Fracture Mechanics - Fracture Toughness Determination

Fracture Mechanics has great potential in solving rock mechanics challenges. Therefore software packages like FRACOD2D which make use of such models are being developed. Input to such codes are e.g. fracture toughnesses. This contribution presents a new laboratory method for determination of the resistance of rock to shear fracturing, i.e Mode II fracture toughness, KIIC, and compares it to Mode I (tensile) fracture toughness, KIC, values. The new testing method, the Punch-Trough Shear with Confining Pressure (PTS/CP) test uses core specimens and a confining pressure representing elevated overburden can be applied separately from the shear load. The experimental data presented gives KIC and KIIC values for some granitic rocks, marble, limestone and sandstones. Emphasis is put on the important influence of confining pressure on the Mode II fracture toughness.