TY - THES A1 - Popiela, Bartosz T1 - Einfluss fertigungsbedingter Eigenspannungen auf die Betriebssicherheit von nassgewickelten Composite-Druckbehältern mit einem nichttragenden Liner N2 - Im Hinblick auf die globale Herausforderung der Energietransformation steigt der Bedarf an Möglichkeiten zur Energiespeicherung. Eine Technologie, die zunehmend in den Fokus rückt, ist die Energiespeicherung mittels komprimiertem Wasserstoffgas. Insbesondere für mobile und Transport-Anwendungen ist eine geringe Masse des Speichers vorteilhaft, weshalb vollumwickelte Composite-Druckbehälter des Typs 4 zum Einsatz kommen. Diese werden überwiegend im Nasswickelverfahren gefertigt, das durch zahlreiche Prozessparameter und physikalische Effekte charakterisiert wird. Die Wahl der Wickelprozessparameter sowie Schwankungen der Materialkennwerte beeinflussen den Eigenspannungszustand in der Composite-Struktur eines Druckbehälters. Somit wirken sie sich auch auf den Spannungszustand im Betrieb aus. Die vorliegende Dissertation beinhaltet Untersuchungen des Einflusses von fertigungsbedingten Eigenspannungen auf die Sicherheit von Composite-Druckbehältern mit nichttragendem Kunststoff-Liner. Ziel ist es, das mechanische Verhalten von Composite-Druckbehältern besser zu verstehen und deren Sicherheitsniveau sowie Konkurrenzfähigkeit weiter zu steigern. Schwerpunkte der Arbeit sind experimentelle Untersuchungen der Eigenspannungsentstehung und -entwicklung sowie deren Einfluss auf die Behälter-Sicherheit. Im Fokus befindet sich die Exploration von Möglichkeiten zur Verbesserung der Zuverlässigkeit der Behälter durch Variation der Fertigungsparameter und eine Konditionierung nach der Fertigung. Der Eigenspannungszustand wird in numerischen Simulationen sowie mit dem zerstörenden Bohrlochverfahren charakterisiert. Die Überwachung der Spannungsumlagerung während einer Konditionierung unter Zeitstandbelastung erfolgt mit eingebetteten faseroptischen Sensoren, die später zur Dehnungsmessung in zerstörenden, langsamen Berstprüfungen eingesetzt werden. Zur Vertiefung des Verständnisses des Versagensverhaltens der verwendeten 6,8 l-Druckbehälter wird die Finite-Elemente-Methode eingesetzt. Darüber hinaus werden Qualitätsuntersuchungen der Composite-Struktur mittels Mikro-Computertomographie und Impuls-Echo-Verfahren beschrieben. Die Ergebnisse der Untersuchungen zeigen, dass eine Steigerung der Zuverlässigkeit durch eine gezielte Innendruckbeanspruchung der gewickelten Behälter nahezu kostenneutral möglich ist. Dies wird im Rahmen der Arbeit anhand eines Baumusters demonstriert. Darüber hinaus wird die Verbesserung der Zuverlässigkeit der Behälter im Rahmen einer Konditionierung unter Zeitstandbelastung vertieft diskutiert. Diese stellt eine weiterführende Möglichkeit dar, das Behälterverhalten positiv zu beeinflussen und das Sicherheitsniveau zu steigern. N2 - Considering the global challenge of energy transformation, the demand for energy storage solutions is increasing. One of the technologies, which is gaining attention, is the storage of hydrogen gas under high operating pressures. Particularly for on-board and transport applications, lightweight storage systems are advantageous. Therefore, fully wrapped composite pressure vessels of Type 4 are increasingly used. These are mostly manufactured using the wet filament winding process, which is characterized by numerous process parameters and physical effects. The choice of winding process parameters and variations in material properties influence the residual stress state in the finished component and thus also the stress state under operational loads. This dissertation includes insights into the impact of manufacturing-induced residual stresses on the safety of Type 4 pressure vessels, which contribute to a deeper understanding of the mechanical behavior of composite pressure vessels and support the further enhancement of safety levels and competitiveness. The work focuses on experimental investigations of the induction and development of residual stresses and their impact on the safety of the composite pressure vessels. A core of the dissertation is an exploration of the possibilities to improve pressure vessel performance through variation of manufacturing parameters and conditioning after manufacturing. The residual stress state is characterized in numerical simulations as well as with the destructive hole-drilling method. Embedded fiber optic sensors are used for the monitoring of stress redistribution during conditioning. The fiber optic sensors are later used for strain measurement in destructive, slow burst tests. Finite element analyses are performed to deepen the understanding of the failure behavior of the used 6.8-liter pressure vessels. Additionally, quality investigations of the composite structure using micro-computed tomography and impulse-echo ultrasonic propagation imaging are described. The results of the investigations show that an increase in performance is possible through targeted internal pressure regulation during the winding process pressure vessels. This is demonstrated almost cost-neutrally, i.e., without increasing process time and material usage. Furthermore, the improvement of vessel performance through conditioning under increased pressure and temperature is discussed in depth. This represents a further possibility to favorably influence vessel behavior and enhance safety levels. KW - Composite KW - Druckbehälter KW - Eigenspannung KW - Faserverstärkter Kunststoff KW - Nasswickelverfahren PY - 2026 UR - https://nbn-resolving.org/urn:nbn:de:kobv:co1-opus4-72383 DO - https://doi.org/10.26127/BTUOpen-7238 SP - 1 EP - 153 CY - Cottbus, Deutschland AN - OPUS4-65348 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Lengas, Nikolaos T1 - Parameter study of impact targets in the drop test of packaging for dangerous goods N2 - Within the transportation chain, impact loading of dangerous goods packagings can happen. Thus, a package’s resistance against mechanical damage needs to be assessed. In the context of dangerous goods transport, drop tests are used for damage assessment as a part of packaging approval. Hence, a horizontal, flat unyielding surface must be provided to ensure maximum damage on impact and univocal test results. Leading adopted regulations like ADR/RID reference ISO 2248 to specify the requirements for the impact surface. The main requirement states that the impact surface must belong to an impact target with a mass at least 50 times higher than that of the heaviest package to be tested. However, many manufacturers in Germany, especially manufacturers of fibreboard boxes, do not have their own testing device with the required mass ratio for the drop test. Furthermore, the necessity of requirement revision has been addressed at UN level. It is unclear if mass ratio is the decisive criterion or if alternative design parameters can be defined to guarantee rigidity of the impact surface. The focus of the research reported in this thesis lays in the development and implementation of an analysis and testing concept for a comprehensive investigation of impact targets in drop testing. To this end, an experimental setup consisting of regulation compliant model impact targets is used in drop tests with two packaging types of significantly different mechanical properties. The variation of drop test parameters, such as the mass ratio, provides new insights into their respective significance in the drop test outcome. In addition, experimental findings are enhanced with numerical Finite-Element (FE) analyses to propose new improved criteria which incorporate all relevant influencing factors. In this way, firstly, critical impact target designs can be identified, and secondly, the kinetic energy of a real impact target in a drop test can be reliably approximated and compared to the respective theoretical threshold derived from a worst-case assumption. Thus, the rigid mass ratio currently specified in ISO 2248 can be regarded obsolete. The results of this work are highly beneficial for industrial application since they form the basis for introducing a standardized method for evaluating impact targets, replacing the 50 times mass ratio requirement. This would enable manufacturing and testing facilities to ensure a uniform level of safety assessment and to avoid the considerably high construction costs of impact targets with mass ratio of 1:50 in relation to packaging gross masses of several hundred kilograms. Hence, to make the results attained under laboratory conditions usable in practical application, preliminary investigations of the mechanical response of installed impact targets are conducted. For this purpose, important factors such as the interaction between impact target and ground in dynamic impact testing conditions are examined using validated FE models to establish an evaluation method. The investigations aim to create the basis for the revision of ISO 2248 and to define a standardized reference method for impact target characterization. KW - Drop test KW - Structural dynamics KW - Dangerous goods packaging KW - Mass ratio KW - Finite-element-method PY - 2025 DO - https://doi.org/10.14279/depositonce-24333 SP - 1 EP - 189 CY - Berlin AN - OPUS4-64090 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Quackatz, Lukas T1 - In situ Untersuchung der Phasenverteilung und der Schmelzbaderstarrung von Duplexstählen mittels laserinduzierter Plasmaspektroskopie (LIBS) N2 - Nichtrostende Duplexstähle (DSS) werden in allen Branchen eingesetzt, bei denen eine hohe Festigkeit in Verbindung mit einer hohen Korrosionsbeständigkeit in aggressiven Medien ge-fordert wird. Beispiele hierfür sind Kraftwerkskomponenten und maritime Strukturen. DSS ha-ben ein ausgewogenes Phasenverhältnis von Ferrit (α) und Austenit (γ). Im Gegensatz zu einphasigen nichtrostenden Stählen vereinen DSS die Vorteile dieser beiden Phasen und kön-nen daher viele Anforderungen der Industrie erfüllen, wie z. B. Gewichtseinsparung oder hohe mechanische Festigkeit. In vielen industriellen Anwendungen werden diese Stähle ge-schweißt. Die Schweißbarkeit wird weitgehend durch die chemische Zusammensetzung be-stimmt. Legierungen mit ferritischer oder ferritisch-austenitischer Erstarrung weisen die höchste Widerstandsfähigkeit gegen Heißrissbildung auf. Das resultierende Phasengleichge-wicht beeinflusst die endgültigen Eigenschaften des Bauteils. Daher kann es von Vorteil sein, den Ferritgehalt des Schweißguts vorherzusehen bzw. zu messen. Das neueste und präzi-seste Gefügediagramm ist das WRC-1992 Diagramm und basiert auf der chemischen Zusam-mensetzung der Grund- und Zusatzwerkstoffe. In diesem Diagramm kann vor dem Schweiß-prozess abgeschätzt werden, welche Volumenanteile von Ferrit und Austenit im resultierenden Schweißgut vorliegen werden. Genutzt wird es bei der schweißtechnischen Verarbeitung von nichtrostenden, austenitischen bzw. Duplex-Stählen. Verschiedene Quellen berichten, dass diverse Legierungselemente