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., KIc and KIIc), and the ratio of KIIc to KIc 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 KIc and KIIc, the ratio of KIIc to KIc 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.