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

耐火陶瓷分为无碳材料和碳结合材料。无碳材料的好处是，随着闭环回收的建立，它们更具可持续性。此外，由于缺少致癌树脂或沥青成分，无碳材料对工人的风险较低，安全性较高。然而，从技术的角度来看，碳结合材料具有更好的抗热震性，这在使用过程中通常是一个至关重要的要求。抗热震性的特征在于热冲击强度下降。在我的博士论文中，我研究了粗粒耐火材料的粒度分布对热冲击强度行为的影响。根据颗粒堆积，强度下降在0和70%之间。百分之零，意味着原本的力量没有被破坏，这是一个出乎意料的非凡结果。这种显著差异是由于材料结构的调整造成的。提出了导致这些不同行为的能量耗散机制的假设。这些假设包括裂纹在粗晶粒上的偏转以及由于粗晶粒结构的锯齿而导致的裂纹面之间的摩擦等微观力学现象。这些假设的调查是提交的提案的核心主题。澄清的结构影响的结晶力学行为的承诺，机制可以调整的颗粒堆积。因此，未来可能会生产出对工人来说风险更低、安全性更高、抗热震性更好的无碳可回收耐火材料。为了确定其作用机制并将其与颗粒堆积的具体调整联系起来，将首先对样品进行结构分析，然后通过楔形劈裂试验对样品进行机械性能研究。根据劈裂试验的力-位移曲线，可以计算出表征能量完全消耗的断裂能。此外，从曲线可以计算出，如果抵抗裂纹扩展的阻力随着裂纹的扩展而增加，通常与扩大的裂纹过程区有关。加工区可以通过裂纹偏转等方式扩大，这也将在楔形劈裂试验期间通过数字图像相关法观察到。此外，将进行微型楔形劈裂试验，以便在试验期间观察结构的微观变化。因此，力-位移曲线的变化可能与上述的应力-力学机制有关。此外，楔形劈裂试验样品进行了微观研究，以支持从微型楔形劈裂试验的结果。

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.