nicht berücksichtigt werden und Optimierungen nötig sind. Wei-terhin können Legierungselemente während des Schweißens abdampfen, was die Mikrostruk-tur zum Negativen beeinflusst. Diese Arbeit eruiert zunächst die theoretischen Grundlagen zur laserinduzierten Plasmaspekt-roskopie (LIBS, engl.: laser induced breakdown spectroscopy), die zur in situ Messung chemi-scher Konzentrationen während des Schweißens genutzt werden soll. Weiterhin werden die Grundlagen zur Erstarrung und zur Schweißbarkeit von DSS aufgezeigt. Mithilfe verschiede-ner Kalibriermodelle werden quantitative Messungen mittels LIBS ermöglicht. Um die Ergeb-nisse der LIBS-Analysen zu validieren, wurden Schweißproben angefertigt und LIBS-Messun-gen mit konventionellen Messmethoden, wie die Röntgenfluoreszenzanalyse (RFA) und die energiedispersive Röntgenspektroskopie (EDX) verglichen. Folglich wurden dann in situ LIBS-Versuche, während des Wolfram-Inertgas-Schweißens (WIG), mit und ohne Schweißzusatz-werkstoff durchgeführt. Hierbei konnten die chemischen Konzentrationen in der Schweißnaht mittels LIBS mit der gleichen Genauigkeit wie die konventionellen Verfahren gemessen wer-den. Ein weiteres Ziel dieser Arbeit ist es, die Gültigkeit und Vorhersagegenauigkeit des WRC-1992 Diagramms zu überprüfen. Hierfür wurde der Schweißzusatzwerkstoff mittels PVD-Be-schichtung mit den Legierungselementen Kohlenstoff, Nickel, Mangan, Silizium, Niob und Kup-fer beschichtet. Diese Elemente nehmen maßgeblich Einfluss auf das Phasengleichgewicht Austenit/Ferrit im Schweißgut der Duplexstähle, da sie entweder Ferrit- bzw. Austenitstabilisa-toren sind. Die Messung der ferritischen und austenitischen Phasenanteile im resultierenden Schweißgut wurde mit drei verschiedenen Methoden vergleichend durchgeführt. Mithilfe der Bildanalyse im Lichtmikroskop, einem Fischerscope® sowie der Röntgendiffraktion (XRD). Da-mit sollte auch geprüft werden, inwieweit die Verwendung der jeweiligen Messmethode die Aussagekraft des WRC-1992 Diagramms beeinflusst. Die Vorhersage anhand des WRC-1992 Diagramms war für Nickel, Silizium und Mangan akzeptabel, jedoch bei Niob, Kupfer und Koh-lenstoff waren deutliche Abweichungen zu beobachten. Anpassungen im WRC-1992 Dia-gramm sollten daher für die Elemente Niob, Kupfer und Kohlenstoff vorgenommen werden. Die geringste Genauigkeit und die größte Streuung wurden mit dem XRD-Verfahren erzielt. Daher kann dieses Verfahren für Ferritmessungen an Schweißnähten von Duplexstählen nicht empfohlen werden. KW - LIBS KW - Duplexstahl KW - Vorhersage Phasenanteile PY - 2025 SP - 1 EP - 118 AN - OPUS4-62622 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Breese, Philipp Peter T1 - Additive Manufacturing with In-situ Measurement and Closed-loop Control for the Powder Flow in Laser Metal Deposition N2 - The powder mass flow rate is one of the three main factors directly influencing geometry and quality in the Additive Manufacturing (AM; also 3D printing) process of Laser Metal Deposition (LMD), also known as Directed Energy Deposition (DED-LB/M). However, the pneumatic transport of the metal powder lacks stability, repeatability, and traceability. There is currently no reliable in-situ measurement of the mass flow rate available in industry. As a result, time-consuming powder flow measurements before the manufacturing are typical while no recording or feedback takes place during the manufacturing. Based on this problem statement, this thesis introduces a holistic approach for in-situ measurement and closed-loop control of pneumatic powder flows. For the in-situ measurement, a widely available nonintrusive optoelectronic sensor was used. Found mathematical dependencies reliably convert the sensor output into a powder mass flow rate dependent on powder parameters and feeding conditions. Therefore, the model is usable with various powder types while achieving a Mean Relative Error (MRE) of less than 4% at 125 Hz. Similarly, a model was introduced for the powder velocity using a second sensor further downstream. This provided insight into the powder’s movement while the model achieved an MRE of less than 3%. As a second main research endeavor, the sensor output was used to implement and investigate a closed-loop powder flow control on a vibration feeder. PID controller gains were calculated empirically at set operating points for the nonlinear system. Again, a usage with various metal powders is possible as the influences of powder parameters and feeding conditions were investigated and incorporated into the model. In addition, the dependence on the previous powder flow (memory effect) was factored in as well. With this, faster recovery from blockages and a reduction in standard deviation during steady state feeding by more than 20% were demonstrated. Complementary numerical CFD simulations investigated the effect of the carrier gas flow rates on powder flow homogeneity and powder particle size separations. A second modeling approach demonstrated the use of machine learning with the optoelectronic sensor output. A 1D convolutional neural network (CNN) was shown to be able to predict the powder flow with a Weighted Absolute Percentage Error (WAPE) of less than 4% compared to the actual flow. With this, the model’s capability to detect slightly elevated moisture (at <0.4wt%) in the powder as well as differences in particle size distribution was proven on in-situ data from powder feeding. Finally, the methods were validated on the LMD process by additively manufacturing test components. The active closed-loop powder flow control shows a significant improvement in repeatability for LMD. The in-situ measurement allows a monitoring of the powder mass flow rate with the recorded data throughout the entire AM process. In addition, Scanning Electron Microscopy (SEM) images showed potential benefits at the microscopic level like reduced defects. With this, the whole chain for a powder flow improvement method was investigated, implemented, and validated in the context of Laser Metal Deposition. Furthermore, a high potential for retrofitting is given while at low cost. This lays the foundation for a more traceable and digital AM process in industry leading to repeatable and safe products. KW - Pneumatic powder flow KW - Direct Energy Deposition KW - DED-LB/M KW - 3D printing KW - In-situ monitoring PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-650261 DO - https://doi.org/10.14279/depositonce-23032 SP - 1 EP - 198 PB - TU Berlin CY - Berlin AN - OPUS4-65026 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Scharff, Erik T1 - Untersuchungen zur Ausbreitung brennbarer Schwergase in längsdurchströmten Straßentunneln N2 - In combination with new types of drive technologies, more and more flammable gases could be introduced into the traffic area “road tunnel” in future. If these vehicles have an accident and the gases are subsequently released, there is the possibility that the mentioned substances show a heavy gas behavior due to their storage conditions. From a safety point of view, this scenario has to be assessed with regard to its effects on the tunnel structure and the people involved. The aim of the experimental investigations carried out in this work is to create the basis for such an analysis by investigating the spreading behavior of the gases after they have been released in the tunnel and determining the influence of individual geometric and operational parameters on this behavior. Specifically, this work is based on the scenario of a continuous, momentum-free release of propane within a vaulted road tunnel with active longitudinal ventilation. The tunnel-specific boundary conditions that are relevant to this scenario are first worked out by a theoretical analysis. The basis of the subsequent experimental part is formed by two test rigs built as part of the work, which are similar in their essential features, but differ in scale. In both facilities, the aforementioned release scenario was simulated under various boundary conditions based on an idealized tunnel segment. The dispersion behavior is primarily assessed by the averaged concentration distribution near the ground, which results from a large number of detectors arranged in the experimental area. The detectors operate on the principle of weakening infrared light in the presence of hydrocarbons. Measurements of the flow field properties accompany the concentration measurements. The conception of the test rig on a scale of 1:12 is based on dimensional analysis. The actual release campaign comprises a large number of individual experiments in which selected parameters were varied over the tunnel-relevant range. The predicted heavy gas behavior for propane emerged clearly in the experiments. In cases in which the cloud laterally reaches the tunnel walls, the gases are channeled, which is accompanied by reduced longitudinal dilution. It was possible to identify the release rate and the flow velocity as the factors that have the greatest influence. The former basically increased the concentration, while the latter decreased it. All other tested parameters resulted in more complex propagation situations, which force a differentiated consideration of the influence. Lifting the source from the ground also reduced the concentration. In the case of an eccentrically arranged source and a transverse slope of the roadway, the influence is largely limited to the lateral concentration distribution in the immediate vicinity of the source. Nevertheless, both parameters plus a possible longitudinal slope of the roadway only showed a slight effect on the area far-downstream from the source. In addition, the phenomenon of backlayering, which is known from the spreading of fire smoke in the tunnel, could be demonstrated with a steep longitudinal slope. Obstacles increased the complexity of the situation. While globally the dilution of the cloud is partly invariant to obstacles, locally an increase as well as a decrease in concentration can be observed under certain conditions. For the unobstructed tunnel, it was finally possible to define a dimensionless parameter that describes the curve of the longitudinal dilution on the ground within the heavy gas cloud. From this, a simple graphical nomogram is derived for the continuous release of heavy gases in an unobstructed tunnel environment, which can be used to estimate the concentration in relation of a dimensionless source distance. For exploring the real, undistorted behavior experiments were also carried out in original scale. Due to the similarity of both test rigs in terms of scale, the test results can also be used to check the scalability of the spreading situations. For that, two configurations that have already been examined in small scale were selected. The main limitation for test execution and regarding the scalability comparison was the dependence of the flow conditions within the test rig from external wind conditions which occurred despite of taken countermeasures. The