## 3 Results
### Failure Characteristics  
As shown in Figure 6, under uniaxial loading conditions, the single-coal specimen (C) exhibits significant tensile failure, with evenly distributed cracks on the coal surface, a fractured zone at the top edge, and a relatively intact overall morphology. When the proportion of coal in the combination is 90% (CSR (9:1)), the number of cracks on the coal surface increases; some cracks extend from the coal part to the rock part through the interface; and the number of cracks in the coal component decreases with the generation of interface effects, with no overall failure in the rock part. When the proportion of rock in the combination is 50% (CSR (5:5)), shear failure occurs in the primary coal-rock composite specimen, with the main crack penetrating the entire specimen through the coal-rock interface, and multiple cracks appearing in the rock part at the interface; the artificial coal-rock composite specimen exhibits clear tensile failure characteristics in both the coal and rock parts. When the proportion of rock in the combination is 30% (CSR (3:7)), the main cracks are distributed between the coal and rock; the integrity of the specimen is poor; and both the coal and rock parts of the combination exhibit fractured zones, with tensile failure occurring in the rock part, forming a macroscopic fracture zone. A single-rock specimen (R) exhibits only two main cracks with a large inclination angle, and the specimen undergoes overall shear failure. Comparing the failure characteristics of the primary coal-rock combination CSR (5:5) with the artificial coal-rock combination CR (5:5), it is found that the primary coal-rock combination has a larger number of cracks extending into the rock part, with the main crack penetrating the coal-rock interface and extending multiple cracks at the interface, resulting in a more complex failure morphology. The artificial coal-rock combination exhibits obvious tensile failure characteristics, with the main crack in the coal part extending into the rock,  
Figure 6: Damage characteristics and sketches. but not penetrating the combination. Furthermore, the primary coal-rock combination experiences more severe damage. This is because the interface effect at the coal-rock interface of the primary coal-rock combination causes irregular stress concentration due to the unevenness and interlocking of the interface, leading to more developed coal-rock fractures at the interface, resulting in multiple-point initiation of failure at the interface of the primary coal-rock combination. When cracks in the rock part begin to extend and propagate, the failure of the coal induces the failure of the rock, releasing a large amount of energy into the coal, exacerbating the damage and failure intensity of the coal, thus forming a feedback mechanism of failure between the coal and the rock. In summary, the failure modes of the specimens can be divided into two types: tensile failure and shear failure. Tensile failure is characterized by nearly vertical main crack morphology penetrating the entire specimen axis, with parallel tensile stresses densely distributed along the coal specimen's side surface. This is because of the presence of inherent cracks and pore structures in the coal specimen, causing stress concentration near these defects, leading to tensile failure when the stress reaches the tensile strength of the material horizontally. On the other hand, shear failure is characterized by typical \"X\"-shaped shear failure surfaces formed by the main cracks, which occurs when the coal specimen undergoes shear displacement due to the failure of the coal, and the cohesive force of the rock part cannot prevent the overall displacement of the specimen, resulting in shear failure along the coal fractures, eventually leading to shear failure. The following is an inversion of the sample's failure characteristics based on the characteristics of the acoustic emission response.