A general formulation for strength prediction of advanced ceramics by ball-on-three-balls (B3B)-test with different multiaxial failure criteria

The determination of biaxial strength of ceramics plays a large role in the design of ceramic components. The ball-on-three-balls (B3B)-test is one of the most useful methods for measuring the biaxial strength of ceramics. The strength measured by B3B-test, with any specimen, is dependent on the size of the specimen and loading conditions (type and position of loading); therefore, the strength value, measured with a set of specimens, has to be adjusted by effective volume and/or surface. The standardized strength value obtained from this adjustment can be then used for the design process. Consequently, there is a need for calculating the effective volume/surface of the B3B-test specimens. In this article, general fitting functions are provided for effective volume/surface of B3B-test specimens with different multiaxial criteria, these can be used for all ceramic materials and for various test configurations. Verification of numerical effective volume and effective surface values with experimental measurements show that B3B specimens fail due to surface flaws according to normal stress criterion (NSC).