiol-ene chain extension to compete with acrylate crosslinking. DMA and tensile confirmed a decrease in T_g and increased strain-at-break with decreased crosslink density. Other work investigated the synthesis and characterization of first-ever phosphonium polyzwitterions. Free radical polymerization synthesized air-stable triarylphosphine-containing polymers and random copolymers from the monomer 4-(diphenylphosphino) styrene (DPPS). ³¹P NMR spectroscopy confirmed quantitative post-polymerization alkylation of pendant triarylphosphines to yield phosphonium ionomers and polyzwitterions. Systematic comparison of neutral, ionomer, and polyzwitterions elucidated significant (thermo)mechanical reinforcement by interactions between large phosphonium sulfobetaine dipoles. Broadband dielectric spectroscopy (BDS) confirmed the presence of these dipoles through significant increases in static dielectric content. Small-angle X-ray scattering (SAX) illustrated ionic domain formation for all charged polymers. / Doctor of Philosophy / Additive manufacturing (AM) revolutionizes the fabrication of complex geometries, however the utility of these 3D objects for real world applications remains hindered by characteristically poor mechanical properties. As a primary example, many AM process restrict the maximum viscosity of suitable materials which limits their molecular weight and mechanical properties. This dissertation encompasses the design of new photopolymers to circumvent this restriction and enhance the mechanical performance of printed materials, with an emphasis on elastomers. Primarily, my work investigated the use of latex polymer colloids, polymer particles dispersed in water, as a novel route to provide high molecular weight polymers necessary for elastic properties in a low viscosity, liquid form. The addition of photoreactive molecules into the aqueous phase of latex introduces the necessary photocurability for vat photopolymerization (VP) AM. Photocuring in the printer fabricates a three-dimensional object which comprises a hydrogel embedded with polymer particles. Upon drying, these particles coalesce by penetrating through the hydrogel scaffold without disrupting the printed shape and provide mechanical properties comparable with the high molecular weight latex polymer. As a result, this work introduces high molecular weight, high performance polymers to VP and reimagines latex applications beyond 2D coatings. Further investigations demonstrate the versatility of this approach beyond elastomers with successful implementations with glassy polymers and inorganic (silica) particles which yield nanocomposites.