# Research on the Development Mechanism of Three Kinds of Cracks in Rock Cutting
## 2 Experiment and Simulation  
### Rock Cutting Experiment  
The experimental sandstone rock samples were first subjected to UCS (Uniaxial Compressive Strength), MOE (Modulus of Elasticity) and BTS (Brazilian Tensile Strength) studies, and the parameters such as strength and modulus are obtained. The fundamental strength parameters were determined as given in Table 1.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & & **Property** & \\ \hline
**UCS** & **MOE** & **BTS** & **Poisson’s** & **Density** \\
**MPa** & **GPa** & **MPa** & **Ratio** & **g/cm\({}^{3}\)** \\ \hline
135.15 \(\pm\) 3 & 19.37 \(\pm\) 0.6 & 8.02 \(\pm\) 0.4 & 0.26 & 2.32 \(\pm\) 0.03 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic Mechanical Properties of Rocks and Models.  
The uniaxial pulling and pressing tester, as seen in Figure 2 below, served as the basis for the design of the rock-cutting tool. The beam of the tester supplied the loading route and speed for the cutting experiment. A fixture held the thin rock sample to the chassis, and the cutting tool was a shovel-shaped tooth with a 60\({}^{\circ}\) angle. The uniaxial pulling and pushing tester placed restrictions on the data collection technique, allowing for the collection of just the cutting force in one direction.  
In order to study the special phenomenon of fragment breaking apart in the middle, the following experiment was designed with reference to the ductile-small fragmentation-brittle phase mentioned in [PERSON]'s research [13]. This study focuses on the initiation and propagation of cracks, so it does not conduct in-depth research on plastic failure in rock cutting. For the experiments, four cutting depths, 0.5 mm, 1.5 mm, 2.5 mm, and 3.5 mm, and three experiments under each depth, were used, and the crushing circumstances are depicted in Figures 3-6. As can be seen in the figures, no macroscopic fissures and no big rock fragmentations were created when the cutting depth was 0.5 mm. Instead, the crushed rock fragmentation just exited the crushing zone via gravity. When the cutting depth reached 3.5 mm, the rock sample was invaded at the drill teeth's point of contact, causing the rock to sprout cracks. These cracks then spread along the drill teeth's velocity direction to form macro cracks, which eventually turned into semi-dislodged rock fragmentation before falling off.  
Figure 3: Rock-Cutting Experiment (DOC = 0.5 mm).  
Figure 2: Rock Cutting Experimental Device.  
Figure 3 shows clear ductile damage, a powdered crushing region, and a collection of powdered debris the tool created after breaking the rock. The rock fragmentation formed in Figure 4 was continuous and unbroken, and they were produced intermittently but unbrokenly in response to the entry of the tool. The fragmentation was merged into a skin of variable thickness, which was accompanied by ductile damage over time. In Figure 5, the rock fragmentation was also shattered from the center, a phenomenon known as the fracture phenomenon, in addition to the discontinuous formation and ductile damage. This stage of the damage may have been categorically categorized as brittle damage in Figure 6 because a bigger fragmentation and a macroscopic shear crack that appear to have been caused by tool intrusion are created.  
The PFC discrete element method was used for the numerical simulation of rock-cutting experiments in order to more thoroughly investigate the aforementioned experimental phenomena in rock-cutting experiments, the crack development process of ductile-small fragmentation-brittle damage, and the generation mechanism of fracture-shaped rock fragmentation.