Effects of test procedures and lithology on estimating the mode I fracture toughness of rocks using empirical relations

摘要

Empirical estimation is a common method for getting mode I fracture toughness K-IC of rock. By collecting data from tests in this study and literature, 204 sets of K-IC and tensile strength sigma(t) test data are obtained for new empirical K-IC-sigma(t) relations regression. The empirical relations make the estimation of K-IC values from sigma(t) conveniently, but test procedures and lithology will influence its reasonability and reliability. Results indicate that the empirical K-IC-sigma(t) relations obtained from the four different suggested K-IC test methods are all in good but obviously different linear relationship. The analyses show that cracked chevron notch Brazilian disc specimen (CCNBD) test-based empirical relation is more accurate for estimating K-IC than the other three test-based empirical relations. As to different lithology, isotropic rocks such as sandstone and carbonatite may be more appropriate for the application of empirical estimation method. However, for coarse grained or anisotropic rocks such as granite and marble, estimation method should be applied carefully because of possibly weak K-IC-sigma(t) relations.