Technische Universität Bergakademie Freiberg: Qucosa
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Powder Forging of in Axial and Radial Direction Graded Components of TRIP-Matrix-Composite
Get PDFPowder metallurgy is one way of producing complex, graded structures that could allowmaterial systems to be produced with properties tailored to individual applications. However,powder metallurgy requires that the semi-finished products are very similar to the final component.It is much more economical to produce simple semi-finished products and then combine them bypowder forging and simultaneous compaction than forming complex components with the desiredgraded structure. However, it is absolutely necessary that the graded structure of the semi-finishedproducts is maintained during the forming process. In this study, pre-sintered cylindrical semi-finished products, consisting of axially graded as well as radially graded components, were producedby powder forging at 1100◦C. The microstructures, densities and mechanical properties of the finalcomponents were investigated to verify the effectiveness of the process route. It was observed thatthe components formed solid structures after compaction, in which the reinforcing ZrO2particleswere fully integrated into the transformation-induced plasticity steel matrix
Plasma Electrolytic Polishing of Nitinol: Investigation of Functional Properties
Get PDFA novel, environmentally friendly, fast, and flexible polishing process for Nitinol parts is presented in this study. Nitinol samples with both superelastic and shape memory properties at room temperature were investigated. The chemical contamination and surface roughness of superelastic Nitinol plates were examined before and after plasma electrolytic polishing. The shift in phase transformation temperature and tensile strength before and after the polishing process were analysed using Nitinol wire with shape memory properties. The obtained experimental results were compared to the data obtained on reference samples examined in the as-received condition. It was found that plasma electrolytic polishing, when the right process parameters are applied, is capable of delivering Nitinol parts with extremely high surface quality. Moreover, it was experimentally proven that plasma electrolytic polishing does not have a negative impact on functionality or mechanical properties of polished parts
Open Access publizieren: Wozu dienen Policies und Leitlinien?
Get PDFMit dem Ziel, den Open-Science-Gedanken zu unterstützen und die Forschungsleistungen der Freiberger Wissenschaftler:innen besser sichtbar und zugänglicher zu machen, hat die TU Bergakademie Freiberg seit 2022 verschiedene Policies und Leitlinien verabschiedet. Diese Ausgabe des Open-Science-Snacks fasst deren Zweck und Nutzen noch einmal zusammen und ordnet sie in den wissenschaftspolitischen Kontext ein
Experimental study of surfactant-aided enhanced oil recovery in carbonate rock
Get PDFThe application of surfactants and polymers in carbonate reservoirs has a high potential with emerging technology of the manufacture of these chemicals. Tertiary or enhanced oil recovery with chemicals (CEOR) will become more relevant with decreasing new exploration of oil deposits and high remaining oil saturations in huge carbonate oil reservoirs. However, in several oil deposits, high reservoir brine salinity and moderate to high reservoir temperature are encountered. Under such conditions, many chemicals will be insoluble or degrade fast. A selection of commercial and research surfactants and polymers has been investigated for their application under brine salinity of up to 18 percent by weight with significant hardness and a moderate reservoir temperature of 70 °C. Chemical systems were tested towards outcrop limestone rock samples and calcite platelets in combination with a crude oil, which was modified by different organic acids regarding its wetting potential. Wettability alteration from preferentially oil-wet core plugs was pursued with ethoxylated tertiary amines and quaternary ammonium compounds. The main mechanism of wettability alteration towards more water-wet was proposed as extraction of carboxylate anions from the oil phase and the solid samples into aqueous micelles. Thus, high surfactant concentrations would result in improved recovery. From screening of different surfactant combinations in tertiary core flooding, one promising system of an alkyl ether sulfate and hexadecyltrimethylammonium combined with a terpolymer (TP) from acrylic acid, ATBS and NVP is proposed for the examined conditions. Low to moderate adsorption of the single surfactants and their combination as well as a favorable, stabilized phase behavior when combined with the polymer emphasize the applicability of the system. However, long term stability can be an issue with respect to the sulfate surfactant degradation at 70 °C. Analysis of mixed ionic surfactant systems after adsorption testing has been successfully pursued with a combined TC/TNb-determination
Numerische Simulationen zur Rückrechnung und Prognose von Setzungen und Gebirgsdeformation
Get PDFDie stetige Weiterentwicklung von Mess- und Überwachungstechnik ermöglicht Setzungsprozesse und Gebirgsdeformationen mit zunehmender Genauigkeit in numerischen Modellen abzubilden. Mit Hilfe von Laserscans, durchgeführt sowohl vor als auch während der Bauarbeiten, können genauere numerische Modelle erstellt werden. Die baubegleitende Anpassung der Modellgeometrie ermöglicht zudem eine weitere Nachkalibrierung der Simulationen und erhöht damit die Zuverlässigkeit von Prognoseberechnungen. Die Simulationsergebnisse können fortlaufend mit den ursprünglichen Planungen abgeglichen und somit Ausbauplanungen angepasst und optimiert werden.The ongoing development of monitoring and surveillance technology enables us to reproduce subsidence and rock mass deformation in numerical models with increasing precision. Laserscans prior to and during the construction work increase the spatial accuracy of numerical models. Adjustments of the model geometry during the construction work allow a recalibration of models and increase the reliability of forecast simulations. Simulation results can be successively compared to construction plans and allow adjustments and optimizations of support designs
A thermochemical dynamic model of a Top Submerged Lance furnace: Experimental validation with focus on minor elements for the Circular Economy
Get PDFThe trend towards a more circular economy presents a unique challenge for the pyrometallurgical engineer. Secondary feeds bring complexity to the smelter in the form of non-traditional chemistries and minor elements. Models of furnaces will play an important role in this paradigm. Models should be able to predict operations in dynamic systems that do not always operate at equilibrium.The development of a top submerged lance (TSL) model was the subject of this study because the TSL has proven to be capable of treating secondary materials.The furnace consists of a vertical cylindrical vessel, containing molten slag and bullion at the bottom. A lance enters through the roof and the tip is submerged in the slag, into which gas and fuel are blown. Secondary or primary feeds, fluxes and reductants can be fed to the furnace. The reactions and interplay between the liquid phases, gas and added reductants set the temperatures and partial oxygen pressures in the furnace.
The Connected Local Equilibria (CLE) method was followed to model the furnace. This approach offers the benefit that speciation can be modelled simultaneously for many elements from thermochemical databases. The methodology is to divide the furnace into several equilibrium volumes, based on expected material flows. With each time step, equilibrium in each volume is calculated by Gibbs free energy minimization. Material is then exchanged between volumes according to expected flows. To validate the method, small scale crucible experiments were carried out. Molten lead-containing ferric calcium silicate slags (PbO-FCS slag, also containing GeO2, TeO2 and SnO2 in concentrations ˂ 1 wt%) were reduced under controlled CO/CO2 atmospheres to produce lead bullion. The kinetics of the process were measured. Similar experiments were carried out with a copper-containing ferric calcium silicate system. The CLE method was applied to simulate the data, using HSC Sim software. The crucible was divided into four equilibrium volumes: slag-gas contact; slag; slag-hearth contact; hearth. The gas flowrate to the slag-gas contact was determined by following a rate-law in the form of chemical reaction control (e.g. Rg-s = kapp.pCO (mol O.cm-2.s-1)). By using a single fitting factor (kapp), the dynamic behaviour of lead and the minor elements (tin, tellurium, germanium) could be predicted. The same method was successfully used for the CuO-FCS system. The use of this method enhanced understanding of the experiments, by showing the component speciation during reduction. Full-scale TSL models were then developed using HSC Chemistry software and SimuSage software. In both cases the CLE method was applied. The flow patterns in the furnace were gleaned from
published computational fluid dynamics (CFD) work. The interface areas were not known, and assumptions thus needed to be made to model an industrial process for lead-oxide FCS slag reduction. It was shown that the model can provide useful insight into real-world problems. Two branches of modelling might develop from this work. In one, CFD work can quantify interface areas in the furnace, so that CLE models similar to the current work are possible. In the second, only bulk fluid movement might be used. In either case, this work validates the approach of using a thermochemical approach to model kinetics.:1 INTRODUCTION
1.1 THE METALLURGICAL CHALLENGE TO ACHIEVE A CIRCULAR ECONOMY
1.2 APPLICATION OF UNIT MODELS IN TECHNO-ECONOMIC, EXERGY AND ENVIRONMENTAL FOOTPRINT ANALYSES
1.3 FOCUS OF THE CURRENT WORK
2 RESEARCH OBJECTIVES
3 LITERATURE REVIEW
3.1 LEAD METALLURGY (INCLUDING WEEE)
3.2 COPPER METALLURGY
3.3 EQUILIBRIUM BEHAVIOUR OF MINOR ELEMENTS IN LEAD AND COPPER METALLURGY
3.4 SLAG REDUCTION KINETICS
3.5 TSL FURNACE
3.6 MODELLING OF BATH-TYPE SMELTERS
3.6.3 CFD Modelling
4 EXPERIMENTAL METHODOLOGY
4.1 MASTER SLAG PREPARATION
4.2 EXPERIMENTAL SETUP
4.3 REDUCTION EXPERIMENT PROCEDURE
4.4 LIST OF EXPERIMENTS
4.5 ANALYTICAL METHOD
4.6 REACTION OF SLAGS WITH CRUCIBLE WALLS
5 EXPERIMENTAL ERROR EVALUATION
5.1 ERROR IN MASTER SLAG COMPOSITION MEASUREMENTS
5.2 REPEAT TESTS
5.3 EXPERIMENTAL ERROR
6 MODELLING OF KINETICS WITH HSC SIM
6.1 HSC CHEMISTRY DYNAMIC MODULE AND CONNECTED LOCAL EQUILIBRIA MODELLING
6.2 RESULTS FOR MODELLING LEAD EXPERIMENTAL RESULTS WITH HSC CHEMISTRY
6.3 RESULTS FOR MODELLING COPPER EXPERIMENTAL RESULTS WITH HSC CHEMISTRY
7 TSL MODEL IN HSC CHEMISTRY
7.1 FLUID FLOW IN TSL FOR CONNECTED LOCAL EQUILIBRIA MODELLING
7.2 TANKS AND OPERATIONS IN HSC SIM MODEL
7.3 EXAMPLE OF HSC SIM CLE MODEL APPLICATION
8 TSL MODEL ON SIMUSAGE PLATFORM
8.1 METHOD FOR SIMUSAGE MODEL
8.2 SPECIES SELECTION IN SIMUSAGE MODEL
8.3 EXAMPLE OF SIMUSAGE CLE MODEL APPLICATION
9 COMPARISON OF HSC SIM AND SIMUSAGE RESULTS
10 CRITICAL ANALYSIS OF MODEL METHODOLOGY
10.1 MEASUREMENT OF BULK VOLUME COMPOSITIONS
10.2 HEAT TRANSFER IN HSC SIM AND SIMUSAGE MODELS
10.3 USING BULK FLUID FLOWS VS INTERFACE APPROACH
11 CONCLUSIONS
11.1 MOTIVATION
11.2 LABORATORY KINETIC MEASUREMENTS AND MODELLING WITH CLE METHOD
11.3 TSL MODELLING WITH HSC SIM AND SIMUSAGE
12 REFERENCE
A cohesive zone model for thermomechanical fatigue and fracture of metallic materials
Get PDFThermomechanical fatigue is a fatigue failure caused by combined thermal and mechanical loading cycles where both stresses and temperature can vary with time. A cohesive zone model simulates material failure within the finite element method by describing material behaviour and damage evolution through a traction-separation relation. In this work, a viscoplastic cohesive zone model is developed in order to describe the fatigue and fracture behaviour of high performance superalloys undergoing thermomechanical fatigue loading. A micromechanically motivated cohesive potential, incorporating fatigue and creep damage variables, is proposed and its thermodynamic consistency is established. The characteristic behaviour of the cohesive law during cyclic loading is described in terms of both traction and energy.
The developed cohesive zone model is applied to simulate the lifetime behaviour in a smooth specimen. The effect of loading parameters such as temperature, dwell period, and strain rate on isothermal, in-phase and out-of-phase thermomechanical fatigue is successfully demonstrated. Using crack growth simulations in a boundary layer model, the relation between the local behaviour of the cohesive zone and fracture parameters like stress intensity factor, J-integral and crack tip opening displacement is established. The three stages of fatigue crack growth rate curves that are experimentally observed were obtained through simulations. Crack growth in a corner crack specimen is simulated under cyclic stress-controlled loading to obtain the experimentally observed crack profiles. Material parameters for the Nickel based superalloy MAR-M247 are identified using experimental data from the literature
Geometallurgical resource assessment for tailings storage facilities
Get PDFTailings are the fine-grained residues produced by processing operations, and are commonly retain residual contents of valuable and critical metals. Re-mining of tailings storage facilities (TSF) could play a crucial role in alleviating environmental problems associated with mine wastes, while recovering residual value and decreasing the volumes of tailings to be stored. Resource modelling of TSFs is complicated by their heterogeneity, which results from the sedimentary-style deposition of tailings, as well as post-depositional processes like weathering. Tailings particles are sorted based on size and density (i.e., mineralogy), generating strong systematic trends in geochemistry across a TSF. As such, TSFs should not be treated the same way as primary deposits; different sampling, spatial modelling, and processing methods may be needed, as well as adaptions to resource and reserve reporting codes. This thesis provides recommendations for the resource and reserve estimation of TSFs. To achieve this, a series of methods were developed, from best-practise sampling of TSFs for resource estimation, through to geostatistical modelling of a TSF for grade/tonnage estimation with corresponding uncertainties, to geometallurgical modelling using particle-based data
Investigations on the influence of pore structure and wettability on multiphase flow in porous medium using x-ray computed tomography: Application to underground CO2 storage and EOR
Get PDFCapillary trapping plays a central role in the geological storage of CO2, oil recovery, and water soil infiltration. The key aim of this study is to investigate the impact of surface properties (wettability, roughness, heterogeneous mineral composition) on the dynamics of quasi-static fluid displacement process and capillary trapping efficiency in porous medium. We concluded that for homogeneous wet smooth glass beads surfaces, a transition in fluid displacement pattern occurs from a compact (for θ 90°; drainage process) leading to a crossover in capillary trapping efficiency from zero to maximum. The impact of surface roughness on capillary trapping efficiency was also studied, and an opposite trends in terms of wettability dependency was observed. Rough natural sands surfaces depicts a non-monotonous wettability dependency, i.e. a transition from maximal trapping (for θ 90°). For a fractional-wet media, the percolating cluster of hydrophobic sediments (connected hydrophobic pathways) characterize the fluid displacement pattern and trapping efficiency
Interaktion Geogitter-Boden: Numerische Simulation und experimentelle Analyse
Get PDFDie Verbundkonstruktion aus Bodenmaterial und Geogitter bietet vielfältige Möglichkeiten zur kosteneffizienten Realisierung komplexer geotechnischer Bauvorhaben. Die wirkenden Effekte innerhalb des Verzahnungsbereiches von Geogitter und Bodenkörnern, die maßgeblich zur Stabilisierung des Verbundsystems beitragen, sind jedoch bislang nur unzureichend beschrieben bzw. nachgewiesen. Die Fortschritte auf dem Gebiet der numerischen Simulation, insbesondere hinsichtlich diskontinuumsmechanischer Verfahren, eröffnen innovative Möglichkeiten zur Analyse der Wirkungsmechanismen auf mikromechanischer Ebene. Die vorliegende Forschungsarbeit befasst sich daher mit der Entwicklung und Validierung numerischer Modelle in PFC3D, basierend
auf den Randbedingungen und Ergebnissen von systematisch durchgeführten Laborversuchen, zur Reproduktion des natürlichen Interaktionsverhaltens innerhalb eines Geogitter-Boden Verbundsystems.
Ein spezieller Fokus richtet sich auf die Modellierung granularer Böden unter Berücksichtigung der wesentlichen kornspezifischen Merkmale, insbesondere der Kornform. Die modelltechnische Beschreibung von Bodenkörnern erfolgt unter Anwendung der sog. Clump-Logik und basiert hauptsächlich auf den Ergebnissen einer fotooptischen Messmethode. Ein neu entwickeltes Verfahren zur Generierung von Kornzusammensetzungen mit spezifischer Lagerungsdichte wird vorgestellt. Die Kalibrierung eines einheitlichen mikromechanischen Parametersatzes zur Reproduktion des bodenmechanischen Verhaltens erfolgt anhand der Simulation von fünf standardisierten Prüfverfahren. Die charakteristische Struktur eines ausgewählten Geogitters wird modelltechnisch implementiert sowie das Verhalten unter Zug- und Torsionsbeanspruchung reproduziert. Der Nachweis eines realistischen Interaktionsverhaltens umfasst die Kalibrierung der Kontaktparameter zwischen den modellierten Verbundkomponenten anhand der Simulation von Herausziehversuchen. Die labor- und modelltechnische Entwicklung spezieller Interaktionsversuche ermöglicht es, präzise Aussagen zum Verbundverhalten unter verschiedenen Belastungssituationen zu treffen. Die wesentlichen Wirkungsmechanismen und Effekte werden unter Berücksichtigung von signifikanten Kennwerten quantifiziert, um zum einen die Effizienz dieser speziellen polymeren Baustoffe zu analysieren und zum anderen eine Grundlage zur Beurteilung und Bemessung von geogitterbewehrten Konstruktionen anhand von allgemeingültigen Systemparametern zu schaffen