## 5 Conclusions  
This paper presents a new concept that a drill bit's backward and sideways inclination angles affect the core's fidelity and analyzes the influence of backward and sideways  
Figure 15: Three-dimensional surface plots of MSE and standard deviation of maximum stress and cutting force at different side-rake angles.  
inclination angles on the fidelity of the core through theorical modeling and simulation. The optimum backward and sideways inclination angles were found from the simulation results. The improved core drill bit has a better fidelity performance. The following conclusions are drawn:  
1. A parametric analytical model of the drill bit's structure was established by studying the influence of cutting tooth structural parameters on core fidelity performance. Additionally, a three-dimensional finite element analysis of the rock-breaking process was conducted to validate the accuracy of the parametric analytical model.
2. The theoretical model and simulation experiments revealed that in deep extreme environments with varying back-rake and side-rake angles as the drill bit structural parameters, increasing the horizontal mean cutting force and the standard deviation of the cutting force resulted in more severe shear friction on the drill bit. This friction impacted the maximum stress of the core and the specific work of breaking, ultimately affecting the fidelity performance of the core. Therefore, it is crucial to carefully select appropriate back-rake and side-rake angles during the design phase to enhance core fidelity performance.
3. The back-rake angles ranged from 15\({}^{\circ}\) to 25\({}^{\circ}\), with the optimum back-rake angle of 21\({}^{\circ}\) producing a maximum stress and a mechanical specific energy that were 0.69 and 0.85 times higher than the highest point, respectively. The side-rake angles ranged from 5\({}^{\circ}\) to 15\({}^{\circ}\), with the optimum side-rake angle of 10\({}^{\circ}\) producing a maximum stress and a mechanical specific energy that were 0.76 and 0.96 times higher than the highest point, respectively. The FME method error was 1.21%.  
In future research, the comprehensive influence of additional drill bit structural parameters on cutting tooth fidelity performance will be considered. Weighting analysis will also be conducted on factors such as core stress in the fidelity evaluation model.  
Conceptualization, F.S.; methodology, F.S. and L.C.; validation, F.S., L.C. and Y.L.; formal analysis, F.S.; investigation, F.S. and Z.W.; resources, Y.L.; data curation, F.S., B.X. and Z.C.; writing--original draft preparation, F.S.; writing--review and editing, F.S., L.C. and Y.L.; visualization, F.S.; supervision, Y.L.; project administration, Z.W.; funding acquisition, Y.L. All authors have read and agreed to the published version of the manuscript.  
The authors are grateful for the financial support from the National Key R&D Program of China (2022 YFB306604, 2022 YFB3706605), and the National Natural Science Foundation of China (No. 52274133).  
Not applicable.  
Raw or processed data required to reproduce these findings cannot be shared at this time, as the data also form part of an ongoing study.  
The authors declare no conflict of interest.