A universal method for quantitatively evaluating rock brittle-ductile transition behaviors

In this paper, by investigating the coupling law of crack formation and energy release, establish a universal method for evaluating the brittle-ductile transition stages of rocks. This method can continuously describe the dynamic evolution process of rock from brittle to ductile deformation and the deformation stages are divided quantitatively through the brittle-ductile index (BDI):.brittle deformation phase (BDI >0.5), brittle-ductile transition stage (0 <0.5) and ductile deformation phase (BDI <0). The triaxial loading test results from various rocks show that when BDI> 0.5, the failure modes are mainly split fractures or low-angle shear fractures; When 0 <0.5, the conjugate fractures and local fragmentation appear in the rock failure modes; When BDI <0, the rock deformation exhibits no macroscopic damage characteristics, or distributed fine cracks, or distributed fragmentation effect. Therefore, this method can well evaluate the brittle-ductile transition behaviors for various rocks, which has certain universality.