1986 Volume 94 Issue 1085 Pages 163-168
On high-density isotropic graphite, fracture energies, fracture toughness and its change with crack extension were measured by using straight-through notched compact tension type specimens with various sizes. During stable crack growth, unloading-reloading cycles were performed in order to evaluate the plastic deformation. The total fracture energy (work of fracture) γWOF was separated into elastic fracture energy γe and plastic energy dissipation γp. Fracture toughness [KIC]Y was determined according to the linear fracture mechanics and compared to the value calculated from γWOF, [KIC]γ. Graphite showed large work of fracture (about 75J/m2), large plastic deformation and large ratio of plastic energy dissipation to total fracture energy (ca. 40%). The value of [KIC]Y coincided with that of [KIC]γ, which suggested that [KIC]Y was strongly influenced by plastic-elastic fracture behaviour of graphite. The value of [KIC]Y was found to decrease with increasing the dimensionless crack length a/W from about 0.7-0.8. This suggests a strong interaction between the crack front and free surface of the specimen, and also the existence of large process zone at the front of crack.
