Measuring fracture toughness of crystalline marbles under modes I and II and mixed mode I-II loading conditions using CCNBD and HCCD specimens

摘要

Fracture toughness of three crystalline Calcite marbles, which are different only in grain size and distribution, is determined under modes I and II and mixed mode I-II loading conditions using Cracked Chevron-Notched Brazilian Disc (CCNBD) and Hollow Centre Cracked Disc (HCCD) specimens. The results show that mode I fracture toughness (K_(IC)) is correlated negatively with grain size. For each marble, HCCD yields lower values of fracture tpughness, compared with CCNBD. This difference is negligible under mode I loading condition; white it becomes larger as loading condition transits from mode I to mode II. Measured values of P-wave velocity (V_P), Brazilian tensile strength (σ_(tB)) and Schmidt hammer hardness are in direct relation with K_(IC) of the marbles. The obtained results are compared with three fracture criteria, in which the Minimum Strain Energy Density (MSED) criterion has provided better correlations with different critical combinations of modes I and II Stress Intensity Factors.