Fracture prediction of rocks under mode I and mode II loading using the generalized maximum tangential strain criterion

The effects of specimen geometry on mode I and mode II fracture toughness (i.e., K-Ic and K-IIc), and the ratio of K-IIc to K-Ic for a given rock material were derived on the basis of a generalized maximum tangential strain (GMTSN) fracture criterion, in which the effects of T-stress and radial stress on rock fracturing can be taken into consideration. To verify these theoretical predictions, laboratory tests using semi-circular bend (SCB) and center-cracked circular disc (CCCD) specimens were conducted. Experimental results indicate that the GMTSN criterion is capable of estimating the geometry dependence of K-Ic and K-IIc, the ratio of K-IIc to K-Ic and the fracture initiation angle of rocks. Moreover, the GMTSN criterion can provide better estimates for the experimental results than some other frequently-used fracture criteria. In addition, our study reveals that the SCB fracture test using asymmetric bottom supports can be identified as a suitable testing method to estimate the upper bound of mode II fracture resistance. (C) 2017 Elsevier Ltd. All rights reserved.