Abstract
Open-cell ceramic foams are used for the filtration of molten metals with the aim of improving the final quality of cast products. Among the various filter materials that have been developed and studied, carbon-bonded alumina (Al2O3-C) have drawn the most attention due to their superior properties. However, to decrease the hazardous effects of coal tar pitch binder Carbores® P, environmentally friendly Al2O3-C based Tannin and Lactose binder systems have recently received much attention. A systematic characterization and assessment of their properties are required to replace the currently used binders. Considering the service temperature of these filter materials, a test method performed at elevated temperatures is needed. Due to the thermal and mechanical loads applied on these filters, the fracture strength of the bulk material is a key indicator of their structural integrity. The Brazilian Disc Test (BDT) is a method of determining fracture mechanical properties of brittle materials with indirect tensile stresses, formed perpendicular to the loading direction. Due to the porous structure of the materials under investigation, the contact points between the specimen and the loading device are susceptible to major deformation and damage. The aim of this study is on the one hand to define the geometry at the contact points in such a way that valid fracture toughness values can be determined even for small specimen dimensions. For this purpose, the deformations on the surface of the specimens are determined at room temperature using digital image correlation during the test. On the other hand, the optimized test geometry is used to perform high-temperature tests to evaluate their strength and fracture toughness. This evaluation is performed with accompanying finite element analyses using cohesive zone models. The required parameters of these models are identified using methods of nonlinear optimization.
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