# Study on Dynamic Loading Characteristics of Rock Containing Holes
## 5 Discussion  
While prior studies have detailed the progressive failure modes of specimens with varying hole parameters, including diagrams of crack development, compressive failure morphology, and force chain patterns, they have not elucidated the cracking mechanism of macroscopic fractures during specimen degradation. Traditionally, Computed Tomography (CT) and Scanning Electron Microscopy (SEM) have been the primary methods for investigating fracture mechanisms in physical experiments, yet their high costs have limited their frequent use. Conversely, numerical simulation experiments offer a cost-effective alternative for analyzing the cracking mechanisms of macroscopic fractures. Through visual analysis of the displacement field during the loading process, these simulations can yield insights comparable to those provided by CT and SEM, but at a lower cost. Building on the research by [PERSON] et al. [50], the displacement field (DTL) method elucidates the fracture cracking mechanism. This technique involves segregating the displacement field into two vectors based on their orientation--either perpendicular or parallel to the fracture--and then assessing the displacement line components on either side of the fracture. For clarity, Figure 16 illustrates various vector diagrams of displacement that correspond to the rock mass's movement patterns at the fracture's extremities. These patterns are categorized into several types [30;35]: DT (Direct Tensile Fracture), RT (Relative Tensile Fracture), RS (Relative Shear Fracture), TS (Tensile Shear Fracture), and CS (Compressive Shear Fracture). Using the displacement vector diagram of a specimen with a 6 mm hole as an illustrative example, Figure 16a,b display the displacement vector diagrams at the failure threshold under loading conditions with strain rates of 100 s\({}^{-1}\) and 200 s\({}^{-1}\), respectively. Figure 16: Displacement field diagram of specimens with holes at the time of ultimate failure: (**a**) loading condition at a strain rate of 100 s\({}^{-1}\); (**b**) loading condition at a strain rate of 200 s\({}^{-1}\). The arrows' color and length signify the displacement magnitude, whereas colors represent the displacement. Dashed lines within the diagrams delineate macroscopic fractures, and the direction and magnitude of displacement of rock model particles adjacent to the fracture are depicted through arrows, aligning with the trend of the displacement lines. The experimental findings indicate that at the failure threshold, the principal macroscopic fractures in all specimens consist of a combination of TS (Tensile Shear Fracture) and RS (Relative Shear Fracture) cracks at the microscopic level. Specifically, the primary fractures at the specimen's incident end are identified as TS fractures, whereas those at the transmission bar end are categorized as RS fractures. During axial compressive deformation of the rock mass, variations in deformation speed and direction at the edge of the terminal conical block lead to fracture formation due to the relative movement on either side of the rock mass. While all specimens display similar macroscopic fracture patterns, microscopic fracture mechanisms exhibit variations under different strain rates, evidenced by RS-2 and RS-1 types of fractures at the transmission end under strain rates of 100 s\({}^{-1}\) and 200 s\({}^{-1}\), respectively. Despite these differences, the X-shaped failure in specimens with holes under high strain rates is predominantly attributed to shear fractures, with both RS and TS fractures demonstrating shear failure characteristics at the macroscopic level. It is also noteworthy that fractures dividing the rock bridge into separate blocks at the failure threshold in double-hole specimens are primarily CS (Compressive Shear Fracture) and TS fractures. Additionally, initial tensile fractures at the axial vertices of the holes, aligned with the loading direction, do not propagate during subsequent loading phases, with shear fractures continuing to dominate the fracture expansion process.