13 Zentrale Universitätseinrichtungen
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/14
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Item Open Access Investigation of oxide layer development of X6CrNiNb18-10 stainless steel exposed to high-temperature water(2024) Veile, Georg; Hirpara, Radhika; Lackmann, Simon; Weihe, StefanThe oxide layer development of X6CrNiNb18-10 (AISI 347) during exposure to high-temperature water has been investigated. Stainless steels are known to form a dual oxide layer in corrosive environments. The secondary Fe-rich oxide layer has no significant protective effect. In contrast, the primary Cr-rich oxide layer is known to reach a stabilized state, protecting the base metal from further oxidation. This study’s purpose was to determine the development of oxide layer dimensions over exposure time using SEM, TEM and EDX line scans. While a parabolic development of Cr in the protective primary layer and Fe in the secondary layer was observed, the dimensions of the Ni layer remained constant. Ni required the presence of a pronounced Fe-rich secondary layer before being able to reside on the outer secondary layer. With increasing immersion time, the Ni element fraction surpassed the Cr element fraction in the secondary layer. Oxide growth on the secondary layer could be observed. After 480 h, nearly the entire surface was covered by the outer oxide layer. In the metal matrix, no depletion of Cr or Ni could be observed over time; however, an increased presence of Cr and Ni in the primary layer was found at the expense of Fe content. The Nb-stabilized stainless steel was subject to the formation of Niobium pentoxide (Nb2O5), with the quantity and magnitude of element fraction increasing over exposure time.Item Open Access Performance comparison of CFD microbenchmarks on diverse HPC architectures(2024) Galeazzo, Flavio C. C.; Garcia-Gasulla, Marta; Boella, Elisabetta; Pocurull, Josep; Lesnik, Sergey; Rusche, Henrik; Bnà, Simone; Cerminara, Matteo; Brogi, Federico; Marchetti, Filippo; Gregori, Daniele; Weiß, R. Gregor; Ruopp, AndreasOpenFOAM is a CFD software widely used in both industry and academia. The exaFOAM project aims at enhancing the HPC scalability of OpenFOAM, while identifying its current bottlenecks and proposing ways to overcome them. For the assessment of the software components and the code profiling during the code development, lightweight but significant benchmarks should be used. The answer was to develop microbenchmarks, with a small memory footprint and short runtime. The name microbenchmark does not mean that they have been prepared to be the smallest possible test cases, as they have been developed to fit in a compute node, which usually has dozens of compute cores. The microbenchmarks cover a broad band of applications: incompressible and compressible flow, combustion, viscoelastic flow and adjoint optimization. All benchmarks are part of the OpenFOAM HPC Technical Committee repository and are fully accessible. The performance using HPC systems with Intel and AMD processors (x86_64 architecture) and Arm processors (aarch64 architecture) have been benchmarked. For the workloads in this study, the mean performance with the AMD CPU is 62% higher than with Arm and 42% higher than with Intel. The AMD processor seems particularly suited resulting in an overall shorter time-to-solution.Item Open Access Investigating the design and usability of 360° image annotations in the context of campus accessibility(2024) König, SolveighMobility enables equal participation in social life and fulfils basic human needs. Students with mobility impairments face many problems when travelling to target locations at a university caused by the design of the physical environment. This often forces them to choose longer and partially more complex routes. Consequently, they have different travel behaviours and need to develop a more detailed plan in advance than students without disabilities. For developing a plan, reliable and current accessibility information, especially for buildings is crucial. Currently, the amount and level of detail of information, particularly about the interior of university buildings, is rarely provided online. This makes virtual reality technology a promising solution. In this thesis, we want to investigate the design and usability of a virtual 360° tour focusing on accessibility information for a university campus. Therefore a prototype for one building at the University of Stuttgart has been implemented, including visualizations with accessibility information. The requirements for the prototype were collected with a focus group, an online survey and literature research. The virtual tour allows users to individually assess the accessibility of the building by virtually walking around and receiving hints and navigations. The presented approach was evaluated in a user study and is considered a very helpful tool that should be extended to the whole university campus in the future. The results of this work show that visual information sources have great significance and that size data about doors, entrances and corridors is important when planning a campus visit.Item Open Access Theoretical-numerical investigation of a new approach to reconstruct the temperature field in PBF-LB/M using multispectral process monitoring(2024) May, Lisa; Werz, MartinThe monitoring of additive manufacturing processes such as powder bed fusion enables the detection of several process quantities important to the quality of the built part. In this context, radiation-based monitoring techniques have been used to obtain information about the melt pool and the general temperature distribution on the surface of the powder bed. High temporal and spatial resolution have been achieved at the cost of large storage requirements. This contribution aims to offer an alternative strategy of gaining information about the powder bed’s temperature field with sufficient resolution but with an economical amount of data. The investigated measurement setup uses a spectrometer to detect the spectral radiation intensities emitted by an area enclosing the melt pool and part of its surroundings. An analytical description of this process is presented, which shows that the measured spectral entities can be reconstructed by the Ritz method. It is also shown that the corresponding weighting factors can be physically interpreted as subdomains of constant temperature within the measurement area. Two different test cases are numerically analyzed, showing that the methodology allows for an approximation of the melt pool size while further assumptions remain necessary to reconstruct the actual temperature distribution.Item Open Access Development of a hybrid user interface for skill-based robot programming(2024) Kolberg, JanRobot programming is a well-known and time-consuming task.