Experimental and theoretical fracture assessment of rock-type U-notched specimens under mixed mode I/II loading

The aim of this paper is to present a new approach for predicting the mixed-mode fracture resistance of rock-type specimens containing U-shaped notches. The new approach is a modified form of maximum tangential stress (MTS) criterion which states the fracture takes place when the maximum tangential stress at the critical distance from the notch border attains critical value. The critical distance in rock-type specimen is relatively large and the formulations presented in the conventional MTS for characterizing the tangential stress component cannot provide good estimates. Therefore, the modified MTS (MTS-FEM) criterion proposes that the value of maximum tangential stress at the critical distance is determined directly from finite element analysis. Several mixed-mode fracture tests were conducted on the Brazilian disks weakened by central U notches in order to evaluate the MTS-FEM criterion. The comparison between the fracture loads obtained from experiments and those predicted by the MTS-FEM criterion shows that the MTS-FEM criterion can provide good estimates for fracture loads of rock-type U-notched samples under mixed mode loading.