large-scale release was associated with pronounced fog formation. The near-ground spreading corresponding to the heavy gas behavior could be confirmed. However, in detail the spread was far more unsteady. Looking at the time-averaged concentrations, the processes already known from the small-scale test were qualitatively well approximated. Remaining quantitative differences, however, require critical consideration. This discrepancy is more likely a consequence of the experimental compromises have to be made in the specific case. From the observed gas behavior, the development of a surface fire initiated by ignition of the re-leased gases is considered to be the most likely subsequent scenario for the release of heavy, flam-mable gases in tunnel-like enclosures. The thesis concludes with recommendations on the methodological approach to be favored in the future. KW - LNG KW - Schwergas KW - Stoffausbreitung KW - Propan PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:gbv:ma9:1-1981185920-1206411 DO - https://doi.org/10.25673/118683 VL - 2025 SP - 1 EP - 225 PB - Otto-von-Guericke-Universität Magdeburg, Fakultät für Verfahrens- und Systemtechnik CY - Magdeburg AN - OPUS4-65012 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Kianinejad, Kaveh T1 - Multiscale Modelling of Creep Anisotropy in Additively Manufactured IN738LC N2 - Excellent creep resistance at elevated temperatures, i.e. T / Tm> 0.5, due to gamma-gamma’ microstructure is one of the main properties of nickel-based superalloys. Due to its great importance for industrial applications, much research has been devoted to understanding the underlying deformation mechanism in a broad spectrum of temperature and loading conditions. Additive Manufactured (AMed) nickel-based superalloys, while being governed by similar \gamma-gamma’ microstructure, exhibit AM-process specific microstructural characteristics, such as columnar grains, firm crystallographic texture (typically <001> fibre texture parallel to build direction) and compositional inhomogeneity, which in turn leads to anisotropic creep response in both stationary and tertiary phases. Despite the recent insights on the correlation between process parameters and the resulting microstructure, these materials' anisotropic creep behaviour and corresponding deformation mechanism are insufficiently understood. One reason is the lack of capable material models that link the microstructure to the mechanical behaviour. Within the present work, a multiscale approach has been developed to overcome this challenge by combining microstructure-based mesoscale and phenomenological macroscale models. The mesoscale model utilizes the Crystal Plasticity Finite Element Method (CPFEM) to include the microstructural characteristics and the relevant deformation mechanism on the polycrystalline scale. The mesoscale model was then used to perform virtual creep experiments required to calibrate the macroscale model. The developed approach has been applied to characterise the creep behaviour of AMed IN738LC. The effect of different slip systems, crystallographical texture, grain morphology, and Grain Boundary Sliding (GBS) on creep anisotropy at 850°C has been investigated. The approach's ability to capture the AM-specific characteristics and link them to the observed macroscale anisotropic response has been demonstrated, and the contribution of primary underlying deformation mechanisms to creep anisotropy has been elucidated. KW - Creep anisotropy KW - Crystal plasticity KW - Addtively manufactured Nickel-based Alloys alloy PY - 2025 SP - 1 EP - 135 PB - RWTH Aachen CY - Aachen AN - OPUS4-64598 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Cakir, Cafer Tufan T1 - Optimization of depth resolved X-ray absorption spectroscopy in grazing emission mode for characterizing compositionally complex alloys N2 - Layered materials are fundamental to technological advancements, offering distinct properties that differentiate them from bulk materials. In electronics, for instance, thin-film transistors (TFTs) are used to enhance charge transport and flexibility, thereby improving device performance. In the same way, thin-film photovoltaic devices used in renewable energy use strategic layering to absorb light more efficiently and separate electron-hole pairs more effectively, which leads to higher energy conversion efficiency. In recent decades, the development of new alloys has highlighted the importance of layered materials in another context. Compositionally complex alloys, for example, form multiple oxide layers on their surfaces when they oxidize. Studying these corrosion layers is crucial for understanding material-environment interactions. Typical surface analysis techniques, including X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and Meitner-Auger electron spectroscopy (MAES), provide valuable insights but are constrained by their requirements for high Vacuum conditions and their limited depth analysis. In contrast, X-ray absorption near-edge structure (XANES) spectroscopy presents a versatile and advantageous alternative. It operates effectively under ambient conditions and allows time-resolved measurements, enhancing the analysis of materials in real-time as they undergo structural and compositional changes. This adaptability broadens the scope for material analysis, allowing for a more comprehensive understanding of dynamic processes. Grazing Emission X-ray Fluorescence (GEXRF) spectroscopy stands out as a nondestructive, depth-resolved, element-specific characterization technique important for collecting depth-resolved information at the nanometer scale. Its ability to collect in-Depth resolved information based on the grazing emission angle of the fluorescence Radiation makes it ideal for investigating thin films, corrosion layers, and interfaces within layered materials. The integration of XANES in emission mode with GEXRF enables detailed exploration of the chemical states of the analyzed atom and provides depth-resolved information. This study discusses grazing emission X-ray absorption near-edge structure spectroscopy (GEXANES), a novel layer analysis technique that is created by integrating these two methods. This study also innovatively combines machine learning with GEXANES spectroscopy to reduce experimental times. By using active learning, a subset of machine learning, it refines the data acquisition process, enabling more efficient and streamlined methods. The application of active learning in this context illustrates the potential of data-driven approaches to transform experimental methodologies, particularly in resource-limited environments such as synchrotron facilities, thereby accelerating scientific research and discovery. KW - Angle resolved XRF KW - GEXRF KW - BO KW - Active Learning KW - XRF PY - 2025 DO - https://doi.org/10.34726/hss.2025.101302 SP - 1 EP - 129 CY - Technische Univeristät Wien AN - OPUS4-63793 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Abel, Andreas T1 - Microstructural and mechanical characterisation of cast Fe-Al-Mo-Ti-B alloys N2 - With the advent of variable renewable energies, long-term energy storage capacities and flexible power generation technologies will be required for reliable grid stability. Hence, power plant technologies and turbomachinery components will continue to be developed and employed for efficient re-conversion of stored energy. With the introduction of new working fluids for higher thermal efficiencies, the working conditions of exposed components and materials will require higher corrosion resistance, but with the same mechanical performance, manufacturability and cost. Intermetallic iron aluminide alloys with their outstanding oxidation and corrosion resistance and good high-temperature properties depict a possible candidate for use in high-temperature structural applications. A quinary Fe-26Al-4Mo-0.5Ti-1B solid-solution alloy with eutectic particle hardening particularly demonstrated competitive mechanical properties compared to high-alloy P92 steels in previous studies. To derive standard material specifications with industrially relevant casting strategies, centrifugal investment-cast Fe-25Al-3.7Mo-0.4Ti-1B was characterised with respect to microstructure, thermophysical properties and mechanical properties under quasi-static tensile and creep loading up to 700 °C. Compared to P92 steel, the alloy demonstrated superior tensile strength above 550 °C and lower creep rates at 650 °C if stresses increase above 170 MPa. At lower temperatures though, the mechanical properties were inferior to P92 steel and related Fe-Al-Mo-Ti-B alloys, which was correlated to large grain sizes, a high tendency to surface and bulk cracking and a pronounced effect of tension-compression asymmetry. In further studies on alloy composition with varying Al, Mo and B concentration, a non-linear relationship of solid-solution hardening with solute Mo concentration was found. In this regard, halving Mo was the most effective measure for reducing brittleness without decreasing strength at room and elevated temperatures. Higher solidification rates and grain refinement down to 30 µm by die casting had a positive effect on ambient tensile strength, but were not achievable by investment casting. Dilatometry and hardness measurements indicated a low thermal vacancy hardening effect which was less sensitive to low-temperature annealing than in B2 FeAl alloys. Although mechanical properties up to 550 °C could be considerably improved by alloy development and processing, ductility at room temperature generally remained below 1%, necessitating substantial design margins for components from Fe-Al-Mo-Ti-B alloys. Despite the inherent limitations of alloy and casting process, the gained insights will help to prioritise future areas of research to mature cost-effective higher-order Fe Al alloys for high-temperature structural applications. KW - Hardness KW - Iron aluminide alloy KW - Micro structure KW - Tensile strength KW - Creep strength PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-632810 DO - https://doi.org/10.5445/IR/1000181739 SP - 1 EP - 179 PB - Karlsruher Institut für Technologie (KIT) CY - Karlsruhe AN - OPUS4-63281 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Wallis, Theophilus T1 - Density-Based Phase-Field Modeling of Grain Boundary Segregation and Structural Transitions N2 - Polycrystalline materials are central to everyday engineering applications and technological advancements. The mechanical and functional properties of these materials can be influenced either negatively or positively by the presence of grain boundaries (GBs). These properties are interconnected with the structure, chemistry, or a combination of both (referred to as chemo-structure) at the GB. Therefore, an in-depth understanding of GBs, and their associated phenomena is key to tuning these materials properties for desired applications. Nevertheless, the intricate and unique characteristics