Brittle fracture of sharp and blunt V-notches in isostatic graphite under torsion loading

Brittle fracture of polycrystalline graphite under torsion loading is studied experimentally and theoretically using axisymmetric specimens weakened by sharp and rounded-tip V-notches. The main purpose is twofold. First, to provide a new set of experimental data from notched samples made of isostatic polycrystalline graphite with different values of notch opening angles and root radii, which should be useful to engineers engaged with static strength analysis of graphite components. At the best of authors' knowledge, data from notch specimens under torsion are not available in the literature for this material. Second, to apply to the torsion loading case a fracture criterion based on the strain energy density (SED) averaged over a well-defined control volume surrounding the notch tip, extending what was made by the present authors for in-plane tension-shear loading conditions in notched graphite specimens. Good agreement is found between the experimental data related to the critical loads to failure and the theoretical assessments based on the constancy of the mean SED over the material-dependent control volume. (C) 2011 Elsevier Ltd. All rights reserved.