Issue 40

K. Kaklis et alii, Frattura ed Integrità Strutturale, 40 (2017) 1-17; DOI: 10.3221/IGF-ESIS.40.01 16 better determination of the failure load can be achieved, as shown in Fig 13 and 15. This failure load can then be used for the fracture toughness calculations. Using the same experimental data, the mode I fracture toughness is calculated for each one of the different methodologies. Again, these values are comparable to each other and also correlate well with the equation proposed by Zhang [23] relating the tensile strength of rocks to their mode I fracture toughness. The mode II fracture toughness value was only calculated using the methodology proposed by Shetty et al. [5]. Future work could involve the use of an array of several sensors which will be properly positioned on the entire surface of the disc in conjunction with appropriate filtering of AE results, and an investigation of potential correlations with some of the more sophisticated analytic solutions that are available for the entire planar disc, in order to accomplish an overall analysis of the failure mechanism. R EFERENCES [1] ISRM Testing Commission, (co-ordinator: F. Ouchterlony), Suggested methods for determining the fracture toughness of rock. Int J. Rock Mech Min Sci Geomech Abstr., 25 (1988) 71–96. [2] Fowell, R.J., Chen, J.F., The third chevron-notch rock fracture specimen - the cracked chevron-notched Brazilian disk. Proc. 31st U.S. Symp. Rock. Balkema, Rotterdam, (1990) 295– 302. [3] Fowell, R.J., Xu, C., The cracked chevron notched Brazilian disc test - geometrical considerations for practical rock fracture toughness measurement. Int. J. Rock Mech. Mineral Sci. Geomech. Abstr., 30 (7) (1993) 821– 824. [4] Atkinson, C., Smelser, R.E., Sanchez, J., Combined mode fracture via the cracked Brazilian disk test. Int. J. Fract., 18 (4) (1982) 279– 291. [5] Shetty, D.K., Rosenfiled, A.R., Duckworth, W.H., Fracture toughness of ceramics measured by a chevron notch diametral compression test. J. Am. Ceram. Soc., 68 (12) (1985) C325– C327. [6] ISRM Testing Commission (co-ordinator: R.J. Fowell), Suggested method for determining mode I fracture toughness using cracked chevron notched Brazilian disc (CCNBD) specimens. Int J Rock Mech Min Sci Geomech Abstr., 32 (1995) 57–64. [7] Wang, Q.Z., Jia, X.M., Kou, S.Q., Zhang, Z.X., Lindqvist, P.-A., More accurate stress intensity factor derived by finite element analysis for the ISRM suggested rock fracture toughness specimen – CCNBD. Int J Rock Mech Min Sci., 40 (2003) 233–41. [8] Wang, Q.Z., JiaX.M., Wu L.Z., Wide-range stress intensity factors for the ISRM suggested method using CCNBD specimens for rock fracture toughness tests. Int J Rock Mech Min Sci., 41 (2004) 709–716. [9] Wang, Q.Z., Fan H., Gou X.P., Zhang S., Recalibration and Clarification of the Formula Applied to the ISRM - Suggested for Testing Rock Fracture Toughness. Rock Mechanics and Rock Engineering, 46 (2013) 303–313. [10] Amrollahi, H., Baghbanan, A., Hashemolhosseini, H., Measuring fracture toughness of crystalline marbles under modes I and II and mixed mode I-II loading conditions using CCNBD and HCCD specimens. Int. J. Rock Mech. Min. Sci., 48 (2011) 1123–1134. [11] Aliha, M.R.M., Ayatollahi, M.R., Rock fracture toughness study using cracked chevron notched Brazilian disc specimen under pure modes I and II loading – A statistical approach. Theoretical and Applied Fracture Mechanics, 69 (2014) 17-25. [12] Kaklis, K., Mavrigiannakis, S., Agioutantis Z. Bazdanis, G., An investigation of the mechanical characteristics of Nestos Marble. In: Volume in Honor of the late Professor K. Kavouridis, Technical University of Crete Publications, (2010) 57-68 (in Greek). [13] Markides, Ch.F., Kourkoulis S.K., ‘Mathematical’ Cracks Versus Artificial Slits: Implications in the Determination of Fracture Toughness. Rock Mech Rock Eng., 49(3) (2016) 707–729. [14] Chang S-H, Lee C-I, Jeon S., Measurement of rock fracture toughness under modes I and II and mixed-mode conditions by using disc-type specimens. Eng Geol., 66 (2002) 79–97. [15] Wang, Q.Z., Stress intensity factors of the ISRM suggested CCNBD specimen used for mode-I fracture toughness determination. Int J Rock Mech Min Sci., 35 (1998) 977–982. [16] Wang, Q.Z., Formula for calculating the critical stress intensity factor in rock fracture toughness tests using cracked chevron notched Brazilian disc (CCNBD) specimens. Int J Rock Mech Min Sci., 47 (2010) 1006–1011. [17] Markides, C.F., Pazis D.N., Kourkoulis S.K., Stress intensity factors for the Brazilian disc with a short central crack: Opening versus closing cracks. Applied Mathematical Modelling, 35 (2011) 5636–5651.