\enspace Various methods have been developed over the years to simplify this process. However, most of these methods focus on a singular device for programming. This thesis applies the concept of Hybrid User Interfaces (HUI) to skill-based robot programming and tests the potential advantage of combining multiple devices to form a user interface. The developed system consists of a Head Mounted Display (HMD), a desktop application, and a smartphone application. It allows the creation and parameterization of skills to form applications, the definition of 3D positions, the simulation with a virtual robot, and the execution on a real robot. An exploratory user study was conducted to show the benefits of such HUIs for online robot programming for assembly tasks. The results show that users mostly prefer the traditional desktop interface to create the main program flow. However, the HMD and smartphone applications were still used for specific sub-tasks, like creating new positions in the 3D space, visualization of a virtual robot, or finetuning parameter values. Based on the results gathered, research questions for future research were formulated.Item Open Access User-centric approach of visual cues to enhance VR orientation for people with visual impairments(2024) Baric̆ová, KatarinaFor successful navigation through the world, a good orientation is needed. Our orientation is directly influenced by how well we can build and use a cognitive map of the environment around us. Cognitive maps are mental representations of spatial information of an environment. A lack of visual information can impede the successful acquisition of a cognitive map. As such, people with impaired vision can struggle with tasks requiring spatial orientation. With a goal to facilitate orientation, we created a set of visual cues designed to compensate for the lack of information needed for cognitive mapping. To meet the needs of different visual impairment, we followed a user-centric approach for the visual cue design. For this, we first conducted a formative interview with visually impaired people, investigating what information should be highlighted and how. With these insights, we created six different visual cue categories providing information about Obstacles, Points of Interest (POI), Entrances, and Shape Information. The visual cues in each category come in different forms, tailored to different needs. In a subsequent user study, we let participants with impaired vision explore a city scene in Virtual Reality using our visual cues. To evaluate the cues’ efficacy for orientation, our study investigated the participants’ cognitive mapping process. Our study results indicate that four out of five participants were able to successfully build and use a cognitive map of the virtual city. Given a remaining vision of 10%-15% combined with a Field of View of less than 5°, the visual cues could not provide sufficient aid. Nonetheless, all visual cue categories were reported as helpful, with the Shape Information cues being deemed as most important for exploration.Item Open Access Investigation of tool degradation during friction stir welding of hybrid aluminum-steel sheets in a combined butt and overlap joint(2024) Göbel, Robin; Schwertel, Stefanie; Weihe, Stefan; Werz, MartinFriction stir welding, as a solid-state welding technique, is especially suitable for effectively joining high-strength aluminum alloys, as well as for multi-material welds. This research investigates the friction stir welding of thin aluminum and steel sheets, an essential process in the production of hybrid tailor-welded blanks employed in deep drawing applications. Despite its proven advantages, the welding process exhibits variable outcomes concerning formability and joint strength when utilizing an H13 welding tool. To better understand these inconsistencies, multiple welds were performed in this study, joining 1 mm thick steel to 2 mm thick aluminum sheets, with a cumulative length of 7.65 m. The accumulation of material on the welding tool was documented through 3D scanning and weighing. The integrity of the resulting weld seam was analyzed through metallographic sections and X-ray imaging. It was found that the adhering material built up continuously around the tool pin over several welds totaling between 1.5 m and 2.5 m before ultimately detaching. This accretion of material notably affected the welding process, resulting in increased intermixing of steel particles within the aluminum matrix. This research provides detailed insights into the dynamics of friction stir welding in multi-material welds, particularly in the context of tool material interaction and its impact on weld quality.Item Open Access Characterisation of adobe and mud-straw for the restoration and rehabilitation of Persian historical adobe buildings(2024) Hejazi, Bina; Luz, Corinna; Grüner, Friedrich; Frick, Jürgen; Garrecht, HaraldIn the restoration or rehabilitation of traditional buildings, compatible materials with known characteristics must be used. However, the existing literature lacks comprehensive studies on the characterisation of Persian mud-straw plaster, focusing primarily on Persian adobe. Moreover, previous research on Persian adobe has primarily employed XRF and XRD tests, neglecting ion chromatography, moisture sorption isotherm determination, and thermogravimetric analysis with differential scanning calorimetry. Consequently, there is a shortage of information regarding the elemental composition, mineralogical characteristics, moisture sorption behaviour, and thermal properties of Persian mud–straw plaster, as well as Persian adobe bricks. This paper aims to address this research gap by examining historical and new adobe bricks and mud–straw plaster used in Iran, utilising a comprehensive array of analytical techniques. The results from XRF analysis reveal relatively similar chemical compositions across all samples, while XRD analysis indicates predominantly similar mineral phases. Ion chromatography results demonstrate higher conductivity and chloride concentrations in the mud–straw samples than the adobe samples, with higher values for new samples than historical ones. Freshly used straw, clay, or soil may have higher chloride concentrations caused by the arid climate and soil salinisation in the area. Additionally, moisture sorption isotherm determination results show that adobe and mud–straw plaster with a higher salt load of chlorides have significantly higher moisture absorption. The increased straw quantity in the samples increases the moisture content. Furthermore, thermogravimetric analysis and differential scanning calorimetry indicate that, at low heating, adobe and mud–straw plaster lose water due to dehydration, and at high heating, they lose carbon dioxide due to decarboxylation. The comprehensive characterisation of Persian adobe and mud–straw plaster in this study fills a significant gap in the literature and offers invaluable insights for informing restoration and rehabilitation processes, ensuring the compatibility of the materials used.Item Open Access Investigations of metallurgical differences in AISI 347 and their influence on deformation and transformation behaviour and resulting fatigue life(2024) Veile, Georg; Regitz, Elen; Smaga, Marek; Weihe, Stefan; Beck, TillmannDue to variations in chemical composition and production processes, homonymous austenitic stainless steels can differ significantly regarding their initial microstructure, metastability, and thus, their fatigue behavior. Microstructural investigations and fatigue tests have been performed in order to evaluate this aspect. Three different batches and production forms of nominally one type of steel AISI 347 were investigated under monotonic tensile tests and cyclic loading under total strain and stress control in low and high cycle fatigue regimes, respectively. The deformation induced α’-martensite formation was investigated globally by means of in situ magnetic measurements and locally using optical light microscopy of color etching of micrographs. The investigation showed that the chemical composition and the different production processes influence the material behavior. In fatigue tests, a higher metastability and thus a higher level of deformation induced α’-martensite pronounced cyclic hardening, resulting in significantly greater endurable stresses in total strain-controlled tests and an increase in fatigue life in stress-controlled tests. For applications of non-destructive-testing, detailed knowledge of a component’s metastability is required. In less metastable batches and for lower stress levels, α’-martensite primarily formed at the plasticization zone of a crack. Furthermore, the formation and nucleation points of α’-martensite were highly dependent on grain size and the presence of δ-ferrite. This study provides valuable insights into the different material behavior of three different batches with the same designation, i.e., AISI 347, due to different manufacturing processes and differences in the chemical composition, metastability, and microstructure.Item Open Access An innovative technological infrastructure for managing SARS-CoV-2 data across different cohorts in compliance with General Data Protection Regulation(2024) Dellacasa, Chiara; Ortali, Maurizio; Rossi, Elisa; Abu Attieh, Hammam; Osmo, Thomas; Puskaric, Miroslav; Rinaldi, Eugenia; Prasser, Fabian; Stellmach, Caroline; Cataudella, Salvatore; Agarwal, Bhaskar; Mata Naranjo, Juan; Scipione, GabriellaBackground: The ORCHESTRA project, funded by the European Commission, aims to create a pan-European cohort built on existing and new large-scale population cohorts to help rapidly advance the knowledge related to the prevention of the SARS-CoV-2 infection and the management of COVID-19 and its long-term sequelae. The integration and analysis of the very heterogeneous health data pose the challenge of building an innovative technological infrastructure as the foundation of a dedicated framework for data management that should address the regulatory requirements such as the General Data Protection Regulation (GDPR). Methods: The three participating Supercomputing European Centres (CINECA - Italy, CINES - France and HLRS - Germany) designed and deployed a dedicated infrastructure to fulfil the functional requirements for data management to ensure sensitive biomedical data confidentiality/privacy, integrity, and security. Besides the technological issues, many methodological aspects have been considered: Berlin Institute of Health (BIH), Charité provided its expertise both for data protection, information security, and data harmonisation/standardisation. Results: The resulting infrastructure is based on a multi-layer approach that integrates several security measures to ensure data protection. A centralised Data Collection Platform has been established in the Italian National Hub while, for the use cases in which data sharing is not possible due to privacy restrictions, a distributed approach for Federated Analysis has been considered. A Data Portal is available as a centralised point of access for non-sensitive data and results, according to findability, accessibility, interoperability, and reusability (FAIR) data principles. This technological infrastructure has been used to support significative data exchange between population cohorts and to publish important scientific results related to SARS-CoV-2. Conclusions: Considering the increasing demand for data usage in accordance with the requirements of the GDPR regulations, the experience gained in the project and the infrastructure released for the ORCHESTRA project can act as a model to manage future public health threats. Other projects could benefit from the results achieved by ORCHESTRA by building upon the available standardisation of variables, design of the architecture, and process used for GDPR compliance.