Influence of the scatter of strength and of measurement uncertainties on the determination of the subcritical crack growth exponent in ceramics and glasses

Subcritical crack growth (SCCG) in glasses and ceramics causes a decrease of strength with time under applied load. The dependence of the crack growth rate with the stress intensity factor can be approximated by a power law, with n being the SCCG exponent. In this work the effect of the inherent scatter of strength as well as measurement uncertainties on the determination of n is analysed. Constant stress rate tests as proposed in the EN 843-3 standard are simulated using Monte Carlo techniques. It is shown that the large scatter of strength causes large uncertainties on the determination of n, yielding a significant influence of the sampling procedure especially for small samples. Measurement uncertainties have a surprisingly low influence on the determination of n with exception of a special situation that may arise during long time testing campaigns.