Characteristic stresses are critical indicators for microcrack initiation and propagation in rock, a process intrinsically linked to fracture mode. To investigate fracture mode evolution and its feasibility for estimating characteristic stresses, this study conducted uniaxial compression and cyclic loading-unloading tests on fine- and coarse-grained granite with acoustic emission (AE) monitoring. Cyclic target stresses were set within intervals determined by characteristic stresses. Analysis using the AE parameters AF-RA revealed that fracture mode evolution correlates with damage level, and shear microcrack propagation primarily governs macroscopic failure. A characteristic stress estimation method was developed by mapping key points on the shear crack proportion curve: crack closure stress (transition between fluctuating and stable segments), crack initiation stress (inflection point of curve rise), and crack damage stress (slope change point in ascending segment). Comparative analysis with the crack volumetric strain method validated the proposed method. The influences of fracture mode dividing line and statistical interval were discussed, with practical recommendations provided. Compared to conventional AE parameters, the fracture mode proportion exhibits lower sensitivity to AE parameter variations, enabling more reliable identification of characteristic stress points. Furthermore, it directly reflects microcrack evolution behavior, enhancing interpretability and providing a novel perspective for AE-based characteristic stress determination.
Zhao et al. (Sun,) studied this question.