# Vibration Damage Analysis of Bottom Hole Assembly Under Axial Impact Based on Dynamic Analysis
## 4 Conclusions  
To address the vibration damage prone to occur when using axial impactors in the BHA, a finite element model was established to simulate the interaction between the BHA and the borehole wall. The D-P model was employed to describe rock damage and deformation. By taking the control parameters of the axial impactor as the main variables, the dynamic behavior of the drilling process was studied. The main conclusions are as follows:  
1. Under percussive drilling conditions, axial stress in the drill string fluctuates significantly during rock breaking and penetration. When the input impact force of the hydraulic impactor is increased, both the amplitude and frequency of drill string stress variations become more severe. With the increasing impact frequency, the influence of the impact load on drill string vibration first increases and then decreases, indicating that at high frequencies, the amplitude of alternating stress tends to stabilize and the vibration-induced damage to the drill string is reduced.
2. The effects of impact energy and frequency on BHA behaviors--such as bit bounce, buckling, and fatigue--were analyzed. The results indicate that during impact drilling, slender sections like drill pipe connectors are prone to buckling. The usable fatigue life of these components can be up to four times shorter than that of the bit. Combined with fatigue life curve trends, it is demonstrated that under field conditions, a high-frequency range above 100 Hz coupled with appropriate impact energy effectively mitigates BHA vibration and extends the service life of the drill string system.
3. Compared with conventional rotary drilling, the drill string motion in the borehole is more complex under percussive drilling. The rate of rock element damage and failure is higher, and both WOB and dynamic stress in the drill string are significantly greater. The findings from this simulation model help provide insight into the complex downhole behavior of the drill string during percussive drilling. This modeling approach offers a novel method for analyzing drill string fatigue life and holds practical significance for drilling optimization and system design.  
Conceptualization, Q.X. and Y.L.; methodology, Q.X.; software, Q.X.; validation, Q.X., Y.L. and J.J.; formal analysis, Y.L.; investigation, J.J.; resources, J.J.; data curation, Q.X.; writing--original draft preparation, Q.X.; writing--review and editing, Q.X.; visualization, L.Z.; supervision, Y.L.; project administration, L.Z.; funding acquisition, L.Z. All authors have read and agreed to the published version of the manuscript.  
Figure 19: Line chart of available cyclic fatigue life of the drill string assembly under different control parameters.  
**Funding:** This research was funded by Deep Earth probe and Mineral Resources Exploration-National Science and Technology Major Project grant number 2024 ZD1000904.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
**Conflicts of Interest:** Author [PERSON] was employed by the company CNOOC Research Institute Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.