of GBs impose constraints on their general descriptions in existing models designed for studying and understanding them. In this dissertation, a comprehensive tool, the CALPHAD-integrated density-based phase-field (DPF) model \cite{darvishikamachali2020model}, that harnesses atomic-scale GB characteristics, is employed and extended to reveal a deeper understanding of the GB structure, chemistry, chemo-structural coupling and their potential contributions to GB phenomena such as GB structural (and/or chemo-structural) transitions and liquid metal embrittlement. Although GBs possess distinctive crystallographic properties that render them unique and individualistic, it is important to note that they cannot exist independently; rather, they are made of the same constituents as the corresponding bulk material. To this end, the DPF model uses a continuous atomic density field ($\rho$), derived from atomistic simulations, to characterize the GB with reference to its corresponding homogeneous bulk (grain interior). This perspective allows the DPF model to approximate the GB free energy functional based on available bulk thermodynamic data. The DPF model has been utilized to investigate a variety of systems, form unary to multi-component systems \cite{kamachali2024giant,darvishikamachali2020model,darvishikamachali2020segregation,wang2021density,li2020grain,wang2021incorporating,zhou2021spinodal}. Among several novelties in the elucidation of the thermodynamics and kinetics of GBs, the DPF model has shown that GBs can have their own miscibility gap. It further reveals a temporal co-evolution of low and high segregation levels at the GB, which can act as precursor states for the formation of new phases \cite{kwiatkowskidasilva2018phase, kwiatkowskidasilva2019thermodynamics}. In the recent publication on Fe-Mn \cite{darvishikamachali2020segregation} and in various other works \cite{kamachali2024giant,darvishikamachali2020model,darvishikamachali2020segregation,wang2021density,li2020grain,wang2021incorporating,zhou2021spinodal, ikeda2023segregation, ahmadian2023interstitial} of the DPF model, the variation of atomic density field was allowed normal to the GB plane. At the GB plane, the in-plane GB density $\rho^{GB}$ was treated as a constant average value, representing its intrinsic dependence on the GB nature and misorientation. Although this assumption provides a useful simplification in studying GB phenomena, it does have the drawback of overlooking the significance of the in-plane structure variation. This seems to be particularly central in the view of experimental observations that confirm relatively stable grain boundary composition fluctuation \cite{darvishikamachali2020segregation}. In this thesis, the significance and impact of the atomic structure of GBs on their thermodynamics is investigated. This is achieved in two ways: On one hand, by extending the CALPHAD-integrated density-based free energy functional to account for structural degrees of freedom of GBs, and on the other hand, by deducing and linking density-related GB properties to the GB structure through the results of atomistic simulation of the GBs. Naturally, the structure (atomic density) within the GB plane fluctuates. This variation may also be linked to changes in composition due to solute segregation at the GB. While the fact that the GB structure can undergo transitions (referred to as complexions) \cite{frolov2015segregation, cantwell2020grain, cantwell2014grain} is not entirely new, the quantitative measurements of co-existing GB phases are scarce. Recently, instances were reported where the coexistence of two in-plane GB phases was revealed through the application of high-resolution transmission electron microscopy and atomistic simulation \cite{frommeyer2022dual, meiners2020observations}. To this end, the potential of GB structural variation within the DPF model is introduced in this thesis, where the GB in-plane density $\rho^{GB}$ is described as a field, that can vary both in time and space. This extension enables the in-plane GB density $\rho^{GB}$ to evolve and exhibit two distinct low-energy states, denoted as $\rho^{GB} = \rho_1$ and $\rho^{GB} = \rho_2$, where $\rho_2 > \rho_1$. Separating these two structural states is an in-plane line defect. This way, the model allows the studies of the co-evolution between the chemical and structural states of the GB. As a proof of concept and benchmark study, the extended-DPF model is implemented for studying Fe-Mn system. The results show that the GB structure's capacity to respond to chemical variations, as incorporated in the DPF model, enhances the Mn segregation transition at the GB, even in the absence of any alterations to the GB structure. When the GB structure undergo changes (or is non-uniform), the model reveals a coupling between the GB structure and chemical evolution. The ability of the GB structure to change allows the coexistence of spinodally formed low- and high-Mn phases within the GB during segregation transition. The acquired equilibrium segregation isotherms provides insight into the range of alloy compositions where these GB phases remain stabilised. Moreover, the observations indicate that the tendency of the GB to undergo a structural transition (change) is associated with the energy of the in-plane line defect, between low- and high-density domains within the GB plane. The extended-DPF model is further applied to Zn-coated advanced high strength steels (Fe-Zn systems), where Zn segregation to the GB is known to cause severe performance degradation due to liquid metal embrittlement \cite{razmpoosh2021pathway, ikeda2022early, bhattacharya2018liquid}. The effect of GB type and its chemo-structural coupling on Zn segregation is investigated. The results showed a sharp Zn segregation that is strongly influenced by the nature of the GB itself, as well as the coupling between its chemistry and structure. Additionally, GB phase diagrams were constructed across a wide range of alloy compositions and temperatures. The impact of the GB type and chemo-structural coupling on the miscibility gap of GBs is discussed. The DPF model's ability to incorporate atomic-scale characteristics into the construction of Gibbs free energies at the mesoscale ensures it retains key physical insights when predicting microstructure properties. To this end, a robust investigation of the model’s parameters and outputs in comparison to atomistic simulations of GBs is presented. This not only serves as a gauge for the models reliability, but also provide a new framework in establishing an atomistically-informed density-based description of GBs. First, by examining a large dataset of GBs in BCC-Fe and -Mo from atomistic simulations, a connection between their discrete atomic structure and the continuous atomic density function $\rho$ is established. This is achieved by a systematic coarse-graining approach wherein an atomsitically-obtained density function (delta function) is substituted with a normalised Gaussian function, so that, a smooth and continuous atomic density profile in real space can be obtained, where the minimum is the average atomic density at the GB plane $\rho^{GB}$. The investigation revealed a linear proportional relationship between the GB excess free volume and $\rho^{GB}$. This correlation simplifies the computation of the excess free volume as the integration over the portion of the density profile where the atomic density is less than one. Furthermore, the GB energies calculated by atomistic simulations revealed a correlation with $\rho^{GB}$ for certain classification of GB types, therefore enhancing the model's predictive accuracy. Concurrently, the atomic-scale characteristics of GBs can be further harnessed in the DPF models by replacing the simple functional form of the potential energy as given in the original DPF model formulation with a material specific interatomic potential (expressed as a function of the atomic density $\rho$) from molecular dynamic simulations. This way, a reliable prediction of the atomic density gradient energy coefficient for mesoscale simulations can be obtained. KW - Grain boundary structure KW - Grain boundary chemistry KW - Density-based phase-field modelling KW - Grain boundary thermodynamics KW - Grain boundary segregation transition PY - 2025 SP - 1 EP - 134 CY - Aachen AN - OPUS4-64455 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Suárez Ocano, Patricia T1 - Thermodynamic and microstructural stabilities at high temperatures and their effects on mechanical properties in an AlMo0.5NbTa0.5TiZr refractory high entropy superalloy N2 - Today’s industrial demands challenge the research and development sector to make advances in the design and properties of materials that can withstand harsh environments. The AlMo0.5NbTa0.5TiZr refractory high-entropy superalloy (RSA), with a remarkable morphological similarity to the γ/γ' microstructure of Ni-based superalloys and promising high-temperature compressive properties, has been considered as a candidate for structural applications. However, additional properties need to be investigated in order to assess the suitability of this alloy for high temperature applications. Therefore, this work investigates the thermodynamic and microstructural stabilities of the RSA at room temperature and between 900 and 1100 °C, and their influence on the mechanical properties. Although it is possible to improve the mechanical properties at 20 °C by tuning the cooling rate, long-term high temperature exposures lead to phase instabilities that negatively influence the creep behavior. N2 - Die heutigen industriellen Anforderungen erfordern Fortschritte bei Werkstoffdesign und -entwicklung, insbesondere für raue Umgebungen. Die hochentropische Refraktärsuperlegierung (RSA) AlMo0.5NbTa0.5TiZr, die eine bemerkenswerte morphologische Ähnlichkeit mit der γ/γ'-Mikrostruktur von Ni-Basis-Superlegierungen und vielversprechende Hochtemperatur-Druckeigenschaften aufweist, wurde als Kandidat für strukturelle Anwendungen erwägt. Weitere Eigenschaften müssen untersucht werden, um die Eignung dieser Legierung für Hochtemperaturanwendungen zu beurteilen. In dieser Arbeit werden die thermodynamischen und mikrostrukturellen Stabilitäten von RSA bei Raumtemperatur und zwischen 900 und 1100°C sowie deren Einfluss auf die mechanischen Eigenschaften untersucht. Obwohl es möglich ist, die mechanischen Eigenschaften bei 20 °C durch Abstimmung der Abkühlrate zu verbessern, führen langfristige Hochtemperaturexpositionen zu Phaseninstabilitäten, die das Kriechverhalten negativ beeinflussen. KW - Hochentropielegierung KW - Gefüge (Werkstoffkunde) KW - Mikrostruktur KW - Kriechen KW - Thermodynamische Stabilität KW - High entropy alloys KW - Microstructure KW - Creep KW - Thermodynamic stability PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:hbz:294-108415 DO - https://doi.org/10.13154/294-10841 SP - 1 EP - 170 CY - Bochum AN - OPUS4-59929 