Re-interpretation of the Weibull strength distribution of polycrystalline ceramics – characteristic strength and fracture toughness

A Weibull strength distribution pertinent to micro-grain structures can be measured for a polycrystalline ceramic after the influence of micro-cracks is sufficiently suppressed (or nearly all pre-existing processing defects are smaller than or much smaller than the average grain size). We outlined the conditions for measurements of this “intrinsic” micro-grain Weibull strength distribution, and showed the characteristic strength σ_ch, supported by a reasonably high Weibull modulus M, could be used to estimate the fracture toughness K_IC without testing specimens with man-made long cracks. Fine- and coarse-grained alumina ceramics, nano-grain dental ceramic (3Y-TZP), fine- and coarse-grained transparent spinel ceramics, and nano-sized specimens of single crystal silicon were analysed by the simple statistical fracture model proposed in this study. K_IC predictions from the “intrinsic” micro-grain Weibull strength distributions compared well with direct measurements from the standard test methods using specimens with man-made long cracks.