TY - CONF A1 - Höhne, Patrick T1 - Optimized spray granules for dry pressing by means of slurry destabilization and ultrasonic atomization N2 - The homogeneous introduction of organic additives is a prerequisite for good processability of ceramic powders during dry pressing. The addition of organic additives by wet route via ceramic slurries offers advantages over dry processing. The organic content can be reduced and a more homogeneous distribution of the additives on the particle surface is achieved. In addition to the measurements of zeta potential and viscosity, sedimentation analysis by optical centrifugation was also tested and successfully used to characterize the ceramic slurries and accurately evaluate of the suitability of different types, amounts, and compositions of organic additives. Spray drying of well-stabilized slurries usually results in mostly hollow granules with a hard shell leading to sintered bodies with defects and reduced strength and density. By purposefully degrading the slurry stability after dispersion of the ceramic powder, the drying behavior of the granules in the spray drying process and thus the granule properties can be influenced. Destabilization of the slurry and thus partial flocculation was quantified by optical centrifugation. Spray drying of the destabilized alumina slurries resulted in "non-hollow" granules without the detrimental hard shell and thus improved granule properties. Further improvement of the granules was achieved by installing ultrasonic atomization in the spray dryer. A narrower granule size distribution was achieved, which had a positive effect on, among other things, the flowability of the granules. Specimens produced from this granules had fewer defects of smaller size, leading to better results for the density and strength of the sintered bodies. The observations made for alumina could be transferred to zirconia and as well to ZTA with 20 wt% zirconia. T2 - Ceramics in Europe 2022 CY - Krakau, Poland DA - 10.07.2022 KW - Ultrasound KW - Spray drying KW - Slurry PY - 2022 AN - OPUS4-56171 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Chen, Yue T1 - Ontopanel: a diagrams.net plugin for graphical semantic modelling N2 - Ontologies that represent a map of the concepts and relationships between them, are becoming an effective solution for data standardization and integration of different resources in the field of materials science, as efficient data storage and management is the building block of material digitization. However, building a domain ontology is not a simple task. It requires not only a collaborative effort between ontologists and domain experts, but also the modeling approaches and tools play a key role in the process. Among all approaches, graphical representation of domain ontologies based on standard conceptual modeling languages is widely used because of its intuitiveness and simplicity. Various tools have been developed to realize this approach in an intuitive way, such as Protégé plugins and web visualization tools. The Materials-open-Lab (MatOLab) project, which aims to develop ontologies and workflows in accordance with testing standards for the materials science and engineering domains, adopted a UML (Unified Modeling Language) approach based on the diagrams.net. It is a powerful, popular, open-source graphical editor. In practical case studies, however, many users’ needs could not be met, such as reusing ontology, conversion, and data mapping. Users must switch between different tools to achieve a certain step, and thereby invariably increase learning cost. The lack of validation also leads to incorrect diagrams and results for users who are not familiar with the ontology rules. To address these issues, we designed Ontopanel, a diagrams.net-based plugin that includes a set of pipeline tools for semantic modeling: importing and displaying protégé-like ontologies, converting diagrams to OWL, validating diagrams by OWL rules, and mapping data. It uses diagrams.net as the front-end for method modeling and Django as the back-end for data processing. As a web-based tool, it is very easy to expand its functionality to meet changing practical needs. T2 - MSE 2022 CY - Darmstadt, Germany DA - 27.09.2022 KW - Ontology KW - Tools KW - Material digital KW - Mat-o-lab KW - Graphic design KW - Ontology development KW - Data mapping KW - FAIR KW - Materials testing PY - 2022 AN - OPUS4-55884 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Beygi Nasrabadi, Hossein A1 - Skrotzki, Birgit T1 - Ontology-oriented modeling of the Vickers hardness knowledge graph N2 - This research deals with the development of the Vickers hardness knowledge graph, mapping the example dataset in them, and exporting the data-mapped knowledge graph as a machine-readable Resource Description Framework (RDF). Modeling the knowledge graph according to the standardized test procedure and using the appropriate upper-level ontologies were taken into consideration to develop the highly standardized, incorporable, and industrial applicable models. Furthermore, the Ontopanel approach was utilized for mapping the real experimental data in the developed knowledge graphs and the resulting RDF files were successfully evaluated through the SPARQL queries. T2 - ICMMM 2023: 10th International Conference on Mechanics, Materials and Manufacturing CY - Washington, D.C., USA DA - 18.08.2023 KW - Ontology KW - Knowledge graph KW - Data mapping KW - Vickers hardness KW - FAIR data PY - 2023 AN - OPUS4-58100 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Mieller, Björn T1 - Ontologies and data pipelines - a field report from the development of multilayer ferrite inductors N2 - Digitalization is a current and prominent cross-cutting topic in ceramics and materials