Evaluation of the short core in compression (SCC) method for measuring mode II fracture toughness of rocks

As a commonly ignored material property in materials science, the mode II fracture toughness is an important material parameter for rocks. The punch-through shear (PTS) method has been developed and accepted as the suggested method for measuring mode II fracture toughness of rocks by the International Society for Rock mechanics and Rock Engineering (ISRM). Because the PTS method involves complicated specimen preparation, the short core in compression (SCC) method has been recently proposed by Jung et al. (2016) following the earlier short beam in compression (SBC) method. However, the equation to extract the stress intensity factor (SIF) and thus the fracture toughness in either the SBC method or the SCC method has not yet been well established and vigorously validated. In this work, secondary cracks are assumed to initiate from the notch-tips of the SCC specimen, and the SIFs of these secondary cracks are determined using the finite element method (FEM). Subsequently, the SIF of the SCC specimen is determined as the length of the secondary crack tends to zero. To validate this methodology, the SCC method is applied to a fine-grained homogenous rock - Fangshan marble (FM). The mode II fracture toughness value of FM obtained is comparable with that using the PTS method, and both values are larger than the mode I fracture toughness determined using the semi-circular bend (SCB) method. These results demonstrate that the proposed methodology is reliable.