Caracterizacao da resistencia a fractura e fadiga de materiais ceramicos estruturais

The aim of this work was to investigate the influence of different testing methodologies on the values of strength and toughness of ceramic materials (at room temperature and high temperatures). Three materials were selected for this research: tungsten carbide (with 4wt% cobalt content), high purity alumina and alumina containing 7wt% zirconia. These materials were extensively characterized in terms of microstructure. Young moduli were determined through bending and ressonance tests. Four point bending strength was determined and compared to values obtained by equibiaxial bending. The influence of surface roughness on the flexural strenfth was assessed. Weibull statistics was used to analyse the data. Tests carried out using unnotched specimens, allowed to investigate some particular aspects such as the influence of jig articulation and of the static fatique parameter n. Results of four point bending and K_I_C at high temperature (800degC; 1000degC e 1200degC) are also presented for alumina and alumina/zirconia. Four methods, Indentation fracture; Indentation strength by bending, Single Edge Notch Beam and Double Torsion were applied to evaluate the fracture toughness (including in equibiaxial loading). The advantages and/or experimental problems encountered in each of those methods are discussed and guidelines for the correct use of these methods are presentedAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga