Fracture toughness testing of core-based specimens by acoustic emission

Recently, a pair of "Suggested Methods for Determining the fracture toughness of rock" have been proposed by the ISRM. The fracture testing methods specify two chevron-notched specimens, the chevron bend (CB) and the short rod (SR). In this study, fracture toughness tests according to the Suggested Testing Methods were conducted on CB and SR specimens of a granite. In addition to these specimens, straight-notched core specimens with three different geometries were tested, using the J-integral approach combined with an acoustic emission technique to determine the fracture toughness. Results from the two testing methods were compared with special reference to specimen geometry compatibility. The fracture toughness determined by the ISRM Suggested Methods showed a specimen geometry effect, and a possible reason for this result was discussed. In contrast, it was shown that the J-iintegral/AE method as applied to the straight-notched specimens provides a suitable evaluation procedure for core-based fracture toughness testing of rock.