A modified MTS criterion (MMTS) for mixed-mode fracture toughness assessment of brittle materials

A semi-circular specimen containing a vertical edge crack was used to assess mode I, mode II, and mixed mode fracture toughness of a marble rock. The specimen was subjected to three-point bending while the bottom supports were placed asymmetrically with respect to the crack position. Since the critical tangential stress should be the same in various fracture modes, it was shown that the first three terms of tangential stress infinite series in the vicinity of the crack tip should be used to satisfy this condition. Accordingly, a criterion was presented to predict the mixed mode fracture toughness of brittle materials which showed a good agreement with the experimental results.