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Shaheen, Sabahat T1 - Distributed acoustic sensing using geometric phase and its application to seismology N2 - This thesis deals with the development of a novel optical fiber sensing scheme based on geometric phase for sensing strain and its application to seismology. Interference of two coherent frequency offset electromagnetic waves gives rise to a geometric phase in the resulting beat signal. The existence of this phase was recently reported along with requisite conditions for its existence. This thesis proposes to detect and use this geometric phase in the context of distributed and dynamic fiber optic strain sensing, also known as distributed acoustic sensing (DAS). In the first part, I devise a novel DAS hardware setup capable of detecting the geometric phase considering that its measurement methods require the measurement of beam intensities and the beat signal’s envelope. The geometric phase is a function of relative intensity and polarisation state of two interfering beams. Therefore, its measurement is verified by determining its relation on these quantities using a polarisation scrambler and a piezoelectric transducer, inline an optical fiber. It is a fundamental study that has implications in coherent optical communication and novel sensing mechanisms. The second part involves using the geometric phase in DAS for measurement of strain. I attempt to replace the traditionally measured dynamic phase in a DAS setup with the geometric phase. This is made possible by the fact that the geometric and dynamic phases are reportedly coupled over every beat period such that their sum remains constant. However, the spatial resolution for geometric phase is lower as it is measured per beat period. I determine an equivalence for the two phases empirically as well as optimum test parameters such as the required frequency offset between the interfering beams. The advantages offered by the use of geometric phase are demonstrated; geometric phase can be measured even when the two interfering beams have non-identical polarisation states, unlike the traditionally measured dynamic phase. Moreover, it does not require phase unwrapping and is therefore free from unwrapping errors. In the third and final part, the setup, after optimisation, is tested in the field to detect seismic waves travelling on the surface of the Earth in response to a set of blasts carried out at a test-site. The surface waves are used for the characterisation of the structure and material properties of the first tens of meters of the Earth with applications in earthquake monitoring, resource exploration and infrastructure planning. In short, this study is the first of its kind to measure geometric phase in beat signal of light using optical fiber medium and to measure strain with it, for which a novel hardware setup and a novel sensing mechanism is designed and tested in addition to its application in real-world seismology measurements. KW - C-OTDR KW - Distributed fiber optic sensing KW - Distributed vibration sensing KW - Geometric phase measurement PY - 2024 SP - 1 EP - 89 PB - Technische Universität Carolo-Wilhelmina CY - Braunschweig AN - OPUS4-60956 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Nagelschmidt, Sven T1 - Ein Beitrag zur Zusammenführung von Zeit-Temperatur-Äquivalenz-Methoden: Entwicklung und Anwendung am Beispiel ausgewählter Materialverhalten für Zeit-Temperatur-Parameter und Zeit-Temperatur-Superpositionsprinzip N2 - In der Wissenschaft und Technik gibt es verschiedene Gründe, um auf Basis geeigneter Modelle in die Zukunft schauen zu wollen, beispielsweise um zu bewerten, ob ein Bauteil auch noch deutlich länger verwendet werden kann als eigentlich einmal vorgesehen. Eine Methode dieses zu tun, basiert auf dem Zeit-Temperatur-Äquivalenz-Prinzip, welches besagt, dass ein Zustand oder eine Materialeigenschaft gleichwertig bei verschiedenen Zeit-Temperatur-Kombinationen auftritt oder erreicht werden kann. Höhere Temperaturen verkürzen in der Regel die Dauer und umgekehrt. In den letzten Jahrzehnten hat sich ein umfangreiches Methodenspektrum für unterschiedliche Werkstoffe und Anwendungsgebiete entwickelt, sodass die Identifikation einer geeigneten Methode für einen konkreten Anwendungsfall oder neue Materialien eine Herausforderung darstellt. These: „Fortschrittlich wäre, existierende Methoden zusammenzuführen, methodenspezifische Vorteile zu kombinieren, um mit geringerem Aufwand ein geeignetes Prognosemodell zu entwickeln.“ Für metallische Werkstoffe und Polymere verläuft die Entwicklung von Prognosemodellen mit Zeit-Temperatur-Korrelation seit ca. 1940 parallel und unabhängig voneinander. In diesem Zusammenhang bekannte Methoden sind das Zeit-Temperatur-Superpositionsprinzip und Zeit-Temperatur-Parameter, wie der LARSON-MILLER-Parameter. Die jeweiligen methodischen Ansätze sind in der Regel anwendungs- und materialspezifisch und nur einzelnen Fachartikeln zu entnehmen. Eine zusammenführende thematische Übersicht und Untersuchung existierender Methoden wurden bislang nicht publiziert. Diese Forschungsarbeit verfolgt dahingehend einen neuartigen methodischen Ansatz und zeigt untersuchte Gemeinsamkeiten und Unterschiede als auch Analogien für das Zeit-Temperatur-Superpositionsprinzip und Zeit-Temperatur-Parameter anhand bestimmter Merkmale auf. Dafür wurden verschiedene analytische und grafische Ansätze verwendet. Ferner wird eine zusammenführende Untersuchung anhand eines rheologischen Materialmodells sowie anhand eines praktischen Anwendungsbeispiels gezeigt. Hergeleitet wurde u. a., dass das Prinzip der Zeit-Temperatur-Superposition für sogenanntes thermorheologisch einfaches und komplexes Verhalten konkreten Zeit-Temperatur-Parametern zugeordnet werden können. Und dadurch Verschiebefunktionen nicht nur in Abhängigkeit der Temperatur, sondern auch abhängig vom Zustand untersucht und definiert werden können. Ferner ermöglicht eine Skalierung der Zeit-Temperatur-Parameter auf eine Referenztemperatur physikalisch anschaulichere Auswertungen analog zum Zeit-Temperatur-Superpositionsprinzip. Untersuchungen zeigen, dass sich für einen konkreten Anwendungsfall die geeignetste Zeit-Temperatur-Äquivalenz-Methode aus einer gegenseitigen Abhängigkeit bzw. Kompatibilität einzelner Elemente, wie zugrunde gelegte Daten, Koordinatenachsenskalierung, ermittelte Zeit-Temperatur-Äquivalenz, Masterfunktionsansatz und der geforderten Interpolationsgüte herleitet. Der gewählte Forschungsansatz und die erzielten Ergebnisse bieten eine Plattform für die weitere Entwicklung von Prognosemodellen auf Basis des Zeit-Temperatur-Äquivalenz-Prinzips, insbesondere im Hinblick auf eine Zusammenführung und Kombination existierender Methoden. KW - Zeit-Temperatur-Äquivalenz KW - Zeit-Temperatur-Korrelation KW - Zeit-Temperatur-Superposition KW - Extrapolation PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-601530 DO - https://doi.org/10.14279/depositonce-20439 SP - 1 EP - 145 CY - TU Bibliothek online AN - OPUS4-60153 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Keller, Christian T1 - Beitrag zur numerischen Beanspruchungsanalyse an dünnwandigen Stahlblechcontainern im Fallversuch - Schädigungsmechanische Materialmodellierung duktiler Werkstoffe unter Berücksichtigung der Dehnratenabhängigkeit der plastischen Instabilität N2 - Gegenstand der vorliegenden Arbeit ist die Bereitstellung expliziter numerischer Simulationen von Fallversuchen mit dünnwandigen Stahlblechcontainern, die als Endlagerbehälter für radioaktive Abfälle mit vernachlässigbarer Wärmeentwicklung, d. h. schwach- und mittelradioaktive Abfälle, für die Verbringung in das Endlager Konrad vorgesehen sind. Die Betrachtung von potentiellen Absturzszenarien ist ein grundlegender und zentraler Bestandteil der Sicherheitsnachweise zur Auslegung der verschiedenen endlagergängigen Behälter- und Containertypen gegen mechanische Störfallbelastungen. Für dünnwandige Stahlblechcontainer existierten bislang keine sicherheitstechnischen Untersuchungen, die auf numerischen Bewertungsmethoden basieren und eine Bewertung der vorhandenen Sicherheitsreserven hinsichtlich der mechanischen Integrität ermöglichen. Daraus resultierte die Motivation, ein verifiziertes Finite-Elemente-Modell eines repräsentativen Referenzcontainers zu entwickeln, das das dynamische Verformungs- sowie duktile Schädigungs- und Versagensverhalten in numerischen Simulationen von dynamischen Lastfällen physikalisch mit der erforderlichen Güte beschreibt. Duktile Schädigungs- und Versagensvorgänge metallischer Werkstoffe gehen grundsätzlich mit großen plastischen Dehnungen einher und führen somit unweigerlich zu der Notwendigkeit der Diskussion von plastischer Instabilität und damit verknüpften Lokalisierungseffekten, die einen wesentlichen Einfluss auf die Entwicklung des lokalen Beanspruchungszustands haben. Für die schädigungsmechanische Materialmodellierung folgt hieraus das grundsätzliche Erfordernis der korrekten Berücksichtigung des Instabilitätsbeginns, der in der Regel dehnratenunabhängig angenommen wird. Für dynamische Randbedingungen ist der werkstoffspezifische Einfluss der Dehnrate auf das Einsetzen der Lokalisierung jedoch nicht uneingeschränkt vernachlässigbar, so dass im Rahmen dieser Arbeit ein theoretischer Ansatz ausgearbeitet wird, der die plastische Instabilität dehnratenabhängiger Werkstoffe anhand des zeit- und ortsabhängigen Dehnungsgradienten im einachsigen Zugversuch diskutiert. Darüber hinaus ist für eine hinreichend genaue Materialmodellierung neben der korrekten Prognose des Instabilitätsbeginns auch die korrekte Beschreibung des Verformungsverhaltens jenseits der Gleichmaßdehnung notwendig. Zu diesem Zweck wird in dieser Arbeit eine konstitutive Beziehung entwickelt, die sowohl unter Berücksichtigung der plastischen Instabilität als auch unter der Beachtung von ver- sowie entfestigenden Einflussfaktoren der dynamischen Plastizität formuliert werden kann. Insgesamt wird eine praxistaugliche Bewertungsmethode der mechanischen Integrität dünnwandiger Stahlblechcontainer unter Störfallbedingungen auf Basis expliziter dynamischer Simulationen erarbeitet, die die komplexen duktilen Schädigungs- und Versagensmechanismen dehnratenabhängiger Werkstoffe berücksichtigt. Mit der zur Simulation von Fallversuchen entwickelten numerischen Modellbildung und den zur Verifizierung entsprechend mit Testcontainern im Originalmaßstab durchgeführten Fallversuchen wird nachgewiesen, dass anhand des Finite-Elemente-Modells eines repräsentativen Referenzcontainers zum einen eine quantitativ belegte Bestimmung ungünstiger Fallorientierungen hinsichtlich maximaler Verformungen und zum anderen eine realistische Abbildung des duktilen Versagensverhaltens ermöglicht wird. Damit können tatsächlich vorhandene Sicherheitsreserven bei potentiell zu unterstellenden Behälterabstürzen quantitativ aufgezeigt und zukünftig eine verbesserte sicherheitstechnische Beurteilung von Stahlblechcontainern