Fracture toughness of ceramics and ceramic composites

The fracture toughness of zirconia, alumina, and silicon nitride ceramics, zirconia and alumina single crystals, silicon carbide as well as silicon nitride ceramic particulate composites, silicon nitride laminated composites, and other ceramics materials were studied by a single edge V-notched beam (SEVNB) method. Manual and mechanical procedures for V-notch polishing-out and three- and four-point flexure tests were developed. Load-deflection diagrams for V-notched specimens contributed to better understanding of the deformation behavior of ceramics at room temperature and 1300-1400 degreesC. SENB (single edge notched beam) and SEPB (single edge precracked beam) as well as micro-Raman spectroscopy data were used to analyze the SEVPB results. The ratio between SEVNB and SENB results is about 0.6 for elastic materials, over 0.9 for inelastic ones, and about 1.0 for laminated ceramic composite. The polishing-out of a V-notch does not lead to the tetragonal-monoclinic phase transformation in zirconia ceramics. (C) 2003 Elsevier Ltd and Techna S.r.l. All rights reserved.