Experimental evaluation of the transient propagation fracture properties of rocks under dynamic mode I loading: An insight from digital image correlation

Accurate measurement of dynamic fracture properties is crucial for the safety and stability of the engineering applications. In this study, the dynamic mode I fracture tests are conducted on the notched semi-circular bend (NSCB) specimens with the split Hopkinson pressure bar (SHPB) loading system. By virtue of digital image correlation (DIC) technique combined with high-speed photography, the velocity fields of specimen are revealed, and thus an improved method is proposed to accurately calculate the transient kinetic energy and transient propagation fracture toughness of NSCB specimens under dynamic mode I loading. Our method has obvious merits in its specimen preparation and calculation accuracy since no specific assumptions are required. In addition, the crack propagation gauge (CPG) system is also applied into the tests to capture the transient crack propagation velocity and verify the testing results obtained by DIC technique. The results show that the transient propagation velocity of rocks continues to decrease with a three-stage evolution during the process of rock fracture, while the transient fracture energy of rock gradually increases. Moreover, the transient propagation fracture toughness is inversely proportional to the transient crack propagation velocity. Furthermore, the initiation fracrture toughness, propagation fracture toughness, propagation velocity and fracture energy all feature significant loading rate dependence.

Automated summary

Accurate measurement of dynamic fracture properties is crucial for the safety and stability of engineering applications. This study proposes an improved method to accurately calculate the transient kinetic energy and transient propagation fracture toughness of NSCB specimens under dynamic mode I loading, without specific assumptions. The results show a three-stage evolution of transient propagation velocity during the process of rock fracture, and a gradual increase in transient fracture energy. Loading rate dependence is observed in initiation fracture toughness, propagation fracture toughness, propagation velocity, and fracture energy.