Dynamic fracture plays a vital role in various geophysical processes and engineering applications involving rocks (e.g., earthquakes, rock cutting, blasting rock bursts). Accurate measurements of dynamic rock fracture parameters such as fracture initiation toughness, fracture energy, fracture propagation toughness, and fracture velocity are prerequisite for understanding mechanisms of fracture and are also beneficial for rock engineering applications. This paper describes two methods to simultaneously measure key dynamic Mode-I fracture parameters in Split Hopkinson Pressure Bar (SHPB) testing:
the Notched Semi-Circular Bend (NSCB) method and
the Cracked Chevron Notch Brazilian Disc (CCNBD) method. The pulse shaping technique has been employed to achieve force equilibrium on both ends of the samples and thus guarantee a quasi-static stress state in each sample. A strain gauge is mounted on the sample surface near the notch tip to detect the fracture induced strain release and a Laser Gap Gauge (LGG) is developed to monitor the Crack Surface Opening Displacement (CSOD) of the specimen. The initiation toughness is obtained from the peak load given dynamic force equilibrium, and the fracture energy, the propagation toughness and the fracture velocity can be estimated with the aid of the LGG. The feasibility of both methodologies (SCB and CCNBD) is demonstrated with the SHPB experiments on Laurentian granite.
