• Herr Ravi Govindram Kewalramani, M.Sc.
• Mittwoch, 2. Oktober 2024, 09:45 Uhr
• Hörsaal Wärmetechnik, LAM-2090, Lampadius-Bau, Gustav-Zeuner-Straße 7, 2. OG

The aluminothermic (AT) welding process, also known as the Thermit welding, is an essential process for joining and repairing rails due to its simplicity, robustness, portability and economic usage. This thesis presents a multi-fluid, multiphase numerical model to predict the thermal flow field within the mould during the pouring and solidification stages of the AT welding process, developed using the finite volume method based open-source CFD software OpenFOAM. The numerical model is rigorously validated not only against well-documented cases in the literature but also through an in-house, low-cost experiment designed to investigate the temporal and spatial evolution of the solid-liquid interface front during the melting of paraffin wax in a rectangular enclosure in the presence of a gas phase. The simulation results show good agreement with the validation cases. Moreover, insights into the thermal pouring stage with solid-liquid phase change phenomena are provided. For this purpose, the available k − ε turbulence model is also extended to incorporate the solid-liquid phase change phenomena. Finally, the temporal and spatial evolution of the solid-liquid interface front during the solidification stage is examined, and the influence of initial molten metal temperature and thermophysical properties on the final weld profiles is systematically studied.

• Herr Dipl.-Ing. Piotr Malczyk
• Freitag, 25. Oktober 2024, 14:00 Uhr
• Hörsaal Silikattechnik, SIL-0118, Haus Silikattechnik, Agricolastraße 17, EG

The PhD thesis provides detailed description of a successful development of MgO and TiO₂ particle reinforced Steel Ceramic Composites (SCC) for molten aluminum alloy applications. For this purpose, the influence of MgO and TiO₂ addition and subsequent pre-oxidation surface treatment on the structure of SCCs and their corrosion resistance against long-term contact with liquid aluminum alloys was investigated. The initiation and progression of corrosion processes were thoroughly analyzed by means of newly developed DSC-aided corrosion tests, high temperature electrochemical studies and adapted wettability measurements. The gained insights led to the recognition of most important factors contributing to the corrosion, including both the electrochemical and the chemical driving forces arising between the SCCs and aluminum alloy. The evaluation of long-term corrosion resistance was performed with the help of finger immersion tests, crucible corrosion tests and subsequent SEM/EDS/EBSD and XRD analyses aiming at the determination of elements most prone to the dissolution in the liquid aluminum alloy and formation of corrosion phases. The pre-oxidized MgO reinforced SCC revealed superior corrosion resistance, being capable of withstanding more than 168 h of contact with liquid aluminum alloy.

• Herr Hong Ha Tran, M.Sc.
• Dienstag, 29. Oktober 2024, 14:00 Uhr
• Hörsaal Helmut-Härtig-Bau, HHB-1035, Gustav-Zeuner-Straße 1, 1. OG

Land subsidence has been a long-standing issue in Hanoi, causing significant infrastructural damage in urban areas. This study uses PSInSAR and decomposition analysis on Sentinel-1 SAR data to analyze vertical and horizontal ground movements in the study area of Hanoi. A hydro-mechanical (HM) model utilizing Richards‘ mechanics was developed to assess the relation between groundwater drawdown, aquifer recharge, and settlement at selected sites of the study area. InSAR and HM model data revealed significant subsidence in southern Hanoi with rates over 20 mm/yr, while the northern region remained stable. Vertical displacement was primary, with negligible horizontal movement. The HM model indicated that ground-water withdrawal could be compensated by lateral inflow and surface water infiltration. A sensitivity analysis using machine learning (CatBoost model optimized with the GWO-WOA method) identified groundwater recharge and aquifer permeability as key factors in land subsidence. Keywords: land subsidence, InSAR, decomposition, hydro-mechanical modeling, OpenGeoSys, machine learning, CatBoost GWO-WOA, Hanoi

• Herr Dr. rer. nat. Björn Meermann
• Freitag, 1. November 2024
  • 13:15 Uhr - Wissenschaftlicher Vortrag zum Thema:
    "Elementanalytische Verfahren im  Bereich der Nichtmetallanalytik"
  • 14:30 Uhr - Öffentliche Probevorlesung zum Thema:
    "Elementanalytik mit atomspektrometrischen Verfahren"
• Raum LES-1001, Lessingstraße 45, 1. OG