Five groups of impact load-driven fracturing experiments were performed on the granite specimens with different pre-existing crack lengths. The dynamic load was generated by a self-developed impact equipment with an adjustable dropping velocity hammer. The fracturing process of the sample was monitored by using high speed cameras with digital acquisition and the digital speckle correlation method. The characteristics of the dynamic fractures of Type I in the rock specimens under impact loading are quantitatively analyzed

including the development of displacement

the opening displacement of crack tip

expansion history of crack tip and stress intensity factor of dynamic fracturing. Experimental results show that from the moment that the hammer dropped down to the moment when the cracking process began

the crack tip stress intensity factor KI for an individual specimen constantly increase

and the magnitude of KI is greater than that of KII by 1-2 orders. For different specimens with pre-cracks under impact loading

stress intensity factor increases with the pre-cracking length.