DETERMINATION OF DYNAMIC FRACTURE INITIATION, PROPAGATION, AND ARREST TOUGHNESS OF ROCK USING SCDC SPECIMEN

Inevitable man-made or natural disasters, such as explosion, impact, earthquake, etc, often cause the failure of a large number of civil engineering facilities, and hence rock behavior under dynamic loading has become the focus of special attention. Dynamic fracture toughness of rock is the material parameter for characterizing its resistance to dynamic crack initiation, propagation and arrest. Rock dynamic fracture toughness is then classified into three kinds: dynamic initiation, dynamic propagation and dynamic arrest. Although there were some achievements for studying rock dynamic initiation and propagation, the study on rock dynamic arrest, being a puzzling problem, has been so far almost ignored. In the present research, the single cleavage drilled compression (SCDC) specimen of rock was impacted by split Hopkinson pressure bar in the model-I dynamic fracture test, where a crack propagation gauge (CPG) was glued on the SCDC specimen to monitor the whole fracture process, including dynamic initiation, propagation, and arrest. An experimental-numerical-analytical approach was adopted to determine the dynamic initiation, propagation, and arrest toughness of rock material. The CPG signal indicated that after the arrest of the crack in the SCDC, the stopped crack will be reinitiated, and propagated out of the CPG monitoring range. This dynamic arrest process is analyzed from an energy perspective, and some required attentions in determining the dynamic arrest toughness are pointed out. The results show that the rock dynamic initiation toughness and propagation toughness increase with the increasing dynamic loading rate and crack propagation velocity, respectively, and the dynamic initiation toughness is larger than the arrest toughness.