FRACTURE TESTING OF A SOFT ROCK WITH SEMICIRCULAR SPECIMENS UNDER 3-POINT BENDING .2. MIXED-MODE

The mixed-mode I-II fracture toughness envelope has been determined for a water-saturated synthetic mudstone (Johnstone) using semi-circular specimens loaded under three-point bending-the SCB technique. After critical evaluation of existing theories, it was found that none adequately described the experimentally determined fracture envelope. An empirically derived fit to the data yielded the following envelope: (K(II)/K(IIc))beta + (K(I)/K(Ic))gamma = 1 with beta = gamma = 2.55. A long with the previous successful exploitation of the SCB technique for Mode I fracture toughness determination [1], this study affirms the usefulness of the SCB technique for mixed-mode fracture testing of rocks.