Dynamic mode II fracture toughness determination of rocks with short cores in compression method

A method for determining Mode II fracture toughness of rock using Short Core in Compression (SCC) specimens having two notches was introduced. Split Hopkinson Pressure Bar (SHPB) system was used to load the rock specimen dynamically. SCC specimens of granitic rocks were prepared to investigate the Mode II fracture toughness under various ranges of dynamic loading. To achieve the dynamic force balance on the specimen, a pulse shaping technique using different sizes of copper pulse shaper was adopted. The Stress Intensity Factors (SIF) for SCC method were computed by three-dimensional Finite Element Method (FEM) using ANSYS S/W. Fracturing behavior of specimen was observed by high speed camera apparatus to verify the occurrence of intended shear fracture between the notch tips. Experimental results were compared to that of dynamic Mode I fracture toughness tests with same granitic rocks. The dynamic Mode II fracture toughness K ^Dyn _IIC indicates about 1.3 to 1.7 times larger than dynamic Mode I fracture toughness K ^Dyn _IC under 200 to 1,000 GPa⋅m ^1/2 /s of loading rates range. There exist that clear and similar loading rate dependency between K ^Dyn _IC and K ^Dyn _IIC . It was worth nothing that SCC method has many advantages such as simple preparation, applicability for SHPB system and applying confining pressure test.