## 3 Results and Discussion
### Fracture Mechanism  
#### 3.4.1 Macroscopic-Fracture Characteristics  
The fracture mode is an important factor affecting the mechanical properties of materials, and it is often more complex for transversely isotropic rocks. Figure 19 illustrates the  
Figure 18: Evolutions of stress, AE counts and cumulative AE counts with time for specimens under cyclic loading: (**a**) C-0-20; (**b**) C-0-40; (**c**) C-30-20; (**d**) C-45-20; (**e**) C-90-20; and (**f**) C-90-40.  
failure modes of slate specimens under monotonic and cyclic-loading conditions. The results show that the fracture mode of the specimen is closely related to the loading-foliation angle. The fracture mode of the specimen at \(\beta\) = 0\({}^{\circ}\) is splitting failure, with multiple fracture surfaces parallel to the foliation planes. This implies that the specimen at \(\beta\) = 0\({}^{\circ}\) finally fails when more than one foliation plane is peeled off, which corresponds to the obvious precursor of acoustic emission signals prior to the final fracture, as discussed in the previous section. Regardless of loading conditions, the shear fracture along the foliation plane dominates in the specimen at \(\beta\) = 30\({}^{\circ}\). It is noted that a splitting fracture through the foliation plane has occurred in the specimen C-30-20, but the tensile fracture does not penetrate through the entire specimen, with the shear fracture along the foliation plane dominating.  
Additionally, the fracture mode of specimens at \(\beta\) = 45\({}^{\circ}\) is dominated by a shear fracture, including shear fractures along and through the foliation planes. Due to the difference in fracture pattern, the acoustic emission characteristics of specimens under different loading conditions are also very different. For the specimen U-45, two major shear-fracture planes appear, including a small portion of the fracture along the foliation plane and a large portion of the fracture through the foliation plane, and the induced AE counts are distributed evenly throughout the loading process, whereas, for specimen C-45-20, only one single shear-fracture plane along the foliation plane is formed, and the induced AE events are concentrated in the early stage of the loading process. Combined with the results in Section 3.1.1, showing that there is an obvious difference between the acoustic emission results of the \(\beta\) = 45\({}^{\circ}\) and \(\beta\) = 30\({}^{\circ}\) specimens, it is clear that the fracture mode of the rock can indeed influence the distribution of acoustic emission events. For specimens at \(\beta\) = 90\({}^{\circ}\), the fracture mode is dominated by the combination of shear fracture and tension fracture through the foliation plane. It is also noted that the tensile fracture in the horizontal direction occurs in all the specimens at \(\beta\) = 90\({}^{\circ}\), which can be attributed to the low cohesion between foliation planes. Before the specimen completely fails, the end of the specimen is fractured into two parts. Accordingly, the tensile stress, resulting from the  
Figure 19: Failure modes of the slate specimens under (**a**) monotonic and (**b**) cyclic-loading conditions.  
bending moment at the end of the specimen, brings about the emergence of the horizontal fracture along the foliation plane.