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This work seeks to characterize the impact of build interruptions to additively manufactured Al-Si-10-Mg produced by the powder bed fusion (PBF) process. Additive manufacturing represents a significant investment in overhead, machine, and material making an interruption to the process a potential waste of money and time. Interruptions in the form of power outages, lack of powdered feedstock, and/or shielding gas will cause the machine to operate in an unintended manner, potentially even stopping the build process. The process of manufacturing will influence the microstructure, which determine the material’s properties and performance. An interrupted PBF process could exhibit unique microstructural features and reduced mechanical properties that distinguish the resulting material from a continuous PBF process. Experiments were performed to simulate a production interruption with varying time periods of interruption and air exposure. The zone of interruption was characterized using optical micrographs, EDS, and hardness measurements to determine any effects of the interruption.

It was accidentally discovered in the 1940s that the addition of lead to double-base propellants, resulted in beneficial burn rate phenomena. However, due to its toxicity the Department of Defense has been trying to find a replacement for lead over the last decade. Research efforts with this goal in mind have generally used the same methodology of either adding different metals, using different grain sizes, or using different concentrations to obtain the same burn rate effects as lead. Although some metal oxides demonstrated significant promise, they also depleted the double-base propellant stabilizer faster than acceptable, decreasing shelf life. The research explored herein does not take the same approach, but rather attempts to replace lead and solve the stability problem at the molecular level using a novel design. The new method was to synthesize a stabilizer ligand complex with a less toxic metal to create a complex that both stabilized the propellant and provides a burn rate modifying agent. First, the synthesises of two leaded complexes, tetrakis (µ3-(4-methyl-3-nitrophenyl imido lead (II))) and bis(dinitrophenyl imido lead(II)) are reported as both a proof of concept and to determine a feasible synthetic pathway. After various unsuccessful attempts using common stabilizer molecules as ligands, n-phenylurea was identified as a suitable analogous stabilizer molecule and was bonded to a cobalt center to create hexa-1-phenylurea cobalt(II) nitrate. Additionally and serendipitously, unreported complexes of metal ions with dicyanamide were discovered, which generated a discussion between ligand strength and metal center. Each of the complexes are characterized in depth and many physical properties determined. / Chemistry

<p> Rising costs and volatility in aviation fuel and increased regulations resulting from climate change  concerns have driven gas turbine engine manufacturers to focus on reducing fuel consumption.  Implementing centrifugal compressors as the last stage in an axial engine architecture allows for  reduced core diameters and higher fuel efficiencies. However, a centrifugal compressor's  performance relies heavily on its stationary diffusion system. Furthermore, the highly unsteady  and turbulent flow field exhibited in the diffusion system often causes CFD models to fall short of  reality. Therefore, rapid validation is required to match the speed at which engineers can simulate  different diffuser designs utilizing CFD. One avenue for this is through the use of additive  manufacturing in centrifugal compressor experimental research. This study focused on implementing a new generation of the Centrifugal Stage for Aerodynamic  Research (CSTAR) at the Purdue Compressor Research Lab that utilizes an entirely additively  manufactured diffusion system. In addition, the new configuration was used to showcase the  benefits of additive manufacturing (AM) in evaluating diffusion components. Two diffusion  systems were manufactured and assessed. The Build 2 diffusion system introduced significant  modifications to the diffusion system compared to the Build 1 design. The modifications included changes to the diffuser vane geometry, endwall divergence, and increased deswirl pinch and vane  geometries. The Build 2 diffusion system showed performance reductions in total and static  pressure rise, flow range, and efficiencies. These results were primarily attributed to the changes  made to the Build 2 diffuser. The end wall divergence resulted in end wall separation that caused  increased losses. The changes to the diffuser vane resulted in increased throat blockage and lower  pressure rise and mass flow rate. In addition to the experimental portion of this study, a computational study was conducted to study  the design changes made to the Build 2 diffusion system. A speedline at 100% corrected rotational  speed was solved, and the results were compared to experimental data. The simulated data matched  the overall stage and diffusion system performance relatively well, but the internal flow fields of  the diffusion components, namely the diffuser, were not well predicted. This was attributed to  16 using the SST turbulence model over BSL EARSM. The BSL EARSM model more accurately  predicted the diffuser flow field to the SST model.  </p>

