Fakultät für Maschinenbau
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- ItemTowards design- and operating-point selection for fuel cell cathode air-supply systems in aviation(Tōkyō : [Verlag nicht ermittelbar], 2024) Lück, Sebastian; Göing, Jan; Wittmann, Tim; Mimic, Dajan; Friedrichs, JensIn this paper, a hydrogen fuel cell-based propulsion system for regional and future mid-range aircraft is investigated. The main focus herein lies on the exploration of the operating range of the electric cathode gas supply system (ECS) of the fuel cell stack. Subsequently, resulting constraints that limit the design space of the entire propulsion system are shown. Investigations are carried out using the on-design thermodynamic cycle calculation module of the in-house software ASTOR (AircraftEngine Simulation for Transient Operation Research). It includes a fuel cell model which facilitates conservation of mass and energy along the cathode side of the fuel cell system, as well as the specific constraints of the fuel cell stack due to its operating conditions. The second objective of this study is to determine suitable design points for the cathode air supply system which will serve as the starting point for detailed design of turbo components. Optimum fuel cell operating conditions are identified throughout relevant operating points at constant stoichiometry. Furthermore, contradictory requirements of the air supply system in terms of compressor mass flow and pressure ratio are identified. Finally, the off-design performance is estimated in order to derive statements about the coverage of the operating range depending on the choice of the design point. The top-of-climb operating point may be chosen as the design point in order to cover most operating points. At the same time, high altitude operation with a constant-geometry system appears only feasible at unrealistically high stoichiometric ratios or with additional measures such as bleed valves downstream of the compressor.
- ItemUsing computer vision to analyse fracture strains of oxide scale layers on a macro level(Millersville, PA : Materials Research Forum LLC, 2024) Wester, Hendrik; Hunze-Tretow, Jan Niklas; Brunotte, Kai; Behrens, Bernd-ArnoHot forging has established itself as an efficient process for the manufacture of highly stressed components. The high semi-finished product temperatures significantly increase the deformation capacity and enable the production of complex geometries. However, high semifinished product temperatures of up to 1250 °C also lead to increased oxide scale formation. Therefore, oxide scale plays an important role in the context of hot forming processes. Due to the contrasting properties between steel substrates and oxide scale, the appearance of oxide scale affects numerous influencing factors, such as changed friction conditions or thermophysical properties. With increasing interest in numerical process prediction arises the demand to take into account the behaviour of oxide scale in finite-element simulations. In addition to the numerical mapping of the crack behaviour, the challenge in mapping the oxide scale is to determine suitable parameters for describing the failure behaviour. Therefore, this work focuses on a novel procedure to characterise the failure of oxide scale under process relevant conditions of hot forging.
- ItemNumerical process design for the production of a hybrid die made of tool steel X38CrMoV5.3 and inconel 718(Millersville, PA : Materials Research Forum LLC, 2024) Siring, Janina; Heine, Christoph; Till, Michael; Wester, Hendrik; Uhe, Johanna; Behrens, Bernd-Arno; Brunotte, KaiDies used in hot forging are subjected to high cyclic thermo-mechanical loads, which lead to die failure. There are various options for increasing the service life of these dies, for example coatings or heat treatments. Another possibility is to adapt the choice of material, which is the focus of this work. For example, the nickel-based alloy Inconel has a higher strength at elevated temperatures compared to tool steel. However, Inconel is difficult to manufacture and has higher material costs. For this reason, a new process design for the production of a hybrid die consisting of Inconel 718 and tool steel X38CrMoV5.3 is presented within this work. To produce the hybrid dies, the two materials are first friction welded and then formed using hot forging. In addition to the numerical process design, experimental tests are also carried out to manufacture such hybrid dies. Furthermore, a numerical parameter study is done to determine the influence of the forging temperature, the forging speed and the initial Inconel thickness on the process parameters. It can be shown that the production of hybrid dies is possible by using the Tailored Forming process chain. The influencing factors investigated change the required press force and also the material distribution of the Inconel in the hybrid die produced. In the future, further experimental tests will be carried out to determine the service life of the hybrid dies.
