Tensile fracture in coarse-grained polycrystalline graphite weakened by a U-shaped notch

U-notched Brazilian disc specimens made of a type of commercial graphite were used to measure experimentally the mode I notch fracture toughness of material. The experimental results were estimated by means of the mean stress and the point stress fracture criteria. An excellent agreement was found to exist between the results of the mean stress criterion and the experimental results for different notch tip radii. Also, found in this research was that the point stress criterion provides weaker estimates compared to the mean stress model except when one deals with larger values of the notch tip radius.