Flow control has always been an intense research subject with the pursuit of favourable control effects like drag reduction, transition delay, and separation prevention. In practice, these flow control effects are achieved using mechanical actuators such as deflectors, vortex generators, transverse jets and so on. However, such mechanical actuators may face the drag penalty and limitation of actuation response time. In recent years, energy deposition has been suggested as a novel flow control technique in high-speed flow with preferable characteristics like non-intrusive, easy arrangement and high actuation frequency. The motivation of this work is to experimentally explore the flow behaviour after the certain amount of energy is deposited in Mach 5 flow. The energy deposition is implemented using a thermal bump (surface energy deposition) and laser beam focusing (volumetric energy deposition).This work starts with the development of a measurement technique of luminescent paint for the present challenging hypersonic testing environment, which is used for the further energy deposition experiment. The successes of the luminescent paint development is demonstrated both on two-dimensional and axisymmetric models. The luminescent paint shows high spatial resolution and the accuracy comparing to the pressure transducer reading. The surface energy deposition is performed using an embedded heating element (thermal bump) on a flat plate. Qualitative and quantitative measurement techniques are utilised to study the modification to the flow structure and the alteration to the distribution of pressure and heat transfer rate after thermal bump is activated. The results reveal the appearance of induced shock wave and suspicious vortices traces due to the activated thermal bump as reported in other literatures. Re-distribution of surface pressure and heat transfer rate are also found.For the volumetric energy deposition, the laser beam is firstly focused in quiescent air in order to understand the induced flow pattern and the impingement to a solid plate. High-speed schlieren photography is utilised to provide an insight to the dynamic evolution of the induced shock wave propagation and plasma kernel development after laser-induced air breakdown. Then, the laser energy deposition is conducted over a flat plate with the presence of Mach 5 flow. The outward motion of the induced shock wave significantly distorts the boundary layer and changes the surface pressure distribution. The results show the different pattern of boundary distortion when laser beam energy is deposited at different positions downstream of the leading edge of flat plate. The entire induced flow pattern is similar to those induced by a pulsed micro-jet. In spite of the laser pulse width of 4 ns, the entire dynamic process lasts about 100 μs.

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.

In der vorliegenden Arbeit wird ein Maschinenkonzept präsentiert, welches für die Additive Fertigung von großvolumigen Titanbauteilen speziell entwickelt wurdet. Hierbei wird mit den Direct-Energy_Deposition Verfahren das Bauteil in einer separaten Inertgasatmosphäre erzeugt. Zur Führung der Prozesstechnik soll erstmals ein Roboter verwendet werden, der ebenfalls in dieser Atmosphäre verbaut ist. Dieser ist allerdings schwierigen Bedingungen ausgesetzt, da die Spannungsfestigkeit sowie die Isolationsschwelle in Argon im Vergleich zu Luft drastisch reduziert sind.

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.

