ABSTRACT
The presence of heterogeneity, bedding planes, porosity, inherent defects etc. in rocks inevitably generates large scatters in the strength and fracture toughness values which are obtained from fracture tests on rocks. Hence, statistical analyses may provide better estimations for investigating the mechanical behavior of rocks. In this research, using several fracture toughness tests, mode I and mode II fracture toughness was studied statistically for two different rocks (i.e. limestone and marble) tested with different geometry and loading configurations. Disk type specimens including straight through center crack Brazilian disk subjected to diametral compression and straight edge cracked semi–circular bend and chevron notched Brazilian disk specimens which are among common rock fracture toughness testing configurations were employed for experiments. It was observed that the shape and geometry of a specimen and also its loading mode can affect significantly the scatter in fracture toughness test data. It is shown that the observed differences between the experimental results can be estimated well if the effects of higher order stress terms (T and A 3) are considered via a modified maximum tangential stress criterion. The obtained statistical results are then predicted using two- and three-parametric Weibull distribution models. The failure probability curves of tested specimens are also evaluated successfully in terms of the failure probability curve of a reference mode I sample.
