Determining the temperature dependent fracture toughness of carbon-bonded alumina using chevron-notched specimens

Open cell ceramic foam filters are used for metal melt filtration. The aim is to reduce the number of non-metallic inclusions and therefore to enhance the quality of the cast product. A new generation of multifunctional filters, which is investigated within the collaborative research center CRC920, is made of fine grained carbon-bonded alumina. The filter manufacturing process leads to hollow struts with sharp edge cavities, which could act as a crack tip. To evaluate the integrity of the filter, a fracture mechanical characterization of the bulk material at different temperatures is necessary. In the applied chevron-notched beam method (CNB) the small specimens (5 x 6 x 25 mm 3 ) are loaded with a four-point bending test set-up until failure occurs. The test set-up offers the possibility of testing at temperatures up to 1000°C. With the help of the measured load-displacement curve the fracture toughness is calculated. Additionally, an analysis of the microstructure of the fracture surface of the specimens is presented.