science in general. Many research initiatives and levels of significance are associated with this term. The Initiative Platform MaterialDigital (PMD), for example, aims to create a material data space filled with semantically linked data. The concept envisages that semantic relationships between the data are described as ontologies and that processing of data takes place via automated data pipelines. Various research projects from all areas of materials science are working on the implementation of this concept based on specific use cases. In the project presented here, the use case is the development of multilayer ferrite inductors as passive microelectronic components. The inductors are fabricated by ceramic multilayer technology and co-firing of metallized tapes of NiCuZn ferrite and a dielectric base material. Investigations focus on the effects of fabrication technology on the permeability of the ferrite. A data pipeline is introduced that automatically processes the unstructured experimental data into structured, machine-readable and semantically linked data. The concrete implementation of the data pipeline and a domain ontology is presented using examples. Challenges and advantages are discussed. T2 - CERAMICS 2024 / 99th DKG Annual Meeting CY - Höhr-Grenzhausen, Germany DA - 09.09.2024 KW - Ontology KW - Ceramic multilayer KW - MaterialDigital PY - 2024 AN - OPUS4-61037 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Darvishi Kamachali, Reza T1 - On the origin of embrittlement in Mn containing and Zn-coated steels N2 - Grain boundary embrittlement in medium-Mn steels and liquid metal embrittlement (LME) in Zn-coated high strength steels are among key challenges on the way of safe application of sustainable steels for automotive industry. Using a novel density-based model for grain boundaries, we reveal that the affinity of a grain boundary to attract Mn and Zn atoms result in a segregation transition accompanied by interfacial structural changes. In case of the Zn, the simulations show that the amount of segregation abruptly increases with decreasing temperature, while the Zn content in the alloy, required for triggering the segregation transition, decreases. The results are discussed in the context of CALPHAD-integrated density-based grain boundary phase diagrams. T2 - DPG 2024 CY - Berlin, Germany DA - 17.03.2024 KW - Phase-Field Simulation KW - CALPHAD KW - Steels KW - Density-based Thermodynamics PY - 2024 AN - OPUS4-60743 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Fedelich, Bernard T1 - On the modeling of creep anisotropy of single Crystal Superalloys at low temperatures and high stresses N2 - Low-Temperature High Stress (LTHS) creep plays a crucial role in Ni-base Superalloys, particularly affecting components like blades near the root. Below 850°C, the precipitate microstructure remains stable, characterized by periodically arranged ’ cubic precipitates surrounded by the -matrix. In these conditions, macroscopic traces of cubic slip have been observed in <111> oriented tensile specimens, whereas their microscopic origin has been a topic of debate [1]. Later, it was shown by Discrete Dislocations simulations [2] that the apparent cubic slip is rather due to a lack of hardening in <111> specimens, which is related to the special dislocation structures that develop in this case. Furthermore, in LTHS conditions, Superlattice Intrinsic, Extrinsic Stacking Faults (SISF/SESF), or micro-twins are also frequently reported in crept specimens. Usually, these mechanisms are investigated separately, so that a unified picture and a detailed understanding of these mechanisms and their activation conditions have only recently emerged in the literature, despite the intensive investigations of the last decades [3-5]. The objective of this work is to develop a dislocation-based constitutive law that includes these recent developments. In particular, the pseudo-cubic slip mechanism is considered as resulting from the lack of hardening in <111> oriented tensile specimens and is represented by a novel estimate of the back-stresses based on the spectral decomposition of a tensorial representation of the back-stress. An additional novelty is that SISF- and SESF-related slip systems are accounted for as distinct slip systems with corresponding dislocation densities. The model has been implemented as a user-defined constitutive law for commercial Finite Element codes and identified as well as validated with data from the literature obtained with <001>, <011> and <111> oriented crystals [3,6]. It can be used in combination with a Representative Volume Element of the grain structure for simulation of creep in polycrystalline superalloys, including additively manufactured materials [7]. T2 - Materials Structure and Micromechanics of Fracture CY - Brno, Czech Republic DA - 23.06.2025 KW - Creep KW - Superalloy KW - Crystal plasticity KW - Single crystal KW - Model PY - 2025 AN - OPUS4-63551 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Fedelich, Bernard T1 - On the cubic slip effect and creep anisotropy modeling of single crystal superalloys at intermediate temperatures (IT) N2 - Low-Temperature High Stress (LTHS) creep plays a crucial role in Ni-base Superalloys, particularly affecting components like blades near the root. Below 850°C, the precipitate microstructure remains stable, characterized by periodically arranged ’ cubic precipitates surrounded by the -matrix. In these conditions, macroscopic traces of cubic slip have been observed in <111> oriented tensile specimens, whereas their microscopic origin has been a topic of debate. Furthermore, in LTHS conditions, Superlattice Intrinsic, Extrinsic Stacking Faults (SISF/SESF), or micro-twins are also frequently reported in crept