On Reliable Prediction of Fracture Path in Anisotropic Rocks

Abstract

We evaluate the accuracy of two well-known fracture growth theories in predicting crack growth path in anisotropic rocks, through comparison with new experimental data. In doing so, the results of fracture toughness tests on metamorphic Grimsel Granite under four different ratios of mixed-mode I/II loadings are reported, and the experimental kink angle and the effective fracture toughness are compared with the predictions of the maximum tangential stress (MTS), and the maximum energy release rate (MERR) criteria. Comparing theoretical predictions based on the classical forms of the two criteria with the experimental data reveals that the energy-based criterion is unable to accurately describe the fracture growth behavior. We suggest a reformulation of the MERR criterion and show that the modified form give significantly better predictions of fracture growth trajectories. The evaluation of these criteria also illustrates that the MTS and modified MERR criteria cannot provide accurate predictions if T-stress is absent.