Mixed mode brittle fracture of sharp and blunt V-notches in polycrystalline graphite

Brittle fracture of polycrystalline graphite is studied experimentally and theoretically using Brazilian disk specimens containing sharp and rounded-tip V-notches subjected to different degrees of loading mixity, ranging from pure mode I to pure mode II. The main purpose is twofold. First, to provide a new set of experimental results on fracture of V-notched graphite samples, with different values of loading mixities, V-notch angles and notch radii, which may be helpful for researchers because enlarges the very scarce available data; and second, to provide a fracture criterion for polycrystalline graphite under the above-mentioned conditions. The averaged value of the strain energy density over a well-defined volume is used to predict the static strength of the considered specimens. Good agreement is found between the experimentally obtained fracture loads and the theoretical predictions based on the constancy of the mean strain energy density over the material volume.