Wide-range stress intensity factors for the ISRM suggested method using CCNBD specimens for rock fracture toughness tests

摘要

Based on Bluhm's idea, a new slice synthesis method is presented and validated through careful comparison with numerical methods, the finite element method and boundary element method. The new slice synthesis method is both simple and effective. It is adopted to calculate the stress intensity factor for a rock fracture toughness specimen, the CCNBD, which has a complex crack (notch) front configuration (Fig. 1). The CCNBD was suggested by the ISRM for rock fracture toughness test. However, the key parameter in the calculation, i.e. the critical dimensionless stress intensity factor, may not have been given adequately. In order to improve the fracture toughness tests using CCNBD, updated values of the critical dimensionless stress intensity factors are given in tabular form. Then these values are curve-fitted to an exponential function, i.e. Eq. (14); the values of the two parameters of the exponential function are given in Tables 6 and 7. The derived results cover a wide range of specimen geometries; they are also considered more accurate than those given previously.