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 - 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 - 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 - 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 - 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 - 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 - 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 - Ebell, Gino T1 - Zur Deckschichtbildung an feuerverzinkten Betonstählen in chloridhaltigen Mörteln N2 - In der vorliegenden Dissertation wurde das Korrosionssystem verzinkter Stahl in alkalischen, zementbasierten Feststoffelektrolyten untersucht. Dabei kamen drei Zementarten mit je vier Chloridgehalten zur Anwendung. Neben dem Korrosionssystem lag das Augenmerk ebenso auf einer adäquaten Beschreibung der Elektrolyteigenschaften. Hierzu wurde die Masseänderung, die Änderung des elektrischen Mörtelwiderstandes und des IR-Drop über die Zeit sowie die Porosität und die Porenwasserzusammensetzung, um nur einige Kenngrößen zu nennen, untersucht. Das Hauptaugenmerk ruht jedoch auf der Beschreibung des Korrosionssystems verzinkter Stahl in Mörtel. Dazu wurden die gebildeten Deckschichten und deren Einfluss auf den Korrosionsfortschritt in Abhängigkeit von der Zementart und des Chloridgehaltes sowie die daraus resultierenden elektrochemischen Kennwerte bestimmt. Die aus den Untersuchungen hervorgehenden Ergebnisse ermöglichen es, die Korrosionssysteme in Abhängigkeit vom Chloridgehalt oder von geometrischen Inhomogenitäten, im Phasengrenzbereich Mörtel/verzinkter Stahl zu differenzieren. Dabei konnte unabhängig von den verwendeten Zementen eine Klassifizierung der Korrosionssysteme über den Phasenwinkel 0,1 Hz erfolgen. Klassifiziert wurden durchtrittskontrollierte und diffusionskontrollierte Korrosionssysteme, Mischsysteme, Übergangssysteme und Korrosionssysteme mit Spaltgeometrie. Für diese Korrosionssysteme konnte festgestellt werden, welche Deckschichten maßgebenden Einfluss auf die Ausbildung eines durchtrittskontrollierten Korrosionssystem haben. Dazu gehören das bereits bekannte Simonkolleit und eine Deckschichtvariante, die bisher noch nicht in der Literatur als Deckschicht an verzinktem Betonstahl in Mörtel oder Beton beschrieben wurde. Für die Mischsysteme erfolgte eine Darstellung der anteiligen Bedeckung mit Simonkolleit, um den Übergang zu einem durchtrittskontrollierten Korrosionssystemen zu beschreiben. Neben der Klassifizierung der Korrosionssysteme kann über die Bestimmung des Phasenwinkels bei 0,1 Hz jedem Korrosionssystem nun auch ein spezifischer B-Wert zugewiesen werden. In Kombination mit der für diese Korrosionssysteme angepassten LPR-Messungen zur Bestimmung des Polarisationswiderstandes können Korrosionsraten ohne signifikante Beeinflussung des Korrosionssystems bestimmt werden. KW - Korrosion KW - Feuerverzinken KW - Betonstahl PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-631696 DO - https://doi.org/10.26204/KLUEDO/7427 SP - 1 EP - 166 PB - RPTU CY - Kaiserslautern AN - OPUS4-63169 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -