Brittle fracture of U-notched graphite plates under mixed mode loading

Brittle fracture of isostatic polycrystalline graphite is studied experimentally, theoretically and numerically using U-notched samples under mode I and mixed mode loading (I + II) considering different combinations of the notch radius and the tilt angle of the notch. An experimental programme was performed to provide a new set of results. In total 60 new data are provided in the paper. The averaged value of the strain energy density over a control volume is used to assess the static strength of the specimens subjected to different mode mixities. The volume is centred where the principal stress reaches its maximum value on the notch edge, by rigidly rotating the crescent-shaped volume already used in the literature to analyse U- and V-shaped notches subject to mode I loading. The volume size depends on the fracture toughness and the ultimate tensile strength of the material. Good agreement is found between experimental data and theoretical predictions based on the constancy of the mean strain energy density over the control volume.