Stress intensity factors for semi-circular specimens under three-point bending

The semi-circular specimen under three-point bending technique is a versatile, cost-effective and reliable method for determining the mixed-mode (I and II) fracture toughness envelope of rocks. However, existing numerical results on the stress intensity factor variation with specimen geometry are very limited. This study extends previous numerical work to cover a wide range of possible specimen geometries of experimental interest. From this, a number of observations relevant to the practical use of this technique are discussed. Analytical functions are then provided as an approximation to the mode I variation of the stress intensity factors.