Kink angle and fracture load for an angled crack subjected to far-field compressive loading

Fracture of a cracked elastic medium in compression is investigated. For fracture of an angled straight crack in compression, two crack surfaces are in contact under the action of far-field compressive loading. The classical singular terms related to mode-I stress intensity factors (SIFs) at the near-tip field are no longer present. Instead, another nonsingular stress perpendicular to the flaw plane is added. The singular field related to the mode-II SIFs and two nonsingular T-stresses, parallel to and perpendicular to the crack direction, form leading and secondary parts of the asymptotic stress field near the crack tip. The crack-tip stress field is dominated by the mode-I, II SIFs and one T-stress term with positive mode-I SIFs for an opening crack, or by the mode-II SIFs and two T-stress terms with mode-I SIFs less than or equal to zero for a closed crack in compression, respectively. For the case of an inclined crack, the effects of two T-stresses, confinement ratio and Coulomb friction on kink angle and fracture load are discussed for smooth and rough crack surfaces. Our theoretical predictions on fracture initiation direction and critical fracture stress are satisfactory as compared with experimental measurements and field observations for simple compression. The obtained results show that for negative mode-I SIFs, our model containing three parameters (mode-II SIF, and two T-stresses) is superior to the classical model containing the mode-II SIF alone or containing the mode-II SIF and one T-stress term simultaneously. Two T-stresses or two biaxiality ratios play a crucial role in determining the direction of fracture onset for a wing crack being created from a closed crack in uniaxial and biaxial compression.