Under senare år har omfattande insatser gjorts för att främja mer hållbara flygtransporter i Europa. De konventionella tillverkningsmetoderna som används inom flyg- och rymdindustrin kräver betydande mängder råmaterial, vars utvinning, bearbetning och användning har negativa miljöeffekter. Därför finns det ett starkt incitament att utveckla nya, mer material-effektiva tillverkningsmetoder. Additiv tillverkning (AM), även känd som 3D-printining, har fördelen att direkt komma nära den slutliga formen på strukturer genom att lägga till material endast där det behövs, något som minimerar spill och förbättrar materialanvändningen. Dock utgör införandet av AM komponenter i säkerhetskritiska flyg- och rymdtillämpningar en betydande utmaning på grund av komplexiteten hos processerna. Denna komplexitet kan leda till tillverkningsvariationer som i sin tur kan resultera i defekter i de tillverkade strukturerna. Därför är framsteg inom automation genom utvecklingen av lösningar för övervakning och styrning under processens gång ett nödvändigt steg för att uppnå tillräcklig pålitlighet och repeterbarhet. Denna avhandling presenterar en utveckling av multisensorövervakning och styrning av Directed Energy Deposition (DED) med en laservärmekälla (LB). DED-LB är en avancerad teknik som möjliggör tillverkning av storskaliga metallkomponenter nära den slutliga formen. I detta arbete har lösningar undersökts för övervakning av DED-LB med tillsatspulver och tråd. För fallet med tillsatstråd kan denna kompletteras med resistiv förvärmning (så kallad hotwire), vilket ger möjlighet att ytterligare finjustera värmetillförseln och förbättra smältprocessen. För övervakningsändamål undersöktes tre olika in-situtekniker för processens stabilitet och varians. Maskinseende och elektriska givare användes för DED-LB med tillsatstråd (DED-LB/w), medan optisk spektroskopi användes för övervakning både av processen med tillsatspulver (DEDLB/p) samt med tråd. Ett multisensorsystem baserat på de tre teknologierna testades för DED-LB/w. Det kamerabaserade systemet gav tydliga indikationer på avvikelser från nominella processförhållanden. Spännings-och strömgivarnas signaler korrelerade med förändringar i processparametrar och återspeglade tydligt metallöverföringen. Spektrometersystemet indikerade förändringar relaterade till värmeöverföringen. Dessutom möjliggjorde analysen av erhållna spektra en detektering av förluster av viktiga legeringselement under DED-LB/p. Slutsatsen från resultaten understryker behovet av multisensorövervakning, eftersom det inte bara möjliggör detektering och skattning av processförändringar utan även en bättre förståelse av deras grundorsaker. Den presenterade ansatsen är ett viktigt bidrag i utvecklingen av ett framtida robust och feltolerant automatiskt styrsystem. / In recent years, an extensive effort has been made to leap European aviation towards more sustainable transportation. Conventional manufacturing methods used in aerospace industry require significant amounts of raw materials, whose extraction, processing, and utilization have adverse environmental impacts. Thus, there is a strong motivation to develop novel, more material efficient fabrication methods. Additive Manufacturing (AM), also known as 3D-printing, offers the advantage of manufacturing near-net-shape structures by adding material only where it is needed, minimizing waste, and improving material efficiency. However, introducing AM fabricated structures as components in safety-critical aerospace systems poses a significant challenge due to the inherent complexity of AM processes. This complexity can result in variations that may lead to defects or inconsistencies in the fabricated structures. Thus, increasing automation by developing in-process monitoring, and control solutions is the vital step to reach the necessary reliability and repeatability. This thesis presents development towards multi-sensor monitoring and control of Directed Energy Deposition (DED) using a Laser Beam (LB). DED-LB is an advanced technology that allows to manufacture large-scale, near-net-shape metallic parts. In this work, in-process monitoring solutions for DED-LB with feedstock powder and wire were investigated. The set-up of the latter was complemented by resistive pre-heating of the feedstock wire (hot-wire) which provided means of fine-tuning the heat input and improving metal fusion. Formonitoring purposes, three different in-situ techniques were investigated to monitor process stability and variability. Machine vision and electrical sensing were utilized during DED-LB with feedstock wire (DED-LB/w) depositions,while optical emission spectroscopy was used for monitoring processes with feedstock powder (DED-LB/p) as well as wire. A multi-sensorsystem based on the three sensing technologies was tested during DED-LB/w depositions. The vision system gave clear indications of variations from nominal conditions. Voltage and current sensors indications correlated to changes in process parameters and reflected well the metal transfer (liquid bridge) condition.The spectrometer system indicated well changes related to heat input. In addition, analysis of obtained spectra allowed to detect losses of vital alloying element during DED-LB/p. The main conclusion from the results underlines the need for simultaneous multi-sensor monitoring as it allows not only to detect and estimate process changes but also to better interpret their root causes. Such setup will positively enable a future robust, fault tolerant control system. / <p>Paper 3 is under acception but included in this thesis with CC BY-license.</p>

Research in radiotherapy for cancer treatment focuses on finding methods that can improve the compromise between tumour cell inactivation versus damage to the surrounding healthy tissue. As new radiation modalities such as proton therapy become accessible for everyday clinical practice, a better understanding of the variation in biological response of the tumour and healthy tissues would improve treatment planning to achieve optimal outcome. The development of radiobiological models capable of accurate predictions of biological effectiveness is needed. Existing radiation quality descriptors such as absorbed dose and LET are insufficient to explain variation in biological effectiveness for different treatment modalities. The stochastic nature of ionizing radiation creates discrete patterns of energy deposition (ED) sites which can now be analysed through sophisticated computer simulations (e.g. Monte Carlo track structure codes). This opens the possibility to develop a nanometre characterization of radiation quality based on the spatial cluster patterns of ED. The aim of this thesis is to investigate the track structure (ED spatial pattern) properties of several radiation qualities at a micro- and nanometric scale while exploring their influence in biological response through correlations with published experimental data. This work uses track structure data simulated for a set of 15 different radiation qualities: 4 commonly used brachytherapy sources, 6 different proton energies, 4 different carbon ion energies, and 60Co photons used as reference radiation for quantification of biological effectiveness. At a micrometre level, the behaviour of the microdosimetric spread in energy deposition for target sizes of the order of cell nuclei was analysed. The degree of the influence it had in the biological response was found to be negligible for photon sources but for protons and carbon ions the impact increased with decreasing particle energy suggesting it may be a confounding factor in biological response. Finally, this thesis outlines a framework for modelling the relative biological effectiveness based on the frequency distribution of cluster order as a surrogate for the nanometre classification for the physical properties of radiation quality. The results indicate that this frequency is a valuable descriptor of ionizing radiation. The positive correlation across the different types of ionizing radiation encourages further development of the framework by incorporating the behavior of the microdosimetric spread and expanding tests to other experimental datasets.

Wire and Arc Additive Manufacturing is a novel Additive Manufacturing technology. As a result, the process for progressing from a solid model to manufacturing code, i.e. the Part Programming process, is undeveloped. In this report the Part Programming process, unique for Wire and Arc Additive Manufacturing, has been investigated to answer three questions; What is the Part Programming process for Wire and Arc Additive Manufacturing? What are the requirements on the Part Programming process? What software can be used for the Part Programming process? With a systematic review of publications on Wire and Arc Additive Manufacturing and related subjects, the steps of the Part Programming process and its requirements have been clarified. The Part Programming process has been used for evaluation of software solutions, resulting in multiple recommendations for implemented usage. Verification of assumptions, made by the systematic review, has been done by physical experiments to give further credibility to the results.

An exo-atmospheric nuclear detonation releases up to 80 percent of its’ energy as X-rays. Satellite’s solar cells and their protective coatings are vulnerable to low energy X-ray radiation. Cold X-rays (~1-1.5 keV) are absorbed close to the surface of materials causing the blow-off and rapid formation of Warm Dense Plasmas (WDPs), particularly in a gap between the unshielded active elements of solar cells. To understand how WDPs are created, it is necessary to investigate the power density distribution produced by cold X-rays for typical solar panel surface materials. The Monte Carlo stepping model implemented in the GEANT4 software toolkit is utilized to determine the power density created by cold X-rays in a multi-layered target composed of a layer of an active cell shielded by layers of cover glass and anti-reflective coating. The power density generated by cold X-rays in the unshielded semiconductor layer at different incidence angles is also investigated in order to account for different orientations of the satellite’s solar panels with respect to the point of nuclear detonation. The flux spectrum of X-rays originating from a nuclear blast is described by the Planck's blackbody function with the temperature from 0.1 keV to 10 keV. The secondary radiation (photo-electrons, fluorescence photons, Auger- and Compton-electrons) resulting from absorption and scattering of primary X-rays is taken into account in the redistribution of energy deposition within slabs. The profiles of power density within the slab system produced by primary cold X-rays, secondary photons and electrons are calculated as a function of depth. The discontinuity in power density profiles is observed at the interfaces of slabs due to discrete changes in stopping power between slab materials. The power density is found to be higher in slab materials with higher mass density. The power density profiles are then used in the atomistic Momentum Scaling Model (MSM) coupled with the Molecular Dynamics (MD) method (MSM-MD) to predict the spatiotemporal evolution of WDP in vacuum. The spatial and temporal distribution of density and temperature fields of expanding WDP is evaluated from the MSM-MD simulations. These modeling results provide insights into the underlining physics of the formation and spatiotemporal evolution of WDPs induced by cold X-rays.

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