# Investigation of Rock-Breaking Mechanisms Based on the Adaptive Matching Method for Drilling Loads
## 3 Results and Discussion  
### Effect of the Load Factor  
The load factor (denoted \(\alpha\)) in this study is defined as the proportion of the reduction degree of the applied axial force to the initial load. Under the action of different load factors ranging from 0.4 to 1.0, the corresponding drilling load manifested as the reaction force  
Figure 5: The simulation results of a PDC cutter cutting rock. detected in the PDC cutter while drilling, and it exhibited distinct response patterns, as shown in Figure 6.  
As shown in Figure 6, the curves of the displacement and its fluctuation, the applied force, the reaction force, and the number of cracks demonstrate significant differences in variation trends and growth patterns. In correlating Figures 5(a) and 6(a), it is evident that the displacement curves of the PDC cutter exhibit a tendency to oscillate while sticking. Moreover, the oscillation amplitude of the displacement curve in the X direction shows a strong inverse correlation with the load factor (\(\alpha\)); smaller \(\alpha\) values correspond to reduced oscillation amplitudes. Figure 6: Motion and reaction force of the PDC cutter under different load factors. In addition, Figure 6a,b indicate that both the displacement and the motion curves are modulated by the load factor, achieving the designed maximum displacement, 140 mm. When the load factor exceeds 0.7, the PDC cutter will be stuck at a displacement of 94.5 mm. As observed in Figure 6c,d, the applied axial load and the reaction force acting on the PDC cutter and their changing characteristics are significantly influenced by the load factor. While the factor is 0.7 or greater, the applied axial load varies greatly in the latter stage (after the checkpoint, 94.5 mm), but the motion curves and the displacement remain almost unchanged. The main reason for this phenomenon is that when the PDC cutter is stuck, the displacement will not increase continuously but the applied axial force will decrease proportionally based on the load factor set for the program. Figure 6e,f present the number of cracks and their various types with the simulation time detected during the rock-breaking process. The cracks can be divided into tensile cracks and shear cracks, representing different failure modes of rock under the action of the PDC cutter. Figure 6e illustrates the number of total cracks, tensile cracks, and shear cracks with the simulation time while the load factor is 0.6, which show that the proportion of tensile cracks is 85.2-86.13%, indicating that the failure mode of the simulated rock is mainly tensile failure. Figure 6f shows the number of total cracks under different load factors, indicating that the changing characteristics and growth trends of the cracks show significant differences alongside the load factor, as well as similarities with the growth curves of displacement. Figure 7 indicates the key characteristic parameters during rock breaking with the action of the PDC cutter, such as the total number of cracks, the maximum displacement in the X direction, the work power, and the MSE. In view of Figure 7, we know that the number of total cracks, the maximum displacement, and the work power decrease with the increase in the load factor while MSE increases, opposing the trend in the work power. The displacement represents the extent to which the PDC cutter advances during rock breaking. The maximum value of the displacement in the X direction which was preset in the simulation program is 140 mm; the program will stop automatically when it reaches 140 mm. In another way, the higher the MSE, the more energy is consumed during the rock-breaking process. The more cracks that are generated during the rock-breaking process, the more complete the rock failure. The simulation results demonstrate that the load factor exerts significant influence on both the kinematic characteristics of the PDC cutter and the rock fragmentation patterns, thereby directly affecting rock-breaking efficiency.