Triply Periodic Co-continuous piezocomposites, which consist of a ferroelectric-ceramic phase and an elastic-polymer phase continuously interconnected in three dimensions (3D), are emerging flexible piezoelectric materials with high efficiency in absorbing and converting multi-directional mechanical stimuli into electrical signals. Current co-continuous piezocomposites cannot be achieved with controlled piezoelectric properties due to the limited capability of traditional fabrication methods in carefully controlling the morphology of each phase, additive manufacturing such as Suspension-Enclosing Projection-Stereolithography process thus was selected. Porous ceramic skeleton with randomly distributed grain size is commonly observed in sintered ceramic skeleton fabricated by additive manufacturing. The effective piezoelectric properties of the piezocomposites were thus studied utilizing a two-scale method. Through analyzing the simulated results of different process parameters, optimal parameters of 3D printing processes including post-processes was subsequently suggested.

Spring hunting season for wild turkey (Meleagris gallopavo) in Mississippi is designed to coincide with peak gobbling activity. The Mississippi Department of Wildlife, Fisheries and Parks (MDWFP) uses brood surveys and hunter observations to forecast gobbling activity. Hunters claimed hunting season does not coincide with regional gobbling peaks. I conducted statewide surveys to assess latitudinal and climatic influences in gobbling activity and used long-term (1996-2008) MDWFP data to evaluate use as a forecasting tool. I observed ≥ 66% of all spring gobbling with an approximate 2-week difference in peak gobbling activity between northern and southern Mississippi. Gobbling in the north was influenced by temperature, wind speed, and cloud cover; in the south, only cloud cover. Long-term data performed poorly predicting gobbling activity (R2 = 0.02 – 0.047, regionally; R2 = 0.06 – 0.09, statewide). Spring hunting season captures most gobbling, including peaks. Data sources should be used cautiously to forecast gobbling activity.

Composite materials have increasingly been used as an alternative to metals and other isotropic materials for primary structural components in aerospace industries. Unlike traditional isotropic materials, composite materials are known to have complex internal microstructures. Therefore, it is essential to develop methods for the inspection, evaluation, and monitoring of composite materials. Ultrasonic-guided waves and, more precisely, Lamb waves have proven to be an efficient and accurate technique for the non-destructive testing. Since guided waves are dispersive and multimodal, it is important to develop a practical method to manipulate Lamb waves to achieve better structural health monitoring and non-destructive inspection results. There are minimal studies involving manipulating guided waves for the inspection of composite materials. Moreover, the currently proposed methods to manipulate Lamb waves are complex and costly. The objective of this dissertation research is to offer practical and straightforward methods with a simple design to control Lamb waves using additively manufactured lenses used as superstrates on composite plates. This dissertation is organized in three major parts. Part I focuses on the Lamb wave propagation in composite plates with different lay-up and plate orientations. Finite element simulations were performed to investigate the behavior of Lamb wave propagation in different plates. A semi-finite element approach was used to derive the dispersive curves in each plate. In Part II, a lap-joint study was conducted to investigate the interaction of Lamb waves in the lap joint regions. Two different lap joints were considered, composite-aluminum and composite-plastic. In each lap joint the thickness of the top surface (aluminum or plastic) is continuously increased. In Part III, additively manufactured lenses are designed to modulate the wavefront of Lamb waves in thick composite plates. The first design is a prism-shaped lens proposed to steer Lamb waves to a targeted direction. Multiple prism designs are considered to offer a flexible steering direction by either changing the prism thickness or the wedge angle. The second design is a plano-concave shaped lens designed to focus the Lamb wave at a targeted focal point. This dissertation research will provide a clear understanding of Lamb wave propagation in anisotropic material, anisotropic-isotropic lap joints, and wavefront modulation on anisotropic material using additively manufactured lenses. This approach contributes to the development of better quality SHM for online monitoring systems.