Application of mixed-mode fracture criteria for weakest-link failure prediction for ceramic materials

A set of combined experimental and numerical data is presented for the prediction of multiaxial strength for ceramics. Uniaxial and biaxial bend tests were performed on ten different materials. The strength predicted with various mixed-mode fracture criteria was compared with the measured values. A main conclusion was that with the introduction of an additional parameter, a 'size-independent strength', all tests were predicted within 3 % accuracy. However, different criteria had to be used, which could not be interchanged between the various materials. The 'size-independent strength' parameter is interpreted as a measure for the applicability of the weakest-link concept. Its physical meaning is yet uncertain, but predictions on materials for which the porosity was less than one percent showed that for these materials the deviations are largest. This could indicate that basic assumptions in the weakest-link models applied with respect to defect density are violated for these materials.