im Fallversuch bereitgestellt werden. Damit leistet die vorliegende Arbeit einen wichtigen Beitrag für die Bewertung von Sicherheitsnachweisen von Endlagerbehältern für radioaktive Abfälle und trägt dazu bei, den langfristigen Schutz von Mensch und Umwelt vor Schäden durch radioaktive Stoffe zu gewährleisten. N2 - The subject of the present work is the provision of explicit numerical simulations of drop tests with thin-walled sheet steel containers, which are intended as repository containers for radioactive waste with negligible heat generation, i.e. low and intermediate level waste, for shipment to the Konrad repository. The consideration of potential crash scenarios is a fundamental and central component of the safety analyses for the design of the various types of casks and containers suitable for final disposal against mechanical accident loads. For thin-walled sheet steel containers, no safety investigations based on numerical assessment methods existed so far that would allow an evaluation of the existing safety reserves with regard to mechanical integrity. This resulted in the motivation to develop a verified finite element model of a representative reference container that physically describes the dynamic deformation and ductile damage and failure behaviour in numerical simulations of dynamic load cases with the required quality. Ductile damage and failure processes of metallic materials are fundamentally accompanied by large plastic strains and thus inevitably lead to the need to discuss plastic instability and associated localisation effects, which have a significant influence on the development of the local stress state. For damage-mechanical material modelling this results in the fundamental requirement of correctly considering the onset of instability, which is usually assumed to be strain-rate independent. For dynamic boundary conditions, however, the material-specific influence of the strain rate on the onset of localisation cannot be neglected without restriction, so that a theoretical approach is elaborated within the scope of this work that discusses the plastic instability of strain-rate-dependent materials on the basis of the time- and location-dependent strain gradient in the uniaxial tensile test. Furthermore, for a sufficiently accurate material modelling, besides the correct prediction of the onset of instability, the correct description of the deformation behaviour in the postcritical region, i.e., beyond the uniform strain, is necessary. For this purpose, a constitutive relationship is developed in this work, which can be formulated both under consideration of the plastic instability as well as under consideration of hardening as well as softening influencing factors of the dynamic plasticity. Overall, a practical assessment method of the mechanical integrity of thin-walled sheet steel containers under accident conditions is developed based on explicit dynamic simulations, which takes into account the complex ductile damage and failure mechanisms of strain rate-dependent materials. With the numerical modelling developed for the simulation of drop tests and the drop tests carried out accordingly with full-scale test containers for verification, it is demonstrated that, on the basis of the finite element model of a representative reference container, on the one hand a quantitatively proven determination of unfavourable drop orientations with regard to maximum deformations and, on the other hand, a realistic representation of the ductile failure behaviour is made possible. This allows it to quantitatively demonstrate actually existing safety reserves in case of potential container crashes and to provide an improved safety assessment of sheet steel containers in drop tests in the future. This work thus makes an important contribution to the evaluation of safety verifications of final storage containers for radioactive waste and helps to ensure the long-term protection of humans and the environment from damage caused by radioactive substances. KW - FEM KW - Dynamische Plastizität KW - Plastische Instabilität KW - Duktile Schädigung KW - Endlager Konrad PY - 2024 DO - https://doi.org/10.14279/depositonce-21874 SP - 1 EP - 188 PB - DepositOnce CY - Berlin AN - OPUS4-61581 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Wiehle, Philipp T1 - Einfluss der Feuchtigkeit auf das Tragverhalten von Lehmmauerwerk N2 - Im Mittelpunkt der vorliegenden Arbeit steht der Einfluss der Feuchte auf die mechanischen Eigenschaften von Lehmmauerwerk. Der Wissensstand zum feuchteabhängigen Tragverhalten von Lehm(mauerwerk) ist bisher lückenhaft, sodass keine explizite Berücksichtigung der Bauteilfeuchte bei der Bemessung tragender Konstruktionen erfolgt. Aktuelle und verlässliche Daten zum Einfluss der Feuchte auf die mechanischen Kenngrößen moderner Lehmbaustoffe fehlen bisher ebenso wie Messwerte in Bezug auf die Bauteilfeuchte unter natürlichen Klimabedingungen. Deswegen wurden im Rahmen dieser Arbeit umfangreiche Untersuchungen zum mechanischen und hygrothermischen Verhalten von Lehmmauerwerk durchgeführt. Die experimentellen Untersuchungen bestehen im Wesentlichen aus Druckversuchen an Lehmsteinen, -mörteln, kleinformatigen Lehmmauerwerksprobekörpern und geschosshohen Lehmmauerwerkswänden. Um das Feuchteverhalten beschreiben zu können, fanden außerdem erstmalig magnetresonanzspektroskopische Messungen an Lehmsteinen statt und es wurden die tatsächlich auftretenden Feuchtegehalte an einer Lehmmauerwerkswand unter natürlichen Klimabedingungen in Form von Langezeitmessungen ermittelt. Es konnte festgestellt werden, dass ein linearer Zusammenhang zwischen Druckfestigkeit und relativer Luftfeuchte besteht, wobei sich die Druckfestigkeit umgekehrt proportional zur relativen Luftfeuchte verhält. Je Prozent Steigerung der relativen Luftfeuchte kommt es zur Abnahme von einem Prozent der Druckfestigkeit. Gleiches gilt für das Elastizitätsmodul. Weiterhin konnte auf Basis der feuchtetechnischen Untersuchungen ein numerisches Modell zur Berechnung des instationären hygrothermischen Verhaltens für Lehmbaustoffe kalibriert werden. Anhand dieses Modells gelang es die bemessungsrelevanten Feuchtegehalte unter Berücksichtigung des instationären hygrothermischen Verhaltens realitätsnah zu berechnen. Die maximalen Feuchtegehalte im Lehmmauerwerk konnten somit in Form einer Parameterstudie in Abhängigkeit des Anwendungsfalls ermittelt werden, wodurch eine explizite Berücksichtigung des Feuchtegehaltes bei der Bemessung ermöglicht wurde. Die Verknüpfung der Erkenntnisse aus den mechanischen und hygrothermischen Untersuchungen dieser Arbeit bildet die Grundlage für das Bemessungskonzept der im Juni 2023 veröffentlichten DIN 18940: Tagendes Lehmsteinmauerwerk. KW - NMR KW - Lehm KW - Mauerwerk KW - Druckfestigkeit KW - Feuchtigkeit PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-637794 DO - https://doi.org/10.14279/depositonce-20800 SP - 1 EP - 114 CY - Berlin AN - OPUS4-63779 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Artinov, Antoni T1 - On the mathematical analysis of the relationship between the bulging region and the centerline solidification cracking in laser beam welding N2 - The present Ph.D. thesis provides a comprehensive experimental and theoretical study of the bulging-cracking relationship in laser beam welding of thick unalloyed steel sheets. It focuses on experimentally proving the existence of the bulging region and on developing a coupled multiphysics mathematical framework to analyze its influence on the three critical factors controlling the susceptibility to solidification cracking, namely the thermal, metallurgical, and mechanical factors. The research employs a novel experimental setup, utilizing a combination of transparent quartz glass and thick unalloyed steel sheet, enabling real-time visualization of the weld pool geometry and confirming the existence of a distinctive bulging region. To deepen the understanding of these experimental insights, an extensive multiphysics mathematical framework was developed and rigorously verified and validated. This framework introduces an innovative approach using Lamé curves for accurately describing complex three-dimensional weld pool geometries, including the bulging region's characteristics. Through analytical solutions and numerical procedures, it facilitates the computation of solidification parameters, which are crucial for understanding the metallurgical aspects of crack formation. The framework also incorporates a mechanical model to assess and evaluate the local stress distribution within the bulging region. The findings indicate that an elongated, sharply shaped bulging region significantly increases the susceptibility to solidification cracking. This is attributed to its adverse impact on the distribution and local dwell time of liquid metal residing at grain boundaries during solidification, combined with the localized tensile stresses identified in the bulging region. In essence, this research contributes to the broader understanding of solidification cracking in laser beam welding of thick unalloyed steel sheets, with a particular focus on the bulging region. The insights and methodologies developed in this thesis are valuable for future research and advancements in the application of the laser beam welding technology for joining high-thickness unalloyed steel components. KW - Bulging effect KW - Centerline solidification cracking KW - Mathematical modeling KW - Structural steel KW - High power laser beam welding PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-599010 DO - https://doi.org/10.14279/depositonce-20090 SP - 1 EP - 152 CY - Berlin AN - OPUS4-59901 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Schmidt, Selina T1 - Effects of biocides on processes underlying resistance evolution N2 - Antimicrobial resistance (AMR) is a global health problem. It is well known that antibiotics can drive evolutionary processes that underlie antimicrobial resistance (AMR) evolution and spread in clinical and environmental settings. In contrast, less is known about the effects of antimicrobial substances that are used as biocides (i.e. disinfectants and preservatives) on AMR evolution and spread. Biocides are present in various settings, interacting with diverse microbial communities. Therefore, it is crucial to evaluate their role in the evolution and dissemination of antimicrobial resistance. Biocides occur in a wide range of concentrations in various environmental settings. By examining how the various concentrations affect selection mechanisms, we gain insights into potential developments related to antimicrobial resistance. The aim of this PhD thesis is to investigate the effects of biocides on processes underlying resistance evolution. Specifically, the work focused on key mechanisms for resistance spread, resistance evolution, and the effect of selection pressures on evolved resistance mechanisms. The thesis is structured around three