# Characterization of Dolomite Stone Broken Under Axial Impact
## 4 Conclusions and Suggestion  
The present study has provided comprehensive insights into the bit displacement response during drilling operations, particularly focusing on the contrasting effects of conventional rotation and axial impact. The results indicated that conventional rotation led to minor wave-like axial displacement, primarily attributed to fluctuations in axial drilling pressure and the inherent heterogeneity of the rock formation. In contrast, axial impact drilling introduced a periodic wave-like penetration pattern, where the magnitude of axial displacement positively correlated with the impact amplitude. Significantly, the introduction of axial impact drilling was shown to substantially reduce the threshold drilling pressure. Specifically, a 0.3 mm impact amplitude was found to decrease the static load by 44.1% compared with non-impact conditions. Furthermore, increasing the axial impact amplitude not only enhanced the rate of penetration (ROP) but also maintained a constant static load, achieving remarkable efficiency improvements. For instance, a 0.3 mm impact at 10 Hz and a static load of 11 kN resulted in an ROP of 0.76 mm/s, marking a 90% efficiency enhancement. However, as the weight on bit (WOB) increased, the efficacy of raising the torque frequency to further enhance ROP diminished. At an ROP of 0.8 mm/s, the average torque reduction observed at a 20 Hz impact frequency was only 17.4% compared with non-impact conditions, suggesting potential limitations in torque frequency adjustment under high WOB scenarios. The stress analysis revealed intriguing trends. Peak stress increased at lower impact amplitudes, with significant changes occurring at an amplitude of 1.5. At this amplitude, the stress concentration region expanded notably, leading to a 100% increase in Mises peak stress compared with an amplitude of 1.0. The formation of an intrusion pit beneath the cutter underscored the rock-breaking effects of axial impact. Notably, while an impact amplitude of 1.2 showed only minor enhancement in the Mises stress angle, principal stress angle analysis indicated a shift in the tensile stress propagation direction, promoting deep crack formation and the development of a tensile damage zone beneath the cutter. Additionally, a linear relationship between the average cutting force and the average contact area with impact amplitude was established. At an impact amplitude of 1.5, both the cutting force and contact area increased by 46.7% and 27.7%, respectively, compared with a scenario with no impact at an amplitude of 1.0. These findings highlight the complex interplay between impact amplitude, stress distribution, and cutting efficiency. In summary, axial percussion drilling presents significant advantages, such as the reduction in drilling pressure, enhancement of the rate of penetration (ROP), and alteration of stress distribution within geological formations. The future prospects for axial percussion drilling technology remain promising, particularly in northwest and southwest China, where it has demonstrated a speed increase of 20-50% in medium-hard rock types, including sand mudstone, sand conglomerate, and basalt. As drilling operations progress to greater depths, particularly in wells exceeding 8000 m, the challenges associated with high rock strength necessitate advanced speed-boosting tools. Axial percussion drilling technology is well suited to meet these technical demands, especially in certain hard formations like granite and carbonate rocks. However, axial percussion drilling technology is not without its limitations. First, despite the favorable promotion of this technology, there is a lack of effective and standardized parameter evaluation regarding its impact effects, with field applications primarily serving as comparative analyses.