- ItemPrevention of scaling by means of recycled process waste gases(Millersville, PA : Materials Research Forum LLC, 2024) Gerke, Niklas; Peddinghaus, Julius; Rosenbusch, Daniel; Uhe, Johanna; Brunotte, Kai; Behrens, Bernd-ArnoDuring hot forging of steel materials, the blanks are subjected to various heating processes. During these processes, scale is formed, which can lead to a mass loss of up to 3%. The additional mass required to compensate this material loss for a given forging component has a significant impact on the process emissions, as the production of the billet material has the highest impact on the overall CO₂ footprint of metal forming products [1]. Additionally, descaling operations such as upsetting are required to guarantee forging quality and process stability. At the same time, large quantities of process waste gas are emitted in the production of raw materials and components. These burnt gases have lower oxygen concentration due to the prior chemical combustion reaction. This work addresses the question, whether these burnt gases can be utilized as a forging process atmosphere. This would not only reduce material loss, but would also result in a reuse of the process waste gas. In order to retrofit existing forging infrastructure, a tooling system with a gas-tight enclosure was constructed and realized in a forming press. Defined gas combinations were fed into the enclosure to create an oxygen-reduced atmosphere. First, different gas combinations were investigated in annealing tests. The three most promising ones were then selected for the forging tests. The enclosure contained a heating, transport, forming and collecting unit. The blanks were fed in through a magazine and inductively heated to 1200 °C, formed and cooled under the defined atmosphere. In each atmosphere, 100 components were forged from the material 42CrMo4. Furthermore, it was investigated whether forming under a gas atmosphere has an influence on tool wear as scale can act as an abrasive. The investigations showed that both the surface of the starting material and the oxygen concentration of the atmosphere have a significant influence on scale formation. The amount of scale formed was reduced by up to 74% compared to an oxygen atmosphere. The adhesive layer on the upper dies was reduced with decreasing oxygen concentration. On the lower dies was an increased adhesive build-up.
- ItemSoft Robotics: A Route to Equality, Diversity, and Inclusivity in Robotics(New Rochelle, NY : Liebert, 2024) Aracri, Simona; Hughes, Josie; Della Santina, Cosimo; Jovanova, Jovana; Hoh, Sam; Garcia Morales, Ditzia Susana; Barcaro, Rosangela; Tan, Yu Jun; Kortman, Vera G.; Sakes, Aimée; Partridge, Alix J.; Cianchetti, Matteo; Laschi, Cecilia; Mazzolai, Barbara; Stokes, Adam A.; Alvarado, Pablo Valdivia; Yeow, Chen Hua; Odetti, Angelo; Lo Gatto, Valentina; Pisacane, Lucio; Caccia, MassimoRobotics is entering our daily lives. The discipline is increasingly crucial in fields such as agriculture, medicine, and rescue operations, impacting our food, health, and planet. At the same time, it is becoming evident that robotic research must embrace and reflect the diversity of human society to address these broad challenges effectively. In recent years, gender inclusivity has received increasing attention, but it still remains a distant goal. In addition, awareness is rising around other dimensions of diversity, including nationality, religion, and politics. Unfortunately, despite the efforts, empirical evidence shows that the field has still a long way to go before achieving a sufficient level of equality, diversity, and inclusion across these spectra. This study focuses on the soft robotics community—a growing and relatively recent subfield—and it outlines the present state of equality and diversity panorama in this discipline. The article argues that its high interdisciplinary and accessibility make it a particularly welcoming branch of robotics. We discuss the elements that make this subdiscipline an example for the broader robotic field. At the same time, we recognize that the field should still improve in several ways and become more inclusive and diverse. We propose concrete actions that we believe will contribute to achieving this goal, and provide metrics to monitor its evolution.