specimens. Usually, these mechanisms are investigated separately, so that a unified picture and a detailed understanding of these mechanisms and their activation conditions have only recently emerged in the literature, despite the intensive investigations of the last decades. The objective of this work is to develop a dislocation-based constitutive law that includes these recent developments. In particular, the pseudo-cubic slip mechanism is considered as resulting from the lack of hardening in <111> oriented tensile specimens and is represented by a novel estimate of the back-stresses based on the spectral decomposition of a tensorial representation of the back-stress. An additional novelty is that SISF- and SESF-related slip systems are accounted for as distinct slip systems with corresponding dislocation densities. The model has been implemented as a user-defined constitutive law for commercial Finite Element codes and identified as well as validated with data from the literature obtained with <001>, <011> and <111> oriented crystals tested in tension and compression creep. T2 - International Conference on Material Modelling (8) CY - London, GB DA - 15.07.2024 KW - Creep KW - Superalloy KW - Crystal plasticity KW - Single crystal PY - 2024 AN - OPUS4-60744 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Mieller, Björn T1 - Numerical study of electric field distribution in breakdown strength testing of ceramics N2 - Dielectric breakdown of insulators is a combined electrical, thermal, and mechanical failure. The exact breakdown mechanism in ceramics and the formulation of useful models are still subject of investigation. Recent studies highlighted that several experimental aspects of dielectric breakdown strength testing affect the test results, and thus impede the recognition of fundamental principles. Excess field strength near the electrode can lead to premature breakdown in the insulating liquid. This would cause superficial damage to the test specimen and thus falsify the measurement results. The field strength distribution is influenced by the ratio of permittivity of the sample and the surrounding insulating liquid. Premature breakdown depends on the breakdown strength of the liquid and the actual test voltage. The test voltage again depends on the specimen thickness. To systematically investigate these relations, a numerical simulation study (FEM) of the electric field distribution in a typical testing rig with cylindrical electrodes was performed. The permittivity of the sample and the insulating liquid was parameterized, as well as the sample thickness. The electric field distribution was calculated for increasing test voltage. Field strength maxima are compared to experimental breakdown strength of typical insulating liquids and experimental breakdown locations on alumina. Strategies are discussed to adjust the insulation liquid and the sample thickness to reduce the influence of the testing setup on the dielectric breakdown strength results. T2 - Ceramics in Europe 2022 CY - Krakow, Poland DA - 10.07.2022 KW - Ceramics KW - Dielectric breakdown strength KW - Electric field distribution KW - Alumina PY - 2022 AN - OPUS4-55325 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ganesh, Rahul T1 - Numerical calculation of ΔCTOD for thermomechanical fatigue crack growth N2 - The cyclic crack tip opening displacement ΔCTOD is a promising loading Parameter to quantify the crack propagation under thermomechanical fatigue (TMF). In this work, suitable techniques are investigated and compared for an accurate calculation of ΔCTOD under TMF loading using a viscoplastic temperature dependent material model. It turned out that collapsed special crack tip elements give the best results. An efficient FEM-technique is developed to simulate the incremental crack growth by successive remeshing, whereby the deformations and internal state variables are mapped from the old mesh onto the new one. The developed techniques are demonstrated and discussed for two-dimensional examples like TMF-specimens. Recommendations are made regarding important numerical control parameters like optimal size of crack tip elements, length of crack growth increment in relation to plastic zone size and ΔCTOD value. T2 - 53. Tagung des Arbeitskreises "Bruchmechanik und Bauteilsicherheit" CY - Online meeting DA - 18.02.2021 KW - Crack tip opening displacement KW - Thermomechanical fatigue KW - Crack growth PY - 2021 AN - OPUS4-52520 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gesell, Stephan T1 - Numerical calculation of ΔCTOD for thermomechanical fatigue crack growth N2 - The cyclic crack tip opening displacement ΔCTOD is a promising loading Parameter to quantify the crack propagation under thermomechanical fatigue (TMF). In this work, suitable techniques are investigated and compared for an accurate calculation of ΔCTOD under TMF loading using a viscoplastic temperature dependent material model. It turned out that collapsed special crack tip elements give the best results. An efficient FEM-technique is developed to simulate the incremental crack growth by successive remeshing, whereby the deformations and internal state variables are mapped from the old mesh onto the new one. The developed techniques are demonstrated and discussed for two-dimensional examples like TMF-specimens. Recommendations are made regarding important numerical control parameters like optimal size of crack tip elements, length of crack growth increment in relation to plastic zone size and ΔCTOD value. T2 - ESIS Technical Meeting on Numerical Methods (TC8) CY - Online meeting DA - 06.04.2021 KW - Crack tip opening displacement KW - Thermomechanical fatigue KW - Crack growth PY - 2021 AN - OPUS4-52410 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -