Strongly positioned: the working group "Reinforcement of ceramic materials" meets with an extensive program

The Working Group Reinforcement of Ceramic Materials met this time at the University of Bayreuth. The day before, more than 30 doctoral students from all over Germany had already met for an internal exchange of views at the Chair of Ceramic Materials at the University of Bayreuth. The more than 60 participants on site and the approx. 25 online participants took part in lively discussions about the lecture topics.

After the welcome by Dietmar Koch, Md Nurul Karim, University of Bremen, reported on his work on "Deep learning-based characterization of porous ceramics and ceramic composites". Computed tomography-generated 3D data are used as training data for machine learning algorithms to generate virtual structures with desired pore morphologies and adjustable porosity characteristics. The goal is to generatively manufacture these virtual structures via 3D printing. In addition, machine learning can also be used to volumetrically analyze and segment the microstructures of fiber composite ceramics. This makes it possible to observe crack development under load and correlate it with other measurement data such as mechanical stress and acoustic emission signals.

Markus Körzdörfer, Ariane Group Munich, then presented his work on the simulative and optical 2D structural analysis of braided preforms. When braiding C-fibers, a polarization camera is used to record the real laydown angles and compare them with the nominal values. With high accuracy, the fiber laydown can thus be recorded even for complex shaped structures with varying diameters. The mechanical behavior of the braided structures can thus be evaluated on the basis of the measured real laydown angles. In addition, the findings of discard errors are to be used to make corrections in advance when programming the braiding system in order to achieve the desired fiber orientations in the component.

Xufei Fang, TU Darmstadt reported on his activities on the topic of mechanics-tuned dislocations in functional ceramics: a toolbox from room temperature to high temperature. He showed that in single crystalline systems such as SrTiO3, dislocations already occur before cracking. Cyclic loading via Vickers indentations can induce additional dislocations in the microstructure. With an increase of the dislocation density, the fracture toughness can be significantly increased. In the future, these findings will also be used to evaluate the effects of dislocations in polycrystalline structures and also to evaluate pores in real structures.

Cornell Wüstner, Papiertechnische Stiftung (PTS), presented the development of a dimensionally stable hybrid mold insulation in force flow. The aim of his work is to generate pressure-stable insulation materials with sufficient mechanical pressure properties in the thickness direction and the lowest possible thermal conduction. To this end, plate-shaped fiber-ceramic oxide/oxide ceramics were produced by the University of Bayreuth. Frame structures were machined out of these plates, and paper-engineered insulation materials were inserted into the recesses. While the fiber-reinforced frame structure carries the mechanical loads, the paper-engineered highly porous stacked layers provide the required thermal insulation capability. In the papermaking of the layers, cellulose-based green papers are filled with ceramic particles and short fibers and sintered after debinding. In the future, the frames will be made from a plug-in system with fibers aligned in the load direction to further improve the mechanical properties of the overall structure.

After the lunch break, Nancy-Jane Biller, Reutlingen University, presented the wetlaid process for the production of oxide fiber ceramic nonwovens. This process is intended to process commercial short fibers on the one hand, but also offcuts that are left over from the production of oxide fiber-reinforced components from woven fabrics and rovings on the other. The result is nonwovens with adjustable properties and fiber volume fractions. After infiltration of an oxide ceramic matrix, these nonwovens can then be used, for example, as cores for sandwich structures. Cost-effective composites can be produced by using blended fibers.

Low-cost fiber composite ceramics are also the subject of Jens Schmidt, FhG-HTL Bayreuth. In his presentation Low-Cost CMC - Affordable High-Temperature Materials with High Corrosion Resistance and Damage Tolerance, he showed the possibilities for achieving savings along the process chain. Inexpensive alternative fibers made of basalt or glass can be used, adapted to the application conditions. Furthermore, wet-chemical fiber coating methods can be used instead of costly gas-phase processes. By reducing manufacturing costs, new applications such as the use of Ox/Ox fiber ceramics as firewalls become possible.

Peter Wagner, Isovolta, presented the development of prepregs for low-cost CMC. By producing storable prepregs, it is possible to manufacture low-cost components via drape technology. By using ceramic materials, it is possible to produce components at temperatures up to 900°C that offer significant weight savings compared with conventional materials. These materials are used, for example, as fire protection for battery systems in electric cars. The functional verification is carried out with the aid of a particle-laden hot gas flame. The component, which is heated on one side, must withstand this load without damage for a specified period of time.

After the lectures, the participants had the opportunity to visit the Chair of Ceramic Materials at the University of Bayreuth. Nico Langhof and Stefan Schafföner gave a guided tour of the chair's new premises in the TAO building.

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