To reveal the effect of void diameter on the mode-I fracture behavior of basalt, notched semi-circular bend (NSCB) specimens containing pre-existing circular voids with different diameters were tested under three-point bending. Digital image correlation (DIC) was used to monitor crack propagation and characterize fracture toughness, strain localization, crack propagation rate, and fracture process zone (FPZ) evolution. The results show that the peak load and mode-I fracture toughness decrease progressively with increasing void diameter. Compared with the void-free specimen, the average fracture toughness of specimens with void diameters of 2, 4, and 6 mm decreases by 33.75%, 42.57%, and 54.76%, respectively. The crack propagation process can be divided into elastic deformation, microcrack incubation and nucleation, and main crack propagation and coalescence. A larger void diameter shortens the elastic stage and enhances strain concentration at the crack tip. The crack propagation rate increases with void diameter before crack–void coalescence and rises sharply after coalescence, especially in specimens with larger voids. The fully developed FPZ length predicted by the Dugdale–Barenblatt model agrees well with the experimental results, while the FPZ width is more sensitive to void diameter.

Rock mechanics,Fracture process zone,Crack propagation rate,fracture toughness,void