Evaluation of the mechanical performance of zirconia bioceramic based on the size of incipient flaw

The mechanical performance of ceramic materials is highly dependent on the existence of incipient flaws. This paper investigates the relationship betw een the size of the pre-existing flaw and failure stress for disc-shaped sp ecimens of zirconia bioceramic subjected to an equibiaxial stress field. As the size of initiating flaw increased, the stress under which discs failed decreased, sensibly allowing the fracture toughness of the material to be calculated. The value obtained, 8 MPam(1/2), is in reasonable agreement wit h previous experience, giving confidence in the validation procedure used a nd the data obtained. For cyclic loading, periods of stable fatigue crack g rowth occurred with initial defects extending to reach critical values. Bas ed on data for discs that failed under monotonic loading conditions, it was possible to determine the critical flaw size and hence degree of crack gro wth necessary for discs to fail from fatigue at a given peak cyclic stress. Predictive constant flaw size fatigue curves showed reasonable accuracy in that the estimated incipient flaw size at a given fatigue life was equival ent to the true flaw size, measured from the fracture surface of failed dis c specimens. (C) 2000 Kluwer Academic Publishers.