Fracturing Process Visualization of Cracked Chevron-Notched Brazilian Discal and Notch Semicircular Bend Rock Specimens and Comparative Analysis by Combined AE and DIC

Abstract

Abstract A series of homogeneous granite specimens were prepared to investigate the Mode I fracture toughness (KIC) using the cracked chevron-notched Brazilian disk (CCNBD) method and semicircular three-point bending (NSCB) method recommended by the International Society for Rock Mechanics (ISRM). A combination of acoustic emission (AE) and digital image correlation (DIC) was utilized to monitor the crack propagation and analyze the fracture modes at various test stages. The results indicated that the average value of Mode I fracture toughness (KIC-) of the CCNBD specimen was approximately 10% higher than that of the NSCB specimen. The coefficient of variation in the NSCB test was small, which could provide more stable result of Mode I fracture roughness. Compared to the CCNBD test, the failure mode of NSCB specimens was mainly tensile damage with instantaneous damage during the experimental process. Furthermore, the failure process of the NSCB test was mainly controlled by tensile fractures, which exhibited instantaneous failure. The CCNBD test was first controlled by tensile fractures and then by shear fractures when the peak was reached, exhibiting progressive failure. The failure mode and the process may be the main factors controlling the difference between the results of the NSCB and CCNBD tests. This work helps select appropriate methods to measure the Mode I rock fracture toughness.