Issue 40

K. Kaklis et alii, Frattura ed Integrità Strutturale, 40 (2017) 1-17; DOI: 10.3221/IGF-ESIS.40.01 9 Tab. 2 presents the rock fracture toughness calculated by Eq. (11) using parameter values u and v from the original tables of the ISRM [6] and three other publications. It is noteworthy that the difference between the average fracture toughness calculated by the ISRM and the three other publications is about 12%. Note that the IC K values presented in Tab. 2, are calculated using the u and v values proposed by ISRM [6] and those proposed by other researchers [8, 16, 9], while the IC K  value for [5] is calculated using   * 0.4915 m . Specimen Thickness (mm) Diameter (mm)  0 Fracture load (kN) * min Y [6] IC K    1/2 MPa m 2.1 21.00 52.30 0.229 4.35 0.83 0.75 2.2 20.75 52.20 0.234 3.63 0.83 0.64 2.3 20.75 52.20 0.241 4.33 0.83 0.76 3.3 20.80 52.17 0.230 3.72 0.83 0.65 4.2 20.75 52.17 0.264 4.95 0.84 0.88 4.3 20.50 52.23 0.302 3.81 0.85 0.69 Average 4.13 0.83 0.73 St. Dev. 0.46 0.01 0.08 Table 1: Geometrical parameters, fracture loads and fracture toughness of CCNBD specimens under pure mode I loading (the value for * min Y was calculated based on eq. (11) using the values for u and v given by ISRM [6] in table form). Specimen ISRM [6] Wang et al. [8] Wang [16] Wang et al. [9] Shetty et al. [5] 2.1 0.75 0.85 0.84 0.86 0.91 2.2 0.64 0.72 0.72 0.73 0.77 2.3 0.76 0.86 0.85 0.87 0.91 3.3 0.65 0.73 0.73 0.75 0.78 4.2 0.88 0.99 0.99 1.00 1.05 4.3 0.69 0.78 0.78 0.80 0.81 Average 0.73 0.82 0.82 0.84 0.87 St. Dev. 0.08 0.10 0.10 0.10 0.10 Table 2: Comparison of rock fracture toughness    1/2 IC K MPa m for the CCNBD specimens. Figure 10: Correlation between the tensile strength and mode I fracture toughness based on different methodologies.