Mixed mode fracture parameters and fracture characteristics of diorite using cracked straight through Brazilian disc specimen

In this study, the cracked straight through Brazilian disc (CSTBD) specimen was applied to study the I/II mixed mode static fracture of diorite. The fracture load and fracture toughness for different prefabricated crack angles beta were determined. The fracture and morphological characteristics were analyzed using digital image correlation (DIC), scanning electron microscope (SEM) and 3D topography scanning techniques. In addition, the key fracture parameters such as fracture energy, crack mouth opening displacement (CMOD) and fracture process zone (FPZ) were characterized, and a fracture energy calculation method considering the primary crack growth was pro-posed. The results show that the fracture mechanical behavior and fracture trajectories are controlled by the crack angle. At the millimeter measurement scale, the fractal dimensions of fracture surfaces do not vary with crack angle. Further SEM observation shows that intergranular fracture and transgranular fracture are the dominate micro fracture modes of fracture surfaces under mode I and mode II loading, respectively. With the increase of crack angle, the fracture energy first increases and then decreases, while the allowable CMOD de-creases monotonically and even appears negative when beta >= 45 degrees. Based on the displacement gradient method, the calculated width of FPZ for the mode I fracture specimen at peak load is 0.5-1.4 mm and the length is 2.66 mm. Finally, the stress-based and strain-based fracture criteria were modified. It is found that the proposed EEMTSN criterion has the best prediction effect on the mixed mode fracture toughness of diorite.

Automated summary

The cracked straight through Brazilian disc (CSTBD) specimen was used to investigate the I/II mixed mode static fracture of diorite in this study. The results showed that the fracture mechanical behavior and trajectories were influenced by the crack angle. Fracture energy and crack mouth opening displacement (CMOD) were characterized, and a fracture energy calculation method considering primary crack growth was proposed. The proposed EEMTSN criterion had the best prediction effect on the mixed mode fracture toughness of diorite.