# Research on the Development Mechanism of Three Kinds of Cracks in Rock Cutting
## 1 Introduction
Hence, there is pertinent research on the way damage fragmentation form during cratering and how they affect future cutting. When the cutting depth is more than the critical depth for ductile damage during rock cutting, rock fragmentation begins to form. Macroscopic fissures that extend to the free surface from the tip of the drill tooth are what cause the fragmentation to develop. This procedure yields fragmentation that breaks off in the center as well as fragmentation that is completely intact. Figure 1 illustrates this behavior, which has been shown in several experimental experiments [13; 14; 16], which can be found in both brittle damage and the small fragmentation phase that is proposed by [PERSON] [13]. Previous rock cutting experiments can only observe the surface of the phenomenon, which is difficult to analyze from a microscopic point of view. Numerical simulation techniques must be used in order to more thoroughly explore the mechanism of fracture development and expansion. [PERSON], [PERSON] [19] utilized numerical methods to investigate the  
Figure 1: Fracture Phenomenon of Rock Fragmentation by PDC Teeth. Note: (**a**) [PERSON] [16]; (**b**) [PERSON] [13]; (**c**) [PERSON] [14], The red Arrow in figure shows the location of the rock fragmentation fracture. impact of mechanical tools on rock cutting processes and identified that the fragmentation of rocks is primarily attributed to side cracks. [PERSON] and [PERSON] [2] conducted numerical indentation and cutting experiments using discrete element method to verify the influence of the two ratios on the failure mode. [PERSON] and [PERSON] [14] established an experimental device and the discrete element model to further study the force response and fragmentation formation of PDC tools at different DOCs, cutting speeds, and forward inclination angles. It is thought that the fragmentation created during the rock cutting can be divided into three parts. [PERSON] and [PERSON] [18] simulated rock cutting with standard particle creation and rock cutting with particle cluster technique formation by utilizing the PFC2D discrete element software. The damage crack is effectively replicated by both techniques, yielding favorable results in the experimental investigation of crack propagation mechanism in rock cutting. Moreover, the simulation outcomes exhibit superior performance during the small fragment stage and the brittle damage stage. [PERSON] et al. [20] utilized the discrete element method (PFC2D) to numerically simulate the rock cutting process and replicate the transition of rock failure. The investigation encompasses the progression of rock failure and its influencing factors while validating the accuracy of the critical depth of cut model through numerical simulation results and laboratory experiments. [PERSON] et al. [21] examined the rock-breaking mechanism of cross-cutting PDC bits by combining experimental data with numerical simulations. By establishing a nonlinear dynamical model, this study analyzes stress distribution within rock units, sliding fracture characteristics, plastic energy consumption, and stress distribution along the cutter edge during cross-cutting processes. [PERSON], [PERSON] [22] proposed finite-discrete element method (FDEM) combining the finite element method (FEM) and the bonded particle model (BPM) to simulate the process of rock cutting and breaking rock. The crack development in the simulation of rock cutting at different depths is identified as a mixed type I-II crack. Some scholars that used finite element method to simulate rock cutting [23; 24; 25] also had good results. To sum up, in the experiment and simulation of the rock cutting, the development of the rock crack is processional. Main cracks and damaged cracks are both a part of the crack growth process. The damaged cracks can be in the direction of cutting, extending into the rock matrix or sprouting from the middle of the main cracks.