Research on the effect of loading rate on the fracture characteristics of granite using cracked straight through Brazilian disc specimens

Abstract

The loading rate effect is an important mechanical property affecting the failure mechanism of rock materials. In this paper, the effect of loading rate on the mode I fracture characteristics of granite was studied by using Cracked Straight Through Brazilian Disc (CSTBD) specimen. The acoustic emission (AE) and Digital Image Correlation (DIC) techniques were used to monitor the fracture behavior of the specimen. Due to the nonlinearity of specimen deformation, the tested fracture toughness was corrected by equivalent energy method. The test results show that the equivalent fracture toughness has obvious rate dependency effect. Meanwhile, the crack tip opening displacement increases with the increase of the loading rate at low loading rate, and decreases with the increase of the loading rate when the loading rate reaches a certain value. The AE results show that the relationship between the cumulative energy of AE signals and the loading time can be well fitted by the power-law function, and the power exponent gradually decreases with the increase of loading rate. Moreover, b value decreases with the increase of loading rate, and there is a negative linear correlation between b value and fracture toughness. These indicate that with the increase of loading rate, the cracking process of the specimen gradually changes from that dominated by small-scale failure to that dominated by large-scale failure, and more fracture energy is needed for instability failure of specimens. In addition, the relationship between b value and fracture toughness can provide the possibility for estimating the equivalent fracture toughness of the material by the b value obtained from the AE test.