Technische Universität Bergakademie Freiberg: Qucosa
Not a member yet
1431 research outputs found
Sort by
Influence of Plastic Strain Control on Martensite Evolution and Fatigue Life of Metastable Austenitic Stainless Steel
No full textMetastable austenitic stainless steel was investigated during fatigue tests under strain control with either constant total or constant plastic strain amplitude. Two different material conditions with coarse-grained and ultrafine-grained microstructure were in focus. The influence of plastic strain control of the fatigue test on both the martensitic phase transformation as well as on the fatigue lives is discussed. In addition, an approach for calculating the Coffin–Manson–Basquin parameters to estimate fatigue lives based on strain-controlled tests at constant total strain amplitudes is proposed for materials undergoing a strong secondary hardening due to martensitic phase transformation
(E)-N-Phenyl-N-(phenylcarbamoyl)-3-[propyl(trimethylsilyl)amino]acrylamide chloroform hemisolvate
No full textThe title compound, C22H29N3O2Si·0.5CHCl3, crystallizes in the the triclinic space group P[\overline{1}] with two host molecules and one chloroform molecule in the asymmetric unit. The core of the molecule consists of a urea unit bound to a 3-amino-acryloyl group. These units are almost planar in both molecules [average deviation from plane of 0.05 (6) Å in molecule A and 0.04 (5) Å in molecule B]. The main difference between molecules A and B involves the dihedral angles of the phenyl groups. One phenyl ring makes dihedral angles of 71.14 (6)° (molecule A) and 82.81 (7)° (molecule B) with respect to the core (C4N3O2) of the molecule [14.56 (9)° (molecule A) and 5.7 (1)° (molecule B) for the other phenyl ring]. Another prominent feature is the intramolecular N—H⋯O hydrogen bond present in both crystallographically independent molecules
Integrating delivery robots into public transport: Technical challenges and lessons learned
No full textUsing free capacity in public transport vehicles to carry sidewalk delivery robots offers potential benefits for both logistics providers and transportation operators, while also helping to reduce traffic. However, integrating robots into public transport systems poses significant technical, organisational, and regulatory challenges. To date, this integration has only been explored in isolated demonstrations, with little documented experience under real-world conditions. In this contribution, we present findings from five years of applied research on the development and integration of delivery robots into public transport buses in Germany. We describe both the practical constraints encountered and the conceptual approaches developed to address key challenges. Our aim is to provide guidance for researchers and practitioners working toward real-world deployments of delivery robots in public transport environments
4. Freiberger Kolloquium Elektrische Antriebstechnik: Kolloquium im Rahmen des 76. BHT - Freiberger Universitätsforum 2025
No full textDie zunehmende Elektrifizierung der Sektoren, wie z. B. Elektroenergieversorgung, Wärme oder Verkehr, erfordert in der elektrischen Antriebstechnik neben neuen Konzepten für energie- und leistungsdichte Motoren auch schnelle und präzise Regelalgorithmen. Gleichzeitig haben aktuelle Entwicklungen in der Leistungselektronik großes Potenzial hinsichtlich der Einsparung elektrischer Energie, sowie dem Erschließen neuer Anwendungsgebiete.
2025 fand zum vierten Mal das „Freiberger Kolloquium Elektrische Antriebstechnik“ statt. Thematische Schwerpunkte waren: Auslegung und Fertigung neuer Motorenkonzepte, Aktuelle Trends in der Leistungselektronik, Innovative Regelungskonzepte elektrischer Antriebe sowie Ladetechnologien für Elektrofahrzeuge
Modeling and evaluation of thermo-mechanical properties of open-cell ceramic foams for metal melt filtration
No full textOpen-cell ceramic foams are used in metal melt filtration processes to clean and calm the liquid melt. Due to the high temperatures and pressure of the melt, thermo-mechanical stresses occur in the filter structures, which require a corresponding evaluation of strength, deformation, and failure. The ceramic materials used no longer behave elastically and brittle at operating temperatures of up to 1650 ◦ C, but exhibit viscoplastic behavior. Experimental investigations of the deformation of filter structures during the filtration process are difficult or even impossible, which is why simulation methods are used to investigate the filtration process and the filter loading.
The filters considered in this work are manufactured using a replica process in which a ceramic slurry is applied to an open-cell polyurethane foam, which is dried and fired in a thermal process. Real filter structures consist of a network of several thousand struts with varying geometries. Direct numerical simulation of these geometries is possible in principle, but it is very complex and expensive, which is why homogenization methods are used. Representative volume elements of the ceramic foams are generated and analyzed using the finite element method. The micro-macro relations determined in the process are mapped using corresponding continuum mechanical models. These models allow the evaluation of the thermo-mechanical behavior of filter materials and filter structures.
This thesis provides a critical overview of methods for generating, characterizing, and homogenizing foam structures. The generation of realistic foam structures is carried out using various methods from the fields of mathematics and mechanics and is described in detail. Analytical and data-driven approaches are used for the actual homogenization. The analytical approaches use adaptations of continuum mechanical models from the field of granular media. The data-driven approaches use neural networks, which replace or supplement hard-to-describe thermodynamic potentials used in material modeling. Both approaches can be used in a developed general framework for the modeling of any porous structures.
As a result of the research and modeling work carried out, generic and real foams are compared in terms of their topological and geometrical properties. It is discussed how local geometrical variations of foam structures affect the macroscopic behavior, considering different thermo-mechanical properties such as elasticity, viscoplasticity, and fracture strength. The developed homogenization concepts are compared with each other and with other concepts from the scientific literature and evaluated with respect to their accuracy, flexibility, and efficiency. Finally, possible further developments and applications are discussed.:1. Introduction
1.1. Motivation and objectives
1.2. Structure of the thesis
2. State of the art research
2.1. Integration of sub-project B05 into the CRC 920
2.2. Manufacture of open-cell foam structures
2.2.1. Schwartzwalder process
2.2.2. Additive manufacturing
2.2.3. Additional coatings
2.2.4. Bulk material properties
2.3. Characterization of open-cell foam structures
2.3.1. Topological and geometrical characteristics
2.3.2. Thermo-mechanical characteristics
2.3.3. Fluid dynamical characteristics
2.4. Modeling of open-cell foam structures
2.4.1. Geometrical models of foams
2.4.2. Direct numerical simulation
2.4.3. Homogenization approaches
2.4.4. Data-driven and machine-learning approaches
2.4.5. Constitutive models for open-cell foam structures
3. Modeling of open-porous ceramic foams
3.1. Foam surfaces of strut networks based on implicit functions
3.2. Sphere packings and Laguerre tessellations
3.3. Surface evolver, dry foams, wet foams, and foam froth
3.4. Voxel models and isosurfaces of foams
3.5. Finite element model
3.5.1. Models with structural elements
3.5.2. Unstructured tetrahedral meshes
3.5.3. Structured meshes
3.6. Generating foam structures using FoamGUI
3.7. Homogenized constitutive models
3.7.1. Scale bridging, meso and micro models
3.7.2. Effective elastic properties
3.7.3. Elastic limit surfaces
3.7.4. Effective yield surfaces
3.7.5. Modified Ehlers model
3.7.6. Constitutive model for viscoplastic behavior
3.7.7. Constitutive framework for plastic behavior
3.7.8. General return algorithm
3.7.9. Application to the phenomenological models
3.7.10. Hybrid models
3.7.11. Neural networks
3.7.12. Data sampling for the neural network training
3.7.13. Parameter identification for the modified Ehlers model
4. Results
4.1. Geometrical foam models
4.1.1. Foam models based on implicit functions
4.1.2. Foam models based on sphere packings
4.2. Effective thermo-mechanical properties
4.2.1. Geometry dependent elastic properties
4.2.2. Yield and failure surfaces
4.2.3. Fracture mechanical properties
4.2.4. Fracture mechanical properties for thermo-shock loading
4.2.5. Visco-plastic properties
4.2.6. Effective plastic properties
5. Conclusions & Discussio
Selective Recognition of Ammonium over Potassium Ion with Acyclic Receptor Molecules Bearing 3,4,5-Trialkylpyrazolyl Groups
No full textAmong the 1,3,5-trisubstituted 2,4,6-triethylbenzenes bearing pyrazolyl groups, the compounds with 3,5-dimethylpyrazolyl moieties were found to be effective receptors for ammonium ions (NH4 +). The current study investigated the extent to which the incorporation of an additional alkyl group in the 4-position of the pyrazole ring affects the binding properties of the new compounds. 1H NMR spectroscopic titrations and investigations using isothermal titration calorimetry revealed that this small structural variation leads to a significant increase in the binding strength towards NH4 + and also improves the binding preference for NH4 + over K+. In addition to the studies in solution, crystalline complexes of the new triethyl- and trimethylbenzene derivatives, bearing 3,4,5-trialkylpyrazolyl groups, with NH4 +PF6 − were obtained and analyzed in detail. It is noteworthy that two of the crystal structures discussed in this work are characterized by the presence of two types of ammonium complexes. Studies focusing on the development of new artificial ammonium receptors are motivated, among other things, by the need for more selective ammonium sensors than those based on the natural ionophore nonactin
Phytoremediation Potential of Native Hyperaccumulator Plants Growing on Heavy Metal-Contaminated Soil of Khatunabad Copper Smelter and Refinery, Iran
No full textThe characterization of prospective plants is one of the critical issues in the efficiency and success of the phytoremediation process. Due to adaption and tolerance to different environmental stresses, native plant species have priority in this method. This study examined fifty plants of five species, namely Launaea acanthodes, Artemisia sp., Cousinia congesta, Peganum harmala, and Stipa sp., growing near a smelter and refinery in Iran to identify potential species for phytoextraction and phytostabilization. Therefore, Pb, Ni, Mn, Mo, S, and Cu concentrations in sampled plants and soils were analyzed. Three different pollution indices, namely metal accumulation index (MAI), translocation factor (TF), and bioconcentration factor (BCF) were used for evaluating the metal concentrations in roots and shoots of each plant species. The results indicated that Artemisia sp., with values of 3.21, 1.09, and 1.14 for MAI, BCF, and TF, respectively, is appropriate for phytoextraction in the study area. Plants such as Launaea acanthodes and Cousinia congesta with high BCF and low TF values showed the potential for phytostabilization. Investigating the indices for different elements demonstrated that Launaea acanthodes had a BCF value greater than 1 and a TF value less than 1; therefore, this plant could be used in the phytoremediation of arsenic through the phytostabilization technique. Furthermore, copper has very low bioavailability in these plant species. In addition, these native plant species were highly capable of accumulating sulfur from the soil because the BCF and TF indices for all inspected species were higher than 1; for Launaea acanthodes, the relevant TF value was about 10. The proposed native plant could be applied in practical applications of phytoremediation for soil remediation of contaminated sites around the metal factories and mines in southeastern Iran
Asymmetrically Substituted s-Triazine Phosphonates by One-Step Synthesis
No full textAsymmetrically substituted s-triazine phosphonates with up to three different phosphonate groups C3N3RR'R” with R, R’, R”=PO(OR”’) and R”’=for example, methyl, ethyl, isopropyl or n-butyl are interesting as polymer additives like flame retardants. Typically, these compounds are obtained by multiple synthesis steps. However, this leads to high production costs, which are a disadvantage for commercial use. Here we report the one-step synthesis of mixtures of asymmetrical s-triazine phosphonates which is an easy way to adjust the thermal behaviour and other properties such as viscosities of the compounds. The synthesis is based on a Michaelis–Arbuzov reaction. A complete conversion of the reactants to the target compounds is observed which was proofed by detailed 1H, 13C and 31P NMR investigations and elemental analysis. The thermal behaviour was compared with thermogravimetric analysis (TGA)
16. Internationales Symposium Kulturelles Erbe in Geo- und Montanwissenschaften - Bibliotheken, Archive, Museen, Sammlungen
No full textDer Band enthält montan- und geohistorische Beiträge aus acht verschiedenen Ländern zu Themen aus dem Bereich von Bibliotheken, Archiven, Museen und Sammlungen. Dabei steht die internationale Vernetzung bei der Digitalisierung und den Auswirkungen des Klimawandels für historische Bestände und Objekte im Focus
Potentialanalyse einer keramikähnlichen Leiterisolation zur Ausnutzungssteigerung von elektrischen Traktionsmaschinen
No full textIn diesem Beitrag wird eine Potentialanalyse für den Einsatz von Aluminiumoxid (Al2O3) als Leiterisolation in elektrischen Maschinen unternommen. Nach Darlegung der Notwendigkeit für Isolationsmaterialien mit höherer Wärmeleitfähigkeit und den bisher erlangten Erkenntnissen aus vorangegangenen Untersuchungen, wird auf den Prozess der elektrochemischen Oxidation und die daraus erzeugte keramikähnliche Beschichtung eingegangen. Danach werden die im Rahmen des Projekts geplanten und bereits erfolgten Voruntersuchungen an Leiterproben dargestellt. Eine Potentialanalyse erfolgt mittels analytischer und numerischer Berechnung von Erwärmungsmodellen. Die Validierung der Modelle sowie des experimentellen Isolierstoffsystems mit Al2O3-beschichteten Leitern wird durch den Aufbau von Motoretten realisiert. Die hierfür geplanten Untersuchungen einschließlich eines Zyklentests zur Bestimmung der Betriebsfestigkeit werden vorgestellt