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High-Temperatur-High Pressure Stress-Strain Testing of Materials in CO2-Containing Saline Solutions
(2015)
Mit Beginn der Covid-19 Pandemie und dem damit verbundenen ausschließlichen Lehren im online-Format war die Hoffnung verbunden ein Blended Learning Lehrformat für die Studieeingangsphase ohne viel konzeptionelle Änderungen übertragen zu können. Der Kurs Werkstofftechnik als Grundlagenfach für den Maschinenbau baut sich auf inverted classroom Lehrszenarien auf, deren Lerngrundlage hierfür eigens produzierte und auf das Lernziel abgestimmte Lehrfilme und Lightboard-Vorlesungen darstellen. Im Kontext der Studieneingangsphase bieten audiovisuell stimulierende Lehrfilme umfassende Lernmedien, wenn sie analog der Lerninhalte einem technischen und didaktischen Qualitätsanspruch genügen. In der Praxis des SS2020 und WS2020/21 hat sich gezeigt, dass die Moderation und Durchführung eines online-Kurses sich deutlich von dem eins blended learning-Kurses unterscheidet. Um denselben Lernerfolg bei Studierenden zu erzielen, müs-sen Anforderungen viel genauer und detaillierter verfasst werden, Studierende enger und persönlicher begleitet werden und Lehrfilme und Lernmedien in einen Gesamtzusammenhang gestellt werden. Im Folgenden werden aus persönlicher Erfahrung heraus niederschwellige, zum Teil ungewöhnliche praktische Erfahrungen zur erfolgreichen Umsetzung von Lehrfilm-basierten inverted classroom Lehrszenarien zusammengefasst und im Hinblick auf die online-Lehre bewertet.
First year students especially with migration background and language deficiencies rate material science in mechanical engineering as one of the fundamental courses with high work load and necessity of language skills due to the descriptive nature of the course. Therefore a blended learning course structure using based on inverted classroom teaching scenarios was established. Heart of the self-study period are visualizing peer-to-peer lecture films supported by micro-lectures along with various online teaching materials. Although students with migration background generally scored lower in tests due to the lack of language skills improved learning outcomes are demonstrated in high quality class discussions and in overall understanding. This paper introduces the learning structure and graded activities, evaluates the course and compares results of native German-speaking students to those of students with migration background.
Flipping the classroom is a method to let students study on their own and then take time to discuss their questions and do extended hands-on lectures or exercises in class – or in the case of the covid-19 pandemic during plenary online sessions. First year mechanical engineering students use different teaching materials (mainly lecture videos, lightboard videos and micromodule lectures) to study from a distance and comprehend the principle underlying science in theory. Then the online plenary lectures offer the opportunity to apply their knowledge and transfer different scientific aspects of the course to get the bigger picture. Exercises, worked solutions, selfassessed tests and peer-instruction during present time help students to check on their learning progress. However, the self-study periods and (online) plenary sessions need to be guided carefully. To meet the course learning outcome and overcome the diversity of a first year class various practical leads have to be fulfilled to turn flipped classroom teaching into success.
The efficacy of alumina-sol based coatings in a water-free atmosphere at high temperatures suggests a potential solution for enhancing the corrosion resistance of high-alloyed steels in Carbon Capture and Storage (CCS) environments. In this study, coupons of X20Cr13, designed for use as injection pipes with 13% Chromium and 0.20% Carbon (1.4021, AISI 420), were sol-gel coated with water and ethanol-based alumina. These coated coupons were then exposed to CO2-saturated saline aquifer water, simulating conditions in the Northern German Basin, for 1000 h at ambient pressure and 60 °C. Corrosion fatigue experiments were also conducted using specimens of X5CrNiMoCuNb16-4 (1.4542, AISI 630), a suitable candidate for geothermal applications, to assess the impact of the ethanol-based coating on the number of cycles to failure at different stress amplitudes. Unfortunately, the coating exhibited early spallation, resulting in corrosion kinetics and corrosion fatigue data identical to those of uncoated specimens. Consequently, the initially promising Boehmit coating is deemed unsuitable for CCS applications and further research therefore not advisable.
Beim Einsatz von Werkstoffen im menschlichen Körper ist neben der Biokompatibilität ebenso die mechanische und korrosive Beständigkeit entscheidend. Da die im Körper zyklisch-mechanisch belasteten Implantate den hochkorrosiven Körperflüssigkeiten und möglicherweise korrosiven Gasen ausgesetzt sind, ist Schwingungsrisskorrosion (SwRK) eine gefürchtete Ursache für Werkstoffschädigungen. Damit ist unweigerlich eine Verringerung der Lebensdauer dieser Komponenten verbunden, die im schlimmsten Fall zum Versagen des Bauteils führen kann
During carbon capture and storage (CCS) CO2-corrosion of pipe steels is a relevant safety issue when emission gasses are compressed in deep geological layers. The reliability of the steels 42CrMo4, X20Cr13, X46Cr13 and X35CrMo17 is demonstrated in long term laboratory experiments up to 2 years of exposure time. Testings were carried out at ambient pressure under an equivalent corrosive environment as found at the geological onshore CCS-site at Ketzin, Germany (T=60 °C, aquifer water).
In the 3D microstructural analysis of a digital twin of porosity in the sintered steel Astaloy CrA, pore shape, average pore size as well as pore distribution will be analyzed. Porosity plays a major role in powder-metallurgical materials since it greatly impacts the mechanical properties of these materials and therefore represents a key parameter in their characterization. Based on the robot-assisted automated serial sectioning and imaging (RASI) system of the Federal Institute for Materials Research and Testing (BAM, Bundesanstalt für Materialforschung und Prüfung) in Berlin, the technique of metallographic serial sectioning will be used to image the microstructure and reconstruct a digital 3D twin from the stack of images obtained. Compared with an individual 2D microsection, the quantitative microstructural analysis of this 3D twin will enable more accurate conclusions on the shape, size and distribution of pores. This paper will detail the key steps in 3D microstructural analysis, including the metallographic preparation routine, the imaging technique, image alignment as well as the segmentation of pores. After the methodology has been described, the results of the quantitative microstructural analysis will be presented and the validity of quantitative parameters of 3D and 2D images will be compared and discussed. The analysis of more than 10,000 pores revealed a correlation between pore shape and pore size. It was also found that a 2D representation of the material surface is insufficient for a precise quantitative characterization of porosity.
