Weibull analysis of ceramics under high stress gradients

The Weibull parameter m of the strength distribution of ceramics under high stress gradients differs from that for moderate stress gradients. This is shown for contact loading. Bars were loaded by oppositely concentrated forcers via rollers. For most investigated materials, measured contact strengths showed strongly reduced Weibull exponents compared with those from 4-point bending tests. This was the reason for a study, in which the effective volumes and surfaces for the two tests were compared and the influence of the strong stress gradients was considered. Under the assumption of the Weibull theory being valid, the effective surfaces and volumes were computed for the normal stress and the energy release rate criteria. In the second part, it will be shown that the strongly non-homogeneous stresses lead to a reduced Weibull exponent.