Influence of the particle packing on the fracture-mechanical behavior of carbon-free coarse-grained refractories

• Applicant: Dr.-Ing. Jens Fruhstorfer
• Subject Area: Glass, Ceramics and Derived Composites
• Term: from 2020 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 437193866

Refractory ceramics are classified into carbon free and carbon bonded materials amongst other classification types. Carbon free materials have the benefits that they are more sustainable as a closed-loop recycling is established. Furthermore, carbon free materials have a lower risk and higher safety for the workers due to the missing carcinogenic resin or pitch components. From a technological point of view, however, carbon bonded-materials have a better thermal shock resistance which is during service often a crucial requirement. The thermal shock resistance is characterized by the strength drop with thermal shocking. It improves if more energy is dissipated from a propagating crack.In my PhD thesis, I investigated the influence of the particle size distribution of coarse-grained refractories on the strength behavior with thermal shocks amongst other properties. In dependence on the particle packing, strength drops between 0 and 70% occurred. Zero percent means that the initial strength was kept which was an unexpected extraordinary result. The significant differences had to result from the adjusted material structures. Hypotheses were presented which proposed energy dissipating mechanisms acting in the structures to lead to these different behaviors. The hypotheses comprise fracture-mechanical phenomena such as crack deflection on coarse grains as well as friction between the crack faces due to a serration of the coarse-grained structure.The investigation of these hypotheses is the core topic of the submitted proposal. The clarification of the structural influences on the fracture-mechanical behavior promises that the mechanisms can be adjusted by the particle packing. Consequently, carbon-free recyclable refractories with a lower risk and higher safety for the workers and an excellent thermal shock resistance might be manufacturable in the future.To identify the acting mechanisms and to link them to specific adjustments of the particle packing, samples will be firstly analyzed structurally and then investigated fracture-mechanically by aid of wedge-splitting tests. From the force-displacement curves of the wedge splitting tests, the fracture energy can be calculated which characterizes the completely consumed energy. Furthermore, from the curves can be calculated if the resistance against crack propagation increases with the propagating crack, often related to an enlarged crack process zone. The process zone can become enlarged e.g. by crack deflection which will be also observed during the wedge splitting tests by Digital Image Correlation. Moreover, Mini-wedge splitting tests will be conducted which allow to observe microscopically changes in the structure during the test. Therefore, changes in the force-displacement curves might be linkable to the aforementioned fracture-mechanical mechanisms. Additionally, the wedge splitting test samples are investigated microscopically to support the results from the mini-wedge splitting tests.

• DFG Programme: Research Fellowships
• International Connection: Austria
• Host: Professor Dr. Harald Harmuth