major objectives: (i) to determine the effect of biocides on the evolution of resistance by affecting the rate of occurrence of de novo mutations, (ii) to determine the effect of biocides on the spread of resistance genes by modifying the rate of horizontal gene transfer (HGT) processes, and (iii) to investigate the selective drivers of the emergence of antimicrobial resistance in adaptive laboratory evolution (ALE) experiments. De-novo mutations are spontaneous mutations that occur at a certain rate in microorganisms. The effect of biocides at subinhibitory environmentally relevant concentrations on the mutation rate in Acinetobacer baylyi, Bacillus subtilis and Escherichia coli was assessed with the fluctuation assay. The results showed that biocides affected mutation rates in a species and substance dependent matter. The bisbiguanide chlorhexidine digluconate, the quaternary ammonium compound didecyldimethylammonium chloride, the metal copper, the pyrethroid-insecticide permethrin, and the azole-fungicide propiconazole increase mutation rates in E. coli, whereas no increases were identified for B. subtilis and A. baylyi. Horizontal gene transfer refers to diverse mechanisms that mediate the transfer of mobile genetic elements between microorganisms. This work focused on conjugation and transformation. Conjugation is a process whereby a conjugative plasmid is transferred from a donor cell to a recipient cell. Transformation is a process whereby exogenous donor DNA is taken up into a recipient cell and integrated into the recipient’s’ genome. The effects of subinhibitory environmentally relevant biocide concentrations on the conjugation rate of E. coli and the transformation rate of the naturally competent organisms A. baylyi in were assessed. The results showed that benzalkonium chloride (BAC), chlorhexidine and permethrin increased conjugation in E. coli, while none of the biocides increased transformation rates in A. baylyi. To further understand the molecular mechanisms underlying the effects on mutation and conjugation rates, I investigated the induction of the RpoS-mediated general stress and the RecA-linked SOS response upon biocide exposure. The results show a link between the general stress and the SOS response with increased rates of mutation and conjugation, but not for all biocides. One major approach to study the evolutionary response of bacteria to antimicrobials are ALE experiments with growth at subinhibitory concentrations linked to serial subculturing over many generations. Such experiments have been used to study resistance evolution to antibiotics and biocides. However, previous work showed that adaptation to biocide stress may be mediated by different evolutionary drivers. Here, I investigated the contributions of evolution for increased survival as opposed to improved growth in ALE experiments with E. coli exposed to subinhibitory BAC concentrations. Two distinct evolutionary treatments selecting for survival only or survival and growth led to specific evolutionary adaptations apparent in the phenotypes and genotypes of the evolved populations. Populations growing in the presence of BAC evolved increased fitness in the presence of BAC associated with higher resistance to BAC and cross-resistance to antibiotics, while this was not the case for populations evolving for increased survival only. Genotypic characterization by whole genome sequencing of the evolved populations revealed parallelism in mutated genes among replicate populations and distinct differences across treatments. Treatments selecting for survival and growth showed mutations in stress response related genes (hslO and tufA), while selection for survival led to mutations in genes for metabolic regulation (cyaA) and cellular structure (flagella fliJ). In summary, this thesis shows that biocides affect AMR evolution and emphasizes the importance of understanding of how biocides impact the molecular and evolutionary process that underlie AMR evolution. KW - Biocides KW - Antimicrobial resistances KW - Microbial survival mechanisms PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:188-refubium-43383-9 SP - 1 EP - 101 PB - Freie Universität CY - Berlin AN - OPUS4-60678 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Ávila Calderón, Luis T1 - Mechanisches Verhalten von additiv gefertigtem nichtrostendem Stahl X2CrNiMo17-12-2 (AISI 316L) und Vergleich zur konventionell gefertigten Variante T1 - Mechanical behavior of additively manufactured stainless steel X2CrNiMo17-12-2 (AISI 316L) and comparison with a conventionally manufactured variant N2 - Die additive Fertigung (AM) metallischer Werkstoffe ist eine Technologie, die zunehmend Gegenstand von Forschungsaktivitäten und industrieller Anwendung ist. Dennoch steht sie noch vor Herausforderungen, um eine breite Nutzung in sicherheitsrelevanten Anwendungen zu erreichen. Die Hauptgründe für die Verzögerung des technologischen Durchbruchs zugunsten von AM-Metallen gegenüber konventionell hergestellten Varianten sind das Fehlen eines tieferen Verständnisses der Prozess-Struktur-Eigenschafts-Beziehungen und die begrenzte Verfügbarkeit von Daten zu den Materialeigenschaften. In diesem Kontext stellt diese Arbeit einen Beitrag sowohl zum Verständnis der Prozess-Struktur-Eigenschafts-Beziehungen als auch zur Verbesserung der Datenlage von 316L dar, einem häufig als Konstruktionswerkstoff in verschiedenen Hochtemperaturbauteilen verwendeten Werkstoff. Die Arbeit legt den Fokus auf die mittels Laser-Pulverbettschmelzen hergestellte Werkstoffvariante, PBF-LB/M/316L. Eine konventionell hergestellte Variante, HR/316L, wurde auch untersucht. Bei PBF-LB/M/316L wurde zusätzlich der Effekt ausgewählter Wärmebehandlungen ausgewertet. Die Untersuchung umfasste die Charakterisierung der mechanischen Eigenschaften und der Verformungs- und Schädigungsmechanismen bei erhöhten Prüftemperaturen bei LCF und Kriechen, wo die Daten und Wissenslage am spärlichsten ist. Außerdem hat die untersuchte PBF-LB/M/316L-Wersktoffvariante einen geringen Porositätsgrad. Somit hat diese Arbeit die Mikrostruktur stärker in den Fokus genommen als die meisten bisher in der Literatur verfügbaren Studien. Die mechanische Prüfkampagne umfasste Zugversuche zwischen Raumtemperatur und 650 °C, LCF-Versuche zwischen Raumtemperatur und 600 °C sowie Kriechversuche bei 600 °C und 650 °C. In Ermangelung konkreter Richtlinien und Normen wurde die Charakterisierung zumeist anhand der bestehenden internationalen Prüfnormen und Probengeometrien durchgeführt. Aus jedem dieser Prüfverfahren wurden die entsprechenden Festigkeits- und Verformungskennwerte ermittelt. Darüber hinaus wurde mit Hilfe gezielter mikrostruktureller Untersuchungen ein Beitrag zum Verständnis des Zusammenhangs zwischen der Mikrostruktur und den mechanischen Eigenschaften in Bezug auf die Verformungs- und Schädigungsmechanismen geleistet. Die Dehngrenze von PBF-LB/M/316L ist etwa doppelt so hoch wie die von HR/316L und dieser Trend setzt sich mit ansteigender Prüftemperatur fort. Die Bruchdehnung ist bei allen Prüftemperaturen geringer. PBF-LB/M/316L weist über den größten Teil der Ermüdungslebensdauer vor allem bei Raumtemperatur höhere zyklische Spannungen als HR/316L auf. Ausschließlich bei den kleinsten Dehnungs-schwingbreiten sind die Ermüdungslebensdauer ausgeprägt kürzer. Das Wechselverformungsverhalten von PBF-LB/M/316L ist durch eine Anfangsverfestigung gefolgt von einer kontinuierlichen Entfestigung charakterisiert, welche bis zum Auftreten der zum Versagen führenden Entfestigung stattfindet. Die Kriechbruchzeiten und die Dauer jeder Kriechphase sind bei allen Kombinationen von Prüfparametern bei PBF-LB/M/316 kürzer als bei HR/316L. Die Spannungsabhängigkeit von PBF-LB/M/316L ist im Vergleich zu HR/316L geringer und die Duktilität beim Kriechen kleiner. Die minimale Kriechrate wird bei allen geprüften Parameterkombinationen bei deutlich geringeren Kriechdehnungen erreicht. Eine Wärmebehandlung bei 450 °C / 4 h bewirkt keine wesentliche Änderungen der Mikrostruktur und Zugversuchseigenschaften. Eine zusätzliche Wärmebehandlung bei 900 °C / 1 h verursacht eine Abnahme der Dehngrenze des PBF-LB/M/316L. Diese blieb aber immer noch um den Faktor 1,5x höher als bei HR/316L. Die Verformungsmerkmale wurden kaum davon beeinflusst. Bezüglich des Kriechverhaltens hat die Wärmebehandlung bei 900 °C / 1 h längere sekundäre und tertiäre Kriechstadien bewirkt und die Kriechdehnung hat sich signifikant erhöht. Die Bruchbilder unterscheiden sich generell nicht nur aber vor allem mit ansteigender Prüftemperatur, bei der bei PBF-LB/M/316L oft interkristalline Rissbildung beobachtet wurde. Die Zellstruktur trägt als der Hauptfaktor zu den unterschiedlichen mechanischen Eigenschaften im Vergleich zur HR/316L-Variante bei. Darüber hinaus spielen mutmaßlich die Kornmorphologie, die Stapelfehlerenergie und der Stickstoffgehalt eine Rolle. N2 - Metal additive manufacturing (AM) is a technology that is increasingly the subject of research activities and industrial applications. However, it still faces challenges to achieve widespread use in safety-relevant applications. The main reasons for the delay of this technological breakthrough in favor of AM metals over conventionally manufactured variants are the lack of a deeper understanding of process-structure-property relationships and the limited availability of data on material properties. In this context, this work contributes to both achieving a better understanding of process-structure-property relationships and the improvement of data for 316L, an alloy frequently used as a structural material in various high-temperature components. The work focuses on a material variant produced by laser pow-der bed fusion, PBF-LB/M/316L. A conventionally produced variant, HR/316L, was also investigated. For PBF-LB/M/316L, the effect of selected heat treatments was also evaluated. The investigation included the characterization of the mechanical properties and the related deformation and damage mechanisms at elevated test temperatures in LCF and creep, where data and knowledge are scarce. The PBF-LB/M/316L variant studied has a low degree of porosity. Thus, this work is more focused on the microstructure than most studies available in the literature. The mechanical test campaign included tensile tests between room temperature and 650 °C, LCF tests between room temperature and 600 °C, and creep tests at 600 °C and 650 °C. In the absence of concrete guidelines and standards for testing of AM metals, the characterization mostly took place using existing international test standards and specimen geometries. From each of the test methods, corresponding strength, and deformation characteristic values were determined. In addition, targeted microstructural investigations contributed to understanding the relationship between the microstructure and the mechanical properties in terms of deformation and damage mechanisms. The proof stress of PBF-LB/M/316L is about