Influence of specimen size on granite fracture characteristics and acoustic emission phenomena under mode I loading conditions

The rock mode I fracture characteristics and the size effect are of great significance in understanding the crack initiation, nucleation, propagation, and characterizing the fracture toughness of rocks which is essential for predicting the behavior of rock masses and designing underground structures. In this paper, three-point bending fracture experiments were carried out using single-edge notched beam specimens of different sizes. The fracture characteristics of the entire loading stage, including the post peak stage, were analyzed using digital image correlation (DIC) technology and acoustic emission (AE) technology. Specifically, the calculation of the b value uses the Fisher optimal split and global search algorithm (FGS) method. The results show that both the Fracture process zone (FPZ) length and fracture toughness of granite are size-dependent parameters, and the FPZ length growth rate increases with increasing load level. The failure mode of the source during fracture is mainly tensile failure, and the proportion of tensile failure tends to increase with the increase of specimen size. The temporal b value, average AF value and RA value show corresponding stage changes with time, and the minimum b value, minimum AF value and maximum RA value can characterize the maximum of macroscopic growth rate.

Automated summary

Understanding the fracture characteristics and size effect of rocks is crucial for predicting the behavior of rock masses and designing underground structures. In this study, three-point bending fracture experiments were conducted on specimens of different sizes, and the fracture characteristics were analyzed using DIC and AE technologies. The results showed that the Fracture process zone (FPZ) length and fracture toughness of granite are size-dependent parameters, with the FPZ length growth rate increasing with increasing load level. Tensile failure was the dominant failure mode during fracture, and the proportion of tensile failure increased with specimen size. The temporal b value, average AF value, and RA value showed corresponding stage changes with time, with the minimum b value, minimum AF value, and maximum RA value characterizing the maximum macroscopic growth rate.