Brittle failure of key-hole notches under mixed mode I/II loading with negative mode I contributions

Brittle failure of key-hole notches is investigated experimentally and theoretically under mixed mode I/II loading with negative mode I contributions. The key-hole notched Brazilian disk specimen made of the general-purpose Polystyrene is utilized for conducting the fracture experiments. To predict the experimental results, the key-hole notch maximum tangential stress and key-hole notch mean stress criteria are utilized. It is shown that both criteria could provide good predictions to the experimental results of the fracture load. Moreover, the key-hole notch mean stress criterion with the experimentally determined critical distance is shown to be the most accurate failure criterion.