twice that of HR/316L. This trend remains with increasing test temperature. The elongation after fracture is lower at all test temperatures. Regarding LCF, PBF-LB/M/316L exhibits higher cyclic stresses than HR/316L for most of the fatigue life, especially at room temperature. Exclusively at the smallest strain amplitudes, the fatigue lives of PBF-LB/M/316L are markedly shorter than in HR/316L. The cyclic stress-strain deformation behavior of PBF-LB/M/316L features an initial strain hardening followed by a continuous softening, which occurs until the softening leading to failure takes place. The creep rupture times and the duration of each creep stage are shorter for PBF-LB/M/316 than for HR/316L for all combinations of test parameters. The stress dependence of PBF-LB/M/316L is lower, and the creep ductility is smaller compared to HR/316L. The minimum creep rate is reached at significantly lower creep extensions for all parameter combinations tested. A heat treatment at 450 °C / 4 h did not cause significant changes in the microstructure and tensile behavior. An additional heat treatment at 900 °C / 1 h caused a decrease in the proof stress of PBF-LB/M/316L. However, it still remained higher than the one of HR/316L by a factor of 1.5x. The deformation characteristics were hardly affected. Regarding the creep behavior, this latter heat treatment at 900 °C / 1 h caused longer secondary and tertiary creep stages, and the creep strain increased significantly. The fracture characteristics generally differed, which happened not only but especially with increasing test temperature, where intergranular cracking often took place in PBF-LB/M/316L. The cellular structure is considered the main factor contributing to the different mechanical properties compared to the HR/316L variant. In addition, grain morphology, stacking fault energy, and nitrogen content might play a role. KW - AGIL KW - Additive Fertigung KW - Laser-Pulverbettschmelzen KW - Mikrostrukturentwicklung KW - 316L KW - LCF KW - Kriechen KW - Additive Manufacturing KW - Microstructure KW - Mechanical Properties KW - Mechanische Eigenschaften PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-597143 DO - https://doi.org/10.14279/depositonce-19828 SP - 1 EP - 190 CY - Berlin AN - OPUS4-59714 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Han, Ying T1 - Hochtemperaturermüdung der Aluminiumlegierung EN AW-2618A N2 - Abgasturbolader tragen wesentlich zur Effizienzsteigerung moderner Verbrennungsmotoren bei. Die im Abgasturbolader eingesetzten Radialverdichterräder werden überwiegend aus der warmfesten ausscheidungsgehärteten Aluminiumlegierung EN AW-2618A hergestellt. Die Anforderungen an die Radialverdichterräder steigen und die Betriebszeiten verlängern sich. Für eine optimale Auslegung des Bauteils ist unter anderem die Kenntnis des Ermüdungsverhaltens dieser Legierung erforderlich. Es ist bekannt, dass sich die Mikrostruktur dieser Legierung während des Betriebs vergröbert und dadurch die Festigkeit abnimmt. Das niederzyklische Ermüdungsverhalten für den Ausgangszustand des Werkstoffs und Prüftemperaturen bis 190 °C ist bereits gut untersucht. Für das hochzyklische Ermüdungsverhalten, insbesondere für Prüftemperaturen über 190 °C, liegen jedoch nur wenige Ergebnisse vor. Das Ziel dieser Arbeit ist es daher, die Datenbasis hinsichtlich der hochzyklischen Ermüdungslebensdauer bei erhöhten Prüftemperatur zu vervollständigen und das Werkstoffverhalten sowie die Schädigungsmechanismen zu charakterisieren. Zu diesem Zweck wurden axiale Ermüdungsversuche an glatten Proben durchgeführt. Neben dem T61-Ausgangszustand für eine Basischarakterisierung wurden zwei überalterte Zustände, jeweils bei 230 °C für 10 h und 1000 h ausgelagert und anschließend geprüft, um den Einfluss der Überalterung auf die Ermüdungslebensdauer zu erfassen. Die Auslagerungstemperatur von 230 °C der überalterten Zustände liegt deutlich über der Aushärtungstemperatur von 195 °C des T61-Zustands, was zu Veränderungen der optimal eingestellten Mikrostruktur führt, die sich wiederum in den mechanischen Eigenschaften widerspiegeln. Mit der Überalterungszeit von 10 h wurde ein Zustand untersucht, der einem Härteniveau entspricht, der bei Bauteilrückläufern nach Langzeitbetrieb beobachtet wurde und mit der Überalterungszeit von 1000 h wurden die Werkstoffgrenzen ermittelt. Zusätzlich wurde mittels Transmissionselektronenmikroskopie (TEM) die Vergröberung der festigkeitssteigernden S-Phase untersucht. Der Einfluss der Prüftemperatur auf die Ermüdungslebensdauer wurde durch Versuche bei 230 °C untersucht. Die Ermüdungsversuche wurde durch fraktographische Untersuchungen ergänzt und ausgewählte Ermüdungsversuche wurden mit zerstörungsfreien Prüfmethoden begleitet, um die Schädigung mit zunehmender Zyklenzahl dazustellen. Die Ergebnisse dieser Untersuchungen zeigen eine kürzere Ermüdungslebensdauer für die längere Überalterungszeit bei gleicher Spannungsamplitude. Die Transmissionselektronenmikroskopie zeigt, dass der mittlere Radius der S-Phase nach einer Überalterungszeit von 10 h um den Faktor 2,3 und nach 1000 h um den Faktor 2,7 im Vergleich zum Ausgangszustand zunimmt. Eine Erhöhung der Prüftemperatur auf 230 °C führt bei gleicher Spannungsamplitude zu einer Verkürzung der Ermüdungslebensdauer im Vergleich zu Raumtemperatur. Die fraktographischen Untersuchungen zeigen, dass unabhängig vom Werkstoffzustand und der Prüftemperatur die Rissinitiierung überwiegend an der Probenoberfläche oder in der Nähe der Primärphasen erfolgt. Das Risswachstum mit zunehmender Zyklenzahl kann mit der Replika-Methode erfolgreich abgebildet werden. Die Abbildung des Risses in der noch nicht gebrochenen Probe ist auch mit der Computertomographie möglich. KW - Aluminiumlegierung KW - EN AW-2618A KW - Ermüdung KW - HCF KW - Mikroskopie KW - Fraktographie PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-615288 DO - https://doi.org/10.14279/depositonce-21381 SP - 1 EP - 109 PB - Depostit Once CY - Berlin AN - OPUS4-61528 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Charmi, Amir T1 - A multiscale numerical framework for the simulation of anistropic material response of additively manufactured stainless steel 316L undergoing large plastic deformation N2 - Additive manufacturing (AM) offers significantly greater freedom of design compared to conventional manufacturing processes since the final parts are built layer by layer. This enables metal AM, also known as metal 3D printing, to be utilized for improving efficiency and functionality, for the production of parts with very complex geometries, and rapid prototyping. However, despite many technological advancements made in recent years, several challenges hinder the mass adoption of metal AM. One of these challenges is mechanical anisotropy which describes the dependency of material properties on the material orientation. Therefore, in this work, stainless steel 316L parts produced by laser-based powder bed fusion are used to isolate and understand the root cause of anisotropy in AM parts. Furthermore, an efficient and accurate multiscale numerical framework is presented for predicting the deformation behavior of actual AM parts on the macroscale undergoing large plastic deformations. Finally, a novel constitutive model for the plastic spin is formulated to capture the influence of the microstructure evolution on the material behavior on the macroscale. KW - Additive Fertigung KW - Austenitischer Stahl KW - Finite-Elemente-Methode KW - Mehrskalenmodell KW - Simulation PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:gbv:wim2-20240207-173356-002 DO - https://doi.org/10.25643/dbt.59550 SP - 1 EP - 163 PB - Bauhaus-Universität Weimar CY - Weimar AN - OPUS4-59511 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Erdmann, Eileen A. T1 - Genetic tools for targeted genome editing and random mutagenesis of the rock-inhabiting black fungus Knufia petricola N2 - Rock-inhabiting black fungi are ubiquitously found on sun-exposed natural and human-made surfaces. These stresstolerant biofilm-formers are known to force the deterioration of the colonized surfaces. Black fungi belong to different classes of Ascomycota (Arthoniomycetes, Eurotiomycetes, and Dothideomycetes) but evolved the same morpho-physiological adaptations such as strong melanized multilayered cell walls and slow yeast-like or meristematic growth to resist extreme environmental conditions. The rock-inhabitant Knufia petricola was chosen as representative of the polyphyletic group of black fungi for studying mineral weathering, biofilm formation, and interaction with phototrophic microbes. For understanding the molecular basis of these traits, the genetic information and its regulation must be explored. Thus, the genome was sequenced, first -omics datasets obtained and protocols for the transformation of protoplasts and CRISPR/Cas9-based genome editing were implemented to enable genetic studies. In scope of this work, the transformation protocol was optimized to improve the regeneration of K. petricola protoplasts. The successful implementation of multiplexed CRISPR/Cas9 and three additional selection marker systems (geneticin/nptII, glufosinate/bar, chlorimuron ethyl/sur) extended the existing strategies for targeted genome editing. While in the first promoter studies only constitutive promoters (PoliC, PgpdA) were identified as appropriate for expression of fluorescent reporter genes in K. petricola, the functionality of an inducible promoter (synthetic TET-on promoter system) could later be demonstrated. The identification and validation of defined genomic insertion sites enabled the neutral or color-based selection (igr1-5 or pks1, phs1, ade2) as well as the detection of correctly integrated expression constructs. Using the color-based transformant screening (black – pink/white/rose) accelerated the selection of transformants, especially for localization and protein-protein interaction studies (e.g., by studying bimolecular fluorescence complementation). Additionally, the fusion of two or three genes via the viral P2A motif was shown to allow the expression of multiple genes from a single expression cassette/integration site. Finally, the established tools enabled the implementation of a forward genetics tool (customized Ac/Ds transposon system) for regulatable in-vivo mutagenesis of K. petricola. The isolation and characterization of revertants/Ds reinsertion mutants demonstrated the functionality of the system which marks an important milestone for assigning functions to yet unknown species- and/or trait-specific genes. In sum, the genetic engineering toolbox is now fully equipped which paves the way for exploring the biology of K. petricola and other black fungi. KW - Microcolonial fungi KW - Genetic engineering KW - CRISPR/Cas9-mediated genome editing KW - DHN melanin KW - Transposon mutagenesis PY - 2024 SP - 1 EP - 231 CY - Berlin AN - OPUS4-62364 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -