An experimental approach for determining dynamic fracture toughness of rock materials at high strain rate is presented. Split Hopkinson pressure bar (SHPB) system was used to load the SR (Short Rod) sample of Po-cheon granites and Ham-yeol granites which have anisotropy physical properties under static loading and the smaple were prepared to consider main three direction of pre-exist micro-cracks (Rift, Hardway, Grain). In order to make sure dynamic stress uniformity and constant strain rate of the specimen before the failure, a pulse shaping technique is employed to the SHPB system. The dynamic fracture toughness Kic was determined by using loading pressure-time curves measured on the transmitted bar and the failure time of the specimen calculated by non-contact laser gap gauge system.

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