292 than that of spherical inserts, indicating easier rock penetration. The sharp-tip structure facilitates stress concentration, making them suitable for initiating rock failure. (2) Spherical inserts are more effective in generating radial cracks and cuttings during subsequent penetration. Although they require a higher penetration force, they exhibit lower specific energy for rock-breaking in dual-insert configurations. Their blunt shape promotes axial stress distribution, aiding further rock fragmentation. (3) The mechanisms by which penetration velocity and depth affect crater morphology differ between the two insert types. Increasing velocity reduces crater area, with a more pronounced effect on spherical inserts. In contrast, greater depth expands crater area, and conical-conical dual inserts produce larger craters and more cuttings than spherical-spherical dual inserts. This indicates that the final fragmentation pattern is determined by the interaction between insert geometry and penetration parameters. ACKNOWLEDGEMENTS This work was supported by Open Funding of Anhui Province Key Laboratory of Intelligent and Green Mining of Deep Coal Resources (IGMDCR202402), Open Funding of Anhui Key Laboratory of Mining Construction Engineering, Anhui University of Science and Technology (GXZDSYS2024106), the Young Scientists Fund of the National Natural Science Foundation of China (No.52504073). REFERENCES A study on rock cutting efficiency and structural stability of a point attack pick cutter by labscale linear cutting machine testing and finite element analysis (2018). Int J Rock Mech Min. Park, J.Y., Kang, H., Lee, J.W., Kim, J.H., Oh, J.Y., Cho, J.W., Rostami, J., Kim, H.D. Assessment of brittleness using rock strength and density with punch penetration test (2009). Tunn Undergr Sp Tech.Yagiz, S. Development and application of hobbing-cone hybrid PDC bit (2023).Geomech Geophys Geo.Chen, L., Cao, Q., Qi, Q.L., Niu, S.W., Yang, Y.X., Chen, X., Zhao, Z.J., Wu, B. Evaluation of cutting efficiency during TBM disc cutter excavation within a Korean granitic rock using linear-cutting-machine testing and photogrammetric measurement (2013). Tunn Undergr Sp Tech, 37-54.Cho, J.W., Jeon, S., Jeong, H.Y., Chang, S.H. Experimental and analytical study on key factors of rock breaking under a single indenter (2023). Fatigue Fract Eng M. Wang, P., Yue, Z.W., Li, A.K., Ren, M., Gao, D., Bu, W.Y.
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