Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 2007. / Thesis Advisor(s): Alexander L. Julian, William B. Maier. "March 2007." Includes bibliographical references (p. 53). Also available in print.

Approved for public release; distribution is unlimited / Theory and simulations of the railgun and free electron laser are presented, as well as a suggestion for extending the railgun lifecycle. The theory, design, and analysis of an electromagnetic railgun using a numerical model are discussed. The effects of varying electrical pulse formations, rail materials and geometries are explored. The application of a metallurgical process to mitigate hypervelocity gouging in railgun rails is proposed. This concept, to delay the onset velocity of gouging by laser-peening rails surfaces, may significantly increase the velocity at which projectiles acceptably traverse the barrel and extend the useful life of rails. If successful, this process would apply to any pair of materials in sliding contact at high relative velocity, including rocket sled tracks and light gas guns barrels. The status of proof-of-concept tests at LLNL, UC Davis, and UT is covered. FEL simulations investigating the effect that electron beam focal point variations have on the optical mode within the undulator are presented. / Lieutenant, United States Navy

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, June 2004. / Thesis advisor(s): William B. Colson. Includes bibliographical references (p. 49). Also available online.

Thesis (M.S. in Systems Technology)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Orin Marvel, Curt Schleher. Includes bibliographical references (p. 71-74). Also available online.

Thesis (M.S. in Systems Technology)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Orin Marvel, Curt Schleher. Includes bibliographical references (p. 71-74). Also available online.

Additive manufacturing (AM) provides unique opportunities to push the boundaries of material properties and free form fabrication. However with this novel manufacturing technique a number of defects not commonly found in conventional processes such as machining or casting can arise. Both experimental and numerical studies can help better understand the printed material on a more fundamental level in order to optimize the process and mitigate these defects. Electron microscopy can provide essential information about the as-built microstructure and characteristic defects while numerical modelling can help determine a correlation between process parameters and the resulting properties. First, an initial investigation of directed energy deposition (DED) processed 4140 steel was conducted using various microscopy methods to better understand the defects and microstructure of the printed alloy. A martensite dominate microstructure within a bainitic matrix with increasing degrees of tempering further down the build was revealed. Additional sample preparation was conducted with a focused ion beam and analyzed with the transmission electron microscope to investigate features such as grain boundaries, mechanical twins and interplanar spacing. This interplanar spacing was measured for a number of different diffraction images and compared with the theoretical values. The deviation between the measured and theoretical values can be attributed to defects such as residual stress which causes lattice strain and consequently a smaller or larger spacing between atomic planes. Lastly, diffraction images were characterized and compared with the literature to determine the Miller indices and the specific zone axis orientations. A thermo-mechanical-metallurgical finite element model for 42CrMo4 steel was then developed in ABAQUS to identify the correlation between processing parameters and resulting properties by predicting the temperature history, and resulting residual stresses and metallurgical phase fractions for the DED process. A pre-processing framework was implemented in order to allow the modelling of complex geometries and laser trajectories while experiments were conducted to validate the fidelity of the model. Four separate cases were fabricated with varying processing parameters and geometries. In addition to in-situ temperature measurements, post-build residual stress and substrate distortion data was also collected. Furthermore, metallurgical analysis was performed for each case and compared with the simulated phase fractions. The accuracy of the distortion profile increased with increasing dwell time while the accuracy in predicting the metallurgical phase fractions and residual stresses demonstrated the opposite trend. / Graduate / 2022-07-05

Multi-material structures (MMSs) are attractive due to their unique advantages in achieving tailored properties at different locations in a single part. Producing such structures by additive manufacturing has been gaining more and more attention because of the beneficial characteristics of additive manufacturing processes such as its ability in building complex geometries, shortening producing chains, and most importantly, easily integrating with multi-material feeding systems. This PhD thesis investigates the potential of MMSs fabricated by directed energy deposition (DED) using tool steel and copper alloy. Specifically, AISI H13 hot work tool steel is deposited on copper-beryllium alloy (CuBe) substrate using three deposition strategies: directly depositing H13 on CuBe (H13/CuBe), SS316L buffer (H13/SS316L/CuBe), and commercially pure nickel buffer (H13/Ni/CuBe), aiming to minimize cracking issues. The morphology of single-track, single-layer, and multi-layer specimens is analyzed. The microstructure of deposited specimens is also investigated, along with its mechanical and thermal properties, such as microhardness, wear resistance, load-bearing capability (LBC), and thermal conductivity. The results show that directly depositing H13 on CuBe cannot avoid cracking in the H13 layers while preheating the CuBe substrate at 150°C and 250°C reduces the cracking tendency but damages the strength of the CuBe substrate due to over-aging while introducing difficulty to manage processing procedure. Using SS316L buffer can suppress the crack extension in H13 cladding due to a barrier mechanism, i.e., its ability to reduce the Cu penetration into H13 layers. However, SS316L itself is prone to cracking when directly deposited on the CuBe substrate as a buffer layer. Through analysis of cracking morphology, parameter effects, and element distribution, it was possible to identify solidification cracking as the primary cracking mechanism in all specimens. Two metallurgical factors, solidification temperature range and amount of terminal liquid, were found to dominate the cracking tendency. The introduction of Cu into steel can significantly extend the solidification temperature range, thereby increasing the susceptibility to cracking. However, as the Cu composition continuously increases, the cracking susceptibility decreases due to the backfilling of the terminal liquid into cracks resulting in a healing effect. The solidification paths of the Fe-Cu binary system were calculated as a function of Cu composition. Using this data, a map was generated reporting the solidification temperature range and terminal liquid amount as a function of Cu composition for the Fe-Cu binary system. Even if only to a first approximation (the effect of alloying elements in both, steel and CuBe alloy), this map can be used as a tool to estimate the cracking susceptibility of steel/copper alloy MMSs deposited by DED. The experimental results are in good agreement with thermodynamic calculations. Based on this analysis, a pure nickel buffer strategy was selected and proved to be effective in minimizing the cracking issue in H13 due to the narrow solidification temperature range of Ni-Cu and Ni-Fe binary systems induced the high solubility of Ni in Fe and Cu. By employing this strategy, crack-free specimens were produced. The high hardness of the H13 single-layer cladding, with an average value of 740 HV, provided a significant improvement in wear resistance compared to the CuBe (400 HV). However, in multi-layer specimens, a gradual decrease in microhardness of H13 cladding from the outer to the inner layers was observed due to the mixing of remelted soft buffer materials into H13 and the in-situ tempering effect in the previous deposited H13 layers. The above result, further confirms that the load-bearing capability (LBC) cannot be infinitely improved by adding more H13 layers. In general, in the low loading range (From 5 to 10 kN), the LBC of MMS specimens was higher than the CuBe due to the higher hardness of outer H13 layers. However, it became lower in the high loading range due to the presence of soft sublayer materials such as softened martensite, soft buffer layers (H316L = 260 HV or HNi = 130 HV), and the heat-affected zones in the CuBe substrate. The thermal conductivity of MMS specimens first drops rapidly to half of the original value as the cladding thickness ratio (tcladding/tCuBe) increases from 0 to around 20%. After that, the decrease becomes slower, with a further reduction of around 37% in thermal conductivity as the cladding thickness ratio increases from 20% up to 50%. Therefore, a tradeoff between mechanical and thermal properties must be considered looking for the application of these cladding systems. A proper cladding thickness ratio of around 20% is recommended to achieve reasonably high strength while still maintaining thermal conductivity at an acceptable level. Overall, these findings have important implications for the selection of appropriate materials and processing parameters to optimize the mechanical and thermal properties of tool steel/copper alloy MMSs deposited by DED.

As directed energy technology continues to evolve and become a viable weapon alternative, a need exists to investigate the impacts of these applications without a "plug-and-check" method, but rather with an analysis governed by fundamental principles. This thesis examines the transient thermal loads that a high-energy weapon system introduces into a high performance aircraft using fundamental thermodynamic and heat transfer analyses. The high-energy weapon system employed in this research contains power storage, power conditioning equipment, optics, and a solid-state laser. The high-energy weapon system is integrated into the aircraft by a dedicated thermal management system connected to the onboard air and fuel fluid networks. The dedicated thermal management system includes heat exchangers, thermal storage, microchannel coolers, valves, and pumps. Governing equations for the electric directed energy weapon subsystem and thermal management system are formulated for each system component and modeled in Mathwork's Simulink™. System models are integrated into a generic, high-performance aircraft model created as part of the Air Force Research Laboratory's Integrated Vehicle Energy Technology Demonstration (INVENT) program. The aircraft model performs a defined mission profile, firing the directed energy weapon during the high-altitude, transonic cruise segment. When firing a 100-kilowatt directed energy weapon system operating at 16.9% efficiency, large thermal transients quickly heat downstream onboard systems. Real-time heat rejection causes temperature spikes in avionic and environment systems that exceed allowable operation constraints. The addition of thermal storage to the thermal management system mitigates thermal impacts downstream of the directed energy weapon by delaying the time thermal loads are rejected to aircraft, thereby reducing peak and average loads. Although thermal storage is shown to mitigate peak loads in downstream onboard systems, thermal closure is yet to be achieved. This research presents a general and fundamental approach to investigating the thermal impacts of a directed energy weapon system on a high-performance aircraft. Although specific cases are analyzed, this general approach to model development and simulation is conducive to component and system customization for many other cases. Additionally, the supplementation of models with analytical, semi-empirical, and empirical data further tailors model development to each user's need while increasing the potential to enhance accuracy and efficacy. Without the material expenses of a "plug-and-check" method, component and system level modeling of the directed energy weapon system and high-performance aircraft provides valuable insight into the thermal responses of highly-coupled systems. / Master of Science

Approved for public release, distribution is unlimited / An investigation of how fuel cells, an integrated power system, and directed energy weapons will affect the shipboard command and control process. The focus is on the implementation of the new technologies onboard near-term and far-term destroyer variants and the resulting changes to the command and control process. / Ensign, United States Naval Reserve

Die generative Fertigung stellt eine Schlüsseltechnologie der Zukunft für weite Teile der Wirtschaft dar. Der Prozess des Plasma-Pulver-Auftragschweißens soll eine Lücke im bestehenden Portfolio an generativen Prozessen schließen. Zunächst wurde der klassische Beschichtungsprozess an die Erfordernisse der generativen Fertigung angepasst. Im Ergebnis konnten Bauteile, welche aus bis zu vier verschiedenen Materialen bestehen können, prozesssicher generiert werden. Die anschließende Betrachtung des Einflusses der Systemparameter auf das Bauteil ergab, dass die Haupteinflussgrößen auf die Bauteilgeometrie die Schweißstromstärke, die Schweißgeschwindigkeit, der Pulvermassestrom sowie die Plasmagasmenge sind. Die Bauteildichte sowie der Pulverausnutzungsgrad zeigen keine signifikanten Änderungen innerhalb des hier betrachteten Bereiches. Im Mittel konnte eine relative Bauteildichte von 98,7 % und ein Materialausnutzungsgrad von 77 % bestimmt werden. In Summe ist der Prozess durch eine stabile Auftragscharakteristik mit mindestens vergleichbaren Eigenschaften zu bestehenden Systemen zu bewerten und sehr gut als generativer Prozess, insbesondere für die Herstellung von mehrkomponentigen Bauteilen, geeignet. / Additive manufacturing is one of the key technologies of the future for large parts of the economy. The process of plasma powder deposition welding is intended to close a gap in the existing portfolio of generative processes. First, the classical cladding process was adapted to the requirements of additive manufacturing. As a result, components, which can consist of up to four different materials, could be reliably generated. The subsequent consideration of the influence of the system parameters on the component showed that the main influencing variables on the part geometry are the welding current, the welding speed, the powder flow rate and the plasma gas volume. The component density as well as the powder utilization rate show no significant changes within the range considered here. On average, a relative component density of 98.7 % and a material utilization rate of 77 % could be determined. In sum, the process can be characterized by a stable application characteristic with at least comparable properties to existing systems and is very well suitable as an additive manufacturing process, especially for the production of multi material components.