Some methodological features of determination of crack resistance in ceramic materials

The known methods for forming stress concentrators (cracks and notches) in ceramic specimens in order to determine their crack resistance are described. A method for forming a notch with a tip curvature radius of at most 10 µm is suggested. The notch is first formed in the process of pressing the specimen in a specially designed mold and then the green specimen is cut additionally from the tip of the notch by a steel blade with a thickness of 0.1 mm and a grinding angle of 14°. After sintering, this specimen does not contain induced defects that are possible when sintered specimens are notched by a diamond disk by the conventional method. It is shown for a ZrO₂ ceramics partially stabilized by 12 mol.% CeO₂ and an Al₂O₃ ceramics with 0.5 wt.% MgO possessing a layered granular structure that an incorrect choice of the tip curvature radius can result in an erroneous evaluation of the optimality of the structure of the material and an incorrect choice of the technological parameters for its production. Notching by the suggested method made it possible to establish the discrete nature of fracture of the layered granular structure of the ceramics from strain diagrams and the mechanisms of crack propagation causing this kind of fracture.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 9, pp. 